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A Practical Guide to Feline Dermatology

Diagnosis

The diagnosis is based on lesion distribution, skin biopsies, and identification of the bacteria by anaerobic bacterial culture.

Cytological examination of grains reveals filamentous bacteria.

Histopathological examination of deep skin biopsies reveals a nodular or diffuse dermatitis and/or a pyogranulomatous panniculitis in which grains are seen in about 50% of cases. These basophilic grains are surrounded by a Splendore-Hoeppli reaction. Bacteria are not always elear on standard stains.

Prognosis and treatment

The prognosis is guarded, given the very high incidence of recurrence \

Treatment reąuires broad surgical excision, where possible, or debridement with curettage and antiseptic flushing. This treatment must be accompanied by very long courses (3-4 months) of antibiotics, based on sensitivity testing. Penicillin G (100,000 IU/kg SID or BID), given by intramuscular injection, may be continued for one month after clinical resolution²¹ (Table 6:1).

Botryomycosis

Aetiopathogenesis

Botryomycosis is a ubiąuitous and under-diagnosed skin infection, caused by non-filamentous bacteria. Colonies form grains within pyogranulomatous reactions. Various agents are responsible (Staphylococcus spp., Streptococcus spp., Pseudomonas spp., Proteus spp. and Actinobacillus spp.) and sometimes they may be found in combination.

Pathogenesis of these lesions is poorly understood. Bacteria entering subcutaneous connective tissue via a wound (e.g. bite or scratch) probably trigger a hypersensitivity reaction and an alteration in the destructive role of leucocytes. Retrovirus infections might sometimes predispose to botryomycosis³.

Clinical features

Dermatological signs are often chronic and occur mainly on the limbs. They are characterised by single or multiple, uleerated or non-ulcerated, alopecic nodules, containing smali white or yellow grains (Fig. 6 : 15). Ulcers or draining tracts may sometimes be seen.

Systemie signs vary according to the presence of an underlying illness (e.g. retrovirus infection). Diagnosis

The diagnosis is based on lesion distribution, skin biopsies, and identification of the bacteria by bacterial culture.

Cytological examination of grains (after crushing) reveals very large numbers of non-branching bacteria.

Histopathological examination of deep skin biopsies reveals a pyogranulomatous dermatitis, within which there are bacterial colonies surrounded by a Splendore-Hoeppli reaction, composed of polysaccharides and glycoproteins around the bacterial colonies (Fig. 6 : 16).

Bacterial culture is performed on skin biopsies, taken aseptically, and inoculated onto various media. Antibiotic sensitivity testing should be conducted.

Prognosis and treatment

The prognosis is variable, depending on the presence of an underlying illness.

Treatment reąuires broad surgical excision, where possible, or lesion debridement with curettage and antiseptic flushing. This treatment must be accompanied by antibiotic therapy, based on sensitivity testing (Table 6:1). Most antibiotics penetrate these lesions poorly.