Melanoma differentiation-associated gene 5 amyopathic dermatomyositis following an acute Mycoplasma pneumoniae infection: a case report

BACKGROUND: A previously healthy young male of Southeast Asian descent presented with 6 weeks of fevers, cough, mucocutaneous ulcers, arthritis, and myalgias. Initial workup revealed positive Mycoplasma pneumoniae immunoglobulin M, and the patient was treated with antibiotics without relief of symptoms. Rheumatologic workup revealed highly positive melanoma differentiation-associated gene 5 antibody. Viral infections are thought to potentially trigger loss of self tolerance, and prompt the autoimmunity cascade that can result in conditions such as dermatomyositis. To our knowledge, this is the first case report demonstrating a non-viral infection, specifically Mycoplasma pneumoniae, as the inciting infectious trigger for the anti-melanoma differentiation-associated gene 5 dermatomyositis subtype. CASE PRESENTATION: A 20-year-old southeast Asian–American male with no significant past medical history presented with symptoms of intermittent fevers, nonproductive cough, dry eyes, oral ulcers, rash, arthritis, and myalgias. The patient was noted to have erythematous papules across the bilateral hands along the lateral digits and palms, as well as synovitis involving the bilateral hands and feet. Immunoglobulin M antibodies were positive for Mycoplasma pneumoniae. The patient was diagnosed with mycoplasma pneumonia. The patient did not respond to a course of antibiotics, leading to rheumatological testing that found highly positive melanoma differentiation-associated gene 5 autoantibody. Muscle enzyme and electromyography testing were normal, indicating clinically amyopathic disease. Methylprednisolone was initiated, with resolution of fevers and improvement of arthritis and myalgias. The cutaneous lesions on the digits and palms improved. CONCLUSIONS: This patient presented with symptoms of fever, cough, oral ulcers, rashes, and arthritis, and blood work demonstrated the presence of immunoglobulin M antibodies to Mycoplasma pneumoniae. Despite antibiotic treatment for the presumed diagnosis of Mycoplasma pneumoniae infection, the patient did not improve, prompting rheumatological workup and revealing melanoma differentiation-associated gene 5 autoantibodies. This case suggests that infections, other than viral, can trigger the autoinflammatory cascade, leading to the development of amyopathic melanoma differentiation-associated gene 5 dermatomyositis.