Hyperthyroidism
Hyperthyroidism is the most common endocrine disorder in middle-aged to senior cats, caused by excessive production of thyroid hormones (T3 and T4) from a benign thyroid adenoma (97-99% of cases). The resulting hypermetabolic state affects virtually every organ system and, if untreated, leads to heart disease, hypertension, and kidney damage.
Symptoms & Signs
- Weight loss despite increased appetite
- Increased thirst and urination
- Hyperactivity and restlessness
- Vomiting and diarrhea
- Rapid heart rate (tachycardia)
- Heart murmur
- Unkempt coat
- Palpable thyroid nodule
Causes & Risk Factors
Benign adenomatous hyperplasia or adenoma of one or both thyroid lobes. The exact initiating cause is unknown. Proposed risk factors include dietary iodine fluctuations, BPA exposure from canned food linings, flame retardant chemicals (PBDEs), and genetic factors.
Diagnosis
Elevated total T4 (>4.0 μg/dL diagnostic). Free T4 by equilibrium dialysis for equivocal cases. Thyroid scintigraphy (technetium scan) for surgical planning and ectopic tissue detection. Assessment of concurrent conditions (kidney function, blood pressure, heart).
Treatment
Methimazole/carbimazole (anti-thyroid medication) - lifelong oral or transdermal. Radioactive iodine (I-131) - curative, gold standard. Surgical thyroidectomy. Prescription iodine-restricted diet (Hill's y/d). Choice depends on concurrent disease and owner factors.
Prevention
No proven prevention. Regular screening of senior cats (annual T4 from age 7-8). Minimizing exposure to potential environmental triggers. Early detection allows treatment before organ damage.
Prognosis
Excellent with treatment. Radioactive iodine cures >95% of cases. Methimazole controls disease effectively but requires lifelong medication. Untreated hyperthyroidism leads to heart failure, hypertension, and death. Unmasking of concurrent kidney disease is common.
Affected Breeds (1)
| Breed | Species | Size |
|---|---|---|
| Abyssinian | Cat | Medium |