Derm's Dirty Dozen: These six diabolical diseases are bound to plague your patients and your patience

In the first part of this two-part series, I outlined six of the more frustrating dermatology cases I see in my practice. But there are still six to entice you, frustrate you and more importantly, teach you!

Canine hypothyroidism

This condition is the great imitator. It is also a disease that can be very difficult to diagnose, yet it seems to be diagnosed commonly in private practice. I believe the most frustrating aspect of this disease is with all the questions that are raised. What test should I perform to diagnose hypothyroidism? Do I perform the test during a certain time of the day? Do specific medications interfere with the results of diagnostic testing? Could the results of thyroid testing fluctuate normally during a given time period and fall below the normal reference values?

In my practice, we uncommonly diagnose hypothyroidism. Most dogs that have hypothyroidism are generally older than 6 years of age. The common cause is spontaneous lymphocytic thyroiditis, and less commonly, thyroid atrophy. However, some of the larger and giant breeds of dogs can have very early age in onset hypothyroidism, sometimes as early as 1 to 2 years of age. Larger breeds affected at this age include Great Danes, Dobermans, Irish Setters, Newfoundlands and Mastiffs. Other breeds that are predisposed to developing hypothyroidism include Cocker Spaniels, Golden and Labrador Retrievers. Dogs affected with hypothyroidism can present in many different forms, but most commonly a poor hair coat with alopecia can be expected. Some dogs, however, can present with what is called "post-clipping alopecia" (lack of hair regrowth in previously shaven areas). In addition, the constellation of clinical signs and physical examination findings can also include weight gain, seborrhea sicca, recurrent superficial pyoderma, facial myxedema, "rat-tail" appearance (alopecia on distal tail) and lethargy.

Most dogs that I see have been treated with corticosteroids recently (orally, by injection or topically), which interferes with results of thyroid hormone measurements. It is well-known that corticosteroids suppress thyroid hormone values and can significantly impact thyroid hormone measurements, thus falsely providing information to the clinician and leading him or her astray. In addition, it has been well established that other drugs, including the sulfa-type antibiotics, will not only reduce thyroid hormone values, but impact the thyroid gland in such a way to produce clinical, clinicopathologic and histologic (thyroid gland atrophy) evidence of hypothyroidism. Finally, inflammatory conditions and other non-thyroidal illnesses can alter thyroid values causing diminished thyroid values (severe illness, sepsis, Cushing's disease, neoplasia), or in the case of inflammatory bowel disease, elevated thyroid values.

First of all, there is no single test that can diagnose hypothyroidism at any point in time with 100 percent accuracy. What I recommend is performing free thyroid testing at any time during the day. Most investigators believe this thyroid hormone is a true reflection of thyroid status in the dog. It is also less effected by medications and stress. Total thyroid hormone measurement is considered to be a less sensitive test, but it can be of value in private practice because of the reduced cost compared to free thyroid hormone measurement. Borderline values (gray zone) should be rechecked in three to six months. Correlation with the clinical signs and history is also very important when evaluating thyroid values. Measurement of thyroid-stimulating hormone can be valuable as well, and theoretically, it should be elevated in the average case of hypothyroidism. I have found this test to be unreliable and the results very inconsistent. I have also found measurement of thyroid auto-antibodies and other thyroid hormone measurements to be of little value.

After the diagnosis is made, supplementation with thyroid hormone is administered every 12 hours (dosage: 0.1 mg/10 pounds ideal body weight). I also recommend retesting in three to four weeks and measuring trough levels. Most clinicians, however, measure thyroid values four to six hours after the morning dosage (four to six hours post-pill). This value is expected to be in the high—normal, or better yet, in the slightly high reference ranges. Do not lower the dosage if your measurements are in these ranges because as these values are expected at this time during the day after supplementation unless clinical evidence of hyperthyroidism are noted. Trough levels measurement of thyroid hormone immediately prior to a dosage should not fall below reference values and should be low-normal or mid-normal.

The outcome of hypothyroidism treatment results in rapid resolution of lethargy (within one to three weeks), and complete regrowth of hair and resolution of seborrhea within eight to 10 weeks or sooner.

Flea allergy dermatitis

Ctenocephalides felis (C. felis) is the common flea found on most domesticated animals. This cat flea is found on cats, dogs, raccoons, opossums, domesticated rabbits, ferrets, cattle, foxes, coyotes, bobcats, koalas and some avian and rodent species. It is also found to infest the mongoose population in Hawaii. They are rarely found on squirrels or wild rabbits. C. felis stay permanently on these hosts where they feed, breed and eventually die. They do not survive for extended periods of time off the host, however, survival rates of 12 days or more were reported under moist conditions in homes. In addition, adult fleas can on occasion, leap onto clothing of humans and be carried away to a new location.

Fleas are obligate parasites and are a permanent parasite on the host until it dies, usually in about 100 days. The average pet has twice as many female fleas as male fleas. The female flea begins feeding on the pet and starts to lay eggs within 24 hours of hatching and can lay up to 40 to 50 eggs per day. The eggs are not sticky and fall off the pet into the environment. It has been clearly shown that many eggs do not survive and undergo desiccation in dry environments. However, due to the massive reproductive capabilities of the adult flea, a substantial infestation can still occur in the home as well as the outdoors.

The ova of C. felis begin hatching within a few days after they enter the environment (home and outdoors). The proper conditions for survival include adequate temperature (probably the most important factor) and humidity. The ideal temperature is 40 to 85 degrees F and humidity above 50 percent. Dry conditions with humidity below 50 percent can be lethal to ova. Ova and larvae simply desiccate when exposed to hot and dry conditions with inadequate moisture. The surviving eggs hatch into larvae within a few days or weeks. The larvae also undergo several moltings. Larvae survival is also dependent upon similar temperature and humidity values as the ova but are also reliant on a food source such as adult flea feces and dried host blood. The larvae enter the pupal stage by spinning a loosely packed silk cocoon. This sticky cocoon often is coated with environmental particles and is much more resistance to extreme environmental conditions and insecticides. Pupae will hatch in 13 days or less under ideal conditions but can survive for five months or more without an adequate host. The time for pupal development and hatching is termed the pupal window. The time from deposition of eggs to adult flea emergence is called the developmental window and can be up to three months in duration. These pre-adults are found in the carpeting fibers, pet bedding, under furniture, cracks in hardwood floors, under sofa cushions, soil, grass, sand and in animal burrows.

When encountering a flea infestation on a pet, especially a pet with symptoms of flea allergy dermatitis (FAD), a three-step program is recommended to eliminate or reduce flea bites on the pet. Initially, the proper application of adulticides, such as fipronil, imidocloprid or selemectin, on all pets is advised. Some of these products demonstrate larvicidal properties. Cats tend to lick the non-dried product after application, so these products are applied to the base of the head in an area that cannot be groomed. Most animals that have adult active fleas on the coat are most likely exposed to an infested environment thus overwhelming the adulticide product. Frequent shampoo therapy (especially in dogs) with strong soaps or stripping ingredients can remove some of the product as well. It is recommended to apply adulticides on a dry coat and delaying shampoo several days after application.

The second objective is to apply treatment to the home environment. There are at least two insect growth regulators (methoprene and pyriproxyfen) available on the market in the Unites States and are designed to interfere with egg hatchability and larval development. These two stages can comprise greater than 50 percent of the pre-adult population. Most house sprays are water-based and contain an accompanying adulticide, such as permethrin or tetramethrin. The spray should be applied to pet bedding, all carpets, hardwood floors, under furniture, under sofa cushions, closets, carpeted-based cat condominiums, doormats and carpeted areas in the automobile. These insecticides also demonstrated some ovicidal and larvicidal properties but may not persist in the environment for long periods of time. It is therefore recommended to treat the home with a second application two weeks later (pupal-window) thus achieving a quick knockdown of newly emerging adult fleas. A third application is also advised three months to six months later. Finally, sodium polyborate powder has been shown to be effective in controlled indoor pre-adult stages. The powder acts as a desiccant, and when ingested by larvae, it acts as a toxin.

The third and final treatment focuses on the outdoor environment. This area might not be as important as the home due to the extreme variations in temperature, humidity or to the pet's environment. If dogs and cats frequent the yard of a home, then it is advisable to treat these areas monthly with either malathion or diazinon. Newer and safer products also are available and include biologics, such as a nematode spray. The nematode, Steinernema carpocapsa, preferentially parasitizes flea larvae and other destructive insects, such as cutworms and army worms. The nematodes are reported to be safe for outdoor use but are effective only in moist-shade and part-shade areas and should be applied every one month to three months.

With the knowledge of flea reproduction and the proper use of adulticides and environmental treatments, one can deal swiftly and adequately to control flea infestations and the associated flea allergy in pets. Consistency with treatment is also critical and will enhance treatment success. Finally, client education is also very important; an adequate flea control program is not complete without the education of the owner and the monitoring of compliance.

Excessive grooming

Excessive grooming in the cat to the point of alopecia ranks highly in my most frustrating list of dermatology cases. It was once thought that all (or most) cats with symmetrical alopecia on the trunk, caudal half of the body and rear limbs were affected by pyschogenic causes. Many cats were treated with a progesterone-type medication, and some improved. It is now known that most of those cats probably were affected by an allergy. The response to progesterone-type medications can be non-specific, but this drug possesses significant anti-inflammatory effects on the skin as well as possessing diabetogenic properties.

Patterns of alopecia associated with this condition usually is confined to the caudal half of the body, flanks, rear limbs and groin. Some of these cats might have alopecia on the forelimbs, especially near the carpal area. What is most interesting is most cats lick (or pull hair) to the point of partial alopecia, leaving short hairs without excoriations or evidence of epidermal self-trauma.

Cats can be very secretive in their behavior, and some owners fail to observe excessive grooming. Cats are nocturnal, so much of the grooming occurs at night when owners are asleep. Repeated questioning directed to the owner concerning the behavior of the cat, including the incidence of hair balls, which should be increased in this condition, can clarify the clinical picture. Finally, response to corticosteroids (injectable or intermediate strength oral forms are preferred) can be of value in making a diagnosis. Cats with psychogenic alopecia do not respond to these therapies.

My general approach to these cases is to clearly discern whether the cat is over-grooming and then to pursue diagnostics. Skin scrapings are recommended as well as performing trichograms. A trichogram is a simple, inexpensive, non-invasive technique performed by plucking the short hairs in the areas of alopecia and examining the sample on low-power. The hairshafts should be broken or fractured, thus providing definite proof of self-trauma. It is very important to state that self-trauma might not be related to allergy or itch. There are actual cases that definitely are related to psychogenic causes.

My four differentials for cases of symmetrical alopecia include demodicosis caused by the contagious demodex mite, Demodex gatoi, flea allergy, food allergy and atopic dermatitis. The demodex mites are relatively easy to find, but fleas can be very difficult to find and certainly to convince owners of the suspicion of flea infestation, and FAD can be extraordinarily tedious.

Treatment of this type of demodicosis includes weekly sulfur-type dips for four weeks to eight weeks on all cats. We also recommend treatment of the environment with a commercially available home flea spray. Some cases can be recurrent, so long-term treatment with periodic sulfur dips might be needed.

Since the most-common diagnoses I have found in these cats is FAD, I have become more skilled in educating clients and instituting aggressive flea control. Flea control has been described earlier, but there are a few important differences to be noted in the cat. Initially, I routinely administer corticosteroids in severe cases and advise imidocloprid or fipronil topically applied to the base of the skull every two weeks. Treatment of all animals with topical products also is recommended. Home treatment with insect-growth regulators also is advised and should be repeated in two weeks, again in three months, and every three months to six months thereafter if pets are trafficking in and out of the home.

The remaining two allergies also can be difficult. Food trials with either hydrolyzed protein or novel proteins are recommended for at least eight weeks. Cats are very finicky, can show disinterest in the food, develop weight loss and gastrointestinal signs. This results in frustration and lack of owner compliance. I generally recommend Hill's ZD (dry only) with supplementation with canned rabbit-based cat food. Cats enjoy these foods, tend to do well with this combination and usually do not lose weight.

Atopic cats should be referred for a thorough work-up by a boarded veterinary dermatologist as these cases can be difficult to manage.

Finally, pyschogenic alopecia can be a diagnosis of exclusion and can sometimes can be successfully managed with amitriptylline (5 mg/cat twice daily). I should note that this drug might also have some anti-histaminic effects as well. Fluoxetine may also be used (1-3 mg/kg/day), but side effects might be seen more readily, such as vomiting or diarrhea and undesirable behavior.

Primary seborrhea

This is a genetically-based disease observed in the American Cocker Spaniel and other breeds. The basic pathology is an abnormal acceleration/proliferation in the epidermal and sebaceous gland cell turnover rate. There have been several studies that evaluate the kinetics of this hyperproliferative state, and the epidermal cell renewal rate has been calculated at eight days. Normal epidermal cell renewal rate is about 21 days. This results in a major traffic jam of cornified cells, resulting in seborrhea or excessive flaking on the skin that we observe clinically.

Clinically, most dogs present with what is termed seborrhea sicca or dry seborrhea. Much scale is observed on the coat, predominantly on the trunk. Some scales can be seen in the axillae and groin more readily. It is known that seborrhea sicca can be pruritic, and this can be the owner's primary complaint. Some Cocker Spaniels can develop greasy seborrhea (seborrhea oleosa) and have a profound odor. Lesions can extend to involve the pinnae and ear canals, resulting in proliferative otitis.

Some of these dogs effected by primary seborrhea can develop secondary skin infections with Staphylococcus and Malassezia on the skin and in the ear canal, which can increase pruritus and odor further. Cytology can help elucidate these cutaneous infections and is best performed with direct glass slide impressions.

Diagnosis can be difficult because seborrhea is more commonly seen secondary to other causes, such as allergy. The best diagnostic tool (after the elimination of infections) is the skin biopsy. A diagnosis of primary seborrhea can be made with this technique and should be reserved for cases that are highly suspect.

Treatment involves antibiotics for the concurrent pyoderma and anti-fungal therapies for Malassezia dermatitis (oral and topical if severe). Shampoo therapy (performed every three days to five days) is also very important and includes soap-free moisturizing shampoos for mild, dry seborrhea or products that contain sulfur and salicylic acid. In severe cases, especially in greasy seborrhea with odor, I generally recommended benzoyl peroxide or tar-containing shampoos. Rinses with water-based humectants can be a benefit as well.

Systemic therapy has been advocated for severe cases and can include oral fatty-acid supplementation (follow labeled instructions) and oral retinoic acids or synthetic retinoids. Accutane has been used in the past and more so recently because generic equivalent is available. The dosage is 1-3 mg/kg twice daily, but results can be disappointing. Finally, Soriatane (acitretin) at dosages of 1 to 2 mg/kg/day may be of benefit as well.

High dosages of vitamin A can act on the skin much in the same way as the synthetic drugs. It is much less expensive than the synthetic retinoids. I generally recommend 16,000 IU twice daily or higher for three months or more to evaluate effect.

Compliance, expense

The last two frustrating dermatology-related problems that I experience, are actually not skin diseases at all: owner compliance and expense of treatment.

To increase owner compliance, I generally follow these guidelines. First, I ask the client directly if they think they can perform the task or tasks that I recommend. Do you think its realistic that a mother of three at home can bathe a Golden Retriever every three days? Allowing the owner to feel more comfortable with what he or she realistically can do is very important and puts the owner's mind at ease. Alternative treatments or changes in frequency of treatments can be recommended, thus enhancing compliance. Why prescribe an antibiotic that is administered two times or three times daily when you can prescribe a once-daily alternative for a client who works long hours? Why prescribe a capsule to a stubborn, aggressive Lhasa Apso when you can prescribe a pill that can be crushed or a suspension mixed into food? Why recommend a home-cooked diet for a working mother or father? Novel commercially-available pet food should be adequate for an elimination diet. Successful outcome still can be expected in many cases, even when certain frequently performed treatments, such as shampoo therapy, ear cleaning, etc., are performed less frequently. Second, I frequently request a recheck examination in one week to two weeks after initial presentation in animals that are severely effected by disease or were placed on a food trial. Many things can go wrong during the initial stages of a treatment, so this is the best time to catch these problems early and change them. Weight loss and lack of interest in the diet during dietary changes are major concerns, and these can be addressed during this recheck examination. Demonstration of certain difficult tasks, such as instilling otic medications, ophthalmic medications or ear cleaning, clearly will enhance owner compliance and treatment success. I try to educate the client as much as possible by explaining the disease in detail and follow up with client-education handouts.

Finally, I have found a dry-erase board placed in the examination room to be an invaluable tool to illustrate confusing diseases or treatment plans.

We all know about the economics of our field of medicine, and this can directly interfere with our ability to practice properly. Here are some tips to help you and your clients deal with the rising healthcare costs for their pets. First, I tell all my clients to purchase pet insurance; it's that simple. I believe it actually is worthwhile, especially with severe, catastrophic illness or injury.

Third, for the more-expensive off-label medications (especially drugs that are not available in your practice), I have found the warehouse-type prescription pharmacies to be the least expensive. For example, modified cyclosporine 25 mg size, 30 count, is $36, but it costs $79 at the local pharmacy located in the Bay Area. This can be a substantial savings if the pet remains on this drug for life. Finally, referral to a board-certified veterinary dermatologist can save the owner money in the long term. Cases that are very frustrating, severe in nature or chronic and relapsing might be managed better with a specialist. We might be better equipped to deal with these cases, and our specialized expertise and knowledge of newer, safer and more-effective therapies can provide a reasonable and economically feasible treatment plan for those difficult cases.

Editor's note: This story is the second in a two-part series. Check out DVM Newsmagazine's October issue for the first six cases in Derm's Dirty Dozen.