In this VETgirl online veterinary continuing education blog, Dr. Brittany Lancellotti, DVM, DACVD discusses a dermatologist’s approach to Cushing’s disease in dogs. Don’t miss the diagnosis of hyperadrenocorticism in dogs and what “classic” cutaneous skin signs can be seen in dogs!
A Veterinary Dermatologist’s Approach to Cushing’s Disease in Dogs
By Dr. Brittany Lancellotti, DVM, DACVD
Sasha, a 9yo FS Shih Tzu mix, presents for evaluation of itching and red ears. The owners have had her since she was a puppy and she developed skin and ear problems over the last year. Sasha has yeast dermatitis and otitis externa. Before you dive into your allergy spiel with the owner, take a moment to determine whether or not hormonal skin disease, such as Cushing’s disease, may be playing a role in the recurrence of infections.
While environmental allergies typically appear at less than 3 years of age [Hensel et al], Cushing’s disease more often appears in middle aged to older animals [Hoffman et al]. If the patient does not have a clear history of skin and ear disease when they were younger, Cushing’s disease should be added to your list of differentials of diseases that can cause adult-onset skin and ear infections, including hypothyroidism, food allergies, and cancer. A thorough history will identify any exogenous steroid use that could indicate iatrogenic Cushing’s.
When you hear Cushing’s disease in dogs, usually the image that comes to mind is of an animal with a large pot-belly who is panting excessively and urinating constantly. The liver enzymes are elevated and there may be other issues like diabetes or pancreatitis. In dermatologic patients with Cushing’s disease, this type of dog is less common. Cases of Cushing’s disease seen by dermatologists have a different constellation of clinical signs than those seen by internists [Behrend].
Common cutaneous signs of Cushing’s disease include a poor and thinning truncal hair coat, hypotonic (thin) skin and comedones (blackheads) most noticeable on the ventral abdomen, and infection of the skin, ears and claw folds. Other changes include calcinosis cutis (calcium deposits) most often on the back on the neck and shoulders or in the groin, change of hair color, seborrhea oleosa (greasy hair coat), poor wound healing, and demodicosis.
Diagnosis of pets with Cushing’s disease involves tests to evaluate the clinical signs and secondary problems caused by the disease, as well as cortisol function tests to identify the primary disease. Cytology is an invaluable tool in evaluating infections on the skin, in the ears, and in the claw fold. Cytology should be performed if there is evidence of folliculitis, pyoderma, or otitis externa. If the pet owner complains the animal is licking its paws, use a toothpick to obtain debris from the claw fold and smear it on a slide to help determine if the licking is the result of allergic itch or infectious itch. A common reason for antipruritic therapies, such as oclacitinib and lokivetmab, to fail is due to untreated infection. Skin scrape should be performed in areas of folliculitis to evaluate for demodicosis, particularly where comedones are present. If the animal has relapsing bacterial folliculitis, particularly when there is poor or only partial response to empiric antibiotic therapy, a culture and susceptibility of the infection should be considered.
Other diagnostics include complete blood count, serum chemistry, urinalysis, and blood pressure. These diagnostics can help identify other clinical signs that may increase your suspicion of Cushing’s disease, such as hypertension, thrombocytosis, stress leukogram, elevated alkaline phosphatase and alanine aminotransferase, isosthenuria, proteinuria and urinary tract infections. These diagnostics also identify other secondary problems requiring treatment. A key point to remember is that the absence of abnormalities on CBC/Chemistry does not rule out Cushing’s disease [Behrend]. Clinical signs, such as the ones described above, should be used to guide your workup.
Tests to identify the primary disease evaluate cortisol function. These include the urine cortisol:creatinine ratio (UCCR), ACTH stimulation test, and low dose dexamethasone suppression (LDDS) test. Each of these tests has their benefits and drawbacks, with no one test providing a definitive diagnosis in every situation. Each patient should be evaluated on an individual basis to determine which cortisol function test is recommended. The UCCR is a highly sensitive test, often used to screen for Cushing’s disease. Because of the lower specificity, any positive results should be confirmed with either a LDDS test or ACTH stimulation test. The LDDS test has a high sensitivity and specificity. It can also help to differentiate between pituitary dependent hyperadrenocorticism (PDH) and an adrenal tumor, but will not identify patients with iatrogenic Cushing’s. Alternatively, the ACTH stimulation test can be used to identify iatrogenic Cushing’s, as these animals will have minimal adrenal reserve and minimal cortisol response to stimulation by ACTH. The ACTH stimulation test has a lower sensitivity than the LDDS test, and therefore is less preferred as the first line test for identifying naturally occurring Cushing’s disease.
Treatment should be aimed at resolving the secondary infections making the animal uncomfortable and decreasing the cortisol production in the body. Topical antimicrobial therapy is preferred for resolution of superficial bacterial folliculitis whenever the owner is expected to be compliant. The isoxazoline class of parasiticides will effectively clear demodicosis. Culture and susceptibility testing can be used for guiding oral antibiotic therapy. For patients with Cushing’s disease who have otitis externa, care should be taken when selecting otic medications, as many preformulated ear medications contain steroids which can interfere with testing and monitoring of Cushing’s disease.
Trilostane is commonly used to decrease production of cortisol in the body and comes in 5mg, 10mg, 30mg and 60mg capsules. Depending on body size, initial dosing is recommended at 1mg/kg twice daily or 2mg/kg once daily. Morning dosing is preferred to facilitate accurate ACTH stimulation tests when monitoring response to treatment. Monitoring varies, but typically involves ACTH stimulation testing 10-14 days after starting treatment, then 4 weeks later, then 3 months later, then every 6 months as long as the dosing is not changing and the clinical signs of Cushing’s disease are improving or are controlled [Ramsey]. Because cortisol continues to decrease after the first two weeks of starting trilostane, dosing should not be increased until the second ACTH stimulation test in order to decrease the risk of hypoadrenocorticism [Feldman]. If dosing is adjusted, monitoring should be restarted. The goal of monitoring is to evaluate for appropriate adrenal reserve and ensure cortisol levels are not dropping too low.
Cushing’s disease is a complicated and life long disease. Clear, ongoing communication with the pet owner is essential for explaining the diagnostic and treatment process. Making sure the owner is not using any oral or topical steroids prior to hormonal testing will ensure accurate results. Once Cushing’s disease is diagnosed, equipping owners with the knowledge of what to monitor for at home will be helpful in evaluating response to therapy and determining if dose adjustments are needed. Our practice utilizes Episodes 9 through 11 of the Your Vet Wants You to Know podcast to educate owners on the clinical signs, testing and treatment of Cushing’s disease in dermatologic patients, as many pet owner resources are geared towards Cushing’s patients with clinical signs more readily observed in internal medicine patients. It is important to manage expectations that clinical signs may wax and wane, but after several months of treatment, partial to complete control of clinical signs has been reported to occur in more than 75% of cases [Lemetayer].
Behrend et al. “Diagnosis of Spontaneous Canine Hyperadrenocorticism: 2012 ACVIM Consensus Statement (Small Animal).” JOURNAL OF VETERINARY INTERNAL MEDICINE, vol. 27, no. 6, Nov. 2013, pp. 1292–1304.
Feldman EC. Evaluation of twice-daily lower-dose trilostane treatment administered orally in dogs with naturally occurring hyperadrenocorti- cism. J Am Vet Med Assoc 2011;238:1441–1451.
Hensel et al. “Canine atopic dermatitis: detailed guidelines for diagnosis and allergen identification.” BMC Veterinary Research (2015) 11:196
Hoffman, JM, et al. “Canine Hyperadrenocorticism Associations with Signalment, Selected Comorbidities and Mortality within North American Veterinary Teaching Hospitals.” JOURNAL OF SMALL ANIMAL PRACTICE, vol. 59, no. 11, Nov. 2018, pp. 681–90.
Lemetayer, J, and Blois, S. “Update on the Use of Trilostane in Dogs.” CANADIAN VETERINARY JOURNAL-REVUE VETERINAIRE CANADIENNE, vol. 59, no. 4, Apr. 2018, pp. 397–407.
Ramsey IK. Trilostane in dogs. Vet Clin North Am Small Anim Pract 2010;40:269–283.