Acne in Dogs
Causes of Acne in Dogs
Onset of the disease occurs between 5 and 12 months of age. Acne in dogs tends to improve with age. Occasionally, it may persist in adulthood. The exact pathogenesis (development of disease) is unknown, but several theories have been formulated, such as the following:
Hormones. Hormones, more specifically androgens (male sex hormones), have been hypothesized to play a role. However, this disease does not seem to have a sex predilection and both females and neutered males may be affected. In addition, hormones would not explain why only short-coated breeds tend to develop acne.
Genetics. Genetics have also hypothesized to play a role to explain why some breeds are at increased risk.
Trauma. It may lead to hair follicle disruption and release of free keratin in the dermis. Keratin, in turn, could trigger an inflammatory response (foreign body response), and the bacteria present in the hair follicle would cause a deep bacterial infection (furunculosis).
Bacteria. The role of bacteria appears to be secondary, because at the onset of the disease the lesions are sterile, and antibiotic therapy does not significantly improve the clinical signs.
Keratinization. Canine acne does not appear to be a disease of keratinization. Excessive sebum production and sebum breakdown to free fatty acids was hypothesized to induce inflammation and comedo formation. However, in one study, where the lipids obtained form the skin of healthy controls and dogs with acne were evaluated, it was found that the lipids obtained from the acne lesions, such as free sterols, fatty acids, and ceramides, are characteristic epidermal lipids and that sebaceous gland contribution is minimal.
Diagnosis In-depth of Canine Acne
Diagnosis of chin acne is based on history and clinical signs. Additional tests may include:
Deep skin scrapings to rule out the possibility of demodicosis. If a deep pyoderma is present, skin scrapings may be falsely negative due to easy bleeding of the lesions with the scraping, and a biopsy may be necessary to rule out demodicosis.
Fungal culture of hairs
Cytology exam if pustules or draining tracts are present. This gives information on the presence and type of secondary infection. Pustules can be gently opened with a needle and the content smeared on a glass slide. Swabs should be used to collect the material from draining tracts and rolled onto glass slide. Common findings are degenerated neutrophils, eosinophils (typical finding of furunculosis), macrophages and small number of intracellular bacteria (most commonly cocci).
Tape preparation from the muzzle to reveal a secondary yeast (Malassezia) infection.
A biopsy for culture and sensitivity in chronic cases. The area is surgically disinfected and samples are obtained in aseptic conditions to avoid contaminating the culture material.
Biopsy to revealss follicular dilation and keratosis (comedo) and pyogranulomatous folliculitis and furunculosis. The infiltrate is composed of neutrophils and macrophages and is focused on the hair follicles. Sebaceous glands are large and ducts may be dilated.
Treatment In-depth of Canine Acne
In mild cases topical therapy may be sufficient. Topical therapy should be done gently, but avoid aggressive scrubbing of the lesions to limit scar formation.
Benzoyl peroxide gel (5 percent, Oxydex® gel, Pyoben® gel) may be used daily on affected areas. Benzoyl peroxide combines a good antibacterial action against Staphylococcus with a follicular flushing property, which helps in cases of comedones. It could be irritating and some dogs may worsen with this therapy. Prolonged use may also cause excessive drying of the skin and subsequent irritation. Benzoyl peroxide can also be used as a wash at lower concentration (2.5 percent, Oxydex® shampoo). Area should be washed twice weekly with a contact time of 10 minutes.
Mupirocin (2 percent ointment, Bactoderm®) is also effective against localized bacterial infections, especially against Staphylococcus, and has good penetration in the skin. It is bacteriostatic rather than bactericidal, in that it inhibits the growth of bacteria rather than killing the organisms, although high concentrations may be bactericidal. It should be used once or twice daily. Resistance may develop if mupirocin is used over a prolonged period of time. Mupirocin has little potential of causing systemic toxicity of sensitization.
Topical fusidic acid has also good activity against Staphylococcus and could be useful in dogs with chronic acne. Fusidic acid is lipophilic so it has the ability to penetrate the tissues. It is not available in the United States, but it is readily available in combination with bethametasone in United Kingdom and other countries. Studies of the percutaneous absorption of fusidic acid in canine skin demonstrated that therapeutic levels are obtained in the skin within a few hours after application and can be maintained with a twice daily dosing. Irritation or sensitization is extremely rare.
Topical glucocorticoids like Synotic® may help to decrease the inflammation and the granulomatous infiltration triggered by the keratin.
In severe and chronic cases systemic antibiotic therapy is necessary. Antibiotics with activity against Staphylococcus like oxacillin are good empirical choices. In complicated cases a culture and sensitivity may be necessary and broad-spectrum antibiotics such as enrofloxacin, may be more appropriate choices.
The duration of the systemic antibiotic therapy depends on the severity and depth of the lesions. Chronic cases may require 6 to 8 weeks of antibiotics.
In cases complicated by secondary yeast infection antifungal therapy may be necessary. Depending on the severity and the number of yeast found on they cytology exam, either topical or systemic therapy can be used. Topical preparations effective against Malassezia include miconazole and clortrimazole, which are available as lotions or creams. Topical therapy should be used twice daily for a minimum of two weeks. In severe cases oral ketoconazole for two weeks may be necessary.
Retinoids are not recommended for canine acne, as it is believed not to be a disease of keratinization.