A case of skin rash associated with spontaneous pneumomediastinum

Anti-melanoma differentiation-associated gene 5 antibody (Anti-MDA5) positive myositis is a distinctive subtype of dermatomyositis (DM) characterised by minimal or no muscle involvement, aggressive skin features, and, rarely, rapidly progressive interstitial lung disease (RP-ILD). Pneumomediastinum is a rare complication of this subtype, contributing to high mortality often attributed to delayed diagnosis due to its atypical presentation. Raising awareness about this rare complication is crucial, and early diagnosis is imperative for initiating aggressive immunosuppressive therapy. An 81-year-old lady presented to the district hospital with a generalised decline, weight loss over the last month and a recent history of nausea and diarrhoea. She exhibited an erythematous rash mainly on the dorsum of her hands, with a few spots on her elbows and left leg. Approximately 1 year prior, she had been diagnosed with left breast cancer, undergone wide local excision along with left axillary lymph nodes dissection, followed by radiotherapy and was taking Letrozole tablet. Investigations revealed leukopenia, thrombocytopenia and normal CRP. The auto-immune profile showed positive anti-Ds DNA, anti-Ro, and anti-cardiolipin antibodies. Liver function, kidney function, ANCA and complement levels were normal. Myositis-specific antibodies were requested in view of rash. The muscle power was normal in both proximal and distal muscle group. Body CT did not reveal any malignancy, but showed small pulmonary ground glass opacities and bands favouring ILD (Fig 1a). She was treated with oral prednisolone and hydroxychloroquine, with a provisional diagnosis of undifferentiated connective tissue disease. She was discharged to follow up on myositis antibody results in the rheumatology outpatient setting. Within a month, she re-presented with fatigue, odynophagia and ulcers over the rashes. Meanwhile, her myositis antibody panel results returned positive for anti-MDA5 antibodies. A CT scan revealed rapid increase in bilateral lung ground glass opacities with new spontaneous pneumomediastinum (Fig 1b). She was initiated on supplemental oxygen and high-dose intravenous/oral prednisolone, along with fortnightly cyclophosphamide infusions. She responded well with resolution of the skin rash. However, after 10 days of initial cyclophosphamide, her condition deteriorated due to worsening hypoxia secondary to a concurrent COVID-19 infection. Unfortunately, she passed away despite appropriate COVID-19 treatment. Our patient presented with clinically amyopathic dermatomyositis (CADM) due to the normal creatine kinase levels during both admissions. She had progressive acute ILD within a 6-week interval, indicative of RP-ILD. The overall clinical picture aligns with anti-MDA5 antibody positive DM. Pneumomediastinum is a rare life-threatening complication of anti-MDA5 DM associated with a poor prognosis and high mortality. The exact mechanism of this complication is still unknown, although it is often linked to RP-ILD. Treatment is respiratory support and aggressive immunosuppressive therapy; however, outcome can be variable. Clinicians need to remain vigilant for this potentially fatal complication.