No General Association Between Myositis Antibodies and Electromyography Findings

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ABSTRACT Objective Myositis‐specific antibodies (MSAs), myositis‐associated antibodies (MAAs), and concentric needle electromyography (EMG) are routinely used in the differential diagnosis of myositis. Their mutual relationship, particularly between MSAs/MAAs and EMG findings, remains unclear. Methods We retrospectively analyzed the charts of 368 patients suspected of having myositis at a tertiary neurological center over a span of 7 years. They underwent EMG (fibrillations (Fibs), positive sharp waves (PSWs), fasciculations (Fascs), or complex repetitive discharges (CRD), motor unit action potential (MUAP) morphology, maximum MUAP amplitude, interference pattern, assessment of pathological EMG, and myopathic EMG) and MSA/MAA testing (Line Blot: anti−Mi2, −Ku, −PM‐Scl100, −PM‐Scl75, −Jo1, −SRP, −PL7, −PL12, −EJ, −OJ, −Ro52), and were categorized into myositis and non‐myositis diseases. Associations between pathological EMG findings and positive MSA/MAA were then tested. Results No general association was observed between positive MSAs/MAAs and pathological EMG findings; only a slightly significant association between positive MSAs/MAAs and the presence of a myopathic EMG assessment ( p = 0.043, φ = 0.113). Among 63 patients with myositis, 36 (57.1%) had positive MSA/MAA, 35 (55.6%) showed fibrillations/positive sharp waves, 17 (27.0%) had both, and 9 (14.3%) had neither. Discussion The presence of MSA/MAA does not necessarily indicate pathological EMG findings, and vice versa. Both may provide valuable insights into different aspects of myositis, acting as complementary elements in the diagnostic process.

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