Case Presentation: A 44 year-old Hispanic female with a past medical history of hypothyroidism presented from her endocrinologist with a diffuse, maculopapular rash, including the face, hands, wrists, torso, arms and legs. The rash had been intermittent for the past six years, painful, pruritic, and exacerbated by sunlight. She also complained of joint pain and swelling, myalgia and exertional dyspnea. Physical exam revealed Gottron’s papules, a heliotrope rash, joint swelling, and fine crackles on pulmonary auscultation. Dermatomyositis, complicated by an underlying connective tissue disease, causing pulmonary fibrosis was considered. Initial serology was significant for positive anti-nuclear, smooth-muscle and anti-cardiolipin antibodies. Computed Tomography confirmed pulmonary fibrosis. However, her CPK and Aldolase were negative, suggesting Amyopathic Dermatomyositis. Serology for Anti-MDA-5 antibodies was unavailable due to rarity, and treatment was started based on the clinical picture.
She failed azathioprine, but responded to cyclophosphamide induction and mycophenolate maintenance, in addition to hydroxychloroquine and a tapering dose of prednisone. She improved on Nintedanib for her pulmonary fibrosis. Malignancy screening including computed tomography of the chest, mammogram, pap smear, and colonoscopy were negative.
Discussion: Amyopathic Dermatomyositis (ADM) is a distinct subclass of dermatomyositis, distinguished by the classical findings of Gottron’s papules and a heliotrope rash, but without myositis. This is evidenced by negative CPK and aldolase titers. Like dermatomyositis, it is associated with malignancy. Over 25% of ADM patients develop malignancy, so screening is vital. The diagnosis is supported by the presence of anti-MDA-5 (melanoma differentiation-associated gene 5) antibodies. Notably, pulmonary fibrosis is near universal in ADM, while in comparison, its incidence ranges from 20-80% in dermatomyositis and polymyositis. Our patient responded well to nintedanib, a tyrosine kinase inhibitor targeting endothelial growth factor receptors, indicated for idiopathic pulmonary fibrosis. There is also significant clinical and serologic overlap between ADM and other autoimmune conditions. In this case, smooth muscle and cardiolipin antibodies were positive, however the patient did no meet criteria for auto-immune hepatitis, nor was lupus alone, a sufficient diagnosis.
Conclusions: Due to the association with malignancy and the higher incidence of pulmonary fibrosis and rapid disease progression in ADM compared with other myositic conditions, early detection, treatment, and screening is vital. Treatment is debated, but usually revolves around immune-suppressants and intra-venous immunoglobulin (IVIG). This patient did not receive IVIG nor respond to azathioprine, but improved on cyclophosphamide and mycophenolate. The presence of anti-cardiolipin, anti-nuclear and smooth muscle antibodies highlights the overlap with other autoimmune conditions and the difficulty in diagnosing this potentially fatal disease.