Lyme neuroborreliosis causing unilateral cerebellitis presenting as horizontal nystagmus in a 7-year-old: an unusual presentation to an ophthalmology service.

Acute cerebellitis is a rare condition with a highly heterogenous clinical course, ranging from self-limiting mild symptoms to a fulminant presentation. Symptoms include headache, vomiting, fever, ataxia, dysarthria, intention tremor, meningism, seizures, and altered level of consciousness. It warrants a high level of suspicion because of the risk of intracranial hypertension and acute hydrocephalus due to compression of the posterior fossa. We present the case of a 7-year-old boy who presented emergently with new-onset left head turn and horizontal nystagmus. Acute inflammation of a single cerebellar hemisphere (hemicerebellitis) in childhood is extremely rare, diagnosed in this case with magnetic resonance imaging. Symmetrical, diffuse cerebellar hemisphere involvement is more typical of cerebellitis. Our patient was unusual in that he presented initially with predominantly ophthalmological signs, with an otherwise normal neurological assessment. Subsequent positive serological Borrelia burgdorferi antibodies led to a diagnosis of Lyme neuroborreliosis.