Single center muscle bx of 860 pts muscle biopsy had 531 with IIM (61.7%), 253 with non-IIM (29.4%), and 76 undiagnosed (8.8%). 7.9% were classified as immune mediated necrotizing myositis, 40% DM, 9.5% synthetase synd, IBM 0.3% https://t.co/KTsjpu0qPY