Comedones (blackheads) are the first lesions noted on the chin. They result from follicular dilation and plugging with excessive keratin formation. Erythema and alopecia may be present in more advanced cases.
A brown/black discharge may be prominent in cats with a secondary Malassezia infection. Papules, pustules, firm nodules and fistulous tracts may develop as a consequence of a bacterial infection (folliculitis and furunculosis). Lesions ulcerate and discharge a purulent exudate.
Swelling of the chin is variable but it could be severe in some cats. Regional lymphadenopathy (swollen lymph nodes) may be prominent and pain and itchiness may be intense in cats with a secondary skin infection. Cysts may develop in chronic cases.
Diagnosis of acne is usually based on physical examination findings. Sebaceous (oil) glands are usually enlarged. Differential diagnoses include dermatophytosis (fungal infections), and feline demodicosis (mange). Eosinophilic granuloma may be considered as a differential diagnosis in cats with a swollen chin.
Tests may include:
- Deep skin scrapings to rule out demodicosis, skin cytology to evaluate secondary bacterial and yeast infections and fungal culture to rule out dermatophytosis
- Skin biopsy to reveal follicular dilation and keratosis (comdeones). Folliculitis and furunculosis may be present in animals with a significant bacterial infection. Yeast organisms may be visible inside the follicles. The inflammatory infiltrate is mainly composed of neutrophils and macrophages and is focused on the hair follicles.
In mild cases topical therapy may be sufficient. Topical therapy should be done gently and aggressive scrubbing of the lesions should be avoided to limit scar formation. It could exacerbate the inflammation. Clipping of the area may be helpful to increase the efficacy of topical therapy. Additional treatment may include:
- Soaks with Epsom salts to help promote drainage of the lesions
- 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. Benzoyl peroxide may also be used as a shampoo once or twice weekly. It could be irritating in some animals.
- Antiseborrheic shampoos (e.g. SulfOxyDex®) to remove crusting and excessive sebum from the skin
- Tar should not be used in cats due to its toxicity in this species.
- Another topical product that is effective in feline acne is mupirocin (2 percent ointment, Bactoderm®). The efficacy was evaluated in an open, prospective study and mupirocin was used twice daily for three weeks in 25 cats with acne. Excellent response was reported in 15 out of 25 cats while good response was observed in 9 out of 25 cats. Treatment was discontinued in one case due to local irritation. Resistance may develop with prolonged use.
- Topical clindamycin (Cleocin®) has been reported to be very effective in cases of feline acne is a small preliminary study.
- Topical glucocorticoids (e.g. Synotic®) to decrease the inflammation and the granulomatous infiltration triggered by the keratin.
- Topical vitamin A and topical retinoids
- Topical metronidazole
- Topical preparations effective against Malassezia include miconazole and clotrimazole. They are available as lotions or creams. Topical therapy should be used twice daily for a minimum of two weeks.
- Selenium disulfide is a good antiseborrheic product effective for yeast infection but it should not be used in cats, due to its potential for toxicity in this species.
- Retinoids have been tried and been successful in about 30 percent of the cases of feline acne. They work by normalizing epidermal proliferation and decreasing sebum production.
Systemic treatment in severe cases
The duration of the systemic antibiotic therapy depends on the severity and depth of the lesions (average case may require 3 to 4 weeks of antibiotic).
- Antibiotics with activity against Staphylococcus and Pasteurella (e.g. amoxicillin/clavulanic acid)
- If severe inflammation is present systemic glucocorticoids may be needed. A 10 to 14 day course of oral prednisone is usually sufficient to decrease swelling and pain in affected cats.
- In cases complicated by secondary yeast infection, antifungal therapy may be necessary. Depending on the severity and the number of yeast found on cytology either topical or systemic therapy can be used.
- Oral itraconazole is preferred over ketoconazole as it is better tolerated in cats. It should be given for at least two weeks. Itraconazole is available as a solution (Sporonox®), which makes administration to cats easier. Adverse effects of itraconazole therapy include anorexia, vomiting, and diarrhea. Griseofulvin is not an effective treatment for yeast infection.
- Clinical response is usually seen within 30 days. Oral isotretinoin (Accutane®) is the one most commonly used. Animals that respond to this therapy may require it as a life long treatment.