Unmyelinated nerve fiber estimation by immunocytochemistry. Correlation with electron microscopy

Electron microscopy (EM) is currently required for quantitation of unmyelinated nerve fiber (UMNF) densities. Electron microscopy is time-consuming, costly, and generally only considers a fraction of an entire nerve. Anti-PGP 9.5, which recognizes a neuron-associated antigen, may be used in glutaraldehyde-fixed, paraffin-embedded human sural nerve biopsies to identify unmyelinated axons. In nerves counterstained with Luxol fast blue, the correlation between EM-obtained UMNF densities and paraffin-obtained UMNF densities was excellent (p < 0.0001). In addition, myelinated nerve fiber (MNF) densities estimated by the same method from paraffin-embedded nerve gave excellent correlation with traditional morphometric estimates (p = 0.0026). PGP 9.5 immunocytochemistry enables the detection of minute axons (< 0.5 microns) and multiple axons per Schwann cell subunit, but does not allow for the preparation of accurate fiber size histograms or the analysis of UMNF pathology. Whether used for UMNF quantitation or as a qualitative review of the UMNF population of a nerve, this method is quicker and less expensive than traditional EM methodologies.

Microtubules stability in human peripheral nerves

We examined the cold stability of microtubules (MT) in biopsied sural nerves. In control nerves, cold treatment reduced the density of MT in unmyelinated axons. The proportion of cold-insoluble MT was approximately 30% by morphological study. By contrast, the extraction study using essentially the same nerves showed that the ratio of cold-insoluble tubulin was 60-75%. These findings suggest the existence of a subpopulation of cold-stable tubulin which may not make up MT. However, in 2 patients with acute dysautonomia the proportion of cold-stable MT or tubulin was decreased compared to that in controls in both the morphological and extraction study. This suggests the altered local process involving MT in primary axonal degeneration.

[Optic atrophy, sensorineural deafness and sensory neuropathy]

We present a patient with slowly progressing optic atrophy, sensorineural deafness and sensory neuropathy. Clinical examination and testing revealed the exclusively sensorineural nature of this syndrome. Nerve biopsy pointed to primary degeneration. Our review of the literature indicates that this syndrome is categorized as heredo-degenerative.

A comparison of perineurial and vascular basal laminal changes in diabetic neuropathy

Measurements were made of the thickness of the basal lamina of perineurial cells in the sural nerve in a series of patients with diabetic neuropathy and compared with a group of patients with type I hereditary motor and sensory neuropathy (HMSN) and with organ donor control cases. The thickness was significantly greater in the diabetic patients as compared both with the HMSN cases and the organ donor controls. This was most obvious for the intermediate layers of the perineurium. Perineurial basal laminal thickness was only slightly greater in the HMSN cases than in the organ donor controls and the difference was not statistically significant. The thickening of the perineurial cell basal laminae was compared with the thickening of the basal laminal zone around the endoneurial microvessels. No significant correlation was found either for the diabetic neuropathy or HMSN cases or for the organ donor controls. As had been observed previously, the basal laminal zone around the endoneurial capillaries was of increased thickness both in the diabetic neuropathy and the HMSN cases and, although it was greater for the diabetic neuropathy patients, the difference was not statistically significant. Taken together, these findings indicate that the thickening of the basal lamina of the perineurial cells is a more characteristic feature of diabetic neuropathy than is thickening of the basal laminal zone around the endoneurial capillaries. The results suggest that the causative mechanisms are likely to differ, a conclusion supported by the morphological appearances: the basal laminal thickening around the perineurial cells is uniform, whereas that around the capillaries consists of basal laminal reduplication.(ABSTRACT TRUNCATED AT 250 WORDS)

Axonal regeneration in an articular branch following rat sciatic nerve lesions

This study examines the outcome of axonal regeneration in the posterior articular nerve of the adult rat knee joint (PAN), after sciatic nerve lesions. Some animals had previously been subjected to chemical sympathectomy with guanethidine. In crushed cases the number of myelinated PAN axons was 50% above control level. The occurrence of C-fibers was doubled, mainly due to an increased number of sympathetic efferents. In neurotomy/suture cases the number of myelinated fibers was clearly elevated, but the number of C-fibers was close to normal. Most C-fibers were sensory. Similar, but less marked, post-regeneration abnormalities were seen in the nerve to the lateral gastrocnemius muscle. The sural nerve exhibited moderately increased numbers of myelinated and unmyelinated fibers in crushed cases. In neurotomy cases, the myelinated axons had increased and the C-fibers had decreased in number. The size distribution of myelinated PAN axons was less abnormal in crushed cases than after neurotomy, like in the other nerves. These results show that the outcome of axon regeneration in an articular branch of the lesioned rat sciatic nerve differs from that in non-articular branches, and suggest that joints may become hyperinnervated by C-fibers after nerve crush lesions.

Different effects of 4-aminopyridine on regenerated cutaneous and muscular rat sciatic nerve branches

Developing and regenerated myelinated rat dorsal and ventral root fibers respond differently to the fast potassium channel blocking agent 4-aminopyridine (4-AP). To pursue this issue further, we made unilateral sciatic nerve crushes in adult rats. Sural (SN) and lateral gastrocnemius (LGN) nerve branches were collected 4-6 months later, for physiological and morphological examination. Regenerated and control nerves in Ringers solution showed generally similar compound action potential (CAP) waveforms, but CAPs of regenerated SNs and LGNs in 4-AP were markedly different. While regenerated SNs showed a prominent late CAP negativity with a "rippled" appearance and markedly compromised recovery properties, the CAP and recovery properties of regenerated LGNs were minimally changed. Light and electron microscopic examination of SN and LGN fibers failed to reveal any features obviously related to the observed physiological differences. We conclude, that the effect of 4-AP on regenerated cutaneous afferents differs from its action on regenerated muscular afferents and efferents. This physiological diversity lacks obvious structural correlates.

A statistical approach to fiber diameter distribution in human sural nerve

Fifty-one normal sural nerve biopsies were obtained from 800 diagnostic biopsies. The external diameter distribution of myelinated fibers was described using the sum of two beta probability density functions, describing the thin as well as the thick fiber group. A cross-sectional study using these distribution functions showed increasing values of the peak of the larger fiber group, the diameter of the thickest fibers, and the separation between the smaller and the larger groups until the beginning of adult life. The transition from a uni- into a bimodal histogram occurred gradually between 7 and 13 months. Total transverse fascicular area increased with age, whereas fiber density decreased significantly with age. The number of fibers remained stable over age. The relative proportion of the numbers of fibers in both groups described by one of the beta distributions remained constant over age. This occurred despite a marked decrease in the number of small fibers with a diameter less than, e.g., 6.5 microns. The results indicated an outgrowth of especially the larger myelinated fibers with age. This process continues with decreasing intensity into adult life.

Chronic inflammatory demyelinating polyneuropathy or hereditary motor and sensory neuropathy? Diagnostic value of morphological criteria

The pathological changes generally considered to distinguish chronic inflammatory demyelinating polyneuropathy (CIDP) from hereditary motor and sensory neuropathy (HMSN) are: mononuclear cell infiltrates, prominent endoneurial oedema, and marked fascicle-to-fascicle variability. We evaluated the diagnostic significance of these pathological features which are suggestive of CIDP. Nerve biopsies from 42 dominant HMSN type I cases with a normal disease course were investigated for the occurrence of inflammatory features. A small cluster of mononuclear cells was found in 12% of the cases and marked endoneurial oedema in 21%. Variability in pathology between the fascicles was not observed. The histogram configuration yielded additional information for differential diagnosis. Subsequently, we reviewed the clinical, electrophysiological and morphological features of 18 sporadic cases of chronic progressive demyelinating motor and sensory neuropathy with mainly classic onion bulbs in their nerve biopsies and a disease onset in the first decade. In all these patients DNA investigation for the 17p11.2 duplication was performed. According to the results of the DNA investigation, autosomal dominant HMSN type Ia was diagnosed in eight patients, although in six slight 'CIDP-positive' features were present. A diagnosis was definite or most probable CIDP in eight patients. In two patients no definite diagnosis could be made. Testing for the presence of the 17p11.2 duplication is, therefore, helpful in distinguishing between CIDP and HMSN type I. The diagnosis of CIDP requires careful evaluation of the clinical, electrophysiological and morphological data to avoid false-positive diagnoses of inflammatory disorders.

Choreo-acanthocytosis like phenotype without acanthocytes: clinicopathological case report. A contribution to the knowledge of the functional pathology of the caudate nucleus

Detailed clinical and neuropathological findings in two unrelated patients with a chorea-acanthocytosis-like phenotype (CA) are reported. One case met all the diagnostic criteria of CA and had a deceased brother with the same disease. The second case had a virtually identical phenotype to the former but without acanthocytes. These findings suggest that both patients are affected by the same disease and that acanthocytes are not essential to the diagnosis. Neuropathological autopsy studies on the brain of the second case showed selective atrophy of the caudate nucleus that seemed to correspond to the movement disorder and behavioural abnormalities prominent in this patient. In both subjects, morphometric and ultrastructural examination of the peripheral nerve showed loss of myelinated fibres, more accentuated distally, and cytoskeletal changes in the axoplasm. These findings support the hypothesis that peripheral neuropathy in CA is caused by distal axonopathy.

Somatosensory evoked potentials induced by stimulating a variable number of nerve fibers in rat

Somatosensory evoked potentials (SEPs) were recorded from rat spinal cord (sSEPs) and cerebral cortex (cSEPs). Stimulus sites included either one or both sural nerve branches having different fiber populations (group A), or distal to a lesion of controlled size of the sural nerve made 1 week earlier (group B). In the two groups of animals, amplitudes of SEPs correlated with the quantity of large myelinated nerve fibers. Peak latencies of sSEPs in group A related to the ratio of sizes of transmitting fibers. sSEPs and cSEPs in both groups A and B could be recorded in a reproducible fashion by stimulating sural nerve branches or lesioned nerve trunks containing only 100 or less nerve fibers greater than 4 microns in size. Thus, presence of sSEPs or cSEPs after stimulation distal to a lesion site does not insure that many nerve fibers have continuity with the central nervous system (CNS).

Dominantly inherited motor and sensory neuropathy with excessive myelin folding complex

The two patients in a family having the clinical and electrodiagnostic features of hereditary motor and sensory neuropathy (HMSN) are described. The main histological features of sural nerve were segmental demyelination and remyelination with moderate to marked loss of myelinated fibers, and myelin folding complex along all of the large and small myelinated fibers. These features appeared morphologically similar to those observed in HMSN with excessive myelin outfolding, or globular neuropathy. Southern blot analysis suggests that there were neither duplication nor deletion of the peripheral myelin protein-22 gene in the patients. The presented two patients may be a rare form of dominantly inherited HMSN with myelin folding complex.

Renaut bodies contain elastic fiber components

Renaut bodies (RB) are fusiform endoneurial structures preferentially found at sites of nerve entrapment, often occupying more than 30% of the cross-sectional area of a nerve fascicle. Their composition and significance, however, are still incompletely understood. In this study, further evidence for the link between the appearance of RB and nerve entrapment is presented. Reanaut bodies were already found at the age of 1 year in the median nerve at the level of the wrist, i.e. in the carpal tunnel, a possible site of entrapment. Here, their number increased with age. Renaut bodies were absent, however, in fetal nerves at this site. Many of the cells in RB resembled perineurial cells or pericytes. They were stained with antibodies against vimentin and epithelial membrane antigen and were partially covered by a basal lamina reactive with antibodies against collagen IV, laminin, and s-laminin. Focally accumulated filaments and bundles of 30-40 nm collagen fibrils were major extracellular components of RB. The diameter of the filaments (8-12 nm) corresponded to the size of the microfibril, i.e. the oxytalan component of elastic fibers. Renaut bodies were intensely stained with antibodies against these microfibrils and several types of collagen glycoproteins. On the basis of these results, we conclude that RB are composed of cells that show perineurial differentiation. These cells produce an extracellular matrix highly enriched in elastic fiber components.

Developmental changes at the node and paranode in human sural nerves: morphometric and fine-structural evaluation

Developmental alterations of paranodal fiber segments have not been investigated systematically in human nerve fibers at the light- and electron-microscopic level. We have therefore analyzed developmental changes in the fine structure of the paranode in 43 human sural nerves during the axonal growth period up to 5 years of age, and during the subsequent myelin development up to 20 years and thereafter. The nodal, internodal, and paranodal axon diameters reach their adult values at 4-5 years of age. The ratio between internodal and paranodal axon diameters remains constant at 1.8-2.0. Despite a considerable increase in myelin sheath thickness, the length of the paranodal myelin sheath attachment zone at the axon does not increase correspondingly, because of attenuation, separation from the axolemma, and piling up of myelin loops in the paranode. Separation of variable numbers of terminal myelin loops from the underlying axolemma results in the formation of bracelets of Nageotte, whereas the transverse bands of these loops disappear. The adaptation of the paranodal myelin sheath to axonal expansion during development probably occurs by uneven gliding of the paranodal myelin loops simultaneously with internodal slippage of myelin lamellae. Since mechanically stabilizing structures (tight junctions and desmosomes between adjacent paranodal myelin processes; transverse bands between myelin loops and paranodal axolemma) are unevenly arranged, especially during rapid axonal growth, paranodal axonal growth with simultaneous adaptation of the myelin sheath is probably discontinuous with time.

Chronic sensorimotor polyneuropathy associated with cerebello-extrapyramidal manifestations in a patient with tomaculous neuropathy

Clinical, electrophysiological and morphological (sural nerve and gastrocnemius muscle biopsies) data of a 57-year-old man with a chronic sensorimotor polyneuropathy of Charcot-Marie-Tooth type associated with a progressive cerebello-extrapyramidal syndrome are reported. Patient's family data were negative. Nerve structural and ultrastructural examinations revealed the morphological picture of a tomaculous neuropathy. The association of different clinical syndromes and the specificity of the tomaculous neuropathy are discussed.

Coexistence of hereditary motor and sensory neuropathy type Ia and IgM paraproteinemic neuropathy

A patient with minimal motor dysfunction dating from early childhood developed more rapidly progressive distal weakness and positive sensory symptoms due to peripheral neuropathy in the fourth decade of life. DNA analysis showed the partial duplication of chromosome 17p associated with hereditary motor and sensory neuropathy type Ia. In addition, the patient had an IgM paraproteinemia and the typical morphological features of IgM paraproteinemic neuropathy on nerve biopsy.

Mechanical hyperalgesias in neuropathic pain patients: dynamic and static subtypes

Two behavioral kinds of mechanical hyperalgesia can be clearly discerned by clinical criteria in patients with neuropathic syndromes, i.e., a dynamic type, elicitable by lightly stroking the symptomatic skin, and a static type, elicitable by steadily applying gentle pressure on it. Of 28 patients studied, 19 had dynamic and 18 had static type mechanical hyperalgesia (9 expressed both types). Experimental compression-ischemia nerve block totally abolished the dynamic hyperalgesia in all patients except in 2, in whom it was markedly diminished. Disappearance of dynamic hyperalgesia occurred contemporaneously with block of myelinated A fibers, as expressed by abolition of the sensations of touch and cold, monitored quantitatively. Static hyperalgesia, however, outlasted A-fiber block in 15 of 18 patients; the phenomenon persisted during the stage when only unmyelinated fibers were available for impulse conduction. It is thus concluded that, at the primary afferent level, dynamic hyperalgesia is mediated by myelinated fibers, whereas static hyperalgesia depends on unmyelinated afferents. These two kinds of hyperalgesia represent discrete pathophysiological entities with distinct clinical connotations.

N-hexane neuropathy in offset printers

In an offset printing factory with 56 workers, 20 (36%) developed symptomatic peripheral neuropathy due to exposure to n-hexane. Another 26 workers (46%) were found to have subclinical neuropathy. The initial change in the nerve conduction study was reduced amplitude of the sensory action potentials, followed by reduced amplitude of the motor action potentials, reduction in motor conduction velocities and increase in distal latencies. These changes indicate primary axonal degeneration with secondary demyelination. Sural nerve biopsy in a severe case showed giant axonal swellings due to accumulation of 10nm neurofilaments, myelin sheath attenuation and widening of nodal gaps. The development of neuropathy bore no direct relationship to the duration of exposure, hence factors such as individual susceptibility may be important. Optic neuropathy and CNS involvement were uncommon and autonomic neuropathy was not encountered.

Chronic peripheral nerve section results in a rearrangement of the central axonal arborizations of axotomized A beta primary afferent neurons in the rat spinal cord

In order to investigate the reorganization of the neuropil of the dorsal horn following peripheral nerve injury, the central terminal arborizations of 35 A beta primary afferent neurons, chronically injured by a cut and ligation of the sural nerve 6-12 weeks previously, were studied by the intra-axonal injection of horseradish peroxidase. Their morphology was compared to 13 intact sural nerve hair follicle afferents. Following axotomy, three kinds of morphological abnormalities were observed in the collateral arbors of the 26 afferents that were hair follicle-like. Atrophy with thin stem axons and reduced terminal branch patterns with few boutons was seen in 5 afferents. Sprouting of bouton-containing terminals into lamina I and IIo was found in 8 afferents. Finally, abnormal arborization patterns in the deeper laminae were observed in 29% of the collateral arbors. Changes included the loss in some arbors of a flame-shaped appearance, which is characteristic of hair follicle afferents, atypical branching patterns and ventrally directed axons producing wider and deeper arbors, compared to normal. Axotomy also caused a disruption of the normal somatotopic organization of sural nerve A beta afferents. This disruption manifested as a variability in the normally mediolaterally restricted terminal sheet, with a consequent loss of the strict somatotopic register in the rostrocaudal direction. Damage to the peripheral axon of A beta primary afferents induces a structural reorganization of their central terminals in the dorsal horn of the spinal cord, which may modify sensory input to the central nervous system.

Immunoelectron microscopic localization of monoclonal IgM antibodies in gammopathy associated with peripheral demyelinative neuropathy

A sural nerve biopsy from a patient with benign monoclonal IgM kappa gammopathy and sensory-motor demyelinative neuropathy, revealed marked loss of myelinated fibers and focal axonal degeneration as well as widespread demyelination and remyelination with onion-skin formation. Almost all myelinated fibers displayed characteristic widening of the myelin lamellae as well as excessive thickness and/or exuberant outfoldings of myelin, reminiscent of that seen in tomaculous neuropathy. Many endoneurial capillaries were lined by fenestrated endothelium, indicating breakdown of a normal blood-nerve barrier. The endoneurium contained large amounts of extracellular proteinaceous material. Immunofluorescence and immunoelectron microscopy performed on the nerve of the patient, demonstrated selective deposition of IgM kappa gammaglobulin, exclusively in the areas of splittings of the myelin lamellae. Schwann cells contained cytoplasmic myelin debris labelled with IgM kappa only. In the indirect immunofluorescence and immunoelectron microscopy, serum of the patient reacted with the whole thickness of compact peripheral myelin of a normal human nerve. There was no immunoreactivity with the central myelin, Schwannoma cells, glial cells, axons or neurons. Demonstration of the selective presence of monoclonal IgM in widened lamellae of myelinated fibers, as well as bound to the internalized myelin debris in Schwann cells and macrophages, indicates a pathogenetic role of monoclonal paraprotein in myelin injury. Demyelination is promoted by development of endothelial fenestrations in the endoneurial capillaries and breakdown of the blood-nerve barrier.

IgG monoclonal paraproteinaemia and peripheral neuropathy

Five patients with peripheral neuropathy and benign IgG monoclonal paraproteinemia are reported, all of whom had a sensorimotor neuropathy with a remitting and relapsing course. The serum paraprotein level did not correlate with the patient's clinical status. Electrophsyiological studies showed marked slowing of conduction velocity and conduction block in four of the patients and mild slowing in the other. Sural nerve biopsies demonstrated a demyelinating neuropathy with inflammatory cell infiltrates in each of the five patients. Three of the patients had evidence of myelin/Schwann cell reactivity on immunofluorescence studies and in all nerves dense expression of major histocompatability complex class I and II molecules was evident within the endoneurium, on invading mononuclear cells, endothelial cells and Schwann cells. All the patients responded to treatment, plasmapheresis being particularly effective. Four patients have achieved prolonged remissions after all treatment had ceased. These five cases of peripheral neuropathy and IgG paraproteinaemia were identical in their clinical, electrophysiological and pathological features to patients with chronic inflammatory demyelinating polyneuropathy.

Peripheral nerve lesions in HTLV-I associated myelopathy (HAM/TSP)

Peripheral nerve dysfunction (PND) was found in as many as 43% of our patients with human T-cell lymphotropic virus type I (HTLV-I)-associated myelopathy (HAM/TSP). To evaluate the PND further we biopsied the sural nerve in 6 patients. The histological features were varying degrees of demyelination, remyelination, axonal atrophy and degeneration, and perineurial fibrosis. "Globule" or "sausage" formation was prominent in two of the specimens. Inflammatory infiltrates were absent. No deposits of IgG, IgM, IgA, or complement were detected in the biopsies. No viral antigen or proviral DNA was detected. It is proposed that the PND and the histological findings noted are part of HTLV-I-associated disease and not an unrelated disorder. The pathogenesis of the PND remains unclear. There was no evidence of direct viral infection. The histological findings could represent primary changes induced by viral-triggered release of soluble factors, such as cytokines or secondary changes to more proximal disease, e.g., root involvement.

An ultrastructural study of the retina in human late infantile neuroaxonal dystrophy

A case involving a girl who died at 11 years of age and who had developed normally until the age of 18 months, at which time further psychomotor maturation stopped and then regressed, is reported. The patient appeared hypotonic and showed loss of deep tendon reflexes, as well as bulbar signs and increasing immobility. Visual impairment resulted in blindness at the age of 7 years. Her disease was diagnosed as late infantile neuroaxonal dystrophy (LINAD) after examination of sural nerve biopsy samples and after autopsy. Under electron microscopy, retinal axons were filled with tubulocisternal profiles and occasional large lamellar clefts close to or distant from synaptic complexes. These lesions, typical of LINAD, were largely found in interior layers of the retina rather than in outer ones. As photoreceptors were preserved and their synaptic contacts within the outer nuclear layer appeared somewhat intact, blindness in LINAD is of the neuronal type, possibly all along the pathway from the bipolar retinal layer to the striate cortex. The findings also indicate that only particular types of axons or synaptic complexes may be involved in LINAD, and that the formation of lesions characteristic of LINAD is not ubiquitous within the retina. The cause for this selective involvement of retinal structures in LINAD remains to be resolved.

Innervation of the vasa nervorum: changes in human diabetics

Transperineurial and epineurial vessels are innervated by plexuses of unmyelinated axons. Human sural nerve biopsies were examined ultrastructurally and immunocytochemically with an antibody which recognizes a neuronal and neuroendocrine protein, PGP 9.5, to characterize perivascular axons of these plexuses. Diabetics exhibited a greater degree of abnormal innervation of the vasa nervorum than nondiabetics with and without neuropathy. Abnormal innervation included: a reduction in the percentage of vessels exhibiting perivascular axons and a concomitant increase in the percentage of vessels having denervated Schwann cell units, particularly around vessels confined to perineurial compartments, and remaining axons in nerves from diabetics exhibited fewer varicosities. Denervated arterioles of diabetics also displayed structural changes indicating injury. The arteriolar structural defects and loss of neurogenic control of neural blood flow may lead to or aggravate endoneurial ischemia or hypoxia. The patchy, focal endoneurial fiber loss that is prominent in proximal nerves and associated with the distal myelinated fiber loss of some diabetic patients may be due in part to perivascular denervation of the vasa nervorum.

[Hereditary motor and sensory neuropathy]

The report consisted of 10 cases of hereditary motor and sensory neuropathy (HMSN). There were 7 males and 3 females. Their ages ranged from 11 to 42 (average 24.6) years, ages of onset varied from 7 to 34 (average 17.3) years. Hereditary history was showed in 4 cases. The clinical features of all 10 cases had peroneal muscular atrophy, 8 of 10 cases also had involvement of the upper limbs, 7 of 10 cases had pes arcuatus. The conduction velocity was obviously slow in 5 cases and slightly slow in the others. Oion-bulb hypertrophic neuropathy was demonstrated in sural nerve biopsies of 5 cases. Neuronal axonal degeneration were found in the remaining 5 cases. Clinical classification, clinical features and pathological characteristics were discussed.