Permanent axotomy, a model of axonal atrophy and secondary segmental demyelination and remyelination

Interruptible demyelination in avian riboflavin deficient neuropathy

BACKGROUND AND AIMS

The evolution of demyelination in individual internodes remains unclear although it has been noticed the paranodal demyelination precedes internodal demyelination in neuropathies with diverse aetiologies. For therapeutic purpose, it is fundamental to know whether the demyelinating procedure in affected internodes can be interrupted. This study aimed to delineate the development of demyelination in individual internodes in avian riboflavin deficient neuropathy.

METHODS

Newborn broiler meat chickens were maintained either on a routine diet containing 5.0 mg/kg riboflavin, a riboflavin deficient diet containing 1.8 mg/kg riboflavin, or initially a riboflavin deficient diet for 11 days and then routine diet plus riboflavin repletion from day 12. Evolution of demyelination in individual internodes was analyzed by teased nerve fibre studies from day 11 to 21.

RESULTS

In riboflavin deficient chickens, demyelination was the predominant feature: it was mainly confined to the paranodal region at day 11; extended into internodal region, but less than half of the internodal length in most affected internodes at day 16; involved more than half or whole internode at day 21. In the internode undergoing demyelination, myelin degeneration of varying degrees was noticed in the cytoplasm of the Schwann cell wrapping the internode. Two days after riboflavin repletion, co-existence of remyelination and active demyelination within individual internodes was noticed. Remyelination together with preserved short original internodes was the characteristic feature 4 and 9 days after riboflavin repletion.

CONCLUSION

Riboflavin repletion interrupts the progression from paranodal to internodal demyelination in riboflavin deficient chickens and promotes remyelination before complete internodal demyelination.

Composite nerve conduction scores and signs for diagnosis and somatic staging of diabetic polyneuropathy: Mid North American ethnic cohort survey

INTRODUCTION/AIMS

In the Diabetes Control and Complications Trial (DCCT), the minimal nerve conduction (NC) criterion for diabetic sensorimotor polyneuropathy (DSPN) was abnormality of NC in more than one peripheral nerve without specifying the attributes of NCs to be evaluated. In the present study, we assess individual and composite scores of NCs meeting the DCCT criterion and signs for improved diagnosis and assessment of DSPN severity.

METHODS

Evaluated were 13 attributes and 6 composite NC scores and signs and symptoms in 395 healthy subjects (HS) and 388 persons with diabetes (DM).

RESULTS

Percent abnormality between subjects with DM and HS was remarkably different among individual attributes and the six composite NC scores. For diagnosis of DSPN using the DCCT criterion, assessment of conduction velocities (CVs) and distal latencies (DLs) provided sensitive diagnoses of DSPN. NC amplitudes provided stronger measures of severity. In studied cohorts, DSPN was staged: N0, no NC abnormality using NC score 2 (CVs and DLs), 60.0%; N1, NC abnormality only, 18.4%; N2, NC abnormality and signs of feet or legs, 16.3%; and N3, NC abnormality and signs of thighs, 5.3%.

DISCUSSION

For sensitive and standard diagnosis of DSPN using the DCCT NC criterion, specifically defined composite scores of CVs and DLs, e.g., score 2, is recommended. A composite score of amplitudes, e.g., score 4, provides a stronger measure of neuropathy severity. Also, provided are HS reference values of evaluated attributes of NCs and estimates of staged severity of DSPN of mid North American DM cohorts.

Immune-Mediated Neuropathies: Pathophysiology and Management

Dysfunction of the immune system can result in damage of the peripheral nervous system. The immunological mechanisms, which include macrophage infiltration, inflammation and proliferation of Schwann cells, result in variable degrees of demyelination and axonal degeneration. Aetiology is diverse and, in some cases, may be precipitated by infection. Various animal models have contributed and helped to elucidate the pathophysiological mechanisms in acute and chronic inflammatory polyradiculoneuropathies (Guillain-Barre Syndrome and chronic inflammatory demyelinating polyradiculoneuropathy, respectively). The presence of specific anti-glycoconjugate antibodies indicates an underlying process of molecular mimicry and sometimes assists in the classification of these disorders, which often merely supports the clinical diagnosis. Now, the electrophysiological presence of conduction blocks is another important factor in characterizing another subgroup of treatable motor neuropathies (multifocal motor neuropathy with conduction block), which is distinct from Lewis-Sumner syndrome (multifocal acquired demyelinating sensory and motor neuropathy) in its response to treatment modalities as well as electrophysiological features. Furthermore, paraneoplastic neuropathies are also immune-mediated and are the result of an immune reaction to tumour cells that express onconeural antigens and mimic molecules expressed on the surface of neurons. The detection of specific paraneoplastic antibodies often assists the clinician in the investigation of an underlying, sometimes specific, malignancy. This review aims to discuss the immunological and pathophysiological mechanisms that are thought to be crucial in the aetiology of dysimmune neuropathies as well as their individual electrophysiological characteristics, their laboratory features and existing treatment options. Here, we aim to present a balance of discussion from these diverse angles that may be helpful in categorizing disease and establishing prognosis.

Reduction in median nerve cross-sectional area at the forearm correlates with axon loss in carpal tunnel syndrome

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The median nerve CSA at the forearm is smaller when CTS is involved with axon loss.

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WFR of the median nerve is highest when CTS causes slight axon loss.

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Axon loss of the median nerve in CTS hampers the diagnostic value of wCSA and WFR.

Objective

To explore the relationship between axon loss and measured cross-sectional areas of the median nerve (MN) in severe carpal tunnel syndrome (CTS).

Methods

In this retrospective study of 158 examined wrists, we compared axon loss to the ultrasound parameters MN cross-sectional area at the wrist (wCSA), MN cross-sectional area at the forearm (fCSA) and wrist-to-forearm ratio (WFR), in patients with moderate to extreme CTS. Axon loss was evaluated by needle electromyography (EMG) of the abductor pollicis brevis muscle (spontaneous activity and reduction of interference pattern).

Results

Both the spontaneous activity and interference pattern reduction correlated negatively to fCSA (r = −0.189, p = 0.035; r = −0.210, p = 0.019; respectively). In moderate CTS, both the spontaneous activity and interference pattern reduction correlated positively to WFR (r = 0.231, p = 0.048; r = 0.232, p = 0.047; respectively). The WFR was highest when slight spontaneous activity was detected. Neither wCSA nor WFR correlated with axon loss in severe and extreme CTS.

Conclusions

The fCSA is smaller when axon loss in CTS is more prominent. The WFR is highest when CTS is associated with slight axon loss of the MN.

Significance

CTS might cause retrograde axonal atrophy detected as small fCSA. Prominent axon loss in CTS may reduce the diagnostic value of WFR.

Axo-glial interaction in the injured PNS

Axons share a close relationship with Schwann cells, their glial partners in peripheral nerves. An intricate axo-glia network of signals and bioactive molecules regulates the major aspects of nerve development and normal functioning of the peripheral nervous system. Disruptions to these complex axo-glial interactions can have serious neurological consequences, as typically seen in injured nerves. Recent studies in inherited neuropathies have demonstrated that damage to one of the partners in this symbiotic unit ultimately leads to impairment of the other partner, emphasizing the bidirectional influence of axon to glia and glia to axon signaling in these diseases. After physical trauma to nerves, dramatic alterations in the architecture and signaling environment of peripheral nerves take place. Here, axons and Schwann cells respond adaptively to these perturbations and change the nature of their reciprocal interactions, thereby driving the remodeling and regeneration of peripheral nerves. In this review, we focus on the nature and importance of axon-glia interactions in injured nerves, both for the reshaping and repair of nerves after trauma, and in driving pathology in inherited peripheral neuropathies.

Morphometric Differences in the Recurrent Laryngeal Nerve in Patients with Vocal Fold Paralysis

OBJECTIVES

Injury to the recurrent laryngeal nerve (RLN), if severe enough, can result in vocal fold paralysis. Reinnervation surgery can improve patient outcomes, but previous studies have reported a negative correlation between time since onset of paralysis and surgical outcomes. The ability of the paralyzed nerve to serve as a conduit for donor nerve fibers may be a factor in the success of reinnervation; however, changes in RLN composition after paralysis have not been well studied. Therefore, we investigated the morphometric composition of explanted RLN sections from patients who had experienced vocal fold paralysis for varying length of times.

METHODS

Nine nerve sections from unilateral vocal fold paralysis (UVP) patients and seven control nerve sections were analyzed for morphometric parameters including fascicular area, fiber count, fiber density, fiber packing, mean g-ratio, and fiber diameter distribution. Nerves from UVP patients were also compared as a function of time since UVP onset.

RESULTS

In comparison to control nerves, paralyzed nerves were found to have significantly lower fiber densities and fiber packing, higher mean g-ratio values, and a shift in diameter distributions toward smaller diameter fibers. With respect to paralysis duration, no significant differences were observed except in fiber diameter distributions, where those with paralysis for >2 years had distributions that were significantly shifted toward smaller diameter fibers.

CONCLUSIONS

The morphometric data presented here suggest that correlations between the time since onset of vocal fold paralysis and reinnervation outcomes may be due to fiber size changes in the paralyzed nerve over time.

Clinical electrophysiology of axonal polyneuropathies

Axonal neuropathies encompass a wide range of acquired and inherited disorders with electrophysiologic characteristics that arise from the unique neurophysiology of the axon. Accurate interpretation of nerve conduction studies and electromyography requires an in-depth understanding of the pathophysiology of the axon. Here we review the unique neurophysiologic properties of the axon and how they relate to clinical electrodiagnostic features. We review the length-dependent Wallerian or "dying-back" processes as well as the emerging body of literature from acquired axonal neuropathies that highlights the importance of axonal disease at the nodes of Ranvier. Neurophysiologic features of individual inherited and acquired axonal diseases, including primary nerve disease as well as systemic immune mediated, metabolic, and toxic diseases involving the peripheral nerve, are reviewed. This comprehensive review of electrodiagnostic findings coupled with the current understanding of pathophysiology will aid the clinician in the evaluation of axonal polyneuropathies.

Uncompacted Myelin Lamellae and Nodal Ion Channel Disruption in POEMS Syndrome

To elucidate the significance of uncompacted myelin lamellae (UML) and ion channel disruption at the nodes of Ranvier in the polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes (POEMS) syndrome, we evaluated sural nerve biopsy specimens from 33 patients with POEMS syndrome and from 7 control patients. Uncompacted myelin lamellae distribution was assessed by electron microscopy and immunofluorescence microscopy. In the POEMS patient biopsies, UML were seen more frequently in small versus large myelinated fibers. Paranodes and Schmidt-Lanterman incisures, where normal physiologic UM is located, were frequently associated with UM. Widening of the nodes of Ranvier (i.e. segmental demyelination) was not associated with UML. There was axonal hollowing with neurofilament condensation at Schmidt-Lanterman incisures with abnormal UML, suggesting axonal damage at those sites in the POEMS patient biopsies. Myelin sheath irregularity was conspicuous in large myelinated fibers and was associated with abnormally widened bizarrely shaped Schmidt-Lanterman incisures. Indirect immunofluorescent studies revealed abnormalities of sodium (pan sodium) and potassium (KCNQ2) channels, even at nonwidened nodes of Ranvier. Thus, UML was not apparently associated with segmental demyelination but seemed to be associated with axonal damage. These observations suggest that nodal ion channel disruption may be associated with functional deficits in POEMS syndrome patient nerves.

Pathophysiology of immune-mediated demyelinating neuropathies--Part II: Neurology

In the second part of this review we deal with the clinical aspects of immune-mediated demyelinating neuropathies. We describe the relationship between pathophysiology and symptoms and discuss the pathophysiology of specific disease entities, including Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, multifocal motor neuropathy, anti-myelin-associated glycoprotein neuropathy, and POEMS syndrome.

Neurophysiological approach to disorders of peripheral nerve

Disorders of the peripheral nerve system (PNS) are heterogeneous and may involve motor fibers, sensory fibers, small myelinated and unmyelinated fibers and autonomic nerve fibers, with variable anatomical distribution (single nerves, several different nerves, symmetrical affection of all nerves, plexus, or root lesions). Furthermore pathological processes may result in either demyelination, axonal degeneration or both. In order to reach an exact diagnosis of any neuropathy electrophysiological studies are crucial to obtain information about these variables. Conventional electrophysiological methods including nerve conduction studies and electromyography used in the study of patients suspected of having a neuropathy and the significance of the findings are discussed in detail and more novel and experimental methods are mentioned. Diagnostic considerations are based on a flow chart classifying neuropathies into eight categories based on mode of onset, distribution, and electrophysiological findings, and the electrophysiological characteristics in each type of neuropathy are discussed.

A quantitative evaluation of gross versus histologic neuroma formation in a rabbit forelimb amputation model: potential implications for the operative treatment and study of neuromas

Background

Surgical treatment of neuromas involves excision of neuromas proximally to the level of grossly "normal" fascicles; however, proximal changes at the axonal level may have both functional and therapeutic implications with regard to amputated nerves. In order to better understand the retrograde "zone of injury" that occurs after nerve transection, we investigated the gross and histologic changes in transected nerves using a rabbit forelimb amputation model.

Methods

Four New Zealand White rabbits underwent a forelimb amputation with transection and preservation of the median, radial, and ulnar nerves. After 8 weeks, serial sections of the amputated nerves were then obtained in a distal-to-proximal direction toward the brachial plexus. Quantitative histomorphometric analysis was performed on all nerve specimens.

Results

All nerves demonstrated statistically significant increases in nerve cross-sectional area between treatment and control limbs at the distal nerve end, but these differences were not observed 10 mm more proximal to the neuroma bulb. At the axonal level, an increased number of myelinated fibers were seen at the distal end of all amputated nerves. The number of myelinated fibers progressively decreased in proximal sections, normalizing at 15 mm proximally, or the level of the brachial plexus. The cross-sectional area of myelinated fibers was significantly decreased in all sections of the treatment nerves, indicating that atrophic axonal changes proceed proximally at least to the level of the brachial plexus.

Conclusions

Morphologic changes at the axonal level extend beyond the region of gross neuroma formation in a distal-to-proximal fashion after nerve transection. This discrepancy between gross and histologic neuromas signifies the need for improved standardization among neuroma models, while also providing a fresh perspective on how we should view neuromas during peripheral nerve surgery.

Proximal axonal changes after peripheral nerve injury in man

Peripheral nerve injury leads to changes in the proximal axon. Traumatic nerve injuries in humans were investigated to characterize such electrophysiological changes. Mixed nerve conduction studies (MNCS) and motor conduction studies (MCS) were performed proximal to the injury. Control values were obtained from the uninjured limb. Median (n = 24) and ulnar (n = 35) nerve injuries were studied. The injured nerves had significant mixed nerve action potential (MNAP) amplitude reductions (median: P < 0.0001; ulnar: P < 0.0001). The majority of the MNAP amplitude reductions were severe and early. There was slowing in the mixed nerve conduction velocity (MNCV) (median: P = 0.09; ulnar: P = 0.04) and motor conduction velocity (MCV) (median: P = 0.046; ulnar: P = 0.005). Axonal loss appears to play a significant role in producing the MNCS changes observed, and its early occurrence is noteworthy. Proximal MCV reduction could be secondary to the effects of injury as well as collateral sprouting of uninjured axons. Proximal axonal changes may have an impact on recovery.

Comparative proteomic profile of rat sciatic nerve and gastrocnemius muscle tissues in ageing by 2-D DIGE

Ageing induces a progressive morphological change and functional decline in muscles and in nerves. Light and electron microscopy, 2-D DIGE and MS, were applied to profile the qualitative and quantitative differences in the proteome and morphology of rat gastrocnemius muscle and sciatic nerve, in healthy 22-month-old rats. At muscle level, morphological changes are associated to fibre atrophy accompanied by myofibrillar loss and degeneration, disappearance of sarcomeres and sarcoplasmic reticulum dilatation, internal migration of nuclei, longitudinal fibre splitting, increment of subsarcolemmal mitochondria aggregates and increment of lipofuscin granules. Sciatic nerve shows myelin abnormalities like enfoldings, invaginations, onion bulbs, breakdowns and side axonal atrophy. Proteomic analysis identified changes correlated to morphological abnormalities in metabolic, contractile and cytoskeletal proteins, deregulation of iron homeostasis, change of Ca(2+) balance and stress response proteins, accompanied by a deregulation of myelin membrane adhesion protein and proteins regulating the neuronal caliber. By comparing proteomic results from the two tissues, 16 protein isoforms showed the same up and down regulation trend suggesting that there are changes implying a general process which may act as a signal event of degeneration. Only beta enolase and tropomyosin 1alpha were differentially expressed in the tissues.

Entrapment in anti myelin-associated glycoprotein neuropathy

Anti-myelin associated glycoprotein (MAG) neuropathy is a chronic disorder in which IgM antibodies react with Schwann cell glycoproteins, including MAG and peripheral myelin protein 22 (PMP22). Nerve conduction studies show features of axon loss and predominantly distal slowing consistent with demyelination. Because a genetic loss of PMP22 function yields hereditary neuropathy with liability to pressure palsies (HNPP), loss of PMP22 function due to anti- MAG antibodies may result in increased sensitivity to entrapment. We investigated this by performing standardized electrophysiological studies in 16 patients with anti-MAG neuropathy and 16 disease controls with genetically confirmed HNPP. Disproportionate slowing relative to adjacent segments occurred in similar proportions of patients with anti-MAG neuropathy and HNPP, and was of the same magnitude in each group. Affected were the elbow, carpal tunnel and the wrist-hand segments of the median and ulnar nerves. However, in anti-MAG neuropathy as compared to HNPP, absolute values of distal motor latencies and conduction velocities outside entrapment sites were slower and amplitudes were lower. In conclusion, increased sensitivity for entrapment may occur in anti-MAG neuropathy and contribute to part of the nerve damage.

The role of forearm mixed nerve conduction study in the evaluation of proximal conduction slowing in carpal tunnel syndrome

OBJECTIVE

A decrease of forearm median motor conduction velocity (CV) is a common electrophysiological finding in carpal tunnel syndrome (CTS), ascribed to two possible mechanisms: either conduction block or slowing of the fastest myelinating fibers in the carpal tunnel, or retrograde axonal atrophy (RAA) with retrograde conduction slowing (RCS). We hope to utilize both direct and derived forearm median mixed nerve conduction studies to clarify the mechanism of the decrease of forearm median motor CV in CTS.

METHODS

Seventy-five CTS patients and 75 age-matched control subjects received conventional motor and sensory nerve conduction studies of median and ulnar nerves and forearm median mixed nerve conduction techniques. First, direct measurement of forearm median mixed conduction velocity (Forearm mixed CV) and nerve action potential amplitude (Forearm mixed amplitude) was determined with recording at elbow and stimulation at wrist. Then, stimulating electrode was placed over palm and recording at elbow and then at wrist to calculate the derived Forearm mixed CV. Electrophysiological parameters, including direct Forearm mixed CV and amplitude and derived Forearm mixed CV, were compared between CTS patients and controls.

RESULTS

CTS patients had significantly prolonged wrist-palm sensory and motor conduction, significantly decreased forearm median motor CV, and normal ulnar nerve conduction. The direct Forearm mixed amplitude was significantly decreased in CTS patients. The direct Forearm mixed CV was similar in CTS patients and controls, but there was a significant decrease in derived Forearm mixed CV in CTS group. The difference between direct and derived Forearm mixed CV was significantly greater in the CTS, suggesting that direct and derived Forearm mixed CV represent CV from different nerve fibers, one passing outside carpal tunnel without undergoing RAA or the other through the carpal tunnel with occurrence of RAA.

CONCLUSION

A decrease of direct Forearm mixed amplitude really occurs in CTS, implying that RAA and RCS will develop over proximal median nerve at distal nerve injury and the decreased forearm median motor CV is best ascribed to RAA and RCS. Furthermore, in CTS, the direct Forearm mixed CV measures the CV from undamaged nerve fibers without passing through carpal tunnel, resulting in the misinterpretation of the cause of proximal conduction slowing secondary to conduction block or slowing over the wrist.

SIGNIFICANCE

We provide a direct evidence of the occurrence of RAA and RCS that would explain the cause of proximal median nerve conduction slowing. However, the clinical significance of RAA and RCS is uncertain.

Length dependence in polyneuropathy associated with IgM gammopathy

OBJECTIVE

In polyneuropathy associated with monoclonal IgM gammopathy, nerve conduction studies may show disproportionate distal slowing consistent with segmental demyelination. This was suggested to represent a length-dependent demyelinating process, starting in distal and proceeding to proximal segments. Because the evidence for this is incomplete, we assessed whether length dependence occurs in IgM neuropathy.

METHODS

In 22 patients with IgM neuropathy, 20 disease controls with chronic inflammatory demyelinating polyneuropathy (CIDP) and 36 normal controls, we investigated motor conduction, sensory conduction, and needle electromyography for nerves with short, intermediate-length, and long axons as well as conduction in short segments of the ulnar nerve from proximal to distal. To compare variables in nerves of different length, we normalized individual values with respect to the median in normal controls.

RESULTS

In IgM neuropathy, distal slowing and features of axon loss increased with nerve length, and ulnar nerve conduction became gradually slower from proximal to distal when the elbow segment was excluded. In CIDP, no clear length dependence was found except for distal amplitude.

INTERPRETATION

The disproportionate distal slowing in IgM neuropathy may be part of a length-dependent process, assuming that this process is randomly distributed due to a generalized exposure to IgM.

Ro5-4864, a synthetic ligand of peripheral benzodiazepine receptor, reduces aging-associated myelin degeneration in the sciatic nerve of male rats

The peripheral-type benzodiazepine receptor (PBR) is a protein predominantly located in the mitochondrial outer membrane that plays an important role in the regulation of cell survival and proliferation. Previous studies have shown an enhanced expression of PBR in the regenerating sciatic nerve, suggesting that this protein may be involved in the regenerative response. The rat sciatic nerve suffers important structural alterations with aging, including alterations in the morphology of myelin sheaths and a decrease in the number of myelinated fibers. In this study, we have assessed the effect of two PBR ligands, Ro5-4864 and PK-11195, to determine whether PBR may influence aging-associated morphological changes in the sciatic nerve. The treatment of 23-month-old, Sprague-Dawley male rats for 1 month with Ro5-4864 significantly reduced the percentage of fibers with myelin decompaction and increased the total number of myelinated fibers. In contrast, PK-11195, a PBR ligand that binds to a different site than Ro5-4864 in the PBR molecule, did not significantly affect any of the parameters analyzed. These findings support the potential role of PBR ligands to prevent aging-associated peripheral nerve degeneration.

Does retrograde axonal atrophy really occur in carpal tunnel syndrome patients with normal forearm conduction velocity?

OBJECTIVE

The cause of decreased median forearm motor conduction velocity (FMCV) in carpal tunnel syndrome (CTS) is best ascribed to retrograde axonal atrophy (RAA); however, the relationships between the occurrence of RAA and electrophysiological or clinical severity remains controversial. We attempt to determine whether RAA really occurs in CTS patients with normal median FMCV and to investigate any relationships between RAA and severity of compression at the wrist.

METHODS

Consecutive CTS patients were enrolled and age-matched volunteers served as controls. We performed conventional nerve conduction studies (NCS) and measured median and ulnar distal motor latencies (DML), FMCV, compound muscle action potential (CMAP) amplitudes, distal sensory latencies (DSL), and sensory nerve action potential (SNAP) amplitudes. Furthermore, palmar median stimulation was done to calculate the wrist-palm motor conduction velocity (W-P MCV). Patients included for analysis should have normal FMCV and needle examination. We compared each electrodiagnostic parameters between the patient group and controls.

RESULTS

The mean+/-SD of the W-P MCV for patients and controls were 33.26+/-6.74 and 52.14+/-5.85 m/s and those of median FMCV were 55.26+/-3.56 and 57.82+/-3.9 m/s, respectively. There was a significant reduction in the W-P MCV (36.2%, P<0.00001), significant decrease in the median FMCV (4.43%, P<0.00001) and SNAP amplitudes, and an increase of the DML and DSL in the patient group (P<0.00001) compared to the controls; however, there were no differences in median and ulnar CMAP amplitudes, ulnar FMCV and DML between the controls and patients.

CONCLUSIONS

RAA and relatively slowed median FMCV do occur in CTS patients with normal median FMCV, regardless of severity of clinical manifestations and electrophysiological abnormalities.

SIGNIFICANCE

This article provides new information for research of the electrophysiological changes of the proximal nerve part at distal injury.

Compound sensory action potential in normal and pathological human nerves

The compound sensory nerve action potential (SNAP) is the result of phase summation and cancellation of single fiber potentials (SFAPs) with amplitudes that depend on fiber diameter, and the amplitude and shape of the SNAP is determined by the distribution of fiber diameters. Conduction velocities at different conduction distances are determined by summation of SFAPs of varying fiber diameters, and differ in this respect, also, from the compound muscle action potential (CMAP) for which conduction velocities are determined by the very fastest fibers in the nerve. The effect and extent of temporal dispersion over increasing conduction distance is greater for the SNAP than CMAP, and demonstration of conduction block is therefore difficult. In addition, the effect of temporal dispersion on amplitude and shape is strongly dependent on the number of conducting fibers and their distribution, and, with fiber loss or increased conduction velocity variability changes of the SNAP may be smaller than expected from normal nerve. The biophysical characteristics of sensory and motor fibers differ, and this may to some extent determine divergent pathophysiological changes in sensory and motor fibers in different polyneuropathies. In this review, different factors that characterize sensory fibers and set the SNAP apart from the CMAP are discussed to emphasize the supplementary and complementary information that can be obtained from sensory conduction studies. Sensory conduction studies require particular effort and attention to theory and practical detail that may be time consuming.

Neuroactive steroids influence peripheral myelination: a promising opportunity for preventing or treating age-dependent dysfunctions of peripheral nerves

The process of aging deeply influences morphological and functional parameters of peripheral nerves. The observations summarized here indicate that the deterioration of myelin occurring in the peripheral nerves during aging may be explained by the fall of the levels of the major peripheral myelin proteins [e.g., glycoprotein Po (Po) and peripheral myelin protein 22 (PMP22)]. Neuroactive steroids, such as progesterone (PROG), dihydroprogesterone (5alpha-DH PROG), and tetrahydroprogesterone (3alpha,5alpha-TH PROG), are able to stimulate the low expression of these two myelin proteins present in the sciatic nerve of aged male rats. Since Po and PMP22 play an important physiological role in the maintenance of the multilamellar structure of PNS myelin, we have evaluated the effect of PROG and its neuroactive derivatives, 5alpha-DH PROG and 3alpha,5alpha-TH PROG, on the morphological alterations of myelinated fibers in the sciatic nerve of 22-24-month-old male rats. Data obtained clearly indicate that neuroactive steroids are able to reduce aging-associated morphological abnormalities of myelin and aging-associated myelin fiber loss in the sciatic nerve.

Alcoholic neuropathy is clinicopathologically distinct from thiamine-deficiency neuropathy

Characteristics of alcoholic neuropathy have been obscured by difficulty in isolating them from features of thiamine-deficiency neuropathy. We assessed 64 patients with alcoholic neuropathy including subgroups without (ALN) and with (ALN-TD) coexisting thiamine deficiency. Thirty-two patients with nonalcoholic thiamine-deficiency neuropathy (TDN) also were investigated for comparison. In ALN, clinical symptoms were sensory-dominant and slowly progressive, predominantly impairing superficial sensation (especially nociception) with pain or painful burning sensation. In TDN, most cases manifested a motor-dominant and acutely progressive pattern, with impairment of both superficial and deep sensation. Small-fiber-predominant axonal loss in sural nerve specimens was characteristic of ALN, especially with a short history of neuropathy; long history was associated with regenerating small fibers. Large-fiber-predominant axonal loss predominated in TDN. Subperineurial edema was more prominent in TDN, whereas segmental de/remyelination resulting from widening of consecutive nodes of Ranvier was more frequent in ALN. Myelin irregularity was greater in ALN. ALN-TD showed a variable mixture of these features in ALN and TDN. We concluded that pure-form of alcoholic neuropathy (ALN) was distinct from pure-form of thiamine-deficiency neuropathy (TDN), supporting the view that alcoholic neuropathy can be caused by direct toxic effect of ethanol or its metabolites. However, features of alcoholic neuropathy is influenced by concomitant thiamine-deficiency state, having so far caused the obscure clinicopathological entity of alcoholic neuropathy.

The reason for forearm conduction slowing in carpal tunnel syndrome: an electrophysiological follow-up study after surgery

BACKGROUND

The exact cause of decreased forearm median motor conduction velocity (FMMCV) in carpal tunnel syndrome (CTS) is still a subject of controversy. A conduction block or an axonal loss in the large myelinating fibers upon wrist compression, or retrograde axonal atrophy, is suspected.

METHODS

In order to attempt a determination of the cause, 10 patients with clinical symptoms and signs of CTS, confirmed using standard electrodiagnosis and with a slowed FMMCV <50m/s, were included in this study. Serial standard median motor conduction studies were performed at baseline, 1 week, 2 weeks, 4 weeks, 8 weeks, and 12 weeks after endoscopic ligament release. Serial median motor distal latencies (MMDL), compound muscle action potential (CMAP) amplitudes, and FMMCV, were determined and compared.

RESULTS

Significant improvement in MMDL had occurred at the 1-week follow-up examination; however, no such improvement in FMMCV was observed. Furthermore, a significant increase in CMAP amplitude was evidenced beginning 4 weeks after surgery. The results revealed an improvement in median motor conduction, across the wrist segment, that did not parallel the increase in FMMCV, suggesting that a conduction block or axonal loss at wrist compression was not the likely cause of the decreased FMMCV.

CONCLUSIONS

Retrograde axonal atrophy, not selective damage to the large myelinating fibers at the wrist, is the direct cause of decreased FMMCV in CTS.

Forearm mixed nerve conduction velocity: questionable role in the evaluation of retrograde axonal atrophy in carpal tunnel syndrome

The objective of this study was to determine whether forearm mixed nerve conduction velocity (Fmix) reflects the real conduction velocity of forearm motor nerve (Fmot) and forearm sensory nerve (Fsen) fibers passing through the carpal tunnel. Forearm mixed nerve conduction velocity is presumed to be indicative of the conduction velocity of the median nerve over the forearm. Therefore, Fmix is used widely to assess the causes of slowing forearm conduction velocity in carpal tunnel syndrome. However, some authors claim that Fmix comes chiefly from the undamaged fibers in carpal tunnel syndrome, and thus cannot replace Fmot or Fsen in the evaluation of retrograde axonal atrophy. Patients with clinical symptoms and signs of carpal tunnel syndrome confirmed with standard electrodiagnosis were included. Age-matched volunteers served as control subjects. Conduction velocities across the wrist and over the forearm were measured, including those of the wrist sensory (Wsen), wrist motor (Wmot), and wrist mixed nerves (Wmix); and forearm mixed (Fmix), forearm motor (Fmot), and forearm sensory nerves (Fsen). The authors compared and correlated Wsen, Wmot, and Wmix; and Fmix, Fmot, and Fsen respectively. The mean values of Wsen, Wmot, Wmix, Fmix, Fmot, and Fsen of the control subjects less those of corresponding conduction velocity of carpal tunnel syndrome patients were designated Wsen N, Wmot N, Wmix N, Fmix N, Fmot N, and Fsen N respectively and were compared and correlated again. Wrist motor nerve conduction velocity, Wsen, and Wmix were significantly lower in carpal tunnel syndrome patients, and Fmot and Fsen but not Fmix were reduced significantly when compared with control subjects. Mean wrist sensory nerve conduction velocity, Wmot N, and Wmix N; and Fsen N and Fmot N showed good correlation except for Fmix N, suggesting that Fmix reflects the conduction velocity of undamaged fibers in carpal tunnel syndrome. Forearm mixed nerve conduction velocity cannot replace Fmot or Fsen in the assessment of retrograde axonal atrophy in carpal tunnel syndrome. In the disease state, Fmix possibly represents the conduction velocity of the palmar cutaneous branch.

Does direct measurement of forearm mixed nerve conduction velocity reflect actual nerve conduction velocity through the carpal tunnel?

OBJECTIVES

The purpose of this study was to determine whether forearm (wrist-elbow) mixed nerve conduction velocity (W-Emix) represents the actual nerve conduction velocity (CV) of nerve fibers passing through the carpal tunnel.

BACKGROUND

W-Emix is presumed to reflect the actual forearm CV through the carpal tunnel. However, it has been argued that W-Emix chiefly originates from the nerve fibers passing outside the carpal tunnel. Therefore, the direct measurement of W-Emix cannot be used to assess retrograde axonal atrophy in carpal tunnel syndrome (CTS).

SUBJECTS AND METHODS

Thirty patients with clinical signs and symptoms of CTS were recruited and the diagnosis was confirmed with standard electrodiagnosis. Fifty age-matched volunteers served as control. Recording electrodes were placed over the elbow and index finger for mixed nerve and sensory nerve conduction studies, respectively. Stimulation was applied at the palm and wrist for the measurement of mixed nerve wrist-palm CV (W-Pmix), wrist-elbow CV (W-Emix), and elbow-palm CV (E-Pmix). Stimulation was applied at the elbow, wrist, and palm for the measurement of wrist-elbow sensory CV (W-Esen), wrist-palm CV (W-Psen), and elbow-palm CV (E-Psen). Comparisons were made between W-Pmix and W-Psen, W-Emix and W-Esen, and E-Pmix and E-Psen.

RESULTS

Correlations between W-Emix and W-Esen, E-Pmix and E-Psen, and W-Pmix and W-Psen were good in the control. In the patient group, there was a strong positive correlation between W-Pmix and W-Psen, and between E-Pmix and E-Psen. However, W-Esen correlated weakly with W-Emix, suggesting that W-Emix chiefly represents the CV of fibers passing outside the carpal tunnel. Therefore, the direct measurement of W-Emix cannot be used to assess retrograde axonal atrophy. Furthermore, the reduction in W-Psen was more marked than the reduction in W-Esen, implying that a conduction block at the wrist is the least likely cause of proximal slowing in CTS.

CONCLUSIONS

W-Emix does not reflect the actual CV of the nerve fibers passing through the carpal tunnel. In addition, retrograde axonal atrophy appears to be the primary cause of decreased forearm CV in CTS.

Can electrophysiology differentiate polyneuropathy with anti-MAG/SGPG antibodies from chronic inflammatory demyelinating polyneuropathy?

OBJECTIVES

Patients with polyneuropathy and antibodies to myelin-associated glycoprotein (MAG) and sulphated glucuronyl paragloboside (SGPG) differ from chronic inflammatory demyelinating polyneuropathy (CIDP) because of a slower, progressive course, symmetrical and predominantly sensory involvement of legs, predominantly distal slowing of motor conductions, and poorer response to therapy. We studied whether a wide set of electrophysiologic parameters may differentiate these two neuropathies.

METHODS

We reviewed the electrophysiological studies of 10 patients with anti-MAG/SGPG antibodies and 22 with CIDP examining: (1) motor conduction velocity and distal compound muscle action potential amplitude; (2) conduction block (CB) and temporal dispersion; (3) distal motor latency and terminal latency index (TLI); (4) F wave and proximal conduction time; and (5) sensory conduction and occurrence of abnormal median with normal sural sensory potential.

RESULTS

Anti-MAG/SGPG neuropathies showed: (1) more severe involvement of peroneal nerves; (2) more frequent disproportionate distal slowing of motor conductions (TLI< or =0.25) and absent sural potential, and (3) no CB. However 3/22 CIDP patients also had at least two nerves with TLI< or =0.25 and no CB.

CONCLUSIONS

Electrophysiologic findings suggest in anti-MAG/SGPG neuropathy a length-dependent process with a likely centripetal evolution. A disproportionate slowing of conduction in distal segments of motor nerves suggests the diagnosis of anti-MAG/SGPG neuropathy, although it is not pathognomonic.

Cerebrotendinous xanthomatosis. Controversies about nerve and muscle: observations in ten patients

Neuromuscular characteristics were documented in ten patients with biochemically and genetically confirmed cerebrotendinous xanthomatosis. An array of genotypes was found in these patients. Only one patient complained of muscle weakness, while clinical signs of peripheral neuropathy were present in six patients. Electromyogram showed predominantly axonal neuropathy in seven patients. Neurogenic changes were seen in muscle biopsies of nine patients. Sural nerve biopsies of three patients showed features of axonal neuropathy. In addition, in one patient, extensive onion bulb formation was seen, which is indicative of a primarily demyelinating process. Five patients had normal mitochondrial respiratory chain enzyme activity. It is concluded that myopathy is not a feature of cerebrotendinous xanthomatosis and that the most prominent neuromuscular abnormality is sensorimotor axonal polyneuropathy.

Microvasculitis in non-diabetic lumbosacral radiculoplexus neuropathy (LSRPN): similarity to the diabetic variety (DLSRPN)

Diabetic lumbosacral radiculoplexus neuropathy (DLSRPN) has been shown to be due to ischemic injury from microvasculitis. The present study tests whether ischemic injury and microvasculitis are the pathologic cause of non-diabetic lumbosacral radiculoplexus neuropathy (LSRPN), and whether the pathologic alterations are different between LSRPN and DLSRPN. We studied distal cutaneous nerve biopsies of 47 patients with LSRPN and compared findings with those of 14 age-matched healthy controls and 33 DLSRPN patients. In both disease conditions, we found evidence of ischemic injury (multifocal fiber degeneration and loss, perineurial degeneration and scarring, characteristic fiber alterations, neovascularization, and injury neuroma) that we attribute to microvasculitis (mural and perivascular mononuclear inflammation of microvessels, inflammatory separation, fragmentation and destruction of mural smooth muscle, and previous microscopic bleeding [hemosiderin]). Teased nerve fibers in LSRPN showed significantly increased frequencies of axonal degeneration, segmental demyelination, and empty nerve strands. The segmental demyelination appeared to be clustered on fibers with axonal dystrophy. The nerves with abnormal frequencies of demyelination were significantly associated with nerves showing multifocal fiber loss. We reached the following conclusions: 1) LSRPN is a serious condition with much morbidity that mirrors DLSRPN. 2) Ischemic injury from microvasculitis appears to be the cause of LSRPN. 3) Axonal degeneration and segmental demyelination appear to be linked and due to ischemia. 4) The pathologic alterations in LSRPN and DLSRPN are indistinguishable, raising the question whether these 2 conditions have a common underlying mechanism, and whether diabetes mellitus contributes to the pathology or is a risk factor in DLSRPN. 5) Both LSRPN and DLSRPN are potentially treatable conditions.

Aging in peripheral nerves: regulation of myelin protein genes by steroid hormones

The process of aging deeply influences morphological and functional parameters of the peripheral nerves. Interestingly, recent observations performed in our laboratory on the rat sciatic nerves have indicated that the deterioration of myelin occurring in the peripheral nerves during aging may be explained by the fall of the messenger levels of the major peripheral myelin proteins (glycoprotein Po, myelin basic protein and peripheral myelin protein 22). At least in the case of the Po, the low levels of its messengers and of the protein itself found in aged animals are increased by the treatment with a physiological progesterone derivative like dihydroprogesterone. It has also been found that in normal adult male rats the levels of the messengers for Po in the sciatic nerve are increased by progesterone, dihydroprogesterone and tetrahydroprogesterone; surprisingly, the gene expression of peripheral myelin protein 22 is stimulated only by tetrahydroprogesterone. These observations have been confirmed in parallel studies performed on Schwann cell cultures. Since tetrahydroprogesterone does not bind to the progesterone receptor but is a ligand for the GABAA receptor, the hypothesis has been put forward that part of the steroidal effects reported might occur not through the classical progesterone receptor, but rather via an interaction with the GABAA receptor. In other experiments it has been found that the gene expression of Po may be decreased by orchidectomy and restored by treatment with the androgen dihydrotestosterone. Altogether, these observations suggest the future use of physiological and/ or synthetic steroid hormones as a possible therapeutic approach for some pathological situations occurring in peripheral nerves during aging and demyelinating diseases.

Myelinated fibers in Charcot-Marie-Tooth disease type 1B with Arg98His mutation of Po protein

This study was undertaken to characterize the clinical, electrophysiologic, and histopathologic features of five presumably unrelated Japanese patients with Charcot-Marie-Tooth (CMT) disease type 1B and Arg98His substitution of Po protein and, in particular, to correlate Arg98His substitution to the ultrastructural abnormalities of the myelin sheath. Systematic morphometric studies of the sural nerve, where the CMT type 1B gene abnormality is expressed, have not been performed, especially on the basis of the type of mutation causing CMT type 1B. Electrophysiologic evaluation of limb nerves and morphometric analysis of sural nerves obtained at biopsy were performed. Ultrastructural myelin abnormalities were precisely examined. Clinical symptoms appeared from the second to the fifth decade. All probands presented with gait disturbance. Motor and sensory conduction velocities in the median and ulnar nerves ranged from 10 to 30 m/s. Segmental demyelination and remyelination and marked loss of myelinated fibers were the main findings. On electron microscopy, widening between major dense lines was found between the paired intraperiod lines, where the extramembranous portion of the Po protein resides. This widening is probably directly related to Arg98His substitution. Focal uncompaction of major dense lines coexisted with this widening. This uncompaction, which directly decreases the number of myelin lamellae, may be a secondary effect of Arg98His substitution on the intramembranous domain of Po protein. In conclusion, myelin changes at both extracellular and cytoplasmic appositions of Schwann cell membranes were found in association with Arg98His substitution of Po protein. This study contributes to a better understanding of myelin abnormalities in patients with CMT type 1B and Arg98His or other similar extramembranous amino acid substitutions of Po protein.

FK506 and the role of the immunophilin FKBP-52 in nerve regeneration

In summary, FKBP-12 does not mediate the neurite outgrowth-promoting properties of neuroimmunophilin ligands (e.g., FK506). Instead, the neurotrophic properties of neuroimmunophilin ligands (FK506) and steroid hormones are mediated by disruption of steroid-receptor complexes. It remains unclear which component mediates neurite outgrowth, although the most likely candidates are FKBP-52, hsp-90, and p23 [42]. Regardless of the underlying mechanism involved, the FKBP-52 antibody data reveal that it should be possible to design, based on the structure of FK506, non-FKBP-12-binding (nonimmunosuppressant) compounds selective for FKBP-52 and test these new libraries for their ability to augment nerve regeneration. It may also be possible to exploit the structure of geldanamycin to develop a new class of hsp-90-binding compounds for use in nerve regeneration.

Age-related biology and diseases of muscle and nerve

Age-related biological changes in neurons and skeletal muscle commonly affect neuromuscular function and strongly influence the expression of neuromuscular disease. Of primary importance is the attrition of entire motor units, with resultant neurogenic atrophy of skeletal muscle. Other age-related processes are sensory neuron loss, distal axonal degeneration, axonal atrophy, accumulation of multiple mitochondrial DNA mutations in muscle, and physical inactivity and deconditioning. The decline for most of these begins in early life and proceeds steadily; the curious lack of an abrupt falloff with age is not yet accounted for by any theory of pathogenesis.

Inhibition of axonal growth from sensory neurons by excess nerve growth factor

Fifteen-day embryonic rat dorsal root ganglion (DRG) neurons were exposed to 1 to 200 ng/ml nerve growth factor (NGF). Maximal neurite outgrowth was obtained with 10 to 20 ng/ml. Neurite outgrowth was reduced to 89% of maximal by increasing NGF to 50 ng/ml, to 66% by 100 ng/ml, and to 18% by 200 ng/ml NGF. Identical effects were seen with mouse 2.5S NGF and recombinant human NGF. Neuron cell counts demonstrated that significant cell death did not occur. In time course experiments, significant inhibition, compared with control, began within 1 hour of adding 200 ng/ml and 3 hours of adding 50 ng/ml NGF. The inhibitory effect of NGF on neurite outgrowth was reversed within 3 hours when DRG were incubated with 5 ng/ml NGF after treatment with 50 or 200 ng/ml NGF medium for 12 hours. The inhibition demonstrated for neurons did not occur in PC12 cells; axonal growth was not inhibited by up to 1,000 ng/ml NGF. Excess brain-derived neurotrophic factor or neurotrophin-3 did not inhibit neurite outgrowth. We conclude that high concentrations of NGF produces specific and reversible arrest of neurite outgrowth from sensory neurons. This observation has important clinical implications, because these inhibitory concentrations have been exceeded when NGF has been administered into the central nervous system of humans and animals.

Recovery of sympathetic skin responses after digit-to-digit replantation and toe-to-digit transplantation in humans

Sympathetic skin response was utilized to study recovery of sudomotor function in 8 patients who had digit-to-digit replantation and 9 patients who had toe-to-digit transplantation. Sympathetic skin responses evoked by median nerve stimulation or magnetic stimulation of the neck were recorded from the tip of the replanted digits or transplanted toes. The contralateral normal fingers served as controls. The mean intervals between surgery and study were 33 and 37 months, respectively, for digit replantation and toe transplantation. In normal subjects, the sympathetic skin responses recorded from the fingertip were abolished by local anesthesia or cooling of the finger, while those recorded from the palm were not affected. Ischemia of the finger only transiently affected the digit sympathetic skin responses. These data indicate that the digit responses were locally generated and mediated by unmyelinated fibers. After digit replantation, the palm and digit sympathetic skin responses were not different between replanted and normal sides. After toe transplantation, palm sympathetic skin responses were normal, but digit ones had prolonged latency and reduced amplitude. The present findings suggest that recovery of sympathetic sudomotor activity can be nearly complete in digit replantation but less satisfactory in toe transplantation.

Target influence on aging of myelinated sensory nerve fibres

Large myelinated fibres in the rat inferior alveolar nerve (IAN) exhibit age-related aberrations partly similar to alterations in target-deprived nerves. Shortly after entering the mandibular canal the rat IAN splits into a mental (MN) and an inferior dental (IDN) portion. This offers a possibility to compare the occurrence of age-related aberrations in the MN and the IDN, which project to different target types. Hence, we examined the relation between internodal length (L) and fibre diameter (D) in teased fibre preparations of MNs and IDNs from adult rats of different ages. The results show that the relation L/D is similar in MNs and IDNs of 6- to 24-month-old rats and that it is significantly more irregular in IDNs than in MNs of 26- to 30-month-old rats. This difference may be related to the fact that the IDN-innervated mandibular dentition is deteriorating in rats older than 2 years, whereas the muco-cutaneous target of the MN is not. We suggest that target deterioration may be one major factor behind the increasing incidence of structural aberrations in large myelinated peripheral nerve fibres.

The neuropathology of cerebrotendinous xanthomatosis revisited: a case report and review of the literature

Cerebrotendinous xanthomatosis (CTX), a rare autosomal-recessive lipid storage disease, has been well characterized clinically and biochemically, and recently also from the molecular biological aspect. However, only a very few publications deal with its neuropathology, and views on its pathogenesis vary. Based on a recently examined case, we propose that central-peripheral distal axonopathy is the major pathogenetic mechanism of nervous system injury in CTX. The latter is characterized by white matter pathology, typically in form of long tract involvement with the more distal parts of the tract more severely affected. Most severely affected are the cerebellar white matter, the optic pathways and the long tracts of the brain stem and spinal cord, particularly the pyramidal tracts, although there is hardly a CNS region which does not display some form of pathology. Lesions are characterized by loss of myelinated fibers and accumulation of lipid products in form of foamy macrophages, clear oil-red-O-positive spaces and crystalline clefts, accompanied by gliosis, occasional axonal spheroids, and in the cerebellum--the most severely affected structure--also by multi-nucleated foreign body giant cells. Demyelination is not seen, and ultrastructurally myelin sheaths are normally structured. Signs of axonal degeneration are also present in the spinal roots. We hypothesize that the basic enzymatic defect in CTX leads to accumulation of metabolites in the brain which may be neurotoxic and may impair the metabolic apparatus of neurons with resultant axonopathy and subsequent nonspecific lipid deposition in the injured tracts.

Differentiation between axonal and demyelinating neuropathies: identical segments recorded from proximal and distal muscles

The presence of significant slowing of motor nerve conduction velocity is considered one of the electrodiagnostic hallmarks of demyelinating neuropathies; however, slowing of conduction velocity may also accompany severe axonal loss. When compound muscle action potential (CMAP) amplitudes are markedly reduced, it is frequently difficult to determine if conduction velocity slowing is due to axonal loss with dropout of the fastest conducting fibers or demyelination. To evaluate the relationship between conduction velocity and axonal dropout, we compared conduction velocities through the same segment of nerve recording from distal and proximal peroneal muscles in patients with chronic neuropathies, in patients with motor neuron disease, and in control subjects. In controls and patients with motor neuron disease, conduction velocities were normal with no significant difference between proximal and distal sites. In patients with axonal neuropathies, conduction velocities were preferentially slowed when recording from distal muscles and relatively normal when recording from proximal sites. Patients with demyelinating neuropathies showed marked slowing of conduction at both sites. We conclude that comparing conduction velocity obtained from proximal versus distal muscle recordings provides a simple, reliable aid for differentiating between chronic axonal and demyelinating polyneuropathies, especially in cases with conduction velocity slowing and low CMAP amplitudes.

Primary sensory neurons in X-linked recessive bulbospinal neuropathy: histopathology and androgen receptor gene expression

Pathology of the primary sensory neurons was examined in 7 autopsied patients and 6 biopsied sural nerves from the patients with X-linked recessive bulbospinal neuronopathy (SBMA). Large myelinated fibers in the central rami (L-4 posterior root, L-4, T-7, and C-6 segment of the fasciculus gracilis), and in the peripheral rami (sural nerve) were diminished in a distally accentuated manner, while small myelinated and unmyelinate fibers were well preserved in number. Demylinating process and axonal atrophy was ubiquitous. The diameter frequency histograms of the dorsal root ganglion (DRG) neurons showed a decrease in the number of large diameter neurons and an increase in the number of small diameter neurons without substantial loss of whole number of neurons, which suggested that neuronal size was atrophied. These data suggested central and peripheral distal axonopathy with neuronal atrophy was the process of sensory neuron involvement. Expression of mutant androgen receptor mRNA with elongated CAG repeat in the DRG and sural nerve supported the view that sensory nerve involvement is the primary process in SBMA.

Teeth and tooth nerves

(1) Although our knowledge on teeth and tooth nerves has increased substantially during the past 25 years, several important issues remain to be fully elucidated. As a result of the work now going on at many laboratories over the world, we can expect exciting new findings and major break-throughs in these and other areas in a near future. (2) Dentin-like and enamel-like hard tissues evolved as components of the exoskeletal bony armor of early vertebrates, 500 million years ago, long before the first appearance of teeth. It is possible that teeth developed from tubercles (odontodes) in the bony armor. The presence of a canal system in the bony plates, of tubular dentin, of external pores in the enamel layer and of a link to the lateral line system promoted hypotheses that the bony plates and tooth precursors may have had a sensory function. The evolution of an efficient brain, of a head with paired sense organs and of toothed jaws concurred with a shift from a sessile filter-feeding life to active prey hunting. (3) The wide spectrum of feeding behaviors exhibited by modern vertebrates is reflected by a variety of dentition types. While the teeth are continuously renewed in toothed non-mammalian vertebrates, tooth turnover is highly restricted in mammals. As a rule, one set of primary teeth is replaced by one set of permanent teeth. Since teeth are richly innervated, the turnover necessitates a local neural plasticity. Another factor calling for a local plasticity is the relatively frequent occurrence of age-related and pathological dental changes. (4) Tooth development is initiated through interactions between the oral epithelium and underlying neural crest-derived mesenchymal cells. The interactions are mediated by cell surface molecules, extracellular matrix molecules and soluble molecules. The possibility that the initiating events might involve a neural component has been much discussed. With respect to mammals, the experimental evidence available does not support this hypothesis. In the teleost Tilapia mariae, on the other hand, tooth germ formation is interrupted, and tooth turnover ceases after local denervation. (5) Prospective dental nerves enter the jaws well before onset of tooth development. When a dental lamina has formed, a plexus of nerve branches is seen in the subepithelial mesenchyme. Shortly thereafter, specific branches to individual tooth primordia can be distinguished. In bud stage tooth germs, axon terminals surround the condensed mesenchyme and in cap stage primordia axons grow into the dental follicle.(ABSTRACT TRUNCATED AT 400 WORDS)

Retrograde effects of digital nerve severance on somatosensory evoked potentials in man

To determine if retrograde conduction changes might occur long after injury of the most distal peripheral nerves, short-latency somatosensory evoked potentials (SEPs) to median or ulnar nerve stimulation at the wrist were studied in 10 subjects who had sustained traumatic digit amputation 4 months to 15 years previously. SEPs were recorded from Erb's point (N9), the cervical region (N13), and the contralateral scalp hand area (N20). While N9 latency was slightly delayed or not affected, the amplitude was either markedly reduced or undetectable. For N13 and N20 components, latency prolongation and amplitude reduction were mild to moderate, but the central conduction time (N13-N20) remained normal. The present data indicate that even the most distal nerve injury may have profound long-term retrograde effects on parental nerve function which are presumed mainly due to an axonopathy.

A quantitative pathological investigation of the cervical cord, roots and ganglia after long-term amputation of the unilateral upper arm

A pathological study was conducted on an autopsied patient who had undergone amputation of the right arm at the level of the shoulder 38 years prior to death. The numbers of anterior horn cell, spinal ganglion cells and myelinated fibers in the anterior and posterior spinal roots at the cervical segments were examined quantitatively and compared with those of age-matched control subjects. On the amputation side, anterior horn cells, spinal ganglion cells and large myelinated fibers of the anterior and posterior roots were decreased in number. In addition, on the spared side, the medium-sized neurons of Rexed's lamina IX were shrunken, or decreased in number, and the number of small- and medium-sized myelinated fibers in the anterior roots was decreased. These findings indicate that the long-term effects of axonal amputation induce retrograde degeneration of the anterior horn and spinal ganglion cells on the amputation side, resulting in atrophy and a decrease of medium-sized neurons in the anterior horn even on the contralateral, spared side.

Hereditary motor and sensory neuropathy: HMSN type II (neuronal type) and X-linked HMSN

The neuronal forms of hereditary motor and sensory neuropathy (HMSN) are genetically heterogeneous with observed autosomal dominant, autosomal recessive and X-linked dominant inheritance. All three forms are characterized by degeneration of select populations of motor and sensory neurons with accompanying atrophy and degeneration of their axons. Large calibre myelinated fibres are predominantly affected and fibre degeneration and fibre loss progresses from distally to proximally. Attempts of regeneration are noted in all except the severe childhood form. The clinical picture is that of peroneal and distal leg muscle wasting and weakness, distal sensory loss and areflexia. Hand muscles may be severely affected in the autosomal recessive and X-linked dominant forms. Motor and sensory nerve conduction velocities are only moderately slowed and evoked maximum compound motor and sensory amplitudes are reduced according to the degree of fibre loss. The gene locus remains unknown in both the autosomal dominant and autosomal recessive types. For the X-linked dominant HMSN, the gene locus has been mapped closely by linkage analysis to DNA loci in the pericentromeric region of the X-chromosome.