Early peripheral nerve abnormalities in impaired glucose tolerance.

Increased prevalence of impaired glucose tolerance (IGT) has been recently detected in patients with painful sensory neuropathy. To determine whether nerve abnormalities are present in IGT we investigated IGT subjects without clinical neuropathy. Nerve conduction studies (NCS) were performed in 12 subjects with IGT without symptoms and signs of neuropathy. The results were compared with those obtained from 12 patients with type 2 diabetes (DM) without clinical neuropathy and 12 healthy controls. Sensory NCS of the sural nerve were performed on different segments, the distal-leg (10 cm proximal to the lateral malleolus) and the proximal-leg segment (10 cm more proximal). The distal conduction velocity of the sural nerve was increased in IGT subjects, compared both to healthy controls and DM patients. No difference was found among the groups with respect to the sensory conduction velocity of the sural nerve fibers in the proximal-leg segment. A reduction of both distal and proximal amplitudes of the sural nerve action potentials was detected in DM patients compared with IGT subjects and controls. The abnormal conduction velocity in the distal segment of the sural nerve, observed in IGT subjects without clinical neuropathy, suggests that the myelin dysfunction of the distal sensory fibers represents the earliest detectable nerve response to the hyperglycemia. The reduced amplitude of the sural nerve action potential in asymptomatic patients with DM arises from the axonal degeneration and represents a more advanced stage of nerve disease.

Criteria for early detection of conduction block in multifocal motor neuropathy (MMN): a study based on control populations and follow-up of MMN patients.

Motor conduction block (MCB) has been used as the main diagnostic criterion in multifocal motor neuropathy (MMN). Nonetheless, no agreed definition of block currently exists; the proposed required percent decrement of proximal compound muscle action potential (CMAP) amplitude varies from > 20% to > 50%. The aim of this work was to evaluate, through a follow-up study of patients with MMN, the behaviour of MCB over time. The percent decrement and temporal dispersion of proximal CMAP have also been calculated in normal controls and in patients affected by amyotrophic lateral sclerosis (ALS). The results show that MCB in patients with MMN is a dynamic entity which greatly varies over time and that a > 50% CMAP amplitued reduction may well be preceded by a smaller decrement that is nonetheless indicative of focal myelin damage in the appropriate clinical context. This datum and the results obtained in the control group and in patients with ALS suggest that a reappraisal of the diagnostic criteria for MCB, in cases with clinical and electrophysiological data strongly indicative of MMN, should be considered. Since MMN is a treatable disorder, the use of the proposed less restrictive criteria for the identification of MCB could allow for a promp and more effective treatment.