Clues the skin yields to internal disease

Photo 1: Elderly Cocker Spaniel with generalized demodicosis secondary to underlying Cushing's disease.
Nothing is more heart warming than watching a patient grow in your practice from infancy to an aged pet. It is truly beautiful to see a caring owner trying to do the best for their geriatric pet to enhance the quality of their remaining years. They look to us for guidance and expertise to extend the quality time they have with that pet. Perhaps our role as veterinarians is more of a prophylactic one, in that we try as the patients get older to "catch" an impending or early disease before it has a chance to take hold. Hence the importance of a good physical exam and geriatric work up which includes education of the client, blood work, and sometimes more extensive diagnostics. Thankfully in dermatology, pets do not seem to parallel humans in their aging changes of the skin. However, certain symptoms which can be "red flags" for other diseases in the aged patient should be identified. The emergence of recurrent pyoderma or demodicosis in a geriatric patient should clue us into looking deeper for an underlying cause. Certain keratinization changes such as those seen in hepatocutaneous syndrome signal us as veterinarians to look for underlying liver pathology including diabetes mellitus. And finally, neoplasia is certainly more prevalent in the older patient, particularly cutaneous lymphoma.

Photo 2: Shetland Sheepdog with adult onset demodicidosis. A bladder tumor was diagnosed one month later.
Reading the signs When an adult canine that has otherwise been healthy with no history of steroid use presents with generalized demodicosis, a search for an underlying disease should be undertaken. One study indicated that 20 percent of generalized adult onset demodicosis patients may have underlying Cushing's disease, 12 percent may be hypothyroid, 24 percent have underlying allergy, 15 percent on chemotherapy, and 29 percent have an unidentified disease. Perhaps the most common breed of elderly patient that presents with Cushing's disease in our practice is the Cocker Spaniel, followed by the Golden Retriever and Labrador Retriever (Photo 1). I have been known to say throughout the day that "an old Cocker Spaniel is Cushing's disease waiting to happen". Cushing's disease is mentioned because in an elderly canine, many times the initial presentation is that of generalized demodicosis. Skin scrapings, blood work, along with further diagnostics should be performed. Once demodex mites are found in skin scrapings, we check a CBC/profile/urinalysis. If you see additional signs of Cushing's disease such as enlarged abdomen, thin skin, muscle atrophy, visible abdominal skin vessels, or calcinosis cutis, an ACTH stimulation test or low dose dexamethasone suppression test should be performed to confirm the diagnosis. Most often, liver enzymes are elevated on the serum profile in a patient with Cushing's disease, but I have had an occasional patient (both Cocker Spaniels) where the liver enzymes were normal. I also hear the comment that the liver enzymes "aren't up very much". An ACTH stimulation test should be performed if the liver enzymes are in the least bit elevated assuming the patient has not been on any topical or systemic steroids, or other medications that will cause liver enzyme elevations such as phenobarbital. We usually start with a one-hour ACTH stimulation test, if the results confirm Cushing's disease, a referral is made to the internist for an abdominal ultrasound to rule out adrenal tumor. If pituitary-dependent Cushing's disease is confirmed, Lysodren therapy is initiated. If the ACTH stimulation test does not confirm Cushing's disease, a low dose dexamethasone suppression test should be performed or wait another eight weeks and recheck the ACTH stimulation test. A elevated resting cortisol level is not diagnostic for Cushing's Disease. An elevated resting cortisol level is merely a reflection of the patient's anxiety level. The real analysis is the one- or two-hour post cortrosyn or ACTH cortisol level as it measures the body's response to a cortisol stimulus.

Neoplasia Underlying neoplasia or "impending" neoplasia should also be considered in a geriatric patient with generalized demodicosis. If a search including blood work, radiographs and/or ultrasound does not yield a neoplasm, the patient should be monitored closely in the future. In one of our patients, an elderly Shetland Sheepdog with generalized demodicosis, a bladder neoplasm was detected a few months after the diagnosis of demodicosis (Photo 2). Not all geriatric patients with generalized demodicosis will have underlying internal medicine issues, but since studies indicate a majority can, it is important to monitor particularly for Cushing's disease, an existing neoplasm or an "impending" neoplasm by routine checkups.

Photo 3: Mast cell tumor on a Boxer.
Skin masses Skin "lumps and bumps" are particularly important to check in elderly patients since neoplastic cells tend to pick on older individuals. It is important to perform fine needle aspirates of any and all skin masses. It is tempting on a busy day to just palpate skin masses and write them off as "lipomas" and "we'll just keep an eye on it". However the few extra minutes it takes for the veterinarian or technician to perform the needle aspirate and read the slide in house or send it to the pathology lab for analysis, may be well worthwhile. Certainly a fine needle aspirate is not a substitute for surgical removal and biopsy but it may give an indication as to which way to proceed. Astute owners and groomers often will detect these skin masses and if they feel they are important enough to point out, it is our responsibility to follow these with diagnostics. Lipomas, mast cell tumors, histiocytomas, and focal lymphoma tumors are probably diagnosable in house but if there is any doubt as to the type of cell or which way to proceed, a second opinion on the cytology should be obtained from the pathologist (Photo 3). In house cytology requires very little time and you will become more proficient the more you do it. Cutaneous lymphoma was discussed in previous articles but it should be remembered that clinically, those lesions can resemble bacterial pyoderma (Photo 4). It is very important to perform skin biopsies on lesions that you feel are not responding normally to therapy.