Cushings Disease in Dogs

Cushing's disease is caused by long-term excess cortisol. In dogs, the most common form is pituitary-dependent disease, where a pituitary tumor causes too much ACTH and overstimulates the adrenal glands. A smaller number of dogs have adrenal-dependent disease caused by a tumor in one adrenal gland. A third form, called iatrogenic Cushing's, can happen after prolonged steroid use and should only be managed by a veterinarian.

Risk factors and predispositions include:

• Middle-aged to older age
• Small-breed predisposition for pituitary-dependent disease, including breeds such as Miniature Poodles, Dachshunds, Yorkshire Terriers, Jack Russell Terriers, Border Terriers, Lhasa Apsos, Bichon Frise, and Miniature Schnauzers
• Larger-breed predisposition for adrenal-dependent disease, with Staffordshire-type terriers and German Shepherds noted by Cornell
• Long-term corticosteroid exposure for other medical conditions
• Possible related complications such as urinary tract infections, skin infections, high blood pressure, diabetes mellitus, gallbladder disease, and blood clots

Diagnosis usually starts with a full history, physical exam, and basic lab work. Your veterinarian will often recommend a complete blood count, chemistry panel, and urinalysis to look for patterns that support Cushing's and to check for other problems such as urinary tract infection.

Common next-step tests may include:

• Low-dose dexamethasone suppression test, often used as a preferred screening test
• ACTH stimulation test, which can help confirm disease and is often used for treatment monitoring
• Urine cortisol:creatinine ratio in selected cases
• Endogenous ACTH testing or high-dose dexamethasone testing to help distinguish pituitary-dependent from adrenal-dependent disease
• Abdominal ultrasound to evaluate adrenal gland size, look for tumors, and assess other abdominal organs
• Blood pressure measurement and urine culture because dogs with Cushing's can develop hypertension and recurrent urinary infections

Owners should expect that diagnosis may take more than one visit and may require several tests, because no single test is perfect in every dog.

Treatment depends on the type of Cushing's disease, the dog's overall health, and how much the symptoms are affecting quality of life.

Common treatment approaches include:

• Trilostane, the FDA-approved oral medication most commonly used to reduce cortisol production in dogs with pituitary-dependent or some adrenal-dependent cases
• Mitotane in selected dogs when a veterinarian feels it is the best fit
• Adrenalectomy for dogs with an adrenal tumor when surgery is appropriate; benign adrenal tumors may be curative if completely removed
• Radiation therapy or specialty referral options for some pituitary tumors, especially larger tumors causing neurologic signs
• Careful tapering of steroids under veterinary supervision for iatrogenic Cushing's; steroids should not be stopped abruptly unless a veterinarian directs otherwise
• Ongoing monitoring with follow-up exams, lab testing, and adjustment of the treatment plan

Management at home often includes monitoring thirst, urination, appetite, energy level, panting, skin health, and any vomiting, diarrhea, weakness, or collapse. If your dog seems suddenly ill while on treatment, call your vet right away.