Atypical Interplay of Dermatomyositis, Metastatic Caecal Carcinoma, and Connective Tissue Disease

This report presents the case of a 71-year-old Chinese female with atypical symptoms leading to the diagnosis of metastatic caecal adenocarcinoma with overlapping connective tissue disease, initially identified as possible paraneoplastic dermatomyositis. The patient, with no significant medical history, was referred for elevated serum creatine kinase (CK) levels and exhibited progressive lethargy, upper limb weakness, and notable weight loss over three months. Clinical examination revealed violaceous rashes and significant muscle weakness, prompting a provisional diagnosis of dermatomyositis. However, extensive investigations, including computed tomography (CT) imaging and colonoscopy, uncovered metastatic disease characterized by peritoneal collections and a caecal tumor. The autoimmune panel indicated elevated anti-ribonucleoprotein (anti-RNP), anti-Sjögren's Syndrome A/Ro (anti-SSA/Ro), anti-topoisomerase I (anti-Scl-70), and anti-Ku antibodies, while key cancer-associated myositis markers were absent. This scenario highlights the complex interplay between malignancy and autoimmunity, emphasizing the necessity for a multidisciplinary approach in diagnostic evaluation. The findings advocate for heightened awareness of malignancy in older adults presenting with inflammatory myopathy, as timely diagnosis and intervention are critical in reducing morbidity and mortality associated with malignancies.