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A Practical Guide to Feline Dermatology

ulcerated. Lesion distribution is multicentric but involves mostly the face, shoulders and limbs ¹⁸'²¹. The diagnosis is based on histopathological examination of lesions which reveals moderate to severe epidermal dysplasia with loss of polarity, variations in the association between nucleus and cytoplasm, variable mitotic figures, isolated dyskeratotic keratinocytes and an absence of rupture in the basement membranę

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Retrovirus infections

Retrovirus infections are the most serious and most common viral illnesses of the cat. They are caused by

two retroviruses: the leukaemia virus (FeLV)²¹ and the feline immunodeficiency virus (FIV)²². Although

human immunodeficiency virus (HIV) is responsible for many, varied skin problems in man ²³, FeLV and

FIV are much morę rarely associated with skin disease in cats.

Skin diseases caused directly by FeLV yirus

A giant celi dermatosis has been reported in FeLV-positive cats. This is a pruritic dermatosis of the face (e.g. eyelids, area behind the ears, chin and lips), pinnae (ulcerative otitis), neck and sometimes trunk, characterised by alopecic, scaling and crusting lesions (Figs 7 : 13,14) ^M. Systemie signs (anorexia, lethargy, weight loss) were seen. The cats died or were euthanased within 4 months. Histopathology of skin biopsies revealed syncytial-type giant cells in the epidermis and follicular outer root sheath. Some of these contained up to thirty nuclei and had abundant eosinophilic cytoplasm. In these areas, there was local absence of keratinocyte maturation along with dyskeratosis of keratinocytes, and sometimes of giant cells (Figs 7 : 15,16). Immunohistochemical studies using gp70 antiserum demonstrated the presence of gp70 antigen in all cats, solely in the areas containing giant cells. Immunohistochemical studies from the skin of FeLV-positive cats without the giant celi dermatosis, did not demonstrate gp70 antigen in the skin. The FeLV virus may have induced a neoplastic alteration of the keratinocytes, by recombination with host oncogenes. The presence of many dyskeratotic keratinocytes is also a sign of neoplastic alteration ²⁴.

Epidermal horns may also be seen in FeLV-positive cats^25,2Ć. These homs, single or multicentric are found mainly on the footpads (Figs 7:17) and sometimes on the face. Histopathology reveals severe, compact orthokeratotic hyperkeratosis (Figs 7 : 18), and in some cases, dyskeratosis and epidermal multinucleate giant cells. Treatment involves surgical excision. These horns resemble other keratinisation disorders such as acąuired ichthyosis or Reiter’s syndrome seen in human AIDS patients ²³. These hyperproliferative dermatoses might be the conseąuence of the same pathophysiological mechanism. It is unknown whether stimulation of keratinocytes is caused directly by the virus or by cytokines released by monocytes or T lymphocytes infected by the HIV virus²³.

Vasculitis associated with FeLV infection has recently been described²⁷. It is characterised by severe necrosis (Fig. 17:19) of the pinnae and tip of the taił (Fig. 7:20). Systemie signs (e.g. pallor of the mucous membranes) may also be seen. Histopathology of peri-lesional skin biopsies reveals leucocytoclastic vasculitis and evidence of vascular thrombosis (Figs 7 : 21,22). Immunohistochemistry using gp70 antibodies demonstrates the presence of the gp70 antigen in the skin and in many blood vessels, both damaged and healthy. This suggests that the necrosis of the pinnae and taił tip is probably due to an immune-complex vasculitis²⁷.

Dermatoses induced by B lymphocyte activation

In feline retrovirus infections, humoral immune system derangement leads to B lymphocyte activation ^2U2. This can sometimes cause plasma celi infiltration in the mouth (plasma celi stomatitis), footpads (plasma celi pododermatitis) and the pinnae (plasma celi chondritis). It should, however, be noted that nonę of these skin and mucous membranę plasma celi proliferative lesions is related specifically to feline retrovirus infection. As a generał rule, plasma celi infiltration should be treated as a chronic reaction pattern that may arise in response to various different antigens (bacteria, viruses, etc...)

Plasma celi stomatitis is characterised by painful proliferative lesions on the palatoglossal folds and arches. It causes anorexia, halitosis, excessive salivation and weight loss, often with associated gingivitis and stomatitis. These proliferative lesions have a tendency to uleerate and

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