Progressive myalgia as the sole manifestation of cancer-associated myositis: A case report and review of the literature.

RATIONALE: Cancer-associated myositis (CAM) is a rare autoimmune disease linked to underlying malignancies and classified as an idiopathic inflammatory myopathy. It is characterized by a complex pathogenesis, poor prognosis, and diverse symptoms such as muscle weakness and myalgia, which may be accompanied by extramuscular manifestations. The presence of comorbidities in elderly patients can mask these symptoms, posing significant diagnostic and treatment challenges. Early recognition of CAM and detection of malignancy are crucial for improving patient outcomes. PATIENT CONCERNS: A 71-year-old male presented with progressive symmetrical proximal muscle pain as the sole manifestation, without typical extramuscular manifestations. Initial tests revealed negative muscle enzyme results, but electromyography indicated myogenic damage in the proximal muscles of the limbs. Further serological testing detected positive anti-TIF1γ and anti-PL-7 antibodies. DIAGNOSES: The patient was diagnosed with CAM based on the presence of specific autoantibodies and a rapid clinical response to corticosteroids. INTERVENTIONS: Treatment with low-dose hormone therapy resulted in significant improvement of symptoms. A comprehensive malignancy screening was performed. OUTCOMES: Subsequent surgical pathology confirmed the presence of colon cancer. The patient's condition improved markedly with timely intervention and targeted treatment. At 6-month follow-up, he remained symptom-free. LESSONS: This case underscores the importance of considering CAM in patients with unexplained symmetrical proximal muscle pain, even in the absence of typical extramuscular symptoms. The detection of myositis-specific autoantibodies is critical for accurate diagnosis. Early identification and treatment of the underlying malignancy can significantly improve prognosis. Future research should focus on elucidating the pathogenesis of CAM, identifying more specific biomarkers, and developing standardized diagnostic and therapeutic guidelines to enhance early diagnosis and treatment outcomes.