Beyond the respiratory tract: a case of acute viral myositis following respiratory syncytial virus infection

Aim: Acute viral myositis is an uncommon complication that typically occurs during the recovery phase of viral infections and is most frequently observed in children. It is rarely reported in adults and usually presents as myalgia of the proximal upper and lower limbs. This case report describes an atypical presentation of acute myositis in an immunocompetent adult occurring shortly after RSV infection. Methods: A 68-year-old male patient presented with sudden-onset bilateral lower limb myalgia and weakness following recent RSV infection. Laboratory evaluation revealed elevated C-reactive protein with normal creatine kinase levels. The extensive infectious and autoimmune workup was not revealing. MRI, muscle biopsy, and electrophysiological studies were conducted to further investigate the etiology of the symptoms. Results: MRI demonstrated diffuse bilateral muscle edema consistent with inflammatory myositis, while muscle biopsy and electrophysiological studies were unremarkable. The patient received supportive care, including hydration, analgesia, and rest, without corticosteroids or antivirals. Complete recovery occurred within two months. Conclusion: This case highlights an atypical presentation of RSV-associated myositis in an adult patient characterized by normal creatine kinase levels but elevated inflammatory markers. Increased awareness of this rare entity may facilitate prompt diagnosis, and prevent unnecessary diagnostic investigations as well as inappropriate immunosuppressive therapy.