From myositis to sarcoidosis: a rare autoimmune continuum.

Background: Sarcoidosis is a multisystem granulomatous disease that may rarely coexist with idiopathic inflammatory myopathies. The overlap of sarcoidosis and idiopathic inflammatory myopathy is exceptional and poses diagnostic difficulties due to overlapping clinical and laboratory findings. Case presentation: A 35-year-old woman presented with progressive proximal muscle weakness and dyspnoea. Electromyography revealed primary muscle fibre involvement, and serum creatine kinase levels were markedly elevated. Initial muscle biopsy was nondiagnostic. Two years later, mediastinal lymph node biopsy showed nonnecrotising granulomatous inflammation, consistent with sarcoidosis. Sarcoidosis was initially managed conservatively due to the absence of organ-threatening involvement. Over time, progressive muscle weakness and respiratory symptoms recurred. Magnetic resonance imaging of the lower extremities revealed diffuse muscle oedema and enhancement consistent with inflammatory myopathy. Repeat electromyography findings supported idiopathic inflammatory myopathy. Laboratory tests showed antinuclear antibody 1:320 cytoplasmic homogeneous positivity, whereas myositis-specific antibodies were negative. The patient was diagnosed with sarcoidosis-idiopathic inflammatory myopathy overlap syndrome. She achieved complete clinical and biochemical remission following treatment with oral corticosteroids and azathioprine. Conclusion: The coexistence of sarcoidosis and idiopathic inflammatory myopathy is rare but should be considered in patients with granulomatous disease and progressive myopathy. Recognition of this overlap is essential for timely diagnosis and immunosuppressive therapy, which may lead to full recovery.