Feline endocrine diseases are prevalent health issues in cats, compromising their general health and quality of life. Accurate and prompt diagnosis is essential for the effective treatment and management of these disorders.
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Common feline endocrine diseases
| Endocrine Condition | Symptoms | Diagnostic Test/s | Treatment |
| Hyperthyroidism | Weight loss, increased appetite, increased thirst and urination, vomiting, diarrhea, hyperactivity; hair coat may appear unkempt, matted, or greasy. | Blood chemistry panel Analysis of thyroid hormone levels (measuring T3, T4, and/or free T4) | There are four treatment options: medication, radioactive iodine therapy, surgery, and dietary therapy. A CBC, serum chemistry, TT4, and urinalysis should be performed 2-4 weeks after commencing therapy and 2-4 weeks after any change in dose |
| Hypothyroidism | Lethargy, dullness, hair loss, low body temperature, decreased appetite, and occasionally decreased heart rate. Retained deciduous teeth, gingival overgrowth, retained kitten hair coat | Thyroid Panel Additional testing for free T4, T3, and thyroid-stimulating hormone (TSH) | Generally, life-long treatment with synthetic thyroid hormone (levothyroxine sodium) for cats with congenital or acquired hypothyroidism; clinical signs may persist for 2–3 months before responding to treatment. |
| Diabetes Mellitus | Polyuria and polydipsia (PU/PD), lethargy, weight loss, and polyphagia. Less common symptoms: weakness, plantigrade stance, depression, and anorexia may be seen (the last especially with ketoacidosis). | Routine serum biochemistry Complete urinalysis, ideally with culture (especially if there is an active sediment) Complete blood count (CBC) Serum fructosamine Serum thyroxine in older cats to exclude hyperthyroidism | Insulin Therapy Dietary Therapy SGLT2 (sodium-glucose cotransporter 2) inhibitors for the treatment of newly diagnosed diabetic cats who are otherwise healthy and have not been previously treated with any injectable insulin |
| Hypoadrenocorticism (Addison’s disease) | Lethargy, anorexia and weight loss, depression, weakness, and mild to severe dehydration. | Resting cortisol test ACTH stimulation test Urinalysis Blood pressure Chest X-rays ECG | Cats with primary hypoadrenocorticism require lifetime mineralocorticoid and glucocorticoid supplementation. Antiemetic, antinausea, and nutritional supportive care |
Diagnostic protocols for feline endocrine conditions
Thyroid function tests
- TSH Baseline. If a thyroid condition is suspected, getting a thyroid-stimulating hormone (TSH) baseline in combination with other thyroid tests is highly recommended.
- Total T4 (TT4) – Automated enzyme immunoassay. Total T4 is the first test used to assess thyroid function. It measures all T4 in the circulation, including protein-bound and Free-T4 (FT4). It is the standard screening test in the determination of baseline thyroid status in cats and dogs. Concurrent disease, certain medications (such as corticosteroids, antibiotics, and anticonvulsants), or conditions that affect serum protein levels can complicate diagnosis. The patient’s clinical history should always be taken into consideration when interpreting results.
- Total Triiodothyronine (T3) Test. In cats with hyperthyroidism, T3 levels are usually elevated or higher than the normal range. T3 is the thyroid hormone’s active form.
Additional protocols for feline endocrine diseases
- Free-T4 (FT4). Free-T4 measures metabolically active, unbound thyroid hormone. A modified equilibrium dialysis method is often used to measure FT4 in cats and dogs and has been shown to be the most reliable technique when measuring FT4. The test can be helpful in confirming a diagnosis of hyperthyroidism in a patient with high normal total T4 along with clinical signs suggestive of hyperthyroidism. Its use should be restricted in cases where confirmation is needed rather than as a screening test. While the test is less affected by non-thyroid conditions and autoantibodies compared to TT4, it’s expensive and labor-intensive. Also, false positives can be recorded in cats without hyperthyroidism. Thus, the test is not recommended as an initial screening test for thyroid disease. But it can be useful for patients whose TT4 results are not compatible with the symptoms exhibited by the patient and if there is a suspicion that autoantibodies, medications, or concurrent non-thyroidal conditions are affecting TT4 concentration.
- Triiodothyronine (T3) Suppression Test.* The T3-suppression test is used for diagnosing hyperthyroidism in cats that have normal T3, T4, and/or free T4 concentrations but exhibit symptoms of hyperthyroidism. The procedure is quite easy and involves the cat owner.
- Technetium Scanning. Thyroid imaging for diagnosing hyperthyroidism in cats has the advantage of effectively assessing the degree of involvement, specifically identifying whether both lobes are affected and if metastasis is present. It also serves as a reliable predictor of thyroid metabolic status.
Hypoadrenocorticism (Addison’s disease)
ACTH stimulation test. The ACTH stimulation test is for a definitive diagnosis of hypoadrenocorticism. It involves measuring the cortisol concentration before and after exogenous ACTH administration to determine how well the adrenal glands respond to ACTH stimulation.
There are several protocols that are being followed, but the most commonly used technique is measuring baseline serum cortisol concentration, followed by administration of synthetic ACTH, and repeat measurement of serum cortisol concentration one hour later.
The ACTH stimulation test is initially performed in patients that are acutely ill or when resting cortisol concentration is below 2 mcg/dL. In normal cats, there will be an increase in cortisol in response to ACTH, a result that is absent in cats with Addison’s disease.
However, it should be noted that corticosteroid treatment (except dexamethasone) prior to the ACTH stimulation test can give a false-positive result. At least 24 hours should pass after steroid treatment for the test result to be valid.
Abdominal ultrasound
During an abdominal ultrasound, finding adrenal glands that are abnormally small is generally confirmatory for Addison’s disease in cats.
Feline Hyperadrenocorticism (Cushing’s Syndrome)
- Low Dose Dexamethasone-Suppression Test. This is a screening test for feline hyperadrenocorticism.
- High-dose dexamethasone test (HDDST). The test is usually performed after Cushing syndrome diagnosis is confirmed. It can distinguish between pituitary-dependent hyperadrenocorticism and adrenal tumor(s).
Between high-dose and low-dose dexamethasone testing, the former is more reliable . It is the preferred method of feline Cushing’s disease screening. Test results should be analyzed along with clinical symptoms. Adrenal resistance and false positives may occur in significantly stressed cats or those with significant systemic illness. In this case, adrenal function should not be performed.
There is suppression when the ration is less than 50% of the baseline value. Suppression is associated with pituitary adenoma, while non-suppression may either have an adrenal tumor or pituitary adenoma.
- ACTH-Response Test. The ACTH-Response Test is indicated for evaluating adrenocortical function after treating the patient for hyperadrenocorticism. It’s also a useful tool for diagnosing iatrogenic hyperadrenocorticism.
- Urine cortisol: Creatinine ratio (UCCR). The test can help rule out Cushing’s disease. A high UCCR is associated with Cushing’s, but the result will have to be confirmed with suppression or stimulation testing.
