Skeletal muscle vasculitis exclusive of inflammatory myopathic conditions: a clinicopathologic study of 40 patients

Vasculitis is an infrequently encountered pathology in skeletal muscle biopsy specimens, the diagnosis of which has significant therapeutic implications. This study retrospectively reviewed the clinicopathologic features of 40 patients with vasculitis (infiltration of vessel walls by inflammatory cells) diagnosed via skeletal muscle biopsy during a 27-year period of time. Cases of vasculitis associated with inflammatory myopathic conditions, such as polymyositis or dermatomyositis, were excluded from study. Forty patients, including 21 women and 19 men ranging in age from 19 to 83 years (mean of 52 years), formed the study group. The most common clinical presentations included muscle pain (n = 22, 55%), paresthesias (n = 16, 40%), and weight loss (n = 15, 38%). Westergren erythrocyte sedimentation rate was known in 31 patients and ranged from 12 to >150 mm/h (mean, 61 mm/h). Necrotizing vasculitis was identified in 35 patients (88%). The vasculitic process involved multiple vessels in 30 cases (75%). Vessel wall scarring and/or fibrosis were identified in 11 patients (28%), thrombi in 3 patients (8%), eosinophils in 2 patients (5%), and granulomas in 1 patient (3%). Neurogenic changes were observed in the majority of biopsy specimens as follows: angular atrophic esterase-positive muscle fibers (n = 35, 88%), grouped atrophy (n = 14, 35%), fiber type grouping (n = 17, 43%), and target fibers (n = 6, 15%). Other commonly identified pathologies included scattered degenerating muscle fibers (n = 15, 38%), regenerating muscle fibers (n = 17, 43%), and type II muscle fiber atrophy (n = 10, 25%). Thirty-three patients also underwent sural nerve biopsy. Vasculitis was identified in the nerve in 26 of 33 of these patients (79%). Peripheral nerve vasculitis was classified as necrotizing in 15 cases (57.7%) and as nonnecrotizing in 11 cases (42.5%). Seventeen of 33 patients (52%) with known follow-up showed clinical improvement with steroid/immunosuppressive therapy. The following 2 conclusions were made: the majority of vasculitis cases arising outside the setting of inflammatory myopathy in skeletal muscle are necrotizing, and the predominant muscle pathology in the setting of vasculitis is neurogenic atrophy, likely caused by concomitant involvement of the peripheral nervous system.