AP3B2 antibody has been associated with primary autoimmune cerebellar ataxia with few cases describing cerebellar ataxia, myeloneuropathy, dysautonomia, and tremors.

We present a rare case of positive AP3B2 antibody with progressive gait disturbance, ataxia, and parkinsonism.

A 56 year-old man with history of hypertension, diabetes, degenerative lumbar disease, chronic progressive gait disturbance and lower extremity numbness, presented with acute onset slowed speech and tremors. Initial symptoms of inability to walk and lower extremity numbness progressed over 2 years with work up revealing severe foraminal narrowing of L4-L5, L5-S1 and EMG confirming lumbosacral radiculopathy. Neurology consult team was re-engaged for 2-month progressive slowed speech, kinetic tremor, bradykinesia, left sided ataxia for which carbidopa-levodopa was started without clinical improvement. 2 months after initial consultation, his symptoms progressed and developed new onset rest tremor.

Neurological exam revealed hypomimia, hypophonia, dysarthria, diffuse bradykinesia, asymmetric upper extremity rest tremor, ideomotor apraxia, proximal and distal weakness of upper and lower extremities, intact deep tendon reflexes, positive Babinski sign. Given rapid progression, differential diagnosis included atypical parkinsonism, autoimmune movement disorders, CJD, and paraneoplastic syndromes.

MRI brain showed evidence of global atrophy with disproportionate cerebellar atrophy. MRI of entire spine showed stable lumbar findings without myelopathic cord changes. Lumbar puncture revealed protein of over 100. Carbidopa-levodopa provided no clinical improvement. Several weeks later, positive AP3B2 titers (>30,000) resulted, and he was started on immunosuppressive therapy including IV pulse steroids for 5 days, 5 sessions of PLEX, 8-month trial of monthly cyclophosphamide without improvement or worsening of symptoms. He was discharged on mycophenolate and lost to follow up.

AP3B2 antibody is a rare cause of primary autoimmune ataxia with cases varying in presentation. In our case, we describe a positive antibody case with ataxia, neuropathy, and parkinsonism.