A Case Report of Anti-Mi-2β Antibody-Positive Dermatomyositis Complicated with Organizing Pneumonia

Background Anti-Mi-2β antibody-positive dermatomyositis (DM), a subtype of idiopathic inflammatory myopathies, is characterized by typical clinical features of concurrent skin and muscle involvement. Organizing pneumonia (OP) is a severe pulmonary complication that may occur during disease progression; presenting primarily with non-specific respiratory symptoms, it is easily confused with infectious pneumonia in clinical practice, which not only leads to diagnostic delay but also increases treatment difficulty, a problem particularly prominent in patients with underlying diseases. From a clinical research perspective, the experience in diagnosing and managing such atypical cases provides important reference value for improving the early detection and timely diagnosis and treatment of inflammatory myopathies. Case Presentation A 62-year-old male patient had a 5-year history of type 2 diabetes mellitus, taking metformin regularly (0.5 g three times daily), with fasting blood glucose controlled at 7–8 mmol/L. In March 2024, the patient developed recurrent fever, cough, and dyspnea without obvious inducement. Initial chest X-ray and routine etiological tests led to a preliminary diagnosis of "community-acquired pneumonia", but symptoms failed to improve after sequential broad-spectrum anti-infective therapy. The patient underwent two hospitalizations for confirmation: during the first hospitalization, chest computed tomography (CT) showed left lung consolidation with the "dry branch sign", CT providing an important imaging clue for the diagnosis of acute organizing pneumonia (AOP); during the second hospitalization, combined with strongly positive anti-Mi-2β antibody IgG, elevated Krebs von den Lungen-6 (KL-6) (997.46 U/mL), and negative respiratory pathogen tests, a definitive diagnosis of anti-Mi-2β antibody-positive dermatomyositis complicated with secondary acute organizing pneumonia was made. Treatment and Outcome The patient initially received sequential anti-infective therapy without significant improvement. Following diagnosis, methylprednisolone (40 mg daily) was promptly initiated, resulting in rapid symptom relief—though multiple relapses occurred during glucocorticoid tapering. Subsequent addition of mycophenolate mofetil for combination therapy failed to achieve optimal disease control; stabilization was ultimately achieved with the addition of tofacitinib to the regimen (in combination with mycophenolate mofetil and glucocorticoids). At the latest follow-up in May 2025, the patient remained in sustained remission with no evidence of recurrence. Conclusion This case highlights the importance of clinicians maintaining a high index of suspicion for autoimmune diseases in patients with imaging-confirmed organizing pneumonia unresponsive to anti-infective therapy. Integrating autoimmune antibody testing with chest CT features is pivotal for diagnosing dermatomyositis (DM)-associated organizing pneumonia—especially in patients lacking prominent cutaneous or muscular manifestations of DM. This diagnostic approach helps mitigate clinical misdiagnosis, refine treatment strategies, and adds valuable clinical insights to the management of DM presenting with atypical symptoms.