PC SYSTEMIC PATHOLOGY
INTEGUMENTARY SYSTEM
September 2022
I-M09 (NP)
Signalment (JPC #1901146): 8-year-old female spayed schnauzer
HISTORY: This dog had chronic dermatosis.
HISTOPATHOLOGIC DESCRIPTION: Haired skin, site not specified: Diffusely, superficial follicular infundibula and ostia are moderately expanded by eosinophilic lamellations of keratin and keratin debris (comedones) with fragmented or missing hair shafts and lined by markedly attenuated epithelium. Multifocally, the epidermis is mildly hyperplastic with moderate orthokeratotic hyperkeratosis. Melanin pigment is present diffusely throughout all layers of the epidermis (hyperpigmentation) as well as free within dermis (pigmentary incontinence) and within keratin debris. Within the superficial dermis there are low numbers of mast cells and rare plasma cells. Dermal collagen fibers are often separated by a basophilic, fibrillar to beaded material (mucinosis). Diffusely, apocrine glands are mildly to markedly ectatic, lined by attenuated epithelium, and variably filled with a pale eosinophilic material (secretory product).
MORPHOLOGIC DIAGNOSIS: Haired skin, site not specified: Follicular infundibular hyperkeratosis and ectasia (comedones), diffuse, moderate, with orthokeratotic hyperkeratosis, Schnauzer, canine.
CONDITION: Schnauzer comedo syndrome
GENERAL DISCUSSION:
- Typically asymptomatic skin disease seen exclusively in young adult miniature schnauzers and their related crossbreeds (similar to nevus comedonicus in humans)
- There is no age or sex predilection
- A comedo is defined as a cystically dilated, keratin-filled hair follicle; follicular distension occurs due to accumulated infundibular stratum corneum and sebum within the lumen of the hair follicle
PATHOGENESIS:
- It is an infundibular keratinization defect due to either an inherited follicular dysplasia or follicular disorder of cornification with an unknown mode of inheritance
- Abnormal cornification results in comedone formation and follicular plugging; can lead to secondary bacterial infections
TYPICAL CLINICAL FINDINGS:
- Typically asymptomatic
TYPICAL GROSS FINDINGS:
- Characterized by multiple small comedones over the dorsal midline
- Secondary bacterial folliculitis, furunculosis, and crusting is common
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Marked orthokeratotic hyperkeratosis
- Dilation and plugging of hair follicles by infundibular stratum corneum and sebum (comedones) with narrow (closed) ostia
- Variable inflammation ranging from none to folliculitis and furunculosis (deep pyoderma) with marked foreign body inflammatory response and secondary bacterial infection
DIFFERENTIAL DIAGNOSIS:
- Multiple comedones on the dorsum of a miniature schnauzer is essentially diagnostic for this disease
- Comedones without the characteristic dorsal distribution can be seen in various breeds secondary to primary seborrhea, hyperadrenocorticism, actinic comedones, canine acne, canine calluses and pyoderma, hypothyroidism and vitamin A responsive dermatosis
COMPARATIVE PATHOLOGY:
- Schnauzer comedo syndrome occurs exclusively in the miniature schnauzer
REFERENCES:
- Mauldin EA, Peters-Kennedy J. Integumentary system. In: Maxie MG Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Elsevier; 2016: 524, 549.
- Welle MM, Linder KE. Integumentary system. In: Zachary JF, Pathologic Basis of Veterinary Disease. 7th ed. Philadelphia, PA: Elsevier; 2022: 1109, 1149, 1235.
