Overview of Feline Miliary Dermatitis
Miliary dermatitis is a papular, crusting skin disease accompanied by varying degrees of pruritis. Cats with miliary dermatitis have multiple, small bumps on their skin that are usually associated with hair loss (alopecia). On closer examination, these bumps are raised, red swellings topped with a crust. Most commonly the bumps and hair loss are found on the cat’s rump, neck, and chin.
Below is an overview of miliary dermatitis in cats followed by in-depth information on the diagnosis and treatment of this condition.
Miliary dermatitis indicates an underlying skin problem; almost always, the skin problem is a pruritic (itchy) skin disease. The itching causes the cat to scratch, chew or groom excessively leading to the typical bumps with scales. Flea allergy is by far the most common cause of this skin pattern. Other allergies, bacterial skin infection, parasites and ringworm fungus are among other causes. Less commonly, a more severe disease that suppresses the immune system and allows bacteria or other infections to become established may cause this symptom.
The health impact on the cat depends on the severity of the itching or any other effects of the underlying cause.
What to Watch For
Scratching or excessive grooming
Small, red bumps topped with a crust
Diagnosis of Miliary Dermatitis in Cats
A complete history and physical exam are essential to diagnosis of the cause of miliary dermatitis. It is important to try and establish if the cat is itchy or if the cat is sick. A flea comb may be used to look for fleas, flea dirt, or evidence of other parasites.
A skin scrape is done to rule out mites and other skin parasites.
A fungal culture is done to rule out dermatophytes (ringworm fungi).
A special diet may be prescribed to see if the cat has a food allergy.
Allergy testing (skin testing or blood testing) may be necessary if above tests do not yield a diagnosis.
A skin biopsy may be required to help categorize the type of skin disease that is present.
A blood chemistry profile and CBC may be needed to assess the patient’s general health.Tests for feline leukemia virus and feline immunodeficiency virus (feline AIDS virus) may also be done.
Treatment of Miliary Dermatitis in Cats
Long-term, successful treatment always depends on identifying and treating the underlying cause.
Strict flea control is essential since flea allergy is the most common cause. Many cats respond to flea avoidance alone. Even if fleas are not the primary cause, they always make the skin condition worse.
Corticosteroids are often used to stop the itch and consequently, the self-mutilation. Short-acting oral steroids are safer and easier to control, although long acting injections are sometimes used so that owners do not have to administer pills.
Antihistamines are sometimes successful in controlling itching. Although they have far fewer side effects than steroids, they are also far less reliable.
Moisturizing and soothing shampoos such as colloidal oatmeal shampoos may be helpful.
Fatty acid supplements may help to reduce itching.
A broad-spectrum dewormer may be used to help improve the general health of the cat.
Give all medications as prescribed. Follow-up as directed to make sure that the condition resolves completely. Work with your veterinarian to establish a complete flea control program.
In-depth Information on Feline Miliary Dermatitis
Miliary dermatitis is a pattern of skin reaction to an itchy or an infectious skin disease. Cats with this symptom have small bumps on their skin that are topped with crusts accompanied by hair loss in the affected region of skin. Most commonly the lesions are found over the rump, along the back, and around the neck and chin. This is the most common skin reaction pattern seen in cats.
Miliary dermatitis is usually caused by some sort of an itchy (pruritic) skin problem that leads to self-mutilation. On close observation, it is apparent that the cat is scratching, chewing or licking their skin excessively. Often, excessive grooming is not recognized because it is normal to see cats licking their hair coats. The actual lesion is a papule, which is a raised, red, small bump in the skin. When there are several of these lesions, it is called a papular rash. Less commonly, this symptom is seen because of a more severe disease that has suppressed the immune system, allowing infectious agents like bacteria to infect the skin.
Causes of Miliary Dermatitis in Cats
By far the most common cause of this symptom is flea allergy. Fleas are seldom recognized as a problem is cats with flea allergy because fleas and flea dirt are removed by the excessive grooming. It is therefore important to remember that a lack of fleas does not rule out flea allergy.
Skin parasites can cause intense itching and miliary dermatitis. Mites like Notoedres cati, Cheyletiella blakei, Demodex cati, and Otodectes cynotis (the ear mite) are examples. Lice species also can cause this symptom.
Ringworm is a fungal skin disease that is caused by one of the dermatophyte fungi. This problem is common in cats, particularly in kittens that come from catteries, shelters, pet stores, or any other place where cats from different sources are co-mingled. Rather than the classic circular, hairless lesion that is seen with some cases of ringworm, miliary dermatitis may be seen.
Pyoderma (bacterial skin infection) is another cause of miliary dermatitis. Pyoderma may be induced by another itchy skin disease that causes breakdown of normal skin defense mechanisms. Additionally, diseases that suppress the cat’s immune system may lead to secondary skin infections. A cat that is sick and has miliary dermatitis should be worked up for an underlying immunosuppressive disease.
Autoimmune skin diseases are rare in cats and may cause miliary dermatitis. Drug reactions may also cause a similar lesion.
Poor nutrition and infestation with intestinal worms may also lead to this symptom.
Stress may lead to excessive grooming and miliary dermatitis. This condition is called psychogenic licking. It is a rare cause of this symptom.
History and physical examination are important in the diagnosis of the underlying cause of miliary dermatitis. The veterinarian will ask when the problem started, whether the cat is scratching, chewing or grooming excessively, and whether the cat feels well or feels sick. The physical exam will look at all body systems, but will concentrate on the skin. The distribution of lesions on the body may lend important clues to the underlying cause. A flea comb will be used to look for fleas and flea dirt.
Skin scrapings are very important to assess for parasites. A scalpel blade is used to scrape a sample from the surface of the skin. Deep skin scrapings are needed to find mites, so your veterinarian will scrape until there is mild bleeding. The sample is then examined under a microscope for mites or other parasites.
A fungal culture is often done to rule out ringworm. Hairs are plucked from lesions and are incubated on a special media. The dermatophyte that is most commonly seen in cats will fluoresce sometimes in ultraviolet light, so your veterinarian may examine the cat’s hair in a dark room with a special light called a Wood’s lamp. A lime-green fluorescence of hair shafts confirms the diagnosis and makes culture unnecessary.
A trichogram is a test where hairs are plucked and examined under a microscope to determine if hairs are falling out, or being broken off. With miliary dermatitis due to an itchy disease, hairs appear broken off due to the self-mutilation. This test may help to determine if a pruritic disease should be pursued.
A food trial should be done if miliary dermatitis continues after the above diseases have been rule out. Food allergy is ruled out by feeding a diet that contains ingredients that the cat has not been previously fed. This diet is fed as the only food source for a period of 6-12 weeks or until the cat stops itching. Individual ingredients from the previous food may then be fed to identify the offending ingredient.
Allergy testing for airborne allergens such as pollens, molds, house dust, and house dust mites may be necessary. The most accurate test in a skin test where different airborne allergens are injected into the skin and the skin is then examine to see if it reacts. A blood test is also available that is more convenient and easier but may not be as accurate.
A skin biopsy may help to narrow down the type of disease causing miliary dermatitis. After general or local anesthesia, one or more sections of skin are taken from the cat using either a special biopsy punch or a scalpel blade. Examination of the biopsy by a veterinary pathologist can categorize the problem as allergic, parasitic, fungal, bacterial, autoimmune or hormonal. More specific tests to confirm the exact diagnosis can then be done.
Blood tests may be needed if the cat is sick to assess the underlying immune problem. Blood chemistry profiles can help rule out diseases of major organs like the liver and kidney. A CBC will assess the health of red blood cells, white blood cells and platelets, and may show evidence of infection or immunosuppression. Viral diseases such as feline leukemia virus and feline immunodeficiency virus should be tested for and ruled out.
One or more of the diagnostic tests described above may be recommended by your veterinarian. In the meantime, treatment of the symptoms might be needed, especially if the problem is severe. The following nonspecific (symptomatic) treatments may be applicable to some, but not all pets with miliary dermatitis. These treatments may reduce severity of symptoms or provide relief for your pet. However, nonspecific therapy is not a substitute for definite treatment of the underlying disease responsible for your pet’s condition.
Strict flea control is nearly always the first step in treating miliary dermatitis since flea allergy is by far the most common cause. Many cats respond to flea avoidance without any other treatment. A single fleabite is all that it takes to trigger the pruritus that leads to the symptom. Therefore, quick-kill flea adulticides that kill fleas before they bite are necessary for success.
Corticosteroids are often used to treat this symptom and are frequently successful due to their ability to relieve pruritus. However, unless the underlying cause is eliminated, the problem is likely to recur. In addition, side effects such as increased thirst and urination, liver and adrenal gland effects, and immune suppression make it important that these drugs be used carefully. They are most valuable as an aid to treatment that concentrates on eliminating the underlying cause.
Antihistamines are helpful in treating pruritus in some cats. Although they are effective in all cats, they are much safer than corticosteroids and therefore, are often tried. There are many of these type of drug that have been tried in cats and some may be effective even when others have not been.
Shampoos that soothe and moisturize the skin may be helpful if you can bathe your cat. These shampoos often contain colloidal oatmeal, which has a soothing effect on the skin. Some shampoos also have topical anesthetics or anti-inflammatory medicines for additional help.
Fatty acid supplements contain fatty acids that modulate the immune system to decrease inflammation.
Your veterinarian may treat for internal parasites or adjust the diet to help improve the general help of the cat. This may be particularly important in cats that are found as strays and have not had the benefit of good veterinary care or proper nutrition.