JPC SYSTEMIC PATHOLOGY
INTEGUMENTARY SYSTEM
September 2022
I-M34

Signalment (JPC #2812885-01):  Military working dog

HISTORY:  None provided

HISTOPATHOLOGIC DESCRIPTION:  Haired skin:  The superficial and deep dermis is markedly expanded by a nodule composed of abundant dense collagen that widely separates adnexa and elevates the overlying epidermis; this collagen is organized into dense bands that often orient perpendicularly to the epidermis and parallel to the hair follicles (vertical streaking). Multifocally, the dermis is expanded by dense inflammatory infiltrates centered on ruptured hair follicles and free hair shafts (furunculosis); these infiltrates are composed of many viable and degenerate neutrophils, lymphocytes, plasma cells, and macrophages. Intact hair follicles are markedly elongated, ectatic, and distorted (follicular dysplasia), lined by hyperplastic epithelium, and filled with lamellated keratin debris and fragmented hair shafts admixed occasionally with degenerate neutrophilis and small colonies of 2 um cocci (luminal folliculitis). Multifocally, the overlying epidermis is moderately hyperplastic with acanthosis that forms papillomatous projections, short anastomosing rete ridges, and compact orthokeratotic hyperkeratosis. Multifocally, there is deposition of melanin granules in all layers of the epidermis (hyperpigmentation), and within the superficial dermis, there are scattered melanin laden macrophages and free melanin granules (pigmentary incontinence). Apocrine glands are multifocally ectatic, filled with an amphiphilic homogenous material (inspissated secretory product), and surrounded by aggregates of lymphocytes and plasma cells (perihidradenitis).

MORPHOLOGIC DIAGNOSIS:  Haired skin:  Furunculosis, pyogranulomatous, multifocal, marked, with focally extensive dermal fibrosis with vertical collagen streaking, moderate epidermal and follicular hyperplasia, orthokeratosis, lymphoplasmacytic perihidradenitis, and mild luminal folliculitis with bacterial cocci, breed unspecified, canine.

CONDITION:  Acral lick dermatitis

SYNONYMS:  Acral lick granuloma, acral pruritic nodule, neurodermatitis

GENERAL DISCUSSION:

• Common syndrome characterized by incessant licking and chewing resulting in self-mutilation
• Seen in male dogs 2x > female dogs, but can occur in either sex of any breed
• Most commonly seen in large active-breed dogs < 5-year-old
• Predisposed breeds: German shepherd dog, Rottweiler, and golden retriever

PATHOGENESIS:

• Multifactorial, often categorized as a primary behavioral dermatosis (e.g. obsessive-compulsive disorder, boredom, separation anxiety) +/- underlying organic disease (e.g. allergic disorders, hypersensitivity reaction, bacterial or fungal infection, parasitic disease, trauma, orthopedic disease, neoplasia, or neuropathy)
• Endorphin release during licking may propagate the itch-lick cycle
• May lead to secondary deep pyoderma, further perpetuating clinical signs and drives and maintains itch-lick cycle
• Often there is secondary traumatic furunculosis (displaced free hair shafts deep to follicle)

TYPICAL CLINICAL FINDINGS:

• Persistent licking and chewing, most common on the cranial aspect of the distal forelimb (carpus, metacarpus, radius) > hindlimbs (tibia and metatarsus)
  • Acral = extremity or apex

TYPICAL GROSS FINDINGS:

• Ovoid, erythematous, firm, well-circumscribed, 2-6 cm diameter, haired or hairless, scaly to crusted, patch or plaque
  • Usually solitary, occasionally multiple
• +/- ulcerated center surrounded by a raised ridge (indicates chronicity)
• +/- saliva staining of surrounding hair
• Re-epithelialization of lesion > well-circumscribed, alopecic plaque +/- peripheral hyperpigmentation

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Epidermis: Markedly hyperplastic epidermis that can fold and form papillomatous projections; prominent rete ridge formation; compact orthokeratotic that extends to hair follicle infundibula; erosions and ulcers are common; often no crusts due to constant licking
• Dermis: superficial +/- deep fibrosis with vertical alignment of collagen between rete ridges (vertical streaking), +/- vertical alignment of capillaries
• Follicles: Sebaceous glands and hair follicle infundibula are hyperplastic; parafollicular plasmacytosis; apocrine glands mildly dilated with inspissated bluish secretions with mixed periglandular lymphoplasmacytic to neutrophilic inflammation; secondary bacterial folliculitis and furunculosis; scarring in chronic and severe lesions may destroy the adnexa

ADDITIONAL DIAGNOSTIC TESTS:

• Bacterial culture
• Cytology: Mixed population of mononuclear inflammatory cells, including plasma cells, and intermediate squamous epithelium (related to acanthosis)
  • During healing cytology may yield fibroblastic cells (plump, fusiform) and numerous erythrocytes (increased vascularization)

DIFFERENTIAL DIAGNOSIS:

• For gross and/or histopathological findings: deep pyoderma, bacterial furunculosis, fungal granulomas, dermatophytosis, demodicosis, neoplasia, fibroadnexal dysplasia, collagenous hamartoma
• Other psychogenic disorders in dogs: tail biting (young, long-tailed, long-haired); tail dock neuroma (nerve nodule, Cocker spaniel); flank sucking (Doberman pinscher); self-nursing (females); anal licking (poodle); foot licking (atopy, Malassezia)

COMPARATIVE PATHOLOGY:

• Cats: psychogenic alopecia and dermatitis (excessive grooming, anxiety);
  • Most common in indoor cats and oriental breeds
  • Two clinical forms:
    • Psychogenic dermatitis: lesions grossly resemble eosinophilic plaques
    • Alopecic form: regional hypotrichosis and normal skin
  • Tail sucking (Siamese)
• Horse: equine self-mutilation syndrome
  • No primary lesion, but secondary excoriation may be present

REFERENCES:

1. Mauldin EA, Peters-Kennedy J, et. al. Integumentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Elsevier Saunders; 2016:561-562.
2. Raskin RE, Conrado FO. Integumentary System. In: Raskin RE, Meyer DJ, Boes KM, ed. Canine and Feline Cytopathology. 4th ed. Elsevier; 2023:35, 38.
3. Welle MM, Linder KE. The Integument. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. Elsevier; 2022:1235-2136.

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