Vasculitic Myopathy: Clinical Characteristics and Long-Term Outcomes

Abstract

Background and objectives: Peripheral neuropathy is a common manifestation of systemic and nonsystemic vasculitides; however, there is limited literature on vasculitic myopathy. We aim to describe the clinical, laboratory, and pathologic characteristics and treatment outcomes of vasculitic myopathy.

Methods: A retrospective chart review of patients with a diagnosis of vasculitis and myopathy (1980-2022) was performed. Patients were included with either biopsy-proven vasculitic myopathy or biopsy-proven vasculitis (of nonmuscle tissue) and concomitant active myopathy after excluding alternative causes. All muscle biopsy slides were reviewed, and additional immunohistochemistry studies were performed.

Results: Twenty-five patients with vasculitic myopathy were identified, 60% were female, and the median age at diagnosis was 63 (interquartile range 38-81) years. Ten patients (40%) had a primary systemic vasculitis, 12 secondary systemic vasculitis (48%), and 3 had nonsystemic vasculitic myopathy (12%). Myopathy was the initial manifestation of vasculitis in 20 of 25 patients (80%). Weakness was proximal and symmetric in most cases. Nineteen patients (76%) had pain at presentation: 2 with only neuropathic pain, 10 with only myalgia, and 7 had a combination of neuropathic pain distally and myalgia proximally. Creatine kinase (CK) was elevated in 3 of 23 patients (13%) and aldolase elevated in 10 of 16 patients (63%). Electromyography revealed short duration motor unit potentials in proximal and axial muscles in 23 of 24 patients (96%) and superimposed peripheral neuropathy in 15 of 24 (63%). Muscle biopsy showed perivascular inflammation in all biopsies, vessel wall inflammation and destruction in 18 of 21 (86%), and fibrinoid necrosis in 13 of 21 biopsies (62%). Masson trichrome stain facilitated the detection of fibrinoid necrosis. All muscle specimens had increased major histocompatibility complex class I sarcolemmal reactivity in nonnecrotic fibers. In most patients, the inflammatory infiltrates were predominantly CD4⁺ T cells, with complement deposition on blood vessels in some. Twenty-four patients improved with immunotherapy, and only 3 patients relapsed. Seven patients died during the study period, 1 from vasculitis complications. Probability of survival at 1 and 5 years was 96% and 84%, respectively.

Discussion: Myopathy can be the initial manifestation of a primary or secondary systemic vasculitis or may occur as a nonsystemic form. Most patients present with proximal predominant weakness with normal CK and elevated aldolase levels. Patients usually respond well to immunotherapy.