Top 4 Canine Endocrine Disorders: A Comprehensive NAVLE Guide
Introduction
This guide covers the most critical endocrine disorders in dogs, providing diagnostic and treatment insights essential for veterinary professionals preparing for the NAVLE. Understanding these conditions is vital for effective management in clinical practice.
1. Hypothyroidism
Classic Case:
Typically affects middle-aged dogs (4-10 years) with symptoms like weight gain, lethargy, exercise intolerance, and bilateral symmetrical alopecia. Rarely, myxedema with a “tragic” facial expression may occur.
Diagnosis:
- Etiology: Lymphocytic thyroiditis or thyroid atrophy.
- Initial Screening: CBC for anemia, serum chemistries for hypercholesterolemia, low serum total T4.
- Further Testing: Serum free T4, thyroid-stimulating hormone (TSH) levels, and thyroglobulin autoantibody assays.
Treatment:
- Medication: Oral synthetic T4 (levothyroxine) administered for life.
- Monitoring: Post-pill total T4 checked 4-6 weeks after starting treatment, then every 3-6 months.
Pearls:
Hypothyroidism is common, but congenital forms are rare. Euthyroid sick syndrome can complicate diagnosis.
2. Diabetes Mellitus
Classic Case:
Affects middle-aged dogs of any breed, presenting with polyuria, polydipsia, polyphagia, weight loss, and cataracts.
Diagnosis:
- Etiology: Immune-mediated destruction of pancreatic islet cells.
- Initial Screening: CBC, serum chemistries for hyperglycemia, urinalysis for glucosuria.
- Further Testing: Serum fructosamine to assess blood glucose levels.
Treatment:
- Medication: Long-acting insulin administered subcutaneously every 12 hours.
- Diet: Diabetic-specific diet and monitoring of blood glucose.
Pearls:
Diabetes mellitus requires lifelong management, with common complications including cataracts and secondary infections.
3. Hyperadrenocorticism (Cushing’s Disease)
Classic Case:
Seen in middle-aged to older dogs, with symptoms known as the 4 P’s: polyuria, polydipsia, polyphagia, and a pot-bellied appearance. Other signs include truncal alopecia and muscle weakness.
Diagnosis:
- Etiology: Pituitary-dependent hyperadrenocorticism (PDH) or adrenal tumors (AT).
- Initial Screening: CBC for stress leukogram, serum chemistries for ALP elevation.
- Further Testing: ACTH stimulation test, low-dose dexamethasone suppression test (LDDST), urine cortisolratio.
Treatment:
- For PDH: Trilostane is the first choice.
- For AT: Surgical adrenalectomy is preferred, or medical management with trilostane or mitotane.
Pearls:
PDH prognosis is good with management, but AT prognosis is fair to poor due to potential malignancy.
4. Hypoadrenocorticism (Addison’s Disease)
Classic Case:
Typically affects young to middle-aged female dogs, especially Poodles. Symptoms include lethargy, decreased appetite, vomiting, diarrhea, and weight loss, which may progress to an Addisonian crisis.
Diagnosis:
- Etiology: Immune-mediated destruction of the adrenal cortex.
- Initial Screening: CBC for lack of stress leukogram, serum chemistries for electrolyte imbalances.
- Further Testing: ACTH stimulation test to confirm diagnosis.
Treatment:
- Acute Crisis: IV fluid resuscitation, glucocorticoids, and mineralocorticoids.
- Long-term: Physiologic glucocorticoids and mineralocorticoid injections.
Pearls:
Addison’s disease is known as “the great pretender” due to its nonspecific symptoms. Prognosis is excellent with proper treatment.