Small Animal Dermatology, 3rd edition

CHAPTER 39 PHOTODERMATOSES 577

 Actinic comedones and furunculosis: deep bacterial, fungal, or mycobacterial furun-

culosis, demodicosis, schnauzer comedo syndrome, endocrinopathy, and neoplasia.

 Actinic keratoses: bacterial furunculosis, lichenoid keratosis, squamous cell carci-

noma, topical drug eruption, and severe contact dermatitis.

 Hemangioma and hemangiosarcoma: bacterial furunculosis, other vascular abnormal-

ities, and nonsolar-induced vascular neoplasia.

 Squamous cell carcinoma: other neoplasia, deep vessel thrombosis, vasculitis, sterile

granulomatous disease, deep bacterial, fungal, or mycobacterial furunculosis.

DIAGNOSTICS

 Cytologic examination of aspirated samples: demonstrates infectious organisms.

 Bacterial culture and sensitivity from draining tracts (recurrent infections).

 Dermatohistopathology of representative tissues necessary to establish diagnosis:
Solar elastosis: replacement of collagen of the superficial dermis by basophilic

fibers; characteristic of UVL damage; may be associated with laminar fibrosis

Solar dermatitis: decreased melanocytes, epidermal hyperplasia, intraepider-

mal edema, apoptotic keratinocytes, thickening or obscuring of the dermal-

epidermal junction, vascular dilation, and solar elastosis

Actinic comedones and furunculosis: epidermal hyperplasia, plugging of follic-

ular ostea and intrafollicular accumulation of keratin debris, perifollicular fibro-

sis, solar elastosis; ruptured comedones produce furunculosis with accompany-

ing dermal inflammation and infiltration with neutrophils (similar to bacterial

furunculosis); should be associated with other photodermatoses

Actinic keratoses: epidermal hyperplasia and dysplasia with severe hyperkerato-

sis and/or “stacked” parakeratosis; keratinocytes appear distorted and/or apop-

totic; perivascular to lichenoid dermal infiltrate with solar elastosis and fibrosis;

absence of invasion through the dermal-epidermal junction

Hemangioma: blood-filled vascular ectasia lined by endothelial cells; endothelial

cells may show varying degrees of atypia representing a continuum from HA to

HSA; less well circumscribed than non-UVL-induced HA; associated with dermal

solar elastosis and fibrosis

Hemangiosarcoma: invasive vascular ectasia not uniformly confined by endothe-

lial cells; endothelial cells demonstrate marked cellular and nuclear pleomor-

phism and mitotic activity; associated with dermal solar elastosis and fibrosis

Squamous cell carcinoma: trabeculae of squamous cells invade into the dermis;

neoplastic cell aggregates; keratin pearls (accumulations of compact keratin);

keratinocyte cellular and nuclear pleomorphism; mitotic activity higher in dogs

than cats; associated with dermal solar elastosis and fibrosis.

THERAPEUTICS

 Avoid exposure to UVL by keeping patients indoors and by applying sunblock.

 Use protective clothing.