RESUMO
Opso-myoclonus syndrome (OMS) is a very rare and severe condition. Ataxia, opsoclonus, myoclonus and/or behavioral and sleeping disturbances define that autoimmune disorder syndrome which is paraneoplastic or triggered by an infection. Here, we report a 3 year-old immunocompetent boy who developed an atypical OMS which was later complicated by an acute transverse myelitis. Screening for neuroblastoma was negative and extensive infectious screening revealed an active HHV-6 infection confirmed by blood and cerebrospinal fluid PCR. A parainfectious disease was suggested and immunosuppressive treatment was initiated. After 2 years of follow-up, the patient has a left leg paresia needing a splint and is otherwise normal. Transverse myelitis can be associated with parainfectious OMS and earlier immunosuppressive treatment in these cases may be useful especially in young and immunocompetent children.