We describe a case of "thyrotoxicosis factitia canis."

A 50-year-old woman presented with new-onset nervousness and dizziness. Her medical history was notable for hypertension treated with enalapril, 10 mg four times daily. Further questioning revealed that the patient's dog, which "had no thyroid," was being treated with L-thyroxine, 0.6 mg four times daily (a typical canine dosage). It seems that, at some point, the patient may have inadvertently switched her medication with her dog's medication. The results of physical examination were normal except for tremor. The pulse was 72 beats/min and regular. The patient was followed after correction of her regimen; results of this follow-up are shown in the (Table 1).

Further search for diagnostic clues to the diagnosis, such as a low uptake on I¹²³ scanning or a suppressed thyroglobulin level, was considered unnecessary in this case because of the careful history. Interim treatment with ß-blockers may be needed in some cases but was not in this one.

We suggest that a pet history should be taken when puzzling symptoms are present in previously healthy patients.