The weight loss may be so gradual that some owners will not even realize it has occurred or it may be quite rapid. Affected cats often drink a lot of water and urinate a lot. There may be periodic vomiting or diarrhea, and the hair coat may be unkempt. In some cats, anorexia develops as the disease progresses. Two secondary complications of this disease can be significant.
Hypertension develops as a consequence of the increased pumping by the heart.
In some cats, blood pressure can become so high that retinal hemorrhage or detachment will occur and result in blindness. The heart problems develop because the heart must enlarge and thicken to meet the increased metabolic demands. Both of these problems are reversible with appropriate treatment of the disease. In most instances, diagnoses of this disease is relatively straightforward. Usually, the thyroid is enlarged in size and the T4 level is elevated so there is no question as to the diagnosis.