Myoclonus and hypersensitivity of the hind limbs and tail with urinary retention following neuraxial administration of morphine in a cat.

An adult female domestic shorthair cat developed myoclonus, muscle rigidity, and hypersensitivity of the hind limbs and tail with urinary retention following neuraxial administration of morphine. Myoclonic contractions resolved following treatment with midazolam and a urinary catheter was placed until normal micturition returned. The cat was clinically normal 36 hours after neuraxial morphine injection. The cat underwent a second surgery without neuraxial morphine and control of postoperative pain required more intervention. Key clinical message: Neuraxial morphine may cause myoclonus and urinary retention. The response to pharmacological treatment of myoclonus is varied, but a benzodiazepine drug may be effective.