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, palmar papules and less muscle involvement. It is also associated with increased risk of rapidly progressive interstitial lung disease (RP-ILD) and has a high mortality rate in adults. There is evidence that cases complicated with spontaneous pneumomediastinum (PNM) have an increase in mortality. While most of the evidence for this rare disease is derived from the adult literature, we report a case diagnosed in an adolescent complicated with both RP-ILD and PNM with a good outcome after aggressive immunosuppressive therapy. Our case also illustrates the potential challenges in diagnosis of this condition in the setting of non-specific clinical manifestations, the need for a high index of suspicion, and the importance of testing for myositis-specific antibodies (MSA) early to aid in diagnosis given the risk of rapid progression in these patients. Case presentation A 16-year-old Chinese female presented with fever and cough for 1 day, and finger swelling for 3 weeks. Physical examination revealed arthritis of fingers and wrists, ulcers and palmar papules over fingers, hyperpigmentation of interphalangeal joints, and rash over the neck. The diagnosis of dermatomyositis was made 1 month later with the onset of malar rash, Gottron’s papules, calcinosis and myalgia. The diagnosis was supported by the presence of anti-MDA5 antibody and evidence of inflammatory myopathy on magnetic resonance imaging. 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. She was treated according to adult guidelines with steroid and calcineurin inhibitor. Her disease was resistant to initial therapy and was complicated by RP-ILD and spontaneous PNM. Intensive immunosuppressive therapy including cyclophosphamide and rituximab were required to induce remission. Conclusions Recognition of distinct clinical features of anti-MDA5 antibody-positive dermatomyositis and testing for MSA is crucial in patients with skin ulceration and abnormal pulmonary findings of unknown etiology, as prompt diagnosis with early aggressive treatment and anticipation of complications could make a difference in the outcome of this disease with high mortality.

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.

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