What can cause positional downbeat nystagmus besides bppv? 5mm tonsillar descent noted on mri headaches pulsatile tinnitus dizzy worse with pressure

Some possibilities: The list of possible causes of downbeat nystagmus that the neurologists and neuroophthalmologists think about include: Arnold-Chiari type I malformation, tumors (meningioma, cerebellar hemangioma) at the foramen magnum, demyelination, stroke, cranial trauma, drugs (alcohol, lithium, anticonvulsants), spinocerebellar degenerations, syrinx of the brainstem or upper cervical spinal cord, etc...