[Polyneuropathies with IgM monoclonal gammopathy. 12 cases].

12 cases of polyneuropathy with IgM monoclonal gammapathy are reported. An analysis of the clinical, electrophysiological, histological and immunological features of these cases and of those reported in the literature allows to distinguish 2 groups. In the first group (8./12 cases), the neuropathy showed clinical and electrophysiological features of a mainly demyelinating mechanism involving large fibers. Electromicroscopy disclosed a widening of the spaces between the lamellae of the myelin in half of these cases. A monoclonal deposit of IgM was demonstrated by direct immunofluorescence, on the remaining myelinated fibers in most cases. In this first group, the M-component always reacted with the myelin sheaths of a monkey's peripheral nerve. The results of indirect immunofluorescence were closely correlated with those of immunoblotting, which revealed an anti-M.A.G. (Myelin Associated Glycoprotein) activity. The second group is more heterogeneous: there was an predominantly motor neuropathy (1 case), an asymmetrical and painful neuropathy with an endoneural deposit of IgM (1 case). In 2 other cases which in no other ways differed from those of the first group, the M-component seemed devoid of antimyelinic activity. Nevertheless, the presence of IgM on the myelin sheaths of these 2 cases suggested a relationship between the neuropathy and the gammapathy. In both groups, results from the association of apheresis and chlorambucil were difficult to assess and vary greatly. Therapy appeared beneficent in half of the cases, but only one patient was markedly improved.