Adolescent-Onset Anti-MDA5 Antibody-Positive Juvenile Dermatomyositis with Rapidly Progressive Interstitial Lung Disease and Spontaneous Pneumomediastinum: A Case Report and Literature Review

Abstract Background:Dermatomyositis with positive anti-melanoma differentiation-associated gene 5 (anti-MDA5) antibody has a distinct phenotype associated with small hand joint arthritis, mucocutaneous ulceration, and less muscle involvement. It is reported to be associated with rapidly progressive interstitial lung disease (RP-ILD) and have a high mortality rate in adult studies. There is evidence that cases complicated with spontaneous pneumomediastinum (PNM) have an increase in mortality. Most of the evidence of this rare disease is derived from adult studies. We report a case in adolescent age complicated with both RP-ILD and PNM with a good disease outcome after aggressive immunosuppressive therapy. We illustrate the diagnostic challenge and the importance of test for the myositis-associated antibodies (MSA).Case presentation:A 16-year-old Chinese female presented with fever and cough for one day, and finger swelling for three weeks. Physical examination revealed arthritis of fingers and wrists, ulcers and palmar papules over fingers, hyperpigmentation of interphalangeal joints, rash over the neck and calcinosis over external ears. The diagnosis of dermatomyositis was made one month later until the onset of malar rash, Gottron’s papules and myalgia. The diagnosis was supported by the presence of anti-MDA5 antibody and evidence of inflammatory myopathy on magnetic resonance imaging without performing muscle biopsy or electromyography. In retrospect, she already had interstitial lung disease at first presentation manifested as cough and opacity on chest radiograph, which was later confirmed with chest computed tomography and pulmonary function test. She was treated according to adult guidelines with calcineurin inhibitor and steroid. Her disease was steroid-resistant, which was complicated with RP-ILD and spontaneous PNM. Intensive immunosuppressive therapy including cyclophosphamide and rituximab were required to induce remission.Conclusions:Recognition of distinct clinical features including mucocutaneous ulceration and test for MSA are important for prompt diagnosis of anti-MDA5 antibody-positive dermatomyositis, as early aggressive treatment and anticipation of complications could make a difference in the outcome of this disease with high mortality.