A Comprehensive Guide to Common Endocrine Disorders in Dogs and Cats by Dr Sarah Peters

1. Diabetes Insipidus (DI)

Overview:
Diabetes insipidus is a condition characterised by an inability to concentrate urine, leading to excessive thirst and urination (polydipsia and polyuria). There are two main types: central (deficiency in ADH) and nephrogenic (kidneys do not respond to ADH).

Diagnosis:

• Water deprivation test (classical but complex)
• Desmopressin trial (observing changes in water intake and urine concentration)
• Lab work: hemoconcentration, dilute urine (isosmotic), and occasional azotemia

Treatment & Monitoring:

• Not always necessary if the patient is managing well
• Desmopressin (oral, injectable, intranasal) can be used if treatment is warranted
• Monitor for overhydration, hyponatremia, urine specific gravity, and water intake

2. Cushing’s Disease (Hyperadrenocorticism)

Overview:
Cushing’s disease results from excess glucocorticoids (cortisol). Common in dogs; rare in cats. Causes include:

• Pituitary-dependent (most common, 85%)
• Adrenal-dependent
• Iatrogenic (excess steroid administration)

Clinical Signs (The Five P’s):

• Polyuria, polydipsia, polyphagia, pot-belly, panting
• Alopecia, thin skin, hyperpigmentation, comedones
• Muscle weakness, hypertension, lethargy

Diagnostics:

• Urine cortisol: creatinine ratio (rule-out)
• Low-dose dexamethasone suppression test (diagnosis)
• High-dose dexamethasone (differentiation between pituitary vs adrenal)
• CBC: stress leukogram, thrombocytosis
• Chemistry: elevated ALP, ALT, cholesterol, triglycerides
• Ultrasound: adrenal gland size, hepatomegaly, gallbladder mucoceles

Treatment & Monitoring:

• Trilostane (Vetoryl) inhibits cortisol and aldosterone production
• Mitotane (less common due to side effects)
• Surgery or radiation for pituitary or adrenal tumors (rare)
• Monitor blood pressure, electrolytes, clinical signs, ACTH stimulation test
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3. Addison’s Disease (Hypoadrenocorticism)

Overview:
Addison’s disease is a deficiency of glucocorticoids and, in typical cases, mineralocorticoids (aldosterone). Atypical Addison’s involves only glucocorticoid deficiency.

Clinical Signs:

• Lethargy, weakness, anorexia, vomiting, diarrhoea
• Can present acutely in crisis with shock and hypoglycaemia
• Often “the great pretender” – can mimic many diseases

Diagnostics:

• Typical Addisonian: hyponatremia, hyperkalaemia, low Na:K ratio (<27)
• Atypical Addisonian: may appear normal on basic chemistry
• Basal cortisol: low to very low
• Definitive: ACTH stimulation test

Treatment:

• Acute crisis: IV fluids, correct electrolytes, treat hyperkalaemia and hypoglycaemia
• Long-term: glucocorticoids (prednisone) ± mineralocorticoids (DOCP injections or fludrocortisone)
• Monitoring: electrolytes, clinical signs, stress-dose adjustments during events

4. Hypothyroidism (Dogs)

Overview:
Most commonly primary hypothyroidism due to idiopathic atrophy or immune-mediated destruction. Rarely pituitary-driven.

Clinical Signs:

• Lethargy, weight gain despite normal appetite
• Alopecia, rat tail, skin infections
• Peripheral neuropathy in some cases

Lab Findings:

• Hypercholesterolemia, hypertriglyceridemia
• Low or low-normal T4
• Elevated TSH, low free T4

Treatment & Monitoring:

• Levothyroxine (usually BID for best regulation)
• Recheck thyroid levels 4–6 hours post-pill one month after dose change
• Monitor chemistry and clinical signs every 6 months

5. Hyperthyroidism (Cats)

Overview:
Excess thyroid hormone production, common in older cats, often coexisting with kidney disease.

Clinical Signs:

• Weight loss despite increased appetite
• Hyperactivity, increased drinking/urination
• Vomiting, changes in meow, unkempt coat, thick nails
• Palpable thyroid slip

Lab Findings:

• High T4 and free T4
• Low TSH
• ALT elevation, possible azotaemia

Treatment Options:

• Methimazole (oral, transdermal, or compounded)
• Iodine-restricted diet
• Surgery (thyroidectomy, with caution for parathyroids)
• Radioactive iodine (I-131), gold standard

Monitoring:

• CBC, chemistry, urinalysis, thyroid panel 2–4 weeks after starting therapy
• Regular monitoring for kidney function

6. Acromegaly (Cats)

Overview:
Excess growth hormone (GH) due to pituitary adenoma, leading to IGF-1 elevation.

Clinical Signs:

• Diabetes-like syndrome (PUPD, polyphagia)
• Insulin resistance despite high-dose insulin
• Broad head, enlarged paws, tongue, jaw abnormalities
• Organomegaly, hypertension, heart murmurs

Diagnosis:

• Measure IGF-1 levels, typically six weeks after starting insulin

Treatment & Monitoring:

• Radiation therapy to shrink pituitary adenoma
• Hypophysectomy (rare, technically challenging)
• Medications (somatostatin analogs, dopamine agonists)
• Diabetes management and monitoring IGF-1

7. Hyperparathyroidism

Overview:
Excess parathyroid hormone (PTH) leads to hypercalcemia and affects kidneys, heart, GI tract, and neurologic function.

Clinical Signs:

• Often asymptomatic early
• Later: weakness, anorexia, vomiting, lethargy, PUPD in dogs

Lab Findings:

• Hypercalcemia (total and ionized)
• Inappropriately normal or high PTH despite high calcium

Treatment:

• Surgical removal (parathyroidectomy, sometimes thyroidectomy)
• Ultrasound-guided ethanol or heat ablation for nodules
• Medical management (steroids, diuretics, bisphosphonates) – less effective

Monitoring:

• Calcium levels closely post-procedure (12–24 hours and 3–5 days) to prevent hypocalcemia

Final Thoughts

Endocrine disorders can be complex, but careful attention to clinical signs, lab work, and appropriate treatment options can dramatically improve patient quality of life. With diligent monitoring and owner education, many of these conditions are highly manageable, making endocrinology one of the most rewarding areas of veterinary medicine.