Morphometric evaluation of paraneoplastic neuropathies associated with carcinomas, lymphomas, and dysproteinemias

Paraneoplastic peripheral neuropathies are caused by indirect effects of carcinomas, mainly small cell bronchogenic carcinomas, lymphoproliferative disorders (lymphomas, myelomas, polycythemia vera), and dysproteinemias (benign monoclonal paraproteinemia, Waldenström's macroglobulinemia) including cryoglobulinemias. Those associated with carcinomas are usually considered as severe, those associated with benign gammopathies (monoclonal gammopathies of unknown significance, MGUS) as mild, and those with cryoglobulinemias as of variable severity. In a larger series of 104 autopsy and biopsy cases, we noted a wide range of severity concerning various morphometric parameters of peripheral nerve fibers by evaluating sural nerves. There were no apparent morphometric differences between the groups of disorders. The most valuable parameter of optic-electronic evaluation and comparison turned out to be the myelin area expressed as a percentage of the endoneurial area because this measure comprises the relative number, size, and myelin thickness of the myelinated nerve fibers. In the 104 cases of the three disease groups, most of the cases (38 cases; 36.5%) showed a moderate reduction of the myelin sheath area per endoneurial area of sural nerves. This was followed by 34 cases (32.7%) with severe and very severe reduction. Twenty-nine cases (27.9%) presented with mild reduction. It is concluded that the severity of the neuropathy depends largely on the stage of the disease and the time of progression rather than on the type of the underlying disorder.