Small Animal Dermatology, 3rd edition

CHAPTER 39 PHOTODERMATOSES 575

 Lesions develop in sun-exposed, lightly pigmented or unpigmented skin (naturally

or scarred) in areas not sufficiently protected by hair and in junctions between haired

and nonhaired skin.

 Dogs: nasal planum, dorsal muzzle, axillae, and glabrous areas of the ventral abdomen

and medial thigh.

 Cats: pinnal margins and nasal planum.

 No sex predilection.

 Age: usually older animals; reported as young as 2 years.

 Geographic distribution: higher elevations; animals housed outdoors in tropical,

desert, or mountainous regions.

 Breed predilections: dalmatian, whippet, Italian greyhound, greyhound, American

Staffordshire and bull terrier, beagle, German short-haired pointer, boxer, basset

hound.

CLINICAL FEATURES

 Solar dermatitis (Figures 39.1–39.3):
Extent of damage directly related to duration and intensity of sun exposure
Erythema, swelling, crusting, erosion, ulceration, and exudation
Pruritus variable; develops more in chronic lesions
Vasculopathy may be underrecognized
Lesions may expand as adjacent skin becomes inflamed, depigmented, and

alopecic

Severe cases develop secondary bacterial folliculitis and scarring

Cats: erythema, scaling, scabbing, and thickening of pinnal margins, eyelid mar-

gins, nasal planum, dorsal muzzle, lip margins; white cats; pinnal margins may

curl.

 Actinic comedones and furunculosis (Figures 39.4–39.6):
Seen in conjunction with other chronic actinic dermatoses
Inflamed and dilated follicles with caseous debris result from dermal fibrosis
Nonfolliculocentric dermal cysts and nodules
Ruptured comedones and cysts lead to furunculosis (bacterial)
Scabbing, hemorrhage, and scarring are common sequelae
Large, hemorrhagic bullae develop with chronicity.

 Actinic keratoses (Figures 39.7, 39.8):
Actinic keratoses (AK) may represent a premalignant condition; there is a close

association of and genetic similarities between AK and squamous cell carcinoma

(SCC). Actinic carcinomain situdenotes SCC that has not penetrated to the

dermis

Early erythematous patches appear slightly lichenified or roughened

Epithelial plaques may be palpable as firm thickenings prior to becoming visible

and may be distinguishable from nonthickened (normal) adjacent pigmented

skin

Crusted, indurated, and exfoliating plaques

Severe hyperkeratosis may be seen as cutaneous horns