AQP4+ NMOSD, MDA5+ Clinically Amyopathic Dermatomyositis and sHLH in a Pediatric Patient: A Case Report and Literature Review

Background: Neuromyelitis optica spectrum disorder (NMOSD) is a rare central nervous system (CNS) autoimmune disorder. It is associated with other autoimmune disorders, which included dermatomyositis in rare conditions. Type I interferon (IFN) has been considered a common link between the two diseases. Furthermore, secondary hemophagocytic lymphohistiocytosis (sHLH) results from overactivation of the immune system and is also associated with autoimmune disorders. This study aims to report a pediatric case of NMOSD overlapping with dermatomyositis, who also developed sHLH, and to summarize all similar cases for expanding the clinical spectrum and treatment outcomes of multi-systemic autoimmune overlap syndromes in children. Case Presentation: An 8-year-old girl presented with fever, headache, change of consciousness, vomiting, blurred vision, rash, difficulty urinating and neck and back pain. Based on the history, physical examination, and ancillary investigations, the preliminary diagnosis is NMOSD, dermatomyositis, and secondary hemophagocytic lymphohistiocytosis. After aggressive immunotherapy (including intravenous methylprednisolone, intravenous immunoglobin, rituximab and tacrolimus), she fully recovered and remained relapse-free at last follow-up. Conclusion: NMOSD overlapping dermatomyositis is a rare autoimmune condition with uncertain pathological mechanism. Dermatomyositis should be considered when symptoms such as rash occur in the context of NMOSD. sHLH results from overactivation of the immune system. Aggressive immunotherapy is recommended for better prognosis.