The spectrum of lower motor neuronsyndromes

Abstract. This review discusses the most important lower motorneuron syndromes. This relatively rare group of syndromes hasnot been well described clinically. Two subgroups can bedistinguished: patients in whom motor neurons (lower motorneuron disease (LMND)) are primarily affected or motor axons andtheir surrounding myelin (multifocal motor neuropathy (MMN)),both leading to muscle atrophy and weakness.Both hereditary and sporadic forms of LMND have beendescribed. The discussion of recent advances in the geneticknowledge of several hereditary forms of LMND may lead to abetter understanding of the pathophysiology and the developmentof therapeutic strategies. By contrast, the pathogenesis ofsporadic LMND is largely unknown. It is, therefore, difficult toconsider the various sporadic forms of LMND, discussed in thisreview, as separate diseases. Because the diagnostic andtherapeutic options may differ, it would seem rational toconsider sporadic LMND as a spectrum of syndromes which can bedistinguished from each other on the basis of clinicalpresentation.MMN is a lower motor neuron syndrome with presumedimmunemediated pathogenesis. Evidence of motor conduction blockon nerve conduction studies and a positive response to treatmentwith intravenous immunoglobulins (IVIg) are considered the mostrelevant criteria for the diagnosis of MMN. As it is treatable,it is important to distinguish MMN from LMND. Carefulelectrophysiological analysis in the search for conduction blockis, therefore, required in all adult patients with pure lowermotor neuron syndromes. For the individual patient, dist inctionbetween the various lower motor neuron syndromes is important asit enables the physician to provide adequate information overthe disease course in LMND and to facilitate early treatment inMMN.Supported by a grant from the Prinses BeatrixFonds.