Image Quiz: A dyspneic cat with hyperactivity and fever (Sponsored by Dechra)

Hyperthyroidism is correct!

Routine laboratory testing revealed that Sabrina had a clearly high serum T4 concentration (18 μg/dl; normal < 4.0 μg/dl). Hyperactivity or restlessness is relatively common in cats with hyperthyroidism. Because of the hypermetabolic state, mild hyperthermia can develop. Respiratory and cardiac signs are frequent clinical features of the disease and may include tachypnea, tachycardia, gallop rhythm, murmur, or arrhythmia. When severely stressed, hyperthyroid cats can develop a "panic attack," with severe respiratory distress, rapid breathing, and open-mouth breathing. These cats may become extremely weak and can even collapse from exhaustion and shortness of breath. Therefore, hyperthyroid cats should be handled carefully and gently, especially in the veterinary office during these stressful periods.

Sabrina was treated with methimazole (Felimazole-Dechra; 2.5 mg orally b.i.d.). Her diet was changed to a more energy dense, higher protein food to help restore her lost muscle mass. During a recheck four weeks later, the owner reported that the cat was much calmer and that her respiratory problems had resolved.

Pretreatment (left); post-treatment (right)

Physical examination revealed weight gain (0.3 kg), with resolution of her hyperthermia, tachypnea, tachycardia, cardiac murmur, and arrhythmia. Cervical palpation revealed a large right thyroid nodule in the region of the thoracic inlet. Her serum T4 concentration had fallen into the mid-normal range (2.5 μg/dl) while receiving methimazole, and she did not develop azotemia.

Based on Sabrina's overall good health, relatively young age, the severity of her hyperthyroid state, and the presence of her large thyroid mass, the owner elected definitive treatment with radioactive iodine.

Five months later, Sabrina remains euthyroid, with complete resolution of all signs of hyperthyroidism and associated cardiac or respiratory disease.