The internal medicine service at the Veterinary Medical Teaching Hospital at the University of Wisconsin School of Veterinary Medicine requested a consultation on a 7-year-old intact male Boston terrier in which pituitary-dependent hyperadrenocorticism (PDH) had been diagnosed one month earlier. At the time of the initial diagnosis, the dog had exhibited classic signs of hyperadrenocorticism, including calcinosis cutis on the dorsum. The laboratory test results (i.e. ACTH stimulation testing, low-dose dexamethasone suppression testing, and abdominal ultrasonography) confirmed the diagnosis.
At the time of dermatologic examination, the dog was receiving maintenance mitotane therapy and was being monitored with periodic ACTH stimulation tests. Both the owner and internists were pleased with the dog's response to mitotane therapy; however, severe facial pruritus of 10 days' duration had developed, prompting the consultation. Reviewing the dog's medical records and dermatologic history form and questioning the owner revealed that the dog had no history of pruritus or other skin diseases.
1. The skin in the dorsal scapular area of the dog in this case. Note the alopecic area, which was palpably hard.
Dermatologic examination revealed bilaterally symmetric hair loss on the trunk, mild generalized scaling, thin abdominal skin, comedones on the ventral abdomen and thorax, and diffuse areas of calcinosis cutis on the cranial dorsal trunk. The skin in these regions was hard and erythematous (Figure 1). Mild exudation was present on the lesions' margins. Bilateral hair loss, erythema, and an erythematous papular eruption were present on the face. Several focal areas of exudation were also noted. The facial skin felt thickened but was not palpably hard as were the areas of calcification on the dorsum. The inflammatory lesions on the dog's face were not present at the time of initial diagnosis one month earlier. The results of an otic examination were normal. Raised, hard erythematous plaques compatible with a clinical diagnosis of calcinosis cutis were present in the left inguinal region (Figure 2).
2. The skin in the dog inguinal region. Note the erythematous alopecic areas with well-demarcated borders. These areas were palpably hard.
This patient's primary dermatologic problem was facial pruritus. Atopy and food allergy are commonly associated with facial pruritus and would have been considered as differential diagnoses if the dog had had a prior history of skin disease. The differential diagnoses primarily were infections and infestations secondary to the immunosuppression associated with PDH: demodicosis, dermatophytosis, bacterial pyoderma, and Malassezia pyoderma. Drug reactions were also considered, but hard skin has not been reported as a clinical sign of a drug reaction. The thin skin, hair loss, calcinosis cutis, and scaling were most likely due to PDH.