Peripheral neuropathy profile in various groups of diabetics.

The results of applying a battery of peripheral nerve function tests in three groups of diabetics are reported. The tests examined the integrity of all the major subgroups of nerve fibres. The diabetics were grouped according to the clinical severity of their neuropathy: Group I--11 patients with long standing diabetes but clinically insignificant neuropathy, Group II--27 patients with mild neuropathy and Group III--23 patients with neuropathic foot lesions. As expected the incidence of abnormality of all functions increased from Group I to III, but within a group there was no clear pattern of differential involvement of different fibre types. The study has identified those tests that are suitable for detecting early neuropathy (warming and vibration perception thresholds and sensory nerve action potentials) and those which are likely to be useful in assessing deterioration or improvement (particularly vibration perception threshold), but since the different tests cannot be equally matched for sensitivity it is not possible to interpret the results in terms of the degree of pathological involvement of different fibre groups.

Impaired neurogenic vascular response in patients with diabetes and neuropathic foot lesions.

Peripheral neuropathy plays an important part in the development of foot complications in patients with diabetes. We studied the contribution of impairment of the dual sensory and inflammatory function of unmyelinated nociceptive C fibers in the foot complications of diabetes. The integrity of these fibers was assessed objectively by measuring axon reflex vasodilation in response to stimulation with 10 percent acetylcholine introduced by electrophoresis. This was related to the non-neurogenic capacity of the vessels to dilate in response to a mechanical stroke. These measurements were made on the soles of the subjects' feet. The function of the nociceptive C fibers was abnormal in 1 of 14 patients with longstanding diabetes who had no foot complications, 3 of 9 patients with diabetes and skin sepsis, 8 of 11 patients with typical neuropathic plantar ulcers, and all of 8 patients with neuroarthropathy. In patients with longstanding diabetes but no foot complications, the mean ratio of neurogenic to non-neurogenic vasodilation was not significantly different from that in controls; however, it was significantly lower in the other three groups (P less than 0.01 for those with sepsis; P less than 0.001 for those with ulcer or arthropathy). Impairment of the neurogenic vasodilator response, or flare, correlated with the clinical diminution of pain sensation. This study suggests that the loss of both components of nociceptive C-fiber function--neurogenic inflammation and pain sensation--is an important factor in the development of foot complications in diabetes.

Quantitative objective assessment of peripheral nociceptive C fibre function.

A technique is described for the quantitative assessment of peripheral nociceptive C fibre function by measurement of the axon reflex flare. Acetylcholine, introduced by electrophoresis, is used to stimulate a ring of nociceptive C fibre endings at the centre of which the increase in blood flow is measured with a laser Doppler flowmeter. This flare (neurogenic vasodilatation) has been compared with mechanically or chemically stimulated non-neurogenic cutaneous vasodilation. The flare is abolished by local anaesthetic and is absent in denervated skin. The flare has been measured on the sole of the foot of 96 healthy subjects; its size decreases with age in males, but not in females.

A study of pain threshold in diabetics with neuropathic foot lesions.

Pain thresholds to a pinch stimulus were measured at eight sites on the dorsum of both feet from 17 diabetic patients. Sixteen feet had neuropathic ulcers and seven had Charcot arthropathy. Vibration perception thresholds, radial nerve action potentials, muscle action potentials of flexor digitorum brevis, autonomic cardiovascular reflexes and reflex sweat output were also measured. Pinch pain threshold was abnormal in 15 diabetic feet, 11 having one or more insensitive sites. There was a greater variability in threshold between sites tested in diabetic than control subjects.

Quantitative sweat test in diabetics with neuropathic foot lesions.

The volume of sweat produced by axon reflex stimulation using acetylcholine was measured in one foot each of 35 control subjects and 52 feet of 37 diabetic patients (28 with neuropathic ulceration, 11 with Charcot arthropathy, nine with somatic neuropathy but no foot lesion and four with no evidence of somatic neuropathy). In controls, the volume of sweat was greater in males than females. A flare response was seen in 94% of control feet. In diabetics, the volume of sweat was within the control range in 17 feet, increased in one, reduced in seven, and absent in 27. Sweating was absent in 75% of feet with a neuropathic ulcer; a flare response was absent in 86% of them. Sweating was only absent in 36% of feet with Charcot arthropathy and was increased in one, whereas the flare response was absent in all. Autonomic cardiovascular reflexes were more frequently abnormal than the sweat test; sweating was absent in only one patient with normal cardiovascular reflexes.

Morphometric effects of vincristine on nerve regeneration in the rat.

Administration of vincristine (200, 100 or 50 micrograms/kg/week) for 6 months during regeneration of the sciatic nerve after crush injury caused a dose-dependent reduction in nerve fibre size and failure of removal of myelin debris. Successfully regenerating neurites showed an unusual amount of shape distortion. The ratio of myelin sheath thickness to axon circumference was reduced, but the ratio of myelin sheath thickness to axon area was normal. Microtubule concentration was diminished in axons, but neurofilament density was unaffected. Unmyelinated axons were reduced in number but their axon diameter distribution was not affected. Fibres on the non-crushed side appeared normal. The toxicity of vincristine to regenerating nerves is probably related to increased blood-nerve permeability occurring both at the site of crush and along the degenerating nerve.

The effect of vincristine on nerve regeneration in the rat. An electrophysiological study.

Weekly injections of vincristine to produce a dose-dependent delay in regeneration following sciatic nerve crush. With 20 micrograms/kg/wk recovery was similar to that in control animals. With 50 and 100 micrograms/kg/wk electrophysiological evidence of reinnervation of the foot muscles was significantly delayed and muscle action potential amplitude increased at a slower rate. However, once begun the increase in motor nerve conduction velocity was closer to that in control animals. With 200 micrograms/kg/wk no evidence of reinnervation of the foot muscles was found even after 6 months. These doses produced no abnormality of muscle action potential amplitude or of nerve conduction velocity on the opposite non-crushed side.

A study of the effects of isaxonine on vincristine-induced peripheral neuropathy in man and regeneration following peripheral nerve crush in the rat.

Administration of isaxonine (6 mg/kg powdered diet) had no effect on regeneration following sciatic nerve crush in the rat. In 10 patients undergoing treatment with vincristine (1.4 mg/m2 twice monthly) development of peripheral neuropathy was quantitated by neurological symptoms, signs and electrophysiological tests. Five also received isaxonine (1.5 g daily). All patients developed evidence of neuropathy, but in none was it severe. The three lowest disability scores were obtained in isaxonine treated patients, but the highest score was also in an isaxonine treated patient. The equivocal findings in this small study could not be amplified because the drug was withdrawn from clinical use on account of its hepatotoxicity.

Clinical and morphological findings in acrylamide toxicity.

Clinical features of acrylamide toxicity consist of sensorimotor peripheral neuropathy. In subacute intoxication ataxia occurs and encephalopathy also in severe acute poisoning. Slight reduction in maximal nerve conduction velocity in animals is due to degeneration of large diameter fibres. Neurofilaments accumulate within axons, both in PNS and CNS. Other changes may be important in initiation of degeneration.

A combined morphological and electrophysiological study of conduction block in peripheral nerve.

The reliability of the electrophysiological criterion of conduction block in determining the presence of focal demyelination in a peripheral nerve has been studied in an animal model. Demyelination was produced in the rat tibial nerve by one or two closely spaced microinjections of lysophosphatidylcholine (LPC). Histological and electrophysiological data were obtained on the acute lesion (up to 6 days), and during recovery (up to 11 weeks). Single LPC injections produced a lesion of very variable severity. Double injections more reliably produced a severe lesion with marked conduction block. Slight axonal damage was occasionally seen in nerves showing severe demyelination. The ratio of amplitude of muscle action potentials evoked by stimuli proximal and distal to the sites of nerve injection was calculated to detect the development of conduction block. The post injection ratio was more than 2 standard deviations below the control mean in 86% of nerves showing signs of demyelination. No control saline injected nerves showed such evidence of conduction block. The severity of the electrophysiological abnormality did not prove a reliable indicator of the severity of the histological lesion, however. The possible reasons for this variability are discussed and it is argued that caution should be exercised when interpreting this particular electrophysiological finding in clinical practice.

The effects of the pyrethroids deltamethrin and cismethrin on nerve excitability in rats.

Deltamethrin produced a prolonged period of increased excitability following the passage of a nerve impulse, which was dose-related and lasted up to 400 ms. Excitability changes were detected without neurological signs following a single IV injection of 0.5 mg/kg and feeding 200,100 and 50 ppm in the diet for up to 8 weeks. No changes were detected following 0.3 mg/kg IV or 25 ppm in the diet. No cumulative effects were detected during chronic feeding. Cismethrin produced increased nerve excitability only between 2 and 4 ms after a nerve impulse. Excitability changes after cismethrin were biphasic during the first 20 ms.

Neuromuscular effects of chronic administration of two organophosphorus insecticides to rats.

Groups of rats were fed chlorfenvinphos (at two dose levels) or dicrotophos. Whole blood and plasma cholinesterase activity was markedly reduced. Compared with control animals there was no change in muscle action potential amplitude (M response) to a single stimulus for periods of up to 3 months. Exposed animals developed a prolonged negative potential at the end of the spike potential, lasting up to 15 ms. Superimposed on this, repetitive activity (RA) developed with latency of approximately 4.5 ms. These abnormalities became more marked with time, even on constant dosing. Double and repetitive stimulation reduced or abolished the prolonged negative potential and RA.

Effect of a synthetic pyrethroid deltamethrin on excitability changes following a nerve impulse.

Excitability changes following a nerve impulse were studied in the rat tail. Supernormal nerve excitability in control animals was present, as in other vertebrate nerve fibres, from 4-30 ms and was followed by a period of subnormal excitability extending up to 100-200 ms. Two to seven hours after intravenous administration of 1.5 mg/kg deltamethrin, supernormality was increased in degree and prolonged in duration for up to 400 ms. A minor effect was still detectable 24 hours after injection. This effect of deltamethrin on nerve excitability is probably due to persistent slight depolarisation of the nerve membrane resulting from its known effect of maintaining a proportion of sodium channels open for up to several hundred milliseconds following a nerve impulse.

Conduction velocity in nerve fibres with axonal atrophy due to chronic beta, beta'-iminodiproprionitrile (IDPN).

Serial measurements of maximal motor nerve conduction velocity and muscle action potential amplitude were made on 2 groups of rats for up to 16 months. Group A received 0.05% IDPN in drinking water. Group B received a single injection of 1 g/kg i.p. In the chronically intoxicated animals conduction velocity progressively fell compared with control animals, from a reduction of 7% after 4 months to 22% after 13 months. There was no reduction in muscle action potential amplitude. Marked axonal atrophy was found in distal ventral roots. Many grossly dilated axons were present in proximal ventral roots. In the animals which received a single dose of IDPN no electrophysiological changes were found. A few dilated axons were present in proximal ventral roots, but changes were less severe than in Group A. No distal axonal atrophy was demonstrated.

Electrophysiological investigation of toxic neuropathies.

Electrophysiological changes are correlated with pathological processes. Marked slowing of conduction is found in segmental demyelination due to delayed nodal excitation or short lengths of continuous conduction. Secondary demyelination causes slow conduction in hexacarbon neuropathy. Slight reduction in maximal conduction velocity is attributable to selective damage to large fibres in acrylamide neuropathy. Sensory nerve action potential amplitude is a sensitive measure of peripheral nerve function and comparison of abnormalities in different nerve segments may indicate the nature of the underlying pathological change. Other abnormalities may be elucidated by double stimuli; eg repetitive activity due to cholinesterase inhibition only occurs after the first of two closely spaced stimuli. Activity-related excitability changes may be detected by measuring the amplitude of the response to a submaximal stimulus at varying times after a maximal shock and is increased and prolonged by the pyrethroid deltamethrin.

Effects of edrophonium bromide on neuromuscular transmission in a healthy human subject.

Regional intravenous injections of different amounts (1-3 mg) of edrophonium were given to the hand of a healthy subject. The earliest change was a small negative deflection occurring at the end of the muscle response evoked by nerve stimulation, due to repetitive activity. It did not occur after a second stimulus at 30 ms or immediately after 10 s maximum voluntary contraction. Repetitive stimulation at 0.5 Hz reduced the repetitive activity. With a higher dose of edrophonium the response to a second shock (M2) at 30 ms was reduced in amplitude, but M2 at 80 ms was unaffected. An even larger dose caused depression of M2 at 80 ms also and a decremental response to 50 Hz stimulation. The amplitude of the response to a single shock was unchanged throughout.

Effect on neuromuscular transmission of repeated administration of an organophosphorus compound, metrifonate, during treatment of children with urinary schistosomiasis.

Muscle action potential amplitude recorded from abductor pollicis brevis in response to nerve stimulation was measured in 55 children during treatment of urinary schistosomiasis with metrifonate (3 doses at 2 weekly intervals). Mean erythrocyte cholinesterase activity was 52-75% of pretreatment value in different groups when examined electrophysiologically. Twenty-six children acted as controls. There was no difference in amplitude between control and exposed subjects 2 weeks after the 2nd dose. Six hours after the 3rd dose, amplitude was larger in some subjects. This effect was not related to dose or degree of cholinesterase inhibition and was thought unlikely to be the result of treatment. Three children who received the highest dose of metrifonate had developed repetitive activity 6 hr later. The criteria for its identification are described.