The Overlapping Spectrum of Primary Tubercular Myositis and Immune-Mediated Myositis: Diagnostic Challenges in Three Cases.

Primary tubercular myositis is a rare extra-pulmonary manifestation of tuberculosis (TB). We present three cases of biopsy-proven granulomatous myositis, all of which had an initial clinical picture suggestive of dermatomyositis and serological positivity for a myositis-specific antibody. Case 1 was initially diagnosed as dermatomyositis, but the patient, a 46-year-old woman, deteriorated rapidly after immunosuppression and succumbed to disseminated TB. In Case 2, the patient, a 43-year-old woman, developed subacute proximal weakness after the initiation of anti-tuberculous therapy (ATT) for lymph node TB but recovered with continued therapy and the addition of immunomodulation. Case 3 was initially diagnosed as dermatomyositis, and the patient, a 34-year-old man, showed an inflammatory mass in the right thigh, in addition to generalized proximal weakness, and improved significantly after anti-tubercular treatment. In Case 1, TB likely mimicked dermatomyositis, but the patient deteriorated before the response to ATT could be assessed. Patient 2 developed tubercular granulomatous myositis, along with a possible flare of underlying immune-mediated myositis after the diagnosis of TB lymphadenitis and required both ATT and immunosuppression. Patient 3 showed marked improvement after ATT alone, suggesting TB as the primary pathology. In this series, we highlight the diagnostic challenges in recognizing tubercular myositis in patients who present with generalized proximal weakness resembling autoimmune myositis, emphasizing the need for muscle biopsy in refractory cases and a high index of suspicion for TB in endemic regions. Early recognition and appropriate treatment can lead to favorable outcomes in these patients.