Pruritis or Itchy Skin

Question: Dear Dr Mike: My black and white 1 1/2 year old cat has minute white flakes on the black parts of her coat. She also scratches near the front of her ears. This has been going on for nearly a year now - She was given two courses of antibiotics to no avail and I have restored to an Elizabethan collar to prevent her from harming herself. I also keep her ears clean as at firs I thought she had ear mites. This seemed to help for a few days but now she has restored to scratching herself raw. Please help.

Answer: Suzanne- There are a lot of causes of itchy skin, especially around the ears and head, in cats. It is unlikely that this is due to ear mites since your cat has been examined, but that is a possible cause. Cats get several types of mite infestations, including demodecosis, cheyletielliosis and notoedric mange. Ringworm (a fungal infection) can cause both the skin flakes and the itchiness in some cats. Allergies can cause itching and some cats with allergies have increased dander. Viral infections, such as herpes virus and feline leukemia virus sometimes cause scabby itchy sores on the head or other areas of the body. Pemphigus foliaceus, an immune mediated disease, can cause itchiness around the face and head. There are probably other conditions that I can't think of right now. It is probably going to be necessary to do more diagnostic testing and possibly to try treating for some other conditions, in order to finally find a diagnosis and appropriate treatment. Fungal cultures for ringworm, using a toothbrush culture technique, can be helpful as an early test since it is easy to do and not very expensive. Skin scraping for mites is a good idea, too, for the same reasons. Once these easy tests are done, it gets a little harder to decide what to do next. Skin biopsies are helpful in many cases, referral to a veterinary dermatologist is a good choice, food trials to rule out food allergy might help and sometimes it is better to try a different treatment approach to see if that will help. Your vet can help you decide which direction to go in based on the progress of the disease.

It really might be worth having your black and white cat examined by a veterinary dermatologist if your vet isn't able to find a problem with further examination. She is so young that it seems a shame not to work hard to find a diagnosis so it is possible to work on a treatment that will keep her comfortable. Mike Richards, DVM 12/28/2000

Itching in bengal

Question: Dr. Mike,

My 8 month old female Bengal was spayed two months ago. It might be just coincidence, but since she came home she scratches alot. Mainly around her neck and head. It is not fleas. Do you have any ideas?

M

Answer: M-

I am not sure what to tell you. The most likely cause of prolonged itching related to staying at a veterinary hospital or boarding facility would be a flea bite allergy, which can produce itching for up to three weeks after the last flea bite. Since a single flea might survive undetected on a kitten for several weeks to several months, it could produce long term itchiness.

We see a few reactions to the suture material that cause itchiness but this is usually obviously centered around the incision site.

I can't recall a patient with itchiness that resulted from spaying or neutering and which surfaced this quickly, but there are some hormonal changes and some clinical case reports of skin disease following spaying procedures. Usually this shows up several months later when the hormonal changes have time to produce an effect.

The only way I can think of to figure out what is going on is to start with an examination, looking for signs of allergy, eosinophilic granulomas, miliary dermatitis, etc. and then starting to work up the possible causes through whatever lab work appears to be appropriate based on the examination findings. Hopefully, that will result in a diagnosis and treatment that stops the itching or at least a plan to manage it, since itchiness is often associated with conditions like allergies that are difficult to actually cure.

Mike Richards, DVM 8/16/2000

Pruritis

Pruritis is the name for itchiness that causes pets to scratch. Several chemical reactions occur in the skin that stimulate the nerves, causing the brain to feel the itch. We treat a scratching pet by attempting to eliminate these reactions at the source and controlling the body's response to them as well.

Some of the chemicals involved in itching are prostglandins, arachodonic acid (a specialized fatty acid) and leukotreines. By using treatments that inhibit the action of these factors at the skin level, such as antihistamines and fatty acid competitors, we can sometimes control the itching without using corticosteroids such as prednisone. If we work to control other irritating factors such as fleas, dry skin and secondary bacterial infections we can also further reduce itching. Each of these steps is very important because pets have an "itch threshold". This is the point where all of the sources of itching finally add up to enough irritation to cause the irresistible urge to scratch. Just like pain thresholds, these levels vary from pet to pet. Control of every factor that possible is important to your dog's health and comfort. Pruritis is a complication of many diseases. Only by careful examination, diagnostic tests and sometimes even trial and error can we come to understand what causes the itching in a particular pet and how we can best control it.

Mike Richards, DVM

Stopping the Itch

Cold water will usually reduce itching and produce temporary relief. It doesn't really matter how the water is applied, but it must be at least cool. This effect doesn't last long, usually less than one-half hour. Adding Episoothe Oatmeal Shampoo, Episoothe Oatmeal Creme Rinse, Aveeno Colloidal Oatmeal, Relief Shampoo or Domeboro's solution helps to prolong the effect. All of these products are available over-the-counter. If you use Aveeno, one to two tablespoons per gallon of water, applied as a rinse, works best. Follow the directions on the Domeboro packet and also apply as a rinse.

Shampooing will sometimes help to control itching. Some shampoos such as Pyoben and Oxydex, act to reduce the bacteria level on the skin, one cause of itching. Seba Lyt and other sulfer/salicyclic acid shampoos reduce scaling. Lytar, Clear Tar and other tar containing shampoos reduce itching and oiliness. An emollient or moisturizer used after shampooing will restore some moisture to the skin and this also reduces itching. Expar Creme Rinse can be used to kill fleas after itching and moisturize the skin.

Antihistamines are useful in the treatment of itching in some dogs and cats. Used alone, about 15 to 25% of dogs will respond to antihistamines. Used in combination with fatty acid inhibitors, such as DermCaps, EFA-Z and Omega EFA capsules, about 25 to 40% of dogs will respond, reducing scratching behavior to acceptable levels. Antihistamines available over-the-counter are Benedryl (diphenhydramine, 25mg capsules) and Chlortrimeton (chlorpheniramine maleate, 4mg tablets). There are prescription antihistamines, notably Atarax (hydroxyzine) that work better in some cases. It is necessary to get a dosage for your particular dog or cat from your vet.

Dogs and cats have individual reactions to antihistamines. Since some dogs will respond better to one than another, it is best to try more than one antihistamine before giving up on them to control itching. Some pets will become drowsy when taking antihistamines. If this is unacceptable, they can not be used, or might be best to use at bedtime. Occasionally a pet will get excited when given antihistamines. These pets should not be given these products.

Fatty acid derivatives compete with aracadonic acid, the trigger for itching in the body. By replacing this compound with an inactive competitor, itching can be reduced. It is important that the fatty acid derivative chosen have gamma-linoleic acid, eicosapentanoic acid, or both. These products work best at high dosage levels and when given with a low-fat canned food such as W/D, which is available through veterinarians. Although they can be fairly expensive, their use is preferable to cortisones if they are effective. It is necessary to use these products for at least 6 to 8 weeks to judge their full effect. EFA-Z and DermCaps are examples of these medications.

Antibiotics are used to control skin infections associated with scratching. The itching leads to scratching, which damages the skin. The damaged skin is easier for bacteria to grow in. The bacteria then contribute to the itching, leading to more skin damage. As this cycle progresses, deeper and deeper layers of the skin are affected, sometimes leading to systemic bacterial infections that can even be fatal. Control of skin infections with antibiotics takes time. The usual defense mechanisms of the body, fever, white blood cells and antibodies do not work as well on the skin surface. Antibiotics must do more of the work alone. For this reason, 3 weeks is the minimum recommended time that antibiotics should be given for skin infections. Often, antibiotics must be continued for up to 8 weeks to consistently control skin disease. Several antibiotics seem to work consistently in skin disease. When these antibiotics fail, it is necessary to culture the skin lesions to identify which antibiotic might be appropriate in an individual case. Occasionally it is necessary to continue antibiotic therapy indefinitely to control severe bacterial skin disease.

Some dogs appear to be unable to prevent penetration of staph (staphylococcus) bacteria into the skin. These dogs can be benefited by the use of a product to promote immune responses. Similar to vaccinations (but short acting), these products help the body learn to fight off staph bacteria. They are Staph Lysate and Immunoregulin. Although somewhat expensive and necessitating weekly injections, these products can cost less to use than frequent or continuous antibiotic therapy. We have better success with Staph Lysate.

Hyposensitization, or allergy "shots", are used in dogs. Their use in cats is very limited due to difficulties testing cats accurately for individual allergens. Similar to their use in people, these injections help many pets, but not all. To be used properly, it is necessary to identify the allergy agents affecting a dog and then treat accordingly. This can be done by skin testing, where small quantities of allergens (allergy causing agents such as pollens), are injected into the skin and the response to this monitored. Often, it is necessary for a general veterinary practitioner to refer a pet to a veterinary dermatologist for this testing. Recently, blood tests have been developed to allow allergy testing without injections into the skin. These have become better understood recently and are correlating with the skin testing fairly well, although it is generally agreed that skin testing is still more accurate. Allergy injections require a consistent effort from the pet owner. They are the preferred treatment for inhalant allergies if that is the only condition affecting dog, when effective. Currently, about 70% of dogs are thought to benefit from this therapy.

Fleas cause most the allergic reactions in pets. Flea control is essential to our success in treating itchy dogs. Please ask for flea control information if you have any problem at all with fleas on your pet!

When itching can not be adequately controlled by one of the above methods, we usually use a corticosteroid, such as prednisone. Cortisones are the most consistently effective anti-itch medications that we have. They do have several drawbacks, however. Cortisones increase the amount of water your pet drinks, making it urinate more, too. Sometimes this becomes a problem. These drugs increase appetite and weight control can be difficult while using them. If proper dosage schedules are not followed there can be long-term side effects such as decrease in bone density or an increased chance of pancreatitis. Cortisones depress lymphocytes, a type of white blood cell, making it easier for bacterial infections to occur. Accidental overdosage with these medications or inappropriate long-term use can lead to medication induced Cushing's disease, a cause of hair loss, muscle weakness and other problems. For these reasons, most vets insist on monitoring a pet on cortisones through follow-up office visits. You may be required to allow examination of your pet prior to refilling prescriptions for these drugs.

In spite of these side effects, cortisones can be the best drugs to make an extremely itchy pet comfortable. If they are the only effective drugs for your pet they are worth the small risk to an individual pet of side effects. These drugs are reasonably safe for long term use if given according to directions. Allowing your pet a good quality of life, by controlling the itching, is worth the small risk of using prednisone and related compounds.

These are the methods we use to treat pruritis, the itchiness that causes your dog or cat to scratch. It may take several tries to work out the proper drug and dosage schedule for your pet, but is worth the effort.

Mike Richards, DVM