engleski

Metabolic polyneuropathies

The advancement of modern sciences, genetics, molecular biology, immunology and biochemistry, has given rise, among others, to a striking evolution of knowledge within the field of peripheral polyneuropathies. In major part these entities are of metabolic origin. Taxonomically, however, the term metabolic neuropathy is "reserved" for those derangements of paripheral neurons that develop in diabetes, hypoglicemia, renal insufficiency, amyloidosis and porphyria. Some authors list neuropathies in dysglobulinemia among metabolic neuropathies as well, but refuse to accept in this group deficient and/or toxic neuropathies, peripheral neurolipidoses, such as sulfatidosis and Refsum's disease. This restrictive view of matabolic neuropathies is no doubt arbitrary, but on the other hand an extended conception of these nosological entities would, in our view, be too diffuse and not didactic. The etiology of metabolic polyneuropathies is very broad. Some of them are the consequence of a genetic metabolic anomaly (porfiria, amyloid neuropathy) ; others are acquired, secondary, with known causes: diabetes, hyperinsulinism, uremia, dysglobulinemia. Their diagnosis is based on clinical examination. Simple complementary biological analyses, electrophysiological techniques, and in somecases muscle and peripheral nerve biopsies, can direct the physician towards establishing the right causal diagnosis. According to their evolution, metabolic neuropathies are divided into acute, subacute and chronic ; according to pathophysiological changes they are divided into axonal and demyelinating. Due to the frequency of its incidence, diabetic neuropathy dominates over all other metabolic neuropathies. It remains mysterious, in spite of the hopes incited by the discovery of the role of sorbitol and myo-inositol in its pathogenesis. Recent evidence of vascular lesions of peripheral nerves in diabetics has resuscitated old discussions on the importance of microcirculation for the function of nerves. As regards familial amyloid neuropathy, the abnormal substitution to which it is due is well known today: transthyretin turns into amyloid through substitution of amino acid in one of several rings of tetrameric protein. At least one allele of the chromosome 18 is responsible for this genopaty. The diagnosis can therefore be established by blood analysis, which is of great value for generic advice. It is not always easy to prove the connection between dysglobulinemia and a lesion of the peripheral nerves. In such cases the physician has to bring evidence for the activity of antibodies against constituent elements of nerve. It is feasible today and concerns mainly IgM globulin. The prolongation of life of patients with cronic renal insufficiency owing to dialysis and transplantation, has enabled better understanding of neuropathies in renal insufficiency. As for acute intermittent porphyria, the saying that "the most dangerous factors that carry the disorder are drugs and chemists" still holds. In general, the therapy of metabolic neuropathies remains difficult. In the field of dysglobulinemic polyneuropathies some positive advance ments have been achieved by the use of plasmapheresis, human plasma immunoglobulins, chlorambucil and cyclophosphamide. Regarding the therapy of diabetic neuropathy, tests with reductase of aldose and gangliosides are being carried out.

Metabolic neuropathy

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