Opsoclonus-myoclonus syndrome is also called OMS or dancing eyes-dancing feet syndrome.
Opsoclonus describes seemingly random, involuntary, and rapid eye movements in the horizontal, vertical, and diagonal directions.
Myoclonus describes lightening-like limb movements or limb jerks, that can also be more tremulous.
The syndrome also causes ataxia, which often results in the inability to walk, sit or crawl, and the loss of previously attained abilities, like speech.
Generally speaking, OMS is thought to be an autoimmune condition in which the body attacks the nervous system, resulting in the characteristic signs and symptoms.
The precise cause of OMS is unknown, but in children, it’s often due to a paraneoplastic syndrome.
The idea is that a hidden or occult tumor - like a neuroblastoma or ganglioneuroblastoma - triggers the body’s immune system, and the resulting antibodies unintentionally target healthy cells of the nervous system.
CD20+ B-cells that get into the CSF fluid seem to play an important role.
One brain area that gets affected is the cerebellum, which plays an important role in coordinating body movements.
In older children and adolescents OMS is thought to be triggered by an infection, and in adults, it’s often due to a paraneoplastic process due to lung or breast cancer, for example.
In children with OMS, there’s almost always ataxia, so it’s sometimes referred to as OMAS - with the A representing ataxia.
In fact, most toddlers with OMS are initially misdiagnosed with acute cerebellar ataxia of childhood.
The diagnosis of OMS is also often based on symptoms like opsoclonus and myoclonus which can appear abruptly, progressing over days to weeks.