Small Animal Dermatology, 3rd edition

622 DISEASES/DISORDERS

Dermatohistopathology

 Canine preneoplastic dermatoses:
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

Cutaneous lymphocytosis: perivascular to diffuse infiltration of small lympho-

cytes in the superficial dermis with a zone of acellularity (Grenz zone); nonep-

itheliotrophic; immunohistochemistry demonstrates CD3+T cells; clonality sup-

ports the potential for neoplastic cell population

Cutaneous mastocytosis: perivascular to diffuse infiltration with well-

differentiated mast cells

Nodular fasciitis: poorly demarcated and disorganized accumulation of spindle

cells attached to fascia; highly vascular; immunohistochemistry consistent with

fibroblasts.

 Canine paraneoplastic dermatoses:
Cutaneous (primary nodular) amyloidosis: accumulations of amorphous-

appearing eosinophilic deposits in beta-pleated configuration (electron

microscopy); associated with plasma cells; deposits may be surrounded by

macrophages and giant cells; immunohistochemistry demonstrates amyloid

derived from light-chain immunoglobulin

Cutaneous mucinosis (secondary): epidermal hyperplasia; accumulations of

pale substance (mucin) between collagen fibers in the superficial dermis with

scattered focal, large accumulations; minimal inflammation unless associated

with concurrent dermatitis

Multiple collagenous nevi: nodular dermatofibrosis: increased and thickened

collagen bundles (nodular collagen hyperplasia); subcutaneous lesions may be

well demarcated as opposed to less distinct dermal lesions; collagen bundles sur-

round adnexal structures

Paraneoplastic pemphigus: transepidermal pustulation with suprabasilar and

superficial acantholysis; prominent apoptotic keratinocytes; dermal or submu-

cosal infiltrate of lymphocytes, macrophages, and plasma cells; variable numbers

of neutrophils

Superficial necrolytic dermatitis: parakeratosis and neutrophilic crusting; pallor

of epidermis above the basal layer due to intracellular and intercellular edema;

hyperplastic basal cell layer producing a distinctive “red/white/blue” pattern;

clefting within the epidermis; mild neutrophilic superficial to perivascular der-

mal infiltrate; marked parakeratosis with absence of epidermal pallor noted in

chronic cases.

 Feline preneoplastic dermatoses:
Actinic keratoses: similar to canine
Cutaneous lymphocytosis: moderate to marked perivascular to diffuse, superfi-

cial and deep, round cell infiltrate consisting primarily of T cells; small aggre-

gates of B cells; mild epitheliotrophism; occasional excoriation noted.