60 | dermatomyositis as a cutaneous sentinel of occult intramucosal rectal adenocarcinoma: The critical role of dermatologic recognition and malignancy screening

Dermatomyositis (DM) is an idiopathic inflammatory myopathy characterized by distinctive cutaneous manifestations and a well-established association with malignancy. Adult-onset DM carries the highest cancer risk among idiopathic inflammatory myopathies, with most malignancies occurring within three years of disease onset. Current international recommendations support systematic and risk-stratified cancer screening as an essential component of patient evaluation. A 67-year-old woman presented with a two-month history of erythematous skin lesions associated with muscular asthenia predominantly affecting the scapulohumeral and glenohumeral girdles. Physical examination revealed violaceous erythema of the dorsal hands and forearms, periungual erythema with telangiectasias, symmetric erythema involving the cervico-interscapular, lumbosacral and gluteal regions, the décolleté, lateral abdomen and thighs, and bilateral flagellate erythema of the scapular and dorsal areas. A skin biopsy was performed for histopathological examination and direct immunofluorescence. Autoimmune screening and rheumatologic evaluation were requested. Given the suspicion of cancer-associated DM, comprehensive oncologic screening was undertaken. Histopathological examination demonstrated diffuse vacuolar degeneration of the basal layer, superficial and deep perivascular and interstitial lymphocytic infiltrates, and dermal mucin deposition, consistent with interface dermatitis and supportive of DM. Cancer screening revealed fecal occult blood positivity. Colonoscopy identified an 18-mm distal rectal lesion associated with a 20-mm pseudopedunculated nodule. Histopathological analysis demonstrated a serrated adenoma with high-grade dysplasia and intramucosal adenocarcinoma with a clear implantation base. Prednisone 50 mg/day was initiated, resulting in significant improvement of the cutaneous manifestations. This case highlights the importance of recognizing DM as a potential paraneoplastic syndrome. Dermatologic findings prompted targeted malignancy screening, leading to the diagnosis of intramucosal rectal adenocarcinoma at a potentially curable stage. In line with emerging international recommendations, standardized and risk-based cancer screening should be considered an integral component of the diagnostic work-up of adult-onset DM to facilitate early cancer detection and improve patient outcomes.