FIGURE 12-1 Callus.

Thickening of the skin over the elbow of a dog. The hair is clumped, and skin appears partially alopecic, which is typical of a callus.

FIGURE 12-2 Callus.

Close-up of the lesion in Figure 12-1. The large alopecic area of thickened skin over the elbow is typical of this syndrome. Often in short-coated dogs, the hairs become impacted within the follicles and callus.

FIGURE 12-3 Callus.

Close-up of the lesion in Figure 12-1. The clinician is gently squeezing the callus to express the impacted hairs, which are now exuding from the surface of the skin. These hairs serve as a nidus for recurrent infection.

FIGURE 12-4 Callus.

Close-up of the lesion in Figure 12-1. The exuded hairs are apparent. This technique is not recommended because forcing the hairs to rupture internally could result in cellulitis and scarring.

FIGURE 12-5 Callus.

A focal area of alopecia and thickened skin over the elbow. The large cystic structures are hair follicles that became obstructed and filled with keratin debris.

FIGURE 12-6 Callus.

Severe alopecia and thickening of the skin with ulceration over the hock of a dog. The chronic pressure that causes callus formation can also lead to decubital ulcers.

FIGURE 12-7 Callus.

A sternal plaque demonstrating the focal area of alopecia and comedo formation caused by chronic pressure and friction in deep-chested dogs. This is most often seen in Dachshunds.

FIGURE 12-8 Callus.

Keratin material has been expressed from the comedones of the sternal plaque of a Dachshund. Note the large keratin plugs that were formed by persistent pressure produced when the dog rests in a sternal position.

FIGURE 12-9 Callus.

The ingrown, dead hairs have been removed. Note the unexpected length of the hair shaft, which was embedded in the callus.

FIGURE 12-10 Callus.

Ingrown hairs that have been removed from a callus.

FIGURE 12-11 Callus.

A focal callus with ulceration resulting from extreme focal pressure and secondary infection. Embedded hairs have been removed.

FIGURE 12-12 Callus.

Numerous embedded hairs that were removed from a chronic callus.

FIGURE 12-13 Callus.

Embedded hairs are being removed from a chronic callus. Note how little of the hair shaft is exposed above the surface of the callus.

FIGURE 12-14 Callus.

A chronic callus demonstrating the dilated cystic follicles that develop from chronic pressure and subsequent obstruction of the follicular opening. Note the lack of active infection despite the large cystic follicles.

FIGURE 12-15 Callus.

A chronic callus demonstrating the dilated cystic follicles that develop from chronic pressure and subsequent obstruction of the follicular opening. Note the lack of active infection despite the large cystic follicles.

FIGURE 12-16 Callus.

The comedones create dilated follicles that often become secondarily infected and may rupture, resulting in furunculosis. The follicles are plugged (comedones) as a result of the constant pressure applied when the deep-chested dog rests in a sternal position.

FIGURE 12-17 Feline Acne.

Moist, draining papular lesions on the chin of an adult cat. Furunculosis and cellulitis caused the tissue swelling and exudate.

FIGURE 12-18 Feline Acne.

The hair has been clipped to provide better visualization of the erythema, hyperpigmentation, and comedones.

FIGURE 12-19 Feline Acne.

Alopecia and scarring remained as sequelae after treatment with topical mupirocin ointment.

FIGURE 12-20 Feline Acne.

The hair has been clipped, allowing better visualization of the comedones, papules, and draining lesions in this severe case of feline acne, which usually is limited to the chin.

FIGURE 12-21 Feline Acne.

The brown discoloration is typical of comedo formation associated with feline acne.

FIGURE 12-22 Feline Acne.

Close-up of the cat in Figure 12-21. The lesions extended along the lateral lip surface. This is unusual for feline acne.

FIGURE 12-23 Idiopathic Nasodigital Hyperkeratosis.

Severe frondlike hyperkeratotic projections with crust formation on the nose of an old Boxer.

FIGURE 12-24 Idiopathic Nasodigital Hyperkeratosis.

Severe crusting and frondlike projections on the nose.

FIGURE 12-25 Idiopathic Nasodigital Hyperkeratosis.

Thick, adherent crusts cover most of the nasal planum in this dog.

FIGURE 12-26 Idiopathic Nasodigital Hyperkeratosis.

Mild hyperkeratosis of the footpads without other lesions (which would be more typical of autoimmune skin disease or hepatocutaneous syndrome).

FIGURE 12-27 Idiopathic Nasodigital Hyperkeratosis.

Hyperkeratosis and crusting of the metacarpal pad.

FIGURE 12-28 Idiopathic Nasodigital Hyperkeratosis.

A focal area of hyperkeratosis on the central pad of a Greyhound (Greyhound corns).

FIGURE 12-29 Idiopathic Nasodigital Hyperkeratosis.

Hyperkeratosis and crusting on the footpads.

FIGURE 12-30 Idiopathic Nasodigital Hyperkeratosis.

Hyperkeratosis and crusting with frondlike projections on the footpads.

FIGURE 12-31 Hereditary Nasal Parakeratosis of Labrador Retrievers.

Hyperkeratosis and crusting on the nose of a young adult Labrador.

FIGURE 12-32 Hereditary Nasal Parakeratosis of Labrador Retrievers.

Severe crusting and hyperkeratosis covering almost the entire nasal planum.

FIGURE 12-33 Parasympathetic Nasal Hyperkeratosis.

Hyperkeratosis and crusting asymmetrically affecting the nasal planum.

FIGURE 12-34 Parasympathetic Nasal Hyperkeratosis.

Close-up of the dog in Figure 12-33. The asymmetrical (only half) pattern of crusting is apparent.

FIGURE 12-35 Parasympathetic Nasal Hyperkeratosis.

A symmetrical hyperkeratosis of the nasal planum.

FIGURE 12-36 Parasympathetic Nasal Hyperkeratosis.

The nasal planum is dry and crusted from the lack of normal nasal gland secretions. The normal cobblestone surface remains intact, making a diagnosis of autoimmune skin disease less likely.