Pimples: Pustules And Papules
A pustule is a small, elevated, pus-filled pimple. A papule is a small, elevated pimple filled solidly with inflammatory cells. When they burst they lead to skin erosion. Inflammation is part of natural repair but it leaves the skin prone to infection. Bacterial skin disease is, overwhelmingly, the most common cause of pustules and papules. Within the skin, specialised cells called mast cells, part of the immune system, act as 'gatekeepers' regulating response to threats. Mast cells are like chemical factories. Their chemicals are very efficient for disease and parasite control but trigger local inflammation. Another population of defence cells called memory T cells monitor the skin surfaces for dangerous microbes they have met before. Skin infections start as pustules or papules but within a day these erode and change to scales and crusts, then erosions and skin ulcerations. Minor superficial bacterial and fungal infections are relatively harmless to dogs because skin is constantly being sloughed off from the top and replaced by new healthy skin from below. Licking helps sloughing.
Scales And Crusts
Scales are bits of the surface of the skin. They may flake off as particles of dandruff or remain, building up as calluses. Scaling is often associated with increased activity of the skin's oil-producing sebaceous glands. This is called "seborrhea". In "dry seborrhea" there is increased flaky scaling while in "wet seborrhea" scale is retained in skin oil, producing a greasy, smelly coat. Crusts are produced as a consequence to skin inflammation. Crusts consist of serum, blood and inflammatory cells.
General Bacterial Skin Infection - Pyoderma
Bacteria are very much the most common cause of crusting skin conditions and in most instances multiply because other conditions allow them to. Superficial infection initially causes pustules and pimples rapidly leading to crusting. The hair follicles can be infected (folliculitis). Deep infection causes more generalised inflammation, redness and crusting. A diagnosis is made by culturing the skin for bacteria or seeing them on skin biopsy. A bacterial sensitivity helps us select the best antibiotic for treatment. In the absence of a bacterial culture and sensitivity, we use cephalosporins and potentiated penicillins as the most frequent antibiotics, for a minimum of two weeks for superficial infections and a minimum of four weeks for deep pyodermas. A long acting antibiotic injection is often used in cats. Antiseptic shampoos are very effective for controlling superficial skin infection in dogs.
Malassezia is usually an opportunist yeast infection, common in dogs with allergic skin disease, much less so in cats. Crusting may occur anywhere on the body, including in the ears. Malassezia is seen under the microscope on skin smears. Sometimes, malassezia may be present without causing disease. A true diagnosis depends upon response to treatment, either with a topical antifungal shampoo such as Malaseb or, for more serious infections, oral antifungal medication such as ketoconozole. The ears often need individual attention.
Erosions And Ulcers
Skin damage has many causes. Superficial damage to papules and pustules is called erosion. When an erosion breaks through the full thickness of skin it is called an ulcer. Bacterial infections begin as pustules on the skin or in hair follicles. These break down creating crusts, eventually leading to more dramatic conditions. The evolution of infection from pustule to erosion can be dramatically fast, less than a day for moist dermatitis. Furunculosis is a deep and severe infection. A bacterial infection of hair follicles (folliculitis) can develop into furunculosis. In its most severe form it occurs in the skin tissue around a dog's anus, causing severe discomfort.
Acute Moist Dermatitis - Hot Spot - Summer Eczema - Wet Eczema
The first sign of this multi-named infection is often a sticky, sometimes smelly mat of hair on the body, being scratched or chewed. When the hair is parted the skin underneath is red, hairless and oozing serum. Whether or not the sore is painful seems to depend upon the individual dog's personality. Hot spots are most likely to occur during humid weather, on longhaired dogs with especially dense coats. The Golden Retriever in particular may have a genetic predisposition to this condition. It is rare in cats. Assume there is some underlying cause that has caused your dog to scratch and develop a hot spot. This condition, fleas for example, should be eliminated. We treat Hot Spots by shaving affected areas and cleansing with topical antiseptics. Oral antibiotics are often used along with corticosteroids and protective collars or neck sleeves applied for a week or more to prevent licking.