Diabetic neuropathy

Pathogenesis of diabetic neuropathy

Samples of lumbosacral trunk, posterior tibial nerve, and sural nerve obtained at autopsy from diabetic and nondiabetic patients without mononeuropathy multiplex were evaluated using 1-mu-thick epoxy sections and teased nerve fiber preparations. Focal fascicular lesions characterized by reduced density of myelinated axons within fascicles were found predominantly in the specimens from diabetics, mainly in the posterior tibial nerve and lumbosacral trunk. In severe examples, the perineurium and even surrounding epineurium were damaged, stamping the lesions as ischemic. In addition, identical lesions were found in biopsies of nerves of nondiabetics with vasculitis. Density of myelinated fibers at the three sites demonstrated a proximal-distal graded loss that was significantly greater in the diabetic samples. The loss from the lumbosacral trunk to the posterior tibial nerve was correlated with the density of focal lesions in the lumbosacral trunk in the diabetic (p = 0.025), indicating that distal fiber loss was partly due to the focal lesions. Teased nerve fiber abnormalities were common only in sural nerves of diabetics, suggesting that they are secondary. We conclude that beyond the possible metabolic abnormalities involved in the genesis of diabetic polyneuropathy, focal fascicular lesions, likely due to diabetic microangiopathy, are also important in the development of diabetic neuropathy.

Vasculitic neuropathy in panarteritis nodosa: clinical and ultrastructural findings

Clinical involvement of the peripheral nervous system in panarteritis nodosa is common, but the histological aspects are little known. We describe the sural nerve, muscle and skin biopsy findings in a patient with panarteritis nodosa, affected by mononeuritis multiplex. The data are compared to those reported in other types of vasculitis neuropathy.

Studies of aldose reductase using neuronal cell culture and ligated rat sciatic nerve

Sorbinil (CP 45,634), a potent aldose reductase (AR) inhibitor, has the ability to normalize both sorbitol levels and functional parameters such as orthograde axonal transport and motor nerve conduction velocity in peripheral nerves of diabetic rats, which implicates flux through the polyol pathway in the pathophysiology of diabetic neuropathy. In order to understand more fully the role of this enzyme, it is important to determine the major cellular location of AR in peripheral nerve. Experiments were designed that have taken advantage of the observation that peripheral nerve axons degenerate distal to an injury site, while Schwann cells remain viable. One sciatic nerve in each experimental rat was chronically ligated (up to 6 weeks) before inducing diabetes by an intravenous (iv) injection of streptozotocin (STZ; 65 mg/kg). Two days after the STZ injection, both sciatic nerves were removed from each animal, and the ligated nerve was divided into proximal (Schwann cells and axons) and distal (Schwann cells only) portions before being processed for sorbitol determinations. The intact nerves and the proximal portion of the ligated nerves (having both Schwann cells and axons) retained the ability to accumulate sorbitol after STZ injection, while the distal portion (having Schwann cells only) lost this capacity 4 days after ligation. This lack of ability to accumulate sorbitol was not due to failure of the substrate (glucose) to reach the distal nerve segment. Additionally, homogenates of whole nerves and of proximal portions of ligated nerves were able to form sorbitol from glucose in the presence of NADPH while homogenates of distal portions of ligated nerves had lost approximately 85% of this activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Progression of subclinical polyneuropathy in young patients with type 1 (insulin-dependent) diabetes: associations with glycaemic control and microangiopathy (microvascular complications)

The progression of subclinical polyneuropathy over 2.5 years has been studied in a representative group of 75 young patients with Type 1 (insulin-dependent) diabetes (initial age 16-19 years). The relationships between changes in nerve function, glycaemic control and concurrently developing microvascular complications (retinopathy, microproteinuria) were investigated. Deterioration of motor, sensory and autonomic nerve function, retinopathy and microproteinuria was related to poor glycaemic control. In addition, there was an association between developing neural and microvascular complications which was not diminished when their common relationship to hyperglycaemia was taken into account. These findings suggest that, although poor glycaemic control is an essential permissive factor in the early development of diabetic polyneuropathy, other influences, shared with microvascular complications, must also be important.

Diabetic autonomic neuropathy

The incidence of autonomic dysfunction as a complication of diabetes mellitus is reported to be as high as 20% to 40%. Symptoms of diabetic autonomic neuropathy (DAN) are often vague, and signs difficult to detect on routine physical examination. The early diagnosis of DAN is possible by utilizing several simple noninvasive tests, which may also be helpful in localizing the lesion(s) to specific autonomic pathways. DAN may affect multiple organ systems, to include cardiovascular, gastrointestinal, genitourinary and/or neuroendocrine, and may, in fact, be life-threatening. The same metabolic disturbances of somatic peripheral nerve may also be responsible for DAN. Like somatosensory neuropathy, definitive therapy for DAN is not yet satisfactory, although multiple chemotherapeutic agents have been tried and warrant further investigation.

Structural alterations of the intramuscular nerves and junctional region in extraocular muscles of C57BL/Ks (db/db) diabetic mice

The extraocular muscles of the C57BL/Ks (db/db) diabetic mutant mouse were examined by electron microscopy. The intramuscular myelinated nerves and the junctional apparatus of the singly and multiply innervated muscle fibers were found to exhibit various anomalies. Lamellated inclusion bodies were found in many of the Schwann cells of the myelinated nerve fibers; intra-axonal inclusion bodies resembling polyglucosan bodies were also observed. Junctional abnormalities consisted of various types of inclusion bodies within the junctional sarcoplasm and within sole-plate nuclei; in addition, hypertrophied endplates were observed and often penetrated by networks of axonal terminal branches. At times, pseudopod-like extensions of the junctional sarcoplasm encompassed and made protracted synaptic contacts with the incoming axons.

Predisposing factors in Bell's palsy: a case-control study

The frequency of diabetes mellitus reported in subjects affected by Bell's palsy varies widely. In this investigation, a case-control study, we encountered a frequency of 24.8%. In addition, arterial hypertension and lipid disturbances were found to affect subjects with Bell's palsy more frequently than controls. These findings appear to suggest a primarily ischaemic pathogenesis for most cases of idiopathic peripheral facial paralysis. Furthermore, the finding of significantly lower taste impairment in diabetics than in non-diabetics with Bell's palsy may support the hypothesis of a vascular rather than a metabolic pathogenesis in these cases also. In fact, the vessels supplying the distal portion of the facial nerve, probably more affected in the diabetic patients in order to preserve taste sensation, have such a particular anatomical configuration that this might favour the onset of a diabetic small vessel disease which, in turn, would represent a factor of easier decompensation.

Treatment of peripheral neuropathies

There are three general approaches to treatment of peripheral neuropathy. First, an attempt should be made to reverse the pathophysiological process if its nature can be elucidated. Second, nerve metabolism can be stimulated and regeneration encouraged. Third, even if the neuropathy itself cannot be improved, symptomatic therapy can be employed. This review outlines the options available for each approach.

Experimental diabetic neuropathy: impairment of slow transport with changes in axon cross-sectional area

Analysis of slow axonal transport in the sciatic and primary visual systems of rats with streptozotocin-induced diabetes of 4-6 weeks duration showed impairment of the transport of neurofilament subunits, tubulin, actin, and a 30- and a 60-kDa polypeptide in both systems. The degree of impairment was not uniform. Transport of polypeptide constituents of the slow component b, such as the 30- and 60-kDa polypeptides, appeared to be more severely affected than the transport of constituents of the slow component a, such as neurofilaments. Morphometric analysis of sciatic axons revealed a proximal increase and a distal decrease of axonal cross-sectional area. It is proposed that impairment of axoplasmic transport and changes of axonal size are related. Transport impairment results in a larger number of neurofilaments, microtubules, and other polypeptides in the proximal region of the axon, which increases in size, whereas fewer neurofilaments, microtubules, and other polypeptides reach the distal axons that show a size decrease. Such changes in axonal transport and area are likely to occur in other diabetic animal models and in human diabetes.

Enzymatic regulation of glycoprotein synthesis in peripheral nervous system myelin

The enzyme UDP-N-acetylglucosamine: dolichyl phosphate, N-acetylglucosamine-1-phosphate transferase initiates the synthesis of the oligosaccharide chain of complex-type glycoproteins. In view of the high content of glycoprotein in peripheral nerve myelin, the properties of this enzyme, its changes with age, and the effect of the specific inhibitor tunicamycin were investigated. The enzyme activity in rat peripheral nerve homogenate was completely dependent on the presence of exogenous dolichyl phosphate as well as Mg2+ and a detergent (Triton X-100) and was also greatly stimulated by a high salt concentration (0.4 M KCl) and AMP. The highest specific activity was present in the postmitochondrial membranes. The specific activity in postmitochondrial membranes in the presence of exogenous dolichyl phosphate reached a maximum at 17 days and remained relatively high throughout development, up to 2 years of age, but the activity was much lower when dolichyl phosphate was not added. This indicates that the enzyme level does not decrease with age, but that the content of the lipid cofactor may limit glycoprotein synthesis in vivo. Tunicamycin (5 micrograms) was injected intraneurally into 24-day-old rat sciatic nerve, and the enzyme was assayed from 1 to 24 days after injection. The specific activity of the transferase remained at low levels (5-40% of the level in control nerve) in most injected nerves assayed throughout this postinjection period. A protein previously identified as the unglycosylated P0 protein was synthesized in vitro by the tunicamycin-injected nerve and could be demonstrated to be incorporated into myelin in large amounts at 2 days and in small amounts at 6 days after injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermal discrimination thresholds in normal subjects and in patients with diabetic neuropathy

Using two identical thermostimulators which operated on the Peltier principle, thermal cutaneous sensation of the hand and the foot was investigated in 36 normal subjects and in 20 patients with diabetic neuropathy. Using a two-alternative forced-choice testing procedure, thermal discrimination thresholds were determined twice. The values found in normal subjects are comparable with data from the literature. It was confirmed that thermal discrimination of the foot decreased with increasing age. In patients with diabetic neuropathy the increased thresholds for the foot could be correlated with length-dependent degeneration of small nerve fibres.

Quantitative analysis of myelin and axolemma particle distribution in C57BL/Ks diabetic mice and the effects of ganglioside treatment

By freeze-fracture technique we estimated myelin and axolemma intramembranous particle density in C57BL/Ks mice. A decrease in myelin particle content compared to controls is present in both 180 and 280 day old genetic diabetic mice. In addition, the axolemma of myelinated axons is affected in interparanodal regions while no modification was detected at nodal level. Such alterations of myelin membrane structure may also be responsible for the lower motor nerve conduction velocity (MNCV) observed in these diabetic mice; however this hypothesis cannot be taken into consideration for the reduction in MNCV at the early stage of the neuropathy (prior to 180 days of life). Therefore the structural changes of both myelin sheath and interparanodal axolemma as visualized by freeze-fracture are most likely related to late complications of the disease instead of being responsible for the changes in excitability. The low myelin and axolemma particle density of diabetic mice was found normal after 30 days' treatment with gangliosides. Such findings are in agreement with previous results on a significant effect of ganglioside treatment on MNCV and axonal area alterations in 180 and 280 day old genetic diabetic mice.

Thermal sensitivity in uremic neuropathy

Clinical neurological examination, nerve conduction velocity measurements, and quantitative tests of thermal and vibratory sensitivity were performed in 64 non-diabetic uremic patients, who were all treated with chronic maintenance dialysis. Clinical or neurographic signs of neuropathy were found in 83% of the patients. The most common abnormalities were reduced nerve conduction velocity, increased vibratory perception threshold, loss of tendon reflexes, and impaired temperature sensibility. Hypesthesia to pinprick or touch, or paresis were rarely found and none of them was ever the first sign of neuropathy. Thermal sensation was abnormal in 30% of the patients, which is a much higher prevalence than that which has previously been reported. There were no significant correlations between measures of thermal sensation and measures of large fibre dysfunction. Impaired thermal discrimination was the first sign of neuropathy in 15% of the patients. This indicates that a small fibre uremic neuropathy may exist as a separate entity.

Evaluation of thermal and vibration sensation in diabetic neuropathy

Sensory evaluation of diabetic neuropathy was undertaken by a new technique for assessment of thermal sensitivity. The method is simple and reproducible, and the mean normal value of the lateral border of the foot was 6.0 degrees C (3.6-9.8 degrees C, 95% confidence limits). Four groups of patients with diabetic neuropathy were examined: 22 with neuropathic ulcers and/or Charcot joints (groups 1 and 2); all showed severe abnormalities (range 10.8- greater than 30 degrees C), frequently more than three times the upper limit of normal. In contrast thermal sensitivity in 15 patients with painful neuropathy (group 4) varied from normal to grossly abnormal (range 3.9- greater than 30 degrees C) confirming this form of neuropathy as a distinct entity. The majority of those 10 patients with autonomic neuropathy alone (group 3) had abnormal thermal sensitivity (range 6.4- greater than 30 degrees C). Comparison of thermal sensitivity (a small fibre modality) with vibration perception threshold (a large fibre modality) showed that thermal sensitivity is sometimes selectively affected, especially in those with painful neuropathy, suggesting that the small fibres are more vulnerable in diabetes. Frequent involvement of the hands confirms the "stocking and glove" distribution of diabetic neuropathy. We conclude that impairment of thermal sensitivity is the rule in symptomatic diabetic neuropathy and its assessment provides a simple quantitative measurement suitable for long-term studies of its natural history.

Problems of etiology in femoral neuropathies

29 cases of femoral mononeuropathy are reported. While the clinical features of the femoral neuropathy are easily identified, the etiology is often hard to establish. The cases reported tend to fall into three general categories: 1) cases without major diagnostic difficulties (e.g. diabetic neuropathy); 2) those in which the definite diagnosis results from combined evidence of laboratory and instrumental data (degenerative changes in the lumbar spine, compressions, entrapments, etc.); 3) those in which the negative result of the investigations prevents a positive diagnosis and hence a presumptive etiology (spondylosis, inflammatory process, ischemia of the nerve) may be formulated. Attention is drawn to the favorable course of the condition in the patients of this group.

Regional perfusion in normal and ischemic rat sciatic nerves

We measured regional blood flow in rat sciatic-posterior tibial nerve using an iodo-[14C]antipyrine autoradiographic technique. Average flow was 12.1 +/- 3.3 ml/100 gm/min, considerably less than that of both gray and white matter structures in the cerebral hemispheres. Perfusion was homogeneous along the proximal-distal extent of this nerve and along its radial axis. Acute occlusion of the femoral artery reduced regional sciatic blood flow. Flow was especially depressed within the endoneurial core of the proximal posterior tibial branch, which lies in a watershed zone between adjacent segmental arterial fields. The topography of the arterial supply to nerves and their abundant collateral circulation may explain the centrifascicular distribution of nerve infarcts, and in part can account for the apparent resistance of peripheral nerves to ischemia.

Acute inflammatory demyelinating polyneuropathy in a diabetic patient: predominance of vesicular disruption in myelin sheaths

A diabetic woman underwent an incision of the right big toe for an abscess and developed a typical Guillain-Barré syndrome 48 h later. A biopsy of a peripheral nerve, performed 10 days later, showed modifications usually seen in diabetic patients, as well as the characteristic ultrastructural modifications of the Guillain-Barré syndrome (GBS). Moreover, 22% of myelinated fibers exhibited vesicular disruption of the myelin sheaths. This lesion is rarely encountered on the biopsies of peripheral nerve in GBS and concerns only a few myelinated fibers. Such a prominence of myelinic vesicular disruption and its occurrence in a diabetic patient are discussed.

Polyglucosan bodies in the sural nerve of a diabetic patient with polyneuropathy

In the sural nerve of a 62-year-old woman with impaired glucose tolerance test and polyneuropathy, many intra-axonal polyglucosan bodies were observed. Polyglucosan bodies have been described in spontaneously or alloxan-diabetic rats, but are not usually observed in human diabetic neuropathy. Since intra-axonal polyglucosan bodies can occur in the sural nerve in various diseases and in aging, they are considered as non-specific changes. Their presence is probably related to a primary axonal neuropathy.