A rare case of focal myositis affecting the sternocleidomastoid muscle: diagnostic challenges and management strategies

Introduction. Focal myositis is a rare inflammatory disease characterised by localised involvement of a single muscle or muscle group. Involvement of the sternocleidomastoid muscle represents an extremely rare localisation. Materials and methods. We report the case of a 78-year-old woman who developed progressive left laterocervical swelling and pain following a respiratory infection. Extensive clinical and radiological investigations were performed; however, a definitive diagnosis was achieved only after muscle biopsy. Results. The patient initially responded to corticosteroid therapy but subsequently developed steroid dependence. For long-term disease control, methotrexate was introduced as a steroid-sparing agent. The clinical course was notable for recurrent disease exacerbations associated with fever. Discussion. This case presents several distinctive features, including occurrence in an elderly patient, the presence of fever during disease flares, and a steroid-dependent course requiring second-line immunosuppressive therapy. These aspects contribute to the diagnostic and therapeutic complexity of focal myositis, particularly in atypical localisations. Conclusion. Our experience highlights the diagnostic challenges associated with this rare entity and suggests that prolonged immunosuppressive treatment may be necessary in selected patients with focal myositis.