Acute Moist Dermatitis

contributed by John Macdonald-Cuordha Goldens

"This disorder is caused by self induced trauma as the patient bites, rubs, or scratches at a part of its body in an attempt to alleviate some pain or itch. The majority of cases are complications of flea bite hypersensitivity, but allergic skin diseases, other ectoparasites, anal sac problems, inflammations such as otitis externa (inflamed ears), foreign bodies in the coat, irritant substances, dirty unkempt coats, psychoses and painful musculoskeletal disorders may be underlying causes. Owners usually believe that some factor producing a diet that is too rich may create the problem, but only a severe, essential fatty acid deficiency has been shown to be a cause. These factors initiate the itch-scratch cycle.

The intense trauma produces sever large lesions in a few hours. Animal particularly disposed to this problems are those with a heavy coat that has a dense undercoat, such as Golden and Labrador Retrievers, German Shepherds, Collies and St. Bernards. The problem is much more common in hot humid weather and may have something to do with lack of ventilation in the coat. A typical lesion is red, moist and oozing. There is a crust of proteinaceous exudate in the center of the area surrounded by a halo of red skin.

The hair is lost from the area, but the margins are sharply defined from the surrounding normal skin and hair. The lesion progresses rapidly if appropriate therapy is not started at once. Much pain is associated with the local area, and this may eventually deter the animal from further trauma. Lesions are often located in close proximity to the primary painful process, i.e., near infected ears, anal sacs and flea bites on the rump.

A study of the type of bacteria found in lesions of pyotraumatic dermatitis reveals multiple organisms, with Staphyloccus intermedius being the most common. It also showed that the St. Bernard and Golden Retriever dogs tended to have a deeper pus producing infection. Diagnosis is made by the history of acute onset, the physical appearance, and the association with a more or less primary cause. If the condition is persistent or recurrent, consider bacterial hair follicle inflammation, fungal infections, demodex infections, yeast infections or neoplasia (lymphosarcoma or sweat gland carcinoma) as differential diagnoses. True pyotraumatic dermatitis is a relatively flat, eroded to ulcerated lesion. Lesions that are thickened. plaque like and bordered by papules (bumps) and or pustules should always suggest a primary eruptive process, especially a staphylococcal infection.

Therapy is effective if applied promptly and vigorously. Sedation or anesthesia is usually needed to allow thorough cleansing of the area. Cleansing is the first and most important step in local therapy. The hair is clipped away from the lesion and the skin is thoroughly cleaned with a mild antiseptic solution or scrub such as povidone-iodine. A single application of 5% tannic acid and 5% salicylic acid in 70% alcohol is used as an astringent. This can be followed by wet soaks with 5% aluminum acetate (Domeboro solution) applied three or four times daily for 10 minutes each time. This action is drying, astringent and antiseptic. Topical application of antibiotic cream three times daily is useful. Five days of systemic corticosteroids in anti-inflammatory doses (prednisolone 1.1 mg/kg SID) is useful in alleviating the pruritis, pain and local inflammation. As the lesion becomes dry and crusted, topical medication should be changed to softening creams and emollients. At the time of the initial treatment, it is most important to find the predisposing factor and eliminate or modify it to stop the patient's reflex self-trauma. The treatment to accomplish this varies, depending on the primary cause.

Clients always clamor for ways to prevent future lesions, since some unfortunate dogs may have repeated problems. There is no simple means of prevention. However, constant attention to grooming, hygiene, baths and parasite control and periodic cleaning of the ears and anal sacs will help. Owners should be particularly vigilant during periods of hot, humid weather. Although diet is often suggested as a cause, except for severe fatty acid deficiency or food hypersensitivity this has never been proven."

The above article was taken from "Small Animal Dermatology, Fourth edition and was authored by Muller, Kirk and Scott.

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