Paraneoplastic dermatomyositis-like syndrome preceding diagnosis of small cell lung cancer: a case report.

Paraneoplastic syndromes (PNS) are frequently misdiagnosed as independent neurological, endocrine, cutaneous, or rheumatic immune disorders due to their low incidence, highly variable, and complex clinical presentations. Currently, when faced with clinically unexplainable phenomena, PNS is seldom considered in the differential diagnosis. A 68-year-old non-smoking Chinese male presented with insidious digital clubbing in 2021 and refractory cutaneous eruptions in 2023, which were initially diagnosed as granulomatous rosacea and erythroderma. However, treatment with ketotifen, cetirizine, and the immunosuppressant cyclosporine led only to partial regression of the rash, with persistent pruritus. Approximately 3 years after the insidious onset of digital clubbing and 1 year after the skin lesions flared, in April 2024, chest PET/CT scan revealed a mass in the left lower lobe and a nodule in the dorsal segment of the right lower lobe. A biopsy confirmed extensive-stage small cell lung carcinoma (SCLC).His dermatological manifestations, which progressed to edema and dysphagia, and ancillary examination results were subsequently attributed to a paraneoplastic dermatomyositis-like syndrome. Chemotherapy for SCLC resulted in resolution of the skin lesions and disease control. This case underscores the critical role of PNS as an early indicator of occult malignancy and highlights the therapeutic challenges in managing paraneoplastic dermatomyositis-like syndrome.