Transition from upbeat to pendular nystagmus in MS over years

Acquired pendular nystagmus (APN) is rarely the presenting sign of multiple sclerosis (MS). Usually, the diagnosis of MS is well established, and the patient experiences oscillopsia from APN years later. This patient presented with vertical oscillopsia from upbeat nystagmus (UBN) and diplopia due to bilateral internuclear ophthalmoplegia in the setting of a large disease burden in the brainstem, but years later the patient was seen for horizontal oscillopsia. The UBN had improved substantially, but horizontal pendular APN was diagnosed.