A 10-year-old spayed female cat presented to our hospital exhibiting symptoms of fatigue and a drooping head. Upon examination, the cat was diagnosed with hypokalemia and an enlarged right adrenal gland. Effective management of the hypokalemia was achieved through medication. However, during the course of follow-up, on day 646, the cat developed diabetes mellitus. Subsequently, on day 899, the cat displayed signs of hypertrophic osteopathy. The hypertrophic osteopathy exhibited a progressive course, and the cat died on follow-up day 1109. Although an autopsy was not conducted, the case was characterized by an adrenal tumor accompanied by multiple hormonal abnormalities.