Infectious skin disease in cats, more than you realized (Proceedings)
Pyoderma and bacterial folliculitis in the dog is considered to be very common problems yet in the cat are described as rare or very uncommon in textbooks on small animal dermatology. A study in France of 783 feline derm cases evaluated between 1992 and 1997 diagnosed pyoderma in 4.7%. Pyoderma does occur in cats and is not rare and similar to dogs is most often a secondary problem. Pyoderma plays a role in feline allergic diseases and as a secondary perpetuating factor in other skin diseases. One reason it may not be recognized as much in the cat in contrast to dogs when an allergic cat with pyoderma has its allergies effectively treated the pyoderma may resolve. Antibiotic therapy is associated with a significant improvement in numerous feline cases that present to dermatology referral practices. Preliminary results of a blinded placebo controlled study on the effects of clavulonic/amoxicillin suggest eosinophilic plaques and lip ulcers are often antibiotic responsive.
Clinical presentations of feline pyoderma are quite variable. For most recognized syndromes there is no age, sex or breed predilections. The more common cases are the superficial pyodermas and folliculitis. Lesions that may be seen include superficial crusts over erosions or papules, moist erythematous erosions, linear crusted erosions and ulcers, moist erythematous plaques. Often these cases are referred in as unresponsive cases of miliary eczema or eosinophilic plaques. In addition many feline indolent ulcers, feline acne and some eosinophilic granuloma have responded to antibiotic therapy. Some cases are seen where antibiotic responsive indolent ulcers may be cured following effective flea control or occur intermittently with allergic flare ups. Another syndrome that is often frustrating to treat but has recently been reported doxycycline responsive is feline plasma cell pododermatitis.[.The diagnosis of pyoderma is based on the demonstration of organisms and neutrophils in the cutaneous lesions. This is most often accomplished by cytological examination of direct smears from the lesions, or less commonly on histopathologic examination of representative lesions. One study evaluated blinded cytology from 9 control cats and 9 cats with eosinophilic cutaneous plaques and 8 eosinophilic lip ulcers. Of the 9 control cats sampled, 0/180 oil immersion fields from skin were infected. Conversely 143/160 (89.4%) day 0 ECP fields from 9 cats were infected. Only 12/180 (6.7%) fields from the upper lip mucosa of control cats were infected, while 129/160 (80.6%) day 0 ELU fields from 8 cats were infected. All 9 ECP and all 8 ELU lesions showed evidence of bacterial infection in at least one field, while none of the 9 normal cats showed skin infection and 3/9 showed mucosal infection. Preferable there will be intracellular bacteria as well and occasionally intracellular bacteria may be seen in macrophages or eosinophils. Some of these cases likely reflect secondary pyoderma and may be more prevalent in cats with chronic skin diseases that have been treated with long term or repetitive glucocorticoid therapy.
Treatment is best accomplished with systemic antibiotic therapy. Therapy is more difficult than in the dog for several reasons. Many cats are more difficult to medicate and the incidence of vomiting or diarrhea is somewhat higher. I generally try amoxicillin trihydrate/clavulanate potassium (Clavamox, Pfizer) 62.5 mg BID, Clindamycin HCL 11-22mg/kg q24h or ormetoprim sulfadimethoxine (Primor, Pfizer) 120 mg once a day as initial empirical therapy. If fluoroquinolones are going to be used I prefer marbofloxacin (Zeniquin, Pfizer) 1.5 to 2.2mg/kg because if has not been shown to cause retinal disease as higher dose enrofloxacin (Baytril, Bayer) may.
Malassezia is a genus of yeast that originally contained three species. M. pachydermatis is found primarily in small animal and is most common though M. sympodialis and M. globosa have also been found in cats with skin or ear disease. Malassezia otitis externa and media is the most common problem in cats. In some cases it will only be found from the middle ear and not the ear canal. No specific studies in Malassezia complicated otitis have been done regarding age, breed or sex predilections. The yeast is considered as secondary causes that lead to the perpetuation of disease. Skin lesions may also be seen with or without concurrent otitis. Early lesions may appear relatively normal or be slightly erythematous. A light gray to yellow scale crust or brown crust is often present. Pruritus is variable but may be intense. In the cat the favorite localized sites are chin (acne differential), face (may complicate idiopathic facial dermatitis), and interdigital. Generalized or regional disease is the least common form in the cat and may be associated with seborrhea oleosa, paraneoplastic alopecia and may carry a poor prognosis. Diagnosis is based on cytology showing Malassezia and any may be significant from skin sites but in ears more that 3 per 1000x (oil immersion field) is needed to be significant.
Topical therapy is not very helpful in cats and systemic therapy is preferred. Systemic therapy is most commonly accomplished with ketoconazole 2.5 - 10mg/kg q24. It is best given with food as an acid gastric environment stimulates absorption. In the rare case ketoconazole is ineffective then itraconazole 5-10mg/kg q24hr or fluconazole 5mg/kg q24h may be used.