[Neuromuscular biopsy and diagnosis of vasculitis]

One characteristic histological lesion on biopsy specimens is mandatory to establish the diagnosis of vasculitis. Combined nerve and muscle biopsies, by the same cutaneous incision, improve significantly the percentage of positive results. Nerve fragments should be taken in every patient presenting sensory manifestations. Such vasculitic lesions are present in medium-sized arterioles and/or small vessels, and correspond mainly to 4 necrotizing vasculitis: panarteritis nodosa (PAN), microscopic polyangiitis (MPA), Churg and Strauss syndrome and Wegener granulomatosis. Microvasculitis should be added to these classical entities, because it corresponds to small vessel wall infiltration by inflammatory cells, as observed in PAN and MPA, but without any necrosis. Microvasculitis has to be differentiated from the inflammatory cell infiltrates surrounding small vessels. However, such perivascular inflammatory cell infiltrates enable the diagnosis of probable vasculitis when associated with clusters of neo-vessels, hemosiderin deposits, or a focal damage of nerve fibers. Grossly, one third of vasculitis diagnosis is confirmed on muscle fragments, a second third on nerve fragments, and the last third on both nerve and muscle fragments. Moreover, in the search for vasculitis, an unpredicted diagnosis of lymphoma or amyloidosis is occasionally established on the neuro-muscular biopsy.