Introduction We report a case of dermatomyositis in a 43 year old male who presented with transient mild proximal muscle weakness but died from rapidly progressive pulmonary disease within 3 months of diagnosis.

Case The patient presented with proximal muscle weakness, arthralgia and classic dermatomyositis rashes. He had a history of Huntington’s disease mutation with a positive family history. He had raised creatine kinase (CK) and electromyography showed myopathic changes. The diagnosis was confirmed by skin and muscle biopsy and positive anti-myositis antibodies; PM-Scl(75), MDA5 and SRP. Screening for underlying malignancy was negative but a CT chest scan showed bilateral areas of reverse halo-opacity suggestive of interstitial lung disease (ILD) although he had no respiratory symptoms at the time. He had input from dermatology, rheumatology and respiratory teams and commenced on prednisone 1 mg/kg with pneumocystis prophylaxis. He underwent bronchoscopy and broncho-alveolar lavage that did not isolate any organisms and cell differential was normal. His muscle weakness had resolved even prior to starting steroids and his CK normalised on high dose prednisolone but he developed progressive shortness of breath that led to a second admission within two months. Repeat CT chest showed extensive bilateral infiltrative disease and pneumo-mediastinum. No infective cause was found. He deteriorated rapidly despite intubation, broad-spectrum antibiotics, steroids and extracorporeal membrane oxygenation. He died whilst being considered for lung transplantation.

Conclusion This case provides valuable lessons. Even in cases of mild muscle disease, the extra-muscular involvement can be severe and life threatening in dermatomyositis. Anti-myositis antibodies can be helpful in predicting the course of disease including extra-muscular involvement. The anti-MDA5 antibodies are associated with amyopathic dermatomyositis associated with a rapidly progressive ILD and often with pneumo-mediastinum and has a poor prognosis as in our case. One should consider more aggressive therapy for these patients from the outset.