JPC SYSTEMIC PATHOLOGY
INTEGUMENTARY SYSTEM
September 2022
I-M36 (NP)

Signalment (JPC #4095878):  6-year-old female spayed Great Pyrenees

HISTORY:  This dog has a history of alopecia and skin crusts of unknown origin.

HISTOPATHOLOGIC DESCRIPTION:  Haired skin: Diffusely there is complete loss of sebaceous glands despite normal numbers of hair follicles and apocrine glands. There are occasional foci of perifollicular lymphocytes, macrophages, and fewer neutrophils that are primarily focused on effaced adnexal structures (perifolliculitis and adenitis). Rarely, follicular epithelium is effaced by moderate numbers of neutrophils and macrophages (mural folliculitis). Occasionally, hair follicles are elongate (“stretched out”). There is moderate epidermal orthokeratotic hyperkeratosis composed of lamellar keratin that extends into and often mildly dilates follicular ostia. Multifocally, hair shafts are engulfed by keratin as they emerge from follicular ostia, forming protruding follicular casts. The epithelium is mildly thinned and diffusely undulant. The superficial dermis multifocally contains low numbers of often perivascular neutrophils, lymphocytes, plasma cells, eosinophils, and mast cells. Apocrine glands are multifocally mildly ectatic.

MORPHOLOGIC DIAGNOSIS:  Haired skin: Sebaceous gland loss, diffuse, severe, with multifocal mild lymphohistiocytic and neutrophilic perifolliculitis, moderate epidermal and follicular ostial orthokeratotic hyperkeratosis, and minimal superficial perivascular lymphohistiocytic dermatitis, Great Pyrenees, canine.

CONDITION:  Sebaceous adenitis

SYNONYMS: Granulomatous sebaceous adenitis

GENERAL DISCUSSION:

• Uncommon skin disease primarily observed in dogs but has been reported in horses, rabbits and cats
• Strong breed predilection for Standard Poodle, Akita, Samoyed, Vizla, Lhasa Apso, Havanese, Dachshunds, and German Shepherd Dogs; sex predilection for males (Standard Poodle, Havanese, Springer Spaniel)
• Young adult to middle-aged animals
• Clinical signs, severity, and lesion distribution varies greatly amongst breeds;
• Secondary pyoderma occurs in over 40% of affected dogs

 

PATHOGENESIS:

• Unknown; not fully characterized; several possibilities include:
  • Immune-mediated destruction of the gland leading to secondary hyperkeratosis
  • Primary keratinization defect, resulting in increased amounts of follicular keratin blocking the sebaceous and causing inflammation of the gland
    • Sebaceous duct/gland structural defect resulting in inflammation directed at free sebum
  • Suggested autosomal recessive inheritance in Standard Poodles and Akitas

 TYPICAL CLINICAL FINDINGS:

• Clinical signs vary greatly amongst dog breeds

 TYPICAL GROSS FINDINGS:

Lesions vary by breed (all have scaling and follicular cast or frond formation):

• Long-coated animals:
  • Thinning of hair coat due to loss of undercoat
  • Adherent scales on the hair shaft and follicular casts are characteristic
  • Severely affected areas are characterized by bilateral alopecia with brittle to broken hairs surrounded by yellow to brown follicular casts
  • Lesions typically located on the dorsal trunk, face, temporal region, and pinnae
• Short-coated animals:
  • Early alopecia with expanding and coalescing patches of scales on the ears and dorsum that progress to annular lesions on the trunk and head
  • Secondary bacterial folliculitis is rare

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Early lesions: granulomatous to pyogranulomatous inflammation centered on sebaceous glands
• Chronic lesions: sebaceous adenitis eventually leads to diffuse absence of sebaceous glands, which is the most common histopathologic feature in chronic disease, +/- perifollicular fibrosis; multiple skin biopsies are required to confirm widespread absence of sebaceous glands throughout animal
• Hair follicles commonly assume a “stretched out” appearance and are filled with keratin
• Occasional regeneration of sebaceous glands has been reported
• Breed differences:
  • Long-coated animals: Complete sebaceous gland destruction with little residual inflammation
  • Short-coated animals:
    • Higher degree of inflammation with slow destruction of sebaceous glands
    • Secondary folliculitis from impingement of follicular epithelium

DIFFERENTIAL DIAGNOSIS:

Gross differential diagnoses, hyperkeratotic lesions (scaling):

• Ear margin seborrhea
• Vitamin A responsive dermatosis

Histologic differential diagnoses, sebaceous gland destruction/absence:

• Secondary to inflammation in close proximity to sebaceous glands:
  • Generalized demodicosis (I-P07)
  • Cutaneous leishmaniasis (I-P15)
  • Exfoliative cutaneous lupus erythematosus in German shorthaired pointers
  • Uveodermatologic syndrome
• Normal anatomic site variation: footpads and nasal planum are normally devoid of sebaceous glands, glabrous skin contains rare sebaceous glands

Other causes of perifolliculitis/mural folliculitis:

• Granulomatous mural folliculitis: specific to dogs
• Pseudopelade: mural folliculitis
• Reactive histiocytosis (I-M10): angiocentric atypical histiocytic proliferation
• Feline thymoma-associated exfoliative dermatitis (H-N01)

COMPARATIVE PATHOLOGY:

• Cats:
  • Multifocal circular areas of alopecia with crusting, scaling, and follicular casts on the head, pinnae, and neck that start on the head and spread caudally
  • Dermatophytosis (I-F11) is the prime differential, skin biopsy required to differentiate
• Horses: Nonpruritic progressive patches of scaling, alopecia, crusting, and leukoderma
• Rabbits: Seen in pet rabbits with exfoliative dermatosis lesions
  • Non-pruritic scaling dermatosis with alopecia and scaling lesions
  • Hyperkeratosis, follicular dermatitis, interface folliculitis, and reduction in sebaceous glands with destruction and lymphocytic infiltration, and perifollicular to diffuse dermal fibrosis seen histologically
  • Differentials include malnutrition, ectoparasitism, dermatophytosis
  • Exfoliative dermatosis often associated with thymoma, cutaneous lymphoma, and autoimmune hepatitis

REFERENCES:

1. Barthold SW, Griffey SM, Percy, DH. Pathology of Laboratory Rodents and Rabbits. 4^th Ames, IA. Wiley Blackwell; 2016:309.
2. Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Diseases of the dermis. In: Skin Diseases of the Dog and Cat. 2nd ed. Ames, IA: Blackwell Publishing; 2005: 186-188.
3. Mauldin EA, Peters-Kennedy J. Integumentary system. In: Maxie MG ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. New York, NY: Elsevier; 2016:517, 551-552.
4. Miller WH, Griffin CE, Campbell CL. Muller and Kirk’s Small Animal Dermatology. 7th ed. St. Louis, MO: Elsevier; 2013:695-699, 869.
5. Welle MM, Linder KE. The Integument. In: Zachary JF, eds. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier Inc; 2022:1246-1247.

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