Thymoma removal in a cat with acquired myasthenia gravis: a case report and literature review of anesthetic techniques.

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HISTORY AND PRESENTATION: A 12 year old, 4.2 kg, domestic long hair, castrated male cat was presented with regurgitation, inability to retract the claws, general weakness, cervical ventroflexion and weight loss. A thymic mass was evident on radiographs. Acetylcholine receptor antibody titer was positive for acquired myasthenia gravis (MG). Thymectomy via midline sternotomy was scheduled. ANESTHETIC MANAGEMENT:  Oxymorphone and atropine were administered subcutaneously as premedication, and anesthesia was induced with etomidate and diazepam given intravenously to effect. The cat's trachea was intubated and anesthesia was maintained with isoflurane in oxygen, and continuous infusions of remifentanil and ketamine. Epidural analgesia with preservative-free morphine was administered prior to surgery. Postoperative analgesia was provided by oxymorphone subcutaneously, interpleural bupivacaine, and fentanyl infusion. Postoperative complications included airway obstruction, hypoxemia and hypercapnia.

FOLLOW-UP: The cat was discharged 3 days after surgery. Discharge medications included pyridostigmine and prednisone. Nine days after surgery, the cat had a significant increase in its activity level, and medications were discontinued. Histopathologically, the mass was consistent with a thymoma. Approximately 6 weeks later the cat became weak again and pyridostigmine and prednisone administration was resumed.

CONCLUSION

The perioperative management of patients with MG for transsternal thymectomy is a complex task. The increased potential for respiratory compromise requires the anesthesiologist to be familiar with the underlying disease state, and the interaction of anesthetic and non-anesthetic drugs with MG. Careful monitoring of ventilation and oxygenation is indicated postoperatively.