Downbeat nystagmus and progressive ataxia in adults: consider Chiari malformation type 1

Downbeat nystagmus (DBN) is present in between 4 and 6% of patients with Chiari malformation type 1 (CM1). It is present in primary gaze and is characterized by a pathological phase which drifts the eyes in the upward direction followed by a downward quick-phase. Here, a four-case series of CM1 patients who developed progressive cerebellar ataxia and DBN is presented. Brain magnetic resonance imaging revealed the abnormal projected cerebellar tonsils. Evaluation of the posterior fossa through brain imaging looking for structural abnormalities such as CM1 is mandatory in cases of progressive ataxia combined with DBN, headache, and pyramidal signs.