A case of myositis associated with mixed connective tissue disease mimicking bilateral posterior interosseous nerve palsy.

Overlap myositis (OM) is an idiopathic inflammatory myopathy characterized by proximal muscle weakness. However, atypical patterns of muscle involvement may also occur. We present a challenging case of OM mimicking bilateral posterior interosseous nerve (PIN) palsy. The patient presented with a gradual onset of bilateral finger drop over two years. Despite initial clinical suspicion of PIN palsy, electromyography revealed myopathic features. Laboratory assessments showed anti-ribonucleoprotein antibody positivity, with subsequent muscle biopsies supporting OM associated with mixed connective tissue disease. This case highlights the significance of considering atypical presentations of OM. Furthermore, it emphasizes the pivotal role of targeted muscle biopsies when initial biopsy results are inconclusive.