Severe polymyositis occurring in a cancer patient directly after chemotherapy: etiology and management

A 72-year-old woman was diagnosed with metastatic colorectal cancer and treated with oxaliplatin-based chemotherapy and bevacizumab. One week after the second administration of chemotherapy, she presented acute-onset dysphagia and rapidly progressing proximal muscle weakness, associated with elevation of the creatinine phosphokinase enzymes. Magnetic resonance imaging raised suspicion of polymyositis. Etiology remained unclear but paraneoplastic origin or immune modulation by chemotherapy was considered. High-dose methylprednisolone and intravenous immunoglobulins were started with continuation of chemotherapy. Although there was rapid normalization of muscle enzyme, the general status deteriorated rapidly with aggravation of dysphagia, complete immobilization and death. This case highlights the importance of considering muscle weakness as paraneoplastic syndrome or drug-induced toxicity in colorectal cancer patients. Despite aggressive management, prognosis remains poor.