18 - Outcome of polyneuropathies and mononeuropathies

Summary

Introduction

Peripheral neuropathies are a heterogeneous group of diseases of the peripheral nervous system. It is useful to distinguish three categories based upon the pattern of involvement: polyneuropathy, mononeuropathy and plexopathy. The typical polyneuropathy is a symmetrical disorder, resulting in distal weakness of limb muscles and sensory loss. Mononeuropathies are isolated lesions of peripheral nerves, which may be multifocal (multiple mononeuropathies or mononeuritis multiplex). Plexopathies are lesions affecting the brachial or lumbar plexus, and the presenting symptoms involve one limb or part of a limb.

Diagnosing a neuropathy is relatively simple, but establishing its aetiology can often be cumbersome (Dyck et al. 1981; Notermans et al. 1991; Schaumberg et al. 1991a). Many acquired, and a few hereditary neuropathies can be treated. Most neuropathies have a good prognosis for life expectancy; some may eventually prove to be incapacitating.

First we shall present a brief discussion of some factors which play a role in the outcome of a neuropathy. This will be followed by a review of current knowledge on the outcome of different neuropathies or groups of neuropathies.

Factors which play a role in the outcome

Gene defects

Neuropathies of a similar phenotype can be caused by defects in different genes. This may explain some of the variation in time of onset and course of the neuropathies. The nature of a gene defect may have consequences for the phenotype, the severity and the course of a neuropathy. This is exemplified by recent discoveries concerning the genetic basis of hereditary motor and sensory neuropathy (HMSN) type I and hereditary neuropathy with liability to pressure palsies (HNPP); these will be discussed in more detail below.