From Rhabdomyolysis to a Lymphoproliferative Disorder: A Long Diagnostic Work-Up.

Rhabdomyolysis is characterized by myocyte necrosis with destruction of the skeletal muscle that can lead to severe complications if left untreated. Due to its multiple possible etiologies, identifying the underlying cause can be challenging, especially when the clinical presentation is atypical or evolves. We present the case of a 73-year-old man who developed progressive proximal muscle weakness shortly after COVID-19 vaccination. Laboratory tests were consistent with rhabdomyolysis. Despite supportive treatment and clinical response to corticosteroids, the underlying cause remained initially unclear. Months later, the patient developed dermatomyositis, and further investigation revealed a lymphoma, suggesting a paraneoplastic process. In patients presenting with a first episode of unexplained rhabdomyolysis, particularly when symptoms are progressive, clinicians should maintain a high index of suspicion for inflammatory myopathies. This case highlights the complexity of the diagnostic work-up for paraneoplastic dermatomyositis, especially when the initial presentation is incomplete, and underscores the importance of long-term follow-up and continued investigation to establish a definitive diagnosis and exclude neoplasms that may only become apparent years later.