Common endocrine dermatopathies in dogs

Common endocrine dermatopathies in dogs

A look at dermatologic disorders associated with endocrine disease
Apr 01, 2011

Sam is a 10-year-old 65-lb neutered male black Labrador retriever mix with a history of pruritus, regional hair loss, malodor and a dull coat.

Table 1: Elements of allergic disease vs. endocrine disease
The medical team, using a medical history form (Table 1), determined that Sam has been pruritic for the past six months, and his scratching has become more obvious during the past two months. According to the owners, no other pet or person in the household is affected. Sam has been receiving antibiotics, antihistamines and corticosteroids during the past six months; each has had limited success in resolving his clinical signs.

Sam spends most of his time indoors and eats only a commercial dry adult food. The owners report no fleas in the household. When asked, the owners say Sam's energy level is a little less than normal, and he does not want to play as much as he used to. They have attributed this to his "getting older."

Photo 1: Sam at presentation. Note the generalized hair loss that is most noticeable over the dog's back and tail. (Photos courtesy of Kim Coyner, DVM, Dipl. ACVD, Dermatology Clinic for Animals, Las Vegas, N.V. )
Physical examination shows Sam is mildly pruritic with generalized hair loss that is most noticeable over the back and tail (Photo 1). There's also increased pigmentation on the patient's ventrum; generalized malodor is also evident.

Photo 2: Malassezia (arrows) and coccoid bacteria on skin cytology.
The medical team performs a standard dermatologic diagnostic workup consisting of skin scraping, skin cytology and a dermatophyte culture. Review of the samples shows no parasites on the skin scrape, but numerous Malassezia species and coccoid bacteria are evident on cytology (Photo 2). A thorough initial evaluation shows staphylococcal pyoderma and Malassezia dermatitis.

A three-week antibacterial and antifungal regimen in initiated, and Sam is rechecked in three weeks. During this time, the dermatophyte culture is monitored daily and determined to be negative. The owners report the pruritus and odor have decreased; however, the alopecia has not changed and, in fact, may be worse.

Now the veterinarian must determine the underlying cause of the recently cleared cutaneous infections. Given the information available, an endocrinopathy or an allergy (e.g., atopy, food or parasite hypersensitivity) should be considered. The three most common endocrine disorders to affect a dog's skin are hypothyroidism, hyperadrenocorticism (Cushing's disease) and the more all-inclusive condition known as alopecia X. Several rare endocrinopathies area also known to affect the skin, including estrogen- and testosterone-producing tumors, resulting in abnormal sex hormone concentrations.

Findings suggest Sam has more underlying disorders than a typical allergic patient. Several historical and physical clues suggest endocrine disease. It's important to accurately identify the specific endocrinopathy, since many of them eventually may lead to systemic abnormalities. Since hypothyroidism and hyperadrenocorticism have the most potential for leading to clinical abnormalities and systemic effects, detection of these diseases are the main focus of this article. The following five-step protocol is suggested to help identify dermatologic patients with an endocrinopathy.