Two subtypes of Churg–Strauss syndrome with neuropathy: the roles of eosinophils and ANCA

The aim of this study was to clarify the differences in the pathogenesis of neuropathy between myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA)-positive and -negative patients with Churg–Strauss syndrome (CSS). Eight MPO-ANCA-positive and 14 MPO-ANCA-negative patients were included. In addition to the standard histology, nerve biopsies were examined, employing immunohistochemistry for eosinophil major basic protein and electron microscopy. The groups did not differ significantly in clinical profiles, including the peak disability score and number of blood eosinophils. In nerve biopsies, necrotizing vasculitis was found in 63% (5/8) of the ANCA-positive and 21% (3/14) of the ANCA-negative patients. Fibrinoid necrosis of vessel walls was noted in 4 ANCA-positive patients (50%), and in one ANCA-negative patient (p = 0039). In contrast, a large number of eosinophilic infiltrations in the epineurium was shown in 36% (5/14) of the ANCA-negative patients, with no eosinophilic infiltrations shown in ANCA-positive patients. In 3 ANCA-negative patients, endoneurial eosinophils were seen where focal axonal loss and capillary dilatation were occasionally noted. There may be 2 pathogenetic mechanisms of neuropathy with CSS: ANCA-related vascular fibrinoid necrosis, and a toxic eosinophilic effect on nerve fibers which is independent of ANCA. Therapy targeting activated eosinophils may be a possible treatment for intractable neuropathy of CSS.