037 Dermatomyositis and calcinosis

Abstract

Background: Dermatomyositis (DM) is typically an idiopathic inflammatory myopathy, characterised by features of proximal skeletal muscle weakness, skin manifestations and evidenced by muscle inflammation. A subset of dermatomyositis termed amyotrophic dermatomyositis (historically termed dermatomyositis sine myositis) is a condition in which patients have characteristic skin manifestations without muscle weakness or abnormal muscle enzymes. The combined incidence of dermatomyositis and polymyositis has been estimated at 2 per 100,000 annually in the general population and estimates of prevalence range from 5 to 22 per 100,000. Amyotrophic DM is thought to comprise 10-30% of DM cases. A study of the residents of Olmstead County in Minnesota estimated an annual incidence of 0.2 per 100,000 persons in which the annual incidence of DM of all types was approximately 1 per 100,000. Methods: A 42-year old paramedic presented with a painful, swollen right ankle and associated erythema. His past medical history included whooping cough in childhood and he was a lifelong non-smoker with no pets and no asbestos exposure. On examination, he had hardening of the skin over his knuckles and extensor joints and a pink hue around his eyes, which had been present for a long time according to the patient. These were incidental findings. He also reported a six month history of dry cough but no dypsnoea. He had bi-basal fine end inspiratory crackles and normal muscle power. Results: Investigations revealed a raised erythrocyte sedimentation rate and C-reactive protein with normal total creatine kinase. His chest radiograph appeared normal. Given his clinical findings, he was treated with flucloxacillin for his lower limb cellulitis, but suspected to have amyotrophic dermatomyositis with lung involvement. High resolution CT scan demonstrated patchy and peripheral groundglass opacities, consistent with non-specific interstitial pneumonitis. Further laboratory testing revealed positive serology for anti-nuclear antibodies 4.8 (positive) and extractable nuclear antigen panel negative. Pulmonary function tests revealed FEV1 2.7L (75%), FVC 3.1L (73%) and KCO (65%) - demonstrating no restriction. Bronchoscopy lavage aspirate contained bronchial epithelial cells, histiocytes and inflammatory cells with a raised CD4+:CD8+ T cell ratio, in keeping with non-specific interstitial pneumonitis. CT guided biopsy revealed non-specific inflammatory changes with mild interstitial fibrosis deemed consistent with connective tissue disease at lung multi-disciplinary meeting. At 18 months follow-up, the patient remains well with no muscle weakness and his lung function remains stable. Repeat total CK remains normal but he did mention enlarging scrotal lesions. On urology review, these were considered consistent with calcinosis as part of amyotrophic dermatomyositis and will be excised for cosmetic reasons. Conclusion: This case highlights the importance of assessing for lung involvement and calcinosis in all cases of dermatomyositis, including amyotrophic DM, as patients may not disclose symptoms. Exclusion of malignancy is imperative.