September 2019

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). Multifocally, the epidermis is mildly hyperplastic with moderate orthokeratotic hyperkeratosis. Often, hair shafts are missing or fragmented and follicular infundibula are lined by markedly attenuated epithelium. Melanin pigment is present diffusely throughout all layers of the epidermis (hyperpigmentation) as well as the dermis (pigmentary incontinence), and melanin is occasionally present within the sloughed 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



·      Common, typically asymptomatic skin disease seen exclusively in miniature schnauzers and their related crossbreeds

·      There is no age or sex predilection

·      A seemingly identical syndrome is seen occasionally in Cairn terriers and other rough-coated terriers

·      A comedo is defined as a cystically dilated, keratin-filled hair follicle



·      Exclusive occurrence in miniature schnauzers and early onset suggests a developmental dysplasia of hair follicles with an inherited basis

·      Results in abnormal keratinization with subsequent comedo formation, follicular plugging and often secondary bacterial folliculitis



·      Restriction of lesions to the caudal dorsum of a miniature schnauzer (with no other signs of disease) is virtually pathognomonic of the condition

·      Comedones palpate as sharp, crusted, papular projections above the skin surface; however, some may feel soft and waxy

·      Pruritus uncommon, unless perifolliculitis, folliculitis, or furunculosis develops from secondary bacterial infection



·      Characterized by multiple comedones over the dorsal midline which extend or fan out laterally and can occur from the neck to the sacrum

·      Dilated hair follicles contain inspissated, dark, keratinous, or caseous debris that may be extruded with digital pressure

·      Hair is lost from severely affected follicles



·      Distention of superficial hair follicles with keratin is the diagnostic feature of schnauzer comedo syndrome

·      The size of the follicular ostium may remain nearly normal, resulting in a cystic appearance of the keratin-dilated infundibulum; other affected follicles may have dilated ostia

·      The follicular infundibular wall is generally of normal thickness to mildly acanthotic

·      Epidermal hyperkeratosis usually is mild

·      Superficial crusting originating from secondary pyoderma may be prominent

·      Acanthosis is moderate to severe, and varies with the degree of secondary inflammation present

·      Folliculitis or furunculosis with comedonal rupture may be observed

·      Pustular inflammation may be loosely distributed in the superficial dermis and may involve apocrine sweat glands in severe cases

·      Chronic lesions have mixtures of neutrophils, macrophages, and plasma cells in superficial and periadnexal distribution

·      Note: Hyperpigmentation is normal in schnauzers



For histologic findings:

·      Follicular keratosis of primary seborrhea: Follicular ostia are uniformly dilated by infundibular engorgement with keratin (whereas in schnauzer comedo syndrome follicular ostia often remain relatively closed)

·      Hyperglucocorticoidism (I-M23) (iatrogenic or endogenous): Comedones are accompanied by follicular atrophy and thinning of the infundibular wall +/- calcinosis cutis

·      Actinic comedones: A pale concentric layer of collagen usually surrounds the distended follicle

·      Canine acne: Comedo formation on the chin and lips

·      Canine callus and callus pyoderma: Follicular keratosis with epidermal and follicular infundibular hyperplasia

·      Hypothyroidism (I-M22): Follicular atrophy

·      Vitamin A responsive dermatosis (I-M09): Seen in Cocker spaniels; ventral and lateral chest and abdomen most commonly affected; hyperkeratotic plaques with marked follicular keratosis and casts protruding from follicular ostia



·      Schnauzer comedo syndrome is a distinctive disease which occurs exclusively in the miniature schnauzer breed



1.    Gross TL, Ihrke PJ, Walder EJ, Affolter VK: Diseases with abnormal cornification. In: Skin Diseases of the Dog and Cat Clinical and Histopathologic Diagnosis. Ames, IA: Blackwell Science, Ltd; 2005: 181-183.

2.    Hnilica KA, Patterson AP. Keratinization and Seborrheic Disorders. In: Small Animal Dermatology A Color Atlas and Therapeutic Guide. 4th ed. St. Louis, MO: Elsevier Inc.; 2017: 396.

3.    Mauldin EA, Peters-Kennedy J. Integumentary system. In: In: Maxie MG ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Elsevier; 2016: 524; 549.

4.    Scott DW, Miller WH, Griffin CE. Congenital and hereditary defects. In: Muller and Kirk’s Small Animal Dermatology. 7th ed. Philadelphia, PA: WB Saunders Co.; 2013: 581-582.

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