Cerebellar fit is characterized by paraoxysmal head retroflexion, opisthotonic posturing, decerebrate rigidity and drop attacks with preserved consciousness. Since first reported by Jackson in 1871, cerebellar fit has unsubstantial representation in neurological journals and has been branded as a pediatric pathology, mostly in patients with Chiari malformation.

A 31-year-old female with a history of Chiari II malformation with shunt placement presented with new onset intermittent opisthotonic posturing and head retroflexion without loss of consciousness. Some of the episodes were associated with upward eyeball rolling and stiffening of the extremities. Patient reported 8-9 events throughout a short time frame (30 minutes). Patient endorsed headache and oscillopsia. Nystagmus to all direction was noted on examination. Continuous electroencephalography (EEG) showed diffuse slowing, but no epileptiform abnormalities correlated with those events. Neuroimaging showed existing cerebellar tonsil herniation and interval change of decrease lateral ventricle caliber with slit like configuration. Of note, patient had been taking tacrolimus after kidney transplant.

Despite the recognition of cerebellar fit for more than a century, it is infrequently discussed in neurological literature. Pandy et al reported a series of pediatric Chiari I malformation cases and found thirteen (28%) presented with symptoms of cerebellar fit. No epileptiform discharge had been found on EEG in all previous reported cases. Our case is noteworthy as it shows cerebellar fit is not limited to the pediatric population. The underlying mechanism of cerebellar fit is still unclear. Increased intracranial pressure (ICP) with compression of the brainstem is one hypothesis. Increased ICP can occur in slit ventricle syndrome and following exposure to tacrolimus, which may explain why our patient presented with such symptoms. Neurologist should be aware of this phenomenon when evaluating adults with new onset seizures.