Sporadic inclusion body myositis and primary Sjogren's syndrome: an overlooked diagnosis

Sporadic inclusion body myositis (sIBM) has been reported to occur in association with autoimmune diseases and in particular, primary Sjogren's syndrome (pSS). This brief report describes patients identified with a positive SSA antibody and diagnosis of sIBM at a large academic medical center over a 13.5-year period. A cohort identification tool was used to identify patients with positive SSA antibody and a diagnosis of sIBM between January 1, 2006 and June 1, 2019. All cases of sIBM had diagnostic confirmation by a neuromuscular specialist. Demographics, clinical features, autoantibodies, MRI and EMG findings, and muscle biopsy features were reviewed for each identified case. Eight patients were found to carry the diagnosis of pSS and sIBM. Two additional sIBM patients were SSA antibody positive without other pSS features. The mean time from initial symptom onset of muscle weakness to diagnosis was 5.4 years (range 1-15 years). All patients had alternative diagnoses offered for their myopathic symptoms prior to sIBM identification. The NT5c1A antibody was positive in 7 of 8 patients tested. No patient had a durable response to immunosuppressive therapy. The diagnosis of sIBM went unrecognized for over 5 years in our cohort of SSA antibody-positive patients with myopathy. The patients in this cohort were treated with a variety of immunosuppressive agents prior to diagnosis without benefit. Recognizing the clinical features of sIBM in patients with pSS is crucial in instituting appropriate therapy and avoiding unnecessary immunosuppression.