Non-Generalized Paroxysmal Motor Events Associated with Toceranib Phosphate in a Dog

A 10-year-old spayed female Pomeranian dog was presented for a two-day history of paroxysmal abnormal movements while receiving toceranib phosphate for transitional cell carcinoma. Thirty-six days after starting toceranib phosphate, paroxysmal motor events began and occurred once to twice daily. On presentation, the dog showed sustained dystonic posturing with axial rotation and irregular bilateral pelvic-limb movements with normal mentation. Neurological examination did not reveal persistent neurological deficits, although mild cervical pain was noted. Five days later, the dog re-presented for further evaluation. Computed tomography did not reveal obvious intracranial or spinal abnormalities except mild narrowing at the spinal level of T12–13. Serum neurofilament light chain concentration was 24.24 pg/mL. Toceranib phosphate was discontinued, and the episodes resolved and did not recur for approximately eight weeks until death from progressive disease. The clinical features were suggestive of non-generalized paroxysmal motor events temporally associated with toceranib phosphate administration. Paroxysmal dyskinesia and focal motor seizures remained the main differential diagnoses, while central nervous system disease could not be definitively excluded. This case suggests the need for veterinary clinicians to consider toceranib phosphate as a potential cause of non-generalized paroxysmal motor events.