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P. Prelaud - E. Guaguere

Diagnostic approach to facial dermatoses

Facial dermatoses are a very important and diverse group of diseases. In some cases, the face is affected directly whereas in others, facial involvement is a conseąuence of systemie disease. One reason why the face is freąuently involved is that it is a very exposed part of the body, not easy to groom, and with sparse hair covering offering scant protection. Mucocutaneous junctions (e.g. lips, nose and eyelids) are predisposed to infectious, parasitic and immune-mediated dermatoses.

There is such a plethora of potential causes of facial dermatoses (Table 23 : 1) that a very rigorous and methodical diagnostic approach is essential. The history and clinical examination (generał and dermatological) are used to formulate a differential diagnosis, which can be narrowed down by performing well-chosen diagnostic tests. That said, the main facial dermatoses (excluding those of the extemal ear) are dermatophytosis, allergic dermatoses, superficial pemphigus conditions and sąuamous celi carcinoma.

History

The history helps to steer the clinician towards particular differentials. It is a vital step in the diagnostic process. Important points to consider are :

Breed: Persians are predisposed to dermatophytosis and also, because of their nose and lacrimal duet conformation, to superficial bacterial (e.g. Staphylococcus spp.) and fungal (e.g. Malassezia spp.) skin infections^K2. A condition called idiopathic facial dermatitis has also recently been described in this breed³. The Siamese is predisposed to vitiligo⁴ (Fig. 23 : 1) and to “histiocytic” mast celi tumour⁴. Urticaria pigmentosa has, to datę, only been observed in Sphinx⁵ and Devon Rex cats⁶.

Age of onset: development of a facial dermatosis in a cat under 6 months would suggest congenital hypotrichosis, dermatophytosis ² (Fig. 23 : 2), a parasitic dermatosis ⁷ (e.g. notoedric mange and demodicosis (Fig. 23 : 3)) or an allergic dermatitis^8,9 (e.g. atopic dermatitis (Fig. 23 : 4) and food intolerance (Fig. 23 : 5)). On the other hand, facial lesions (especially when pruritic) in a young adult would initially suggest an allergic dermatitis^8,9 or a viral or post-viral condition (e.g. poxvirus¹⁰ (Fig. 23 : 6), herpesvirus (Fig. 23 : 7) or herpesvirus-associated erythema multiforme (Fig. 23 : 8)). In an older, adult animal, auto-immune dermatoses " (e.g. superficial pemphigus (Figs 23 : 9,10)), dermatoses associated with systemie disease ¹² (Figs 23 : 11,12) or skin tumours¹³ (e.g. sąuamous celi carcinoma, mast celi tumour and cutaneous epitheliotropic T celi lymphoma) (Fig. 23 : 13) would be morę likely.

Sex: entire małe cats, being morę aggressive and likely to come into direct contact with lots of other cats, are morę prone to dermatophytosis, abscesses and “opportunistic” skin infections associated with retrovirus infection.

Life style and environment: feral cats are morę prone to dermatophytosis², parasitic dermatoses⁷ (e.g. notoedric mange, otodectic mange (Fig. 23 : 14) and trombiculiasis), and lesions associated with tick and mosąuito bites⁴ (Figs 23 : 15,16). Contact with wild rodents predisposes hunting cats to poxvirus infection ¹⁰. As for show cats, they are morę prone to dermatophytosis ^l4. In very sunny regions, solar dermatoses (e.g. actinic keratoses and sąuamous celi carcinoma) are especially common in white cats⁴.

Visits to certain countries: a history of foreign travel might suggest notoedric mange or deep mycoses^l4.

Diet: knowing the cat’s diet will allow construction of a suitable elimination diet, where appropriate ^{8 9}.

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