LATENT NEUROPATHY IN DIABETES AND ALCOHOLISM: ELECTROMYOGRAPHIC AND HISTOLOGICAL STUDY

Onset of the neuromuscular block simulated in an anatomical model

AIMS

The aim of this study was to develop a pharmacodynamic model for nondepolarizing muscle relaxants (neuromuscular blocking agents, NMBAs) based on anatomical, physiological, and pharmacological considerations and analyse whether the time to onset of the submaximal neuromuscular block (NMB) depends on the affinities of the NMBAs for the postsynaptic receptors or on the pharmacokinetic properties of the NMBAs.

METHODS

A quantitative description of the development of neuromuscular block was achieved by formulating a pharmacodynamic model based on anatomical, physiological and pharmacological considerations. The principal characteristics of the model are: (1) Diffusion of the NMBAs out of the capillaries into the interstitial space of muscle and from there into the synaptic space of the motor end plates (2) Receptor concentration in the synaptic space of 300 microM and the total amount of receptors in 100 g muscle of between 1.43 x (10(-11) to 10(-10) mol. (3) Interaction of NMBAs with the receptors defined by the association (k(assoc) = 4 x 10(8) min-1 x M-1) and dissociation (k(dissoc) one of 4, 40, or 400 min-1) rate constants.

RESULTS

The simulations demonstrated that different affinities of the NMBAs for the postsynaptic receptors (defined by k(assoc)/k(dissoc)) do not influence the onset of the submaximal NMB. On the other hand, the time to the peak submaximal NMB is dependent on the pharmacokinetic properties of the drugs: Those NMBAs that leave plasma rapidly produce the block faster but the fraction of the dose that contributes to the block is small. This fraction is larger for those NMBAs that produce NMB later and, hence, these NMBAs require smaller equieffective doses.

CONCLUSIONS

We conclude that those muscle relaxants that produce neuromuscular block rapidly require larger equieffective doses due to their more rapid initial disappearance from plasma.

Accelerated desensitization of nicotinic receptor channels and its dependence on extracellular calcium in isolated skeletal muscles of streptozotocin-diabetic mice

1. To elucidate the influence of the diabetic state on desensitization of nicotinic acetylcholine (ACh) receptor channels, we investigated the time course of the decrease in amplitude of ACh potentials elicited by iontophoretic application to isolated diaphragm muscle of streptozotocin-diabetic mice. We also investigated time- and extracellular Ca(2+)-dependent changes in the channel opening frequency of ACh-activated channel currents and the involvement of protein kinases by use of the cell-attached patch clamp technique in single skeletal muscle cells. 2. When ACh potentials were evoked at 10 Hz, the decline in trains of ACh potentials was accelerated in the diabetic state. 3. The time-dependent decrease in the channel opening frequency of diabetic muscle cells was greatly accelerated compared with normal cells in 2.5 mM Ca2+ medium. 4. This accelerated decrease in channel opening frequency was restored by pretreatment with a protein kinase C inhibitor, staurosporine (10 nM) but neither a protein kinase A inhibitor, H-89 (3 microM) nor a calmodulin kinase II inhibitor, KN-62 (5 microM) were able to restore the fall in opening frequency. 5. These results demonstrate that in the diabetic state the desensitization of nicotinic ACh receptor channels may be greatly accelerated by activating protein kinase C, which is caused by an increase in the amount of available intracellular Ca2+.

Evaluation of peripheral nerve conduction and central visual conduction in chronic alcoholics and in chronic alcoholics after prolonged abstention

Classic statistical method (mean, standard deviation, variance) were used to analyze peripheral nerve conduction tests and visual evoked potentials in 13 chronic alcoholics and in 11 chronic alcoholics who had abstained for at least one year, in order to assess the repercussions of alcohol on the PNS and on the visual pathways and their reversibility. The sensory fibers were more affected than the motor fibers, and while the damage to the motor fibers was transient the damage to the sensory fibers was permanent and also significantly different, at least in the early stages, in the two lower limbs. Our results showed constant involvement, without clinical symptoms, of the visual potential, especially of the earliest component N70 and of the amplitude of the response. This would suggest greater involvement of the peripheral visual nervous structures, that is retino-geniculo-cortical, than of the more properly cortical structures, though these are also affected. For the visual damage too withdrawal of alcohol seems to determine a regression, though only partial, of the neurophysiological changes. The simultaneous involvement of VEP and peripheral nerve function is at variance with the assertion that optic nerve damage is a very rare event in alcoholism.

Alcoholic facial neuralgia: report of three cases

Three cases of jaw pain recurrently precipitated by consumption of alcohol are described. Alcohol-induced neuralgia is added to the differential diagnosis of atypical orofacial pain.

Morphologic alterations in leg muscles of chicks treated with triorthocresyl phosphate in ovo

Chick embryos were injected on incubation Day 14 with 62 microliter of triorthocresyl phosphate (TOCP)/kg egg. Muscles of the leg were examined from 5 to 25 days after hatching. The sartorius from the thigh and the external gastrocnemius and peroneus longus from the tibial leg region were compared for muscle fiber size and end-plate length over this period. Treated chicks showed no acute toxic effects or overt ataxia and were equal in body weight to controls. At 5, 15, and 25 days after hatching, morphologic alterations consistent with denervation were detected. Muscle fibers were smaller than controls on Day 5 and were hypertrophic on Days 15 and 25. On Day 5 growth of fibers was retarded, an effect consistent with denervation, and the subsequent hypertrophy is predicted as compensation for denervated fibers. Small end plates were seen on Day 15, characteristic of end plates that were delayed in development by denervation. Each of these differences was greater in the tibial muscles than in the more proximally located sartorius. This is consistent with a distal neuropathy, such as that caused by TOCP in adult hens. Some recovery was apparent at the low dose 25 days after hatching. It is suggested that this resulted from reinnervation by repaired axons. This study of the myoneural apparatus and muscle fiber response to TOCP adds evidence to the possibility that the developing chick embryo may develop delayed neuropathy from organophosphorus compounds which produce this effect in adult hens.

Prognosis of alcoholic peripheral neuropathy

Ten male alcoholics aged 38-72 years with clear clinical and electroneurographical signs of peripheral neuropathy were re-examined three to five years later. Conduction velocities, latencies and nerve action potential amplitudes were measured from median, peroneal and sural nerves on both occasions and the results were compared with age-matched reference values from 80 healthy men. Seven of the alcoholics showed normal or nearly normal scores in electroneurographical and clinical examination and they had all managed to stop drinking alcohol. The results suggest that the prognosis of alcoholic peripheral neuropathy is good and independent of age provided that intake of alcohol is discontinued and other causes of neuropathy (malignancy, diabetes, nerve trauma) are carefully excluded.

The effect of acute alloxan diabetes on the sensitivity of the rat skeletal neuromuscular junction to drugs

Preparations from alloxan diabetic rats showed a reduced sensitivity to the neuromuscular blocking action of (+)-tubocurarine but no alteration in sensitivity to the depolarizing neuromuscular blocking drug decamethonium. Physostigmine was less effective in augmenting twitch height in preparations from alloxan diabetic rats and such preparations had a significantly lowered total cholinesterase activity compared with control preparations. An additional observation was a reduction in the effectiveness of the pre-junctionally active agent beta-bungarotoxin in producing neuromuscular blockade in physostigmine-treated preparations from alloxan diabetic rats. All the changes produced by alloxan administration were prevented by treatment with insulin.

The syndrome of diabetic amyotrophy

Changes in the electromyograms and motor nerve conduction velocities in 12 patients with diabetic amyotrophy suggested mild distal and moderate proximal neuropathy in the lower limbs. Histological and histochemical findings in the vastus medialis muscles were consistent with denervation. Electron microscopical examination of the vastus medialis muscles in 6 patients revealed myofibrillar degeneration. One patient had abnormal mitochondria and tubular aggregates. The basement membranes of the intramuscular capillaries were thickened in all but 1 patient. Histochemical staining of the myoneural junctions showed changes consistent with degeneration and regeneration. We conclude that diabetic amyotrophy is a distinct clinical entity and is secondary to metabolic derangement rather than diabetic microangiopathy.

Pattern of muscle and nerve pathology in alcoholism

One hundred and ninety-one inpatients undergoing detoxification from alcoholism were studied electrodiagnostically. Of them, 115 (57%) exhibited muscle pathology; only 11 (5%) showed no electrodiagnostic evidence of pathology. A common occurrence in the more severely toxic patients was a phenomenon called "burst suppression," which revealed an inability of the patient to sustain a normal consistent firing of motor units upon muscle contration; the significance of this phenomenon is not thoroughly understood. Electrodiagnosis is a helpful tool in the diagnosis, prognosis, treatment, and follow-up of patients with alcoholism.

[Alcoholic polyneuropathy. Electrophysiological and clinical findings in 85 patients (author's transl)]

Maximum motor and sensory nerve conduction velocities, amplitudes of muscle action potentials (surface electrodes) and of sensory nerve action potentials, and needle electromyograms were studied in 80 patients with alcoholic neuropathy and in 5 chronic alcoholics without clinical signs of neuropathy. The electrophysiological results were compared to the clinical findings. Neurographic criteria compatible with the diagnosis "alcoholic neuropathy" were defined. Neurographic findings contrary to a diagnosis of alcoholic etiology were demonstrated in 3 patients. Only in a smaller group of patients could a reduction of conduction velocity be found, especially in regions of peripheral nerve entrapment. A decrease in conduction velocity outside of the entrapment sites can be explained in some cases by segmental demyelination in chronic hepatitis or cirrhosis of the liver.

Neuropathology of the oesophagus in diabetes mellitus

Abnormalities of the innervation of the oesophagus have been shown in 18 out of 20 unselected diabetics without clinical dysphagia or neuropathy. The changes appear to be in the axons of the extrinsic and intrinsic parasympathetic fibres. It is probable that, as in the peripheral nerves, the major changes are in the Schwann cells, although here the affected fibres are unmyelinated.

Electrophysiological evidence for a distal lesion in alcoholic neuropathy

Nerve conduction studies were carried out on 16 alcoholic subjects with minimal or no clinical evidence of peripheral neuropathy. Digital nerve action potentials recorded at the base of the finger were reduced in amplitude in five but the potential at the wrist was reduced in only one. In two other patients, even though the values were within the control range, the ratio of the amplitude recorded from the finger and from the wrist was smaller than in control subjects. Thus, by recording both digital and wrist action potentials, abnormalities have been demonstrated in seven of 16 patients, whereas the wrist potential was abnormal in only one. Conduction velocity was slightly reduced in the fingers in three patients.

Electrophysiological studies in alcoholism

Using a range of electrophysiological techniques, it has been possible to demonstrate impaired function in smaller calibre motor fibres and in distal large cutaneous sensory nerve fibres in both alcoholic patients without neuropathy and in those alcoholics with clinical manifestations of peripheral nerve disease. Evidence of more proximal involvement of Ia sensory fibres was obtained, but in the majority of our patients, large motor fibres functioned normally. The nature of the underlying pathological process is discussed.