Fungal Skin Diseases

CHAPTER | 4 Fungal Skin Diseases

Malasseziasis (Malassezia dermatitis)

Features

Malassezia pachydermatis is a yeast that is normally found in low numbers in the external ear canals, in perioral areas, in perianal regions, and in moist skin folds. Skin disease occurs in dogs when a hypersensitivity reaction to the organisms develops, or when cutaneous overgrowth occurs. In dogs, Malassezia overgrowth is almost always associated with an underlying cause, such as atopy, food allergy, endocrinopathy, keratinization disorder, metabolic disease, or prolonged therapy with corticosteroids. In cats, skin disease is caused by Malassezia overgrowth that may occur secondary to an underlying disease (e.g., feline immunodeficiency virus, diabetes mellitus, an internal malignancy). In particular, generalized Malassezia dermatitis may occur in cats with thymoma-associated dermatosis or paraneoplastic alopecia. Malasseziasis is common in dogs, especially among West Highland White terriers, Dachshunds, English setters, Basset hounds, American cocker spaniels, Shih tzus, Springer spaniels, and German shepherds. These breeds may be predisposed. Malasseziasis is rare in cats.

Dogs

Moderate to severe pruritus is seen, with regional or generalized alopecia, excoriations, erythema, and seborrhea. With chronicity, affected skin may become lichenified, hyperpigmented, and hyperkeratotic (leathery or elephant-like skin). An unpleasant body odor is usually present. Lesions may involve the interdigital spaces, ventral neck, axillae, perineal region, or leg folds. Paronychia with dark brown nail bed discharge may be present. Concurrent yeast otitis externa is common.

Cats

Symptoms include black, waxy otitis externa, chronic chin acne, alopecia, and multifocal to generalized erythema and seborrhea.

Top Differentials

Differentials include other causes of pruritus and seborrhea, such as demodicosis, superficial pyoderma, dermatophytosis, ectoparasites, and allergies.

Treatment and Prognosis

1 Any underlying cause (allergies, endocrinopathy, keratinization defect) must be identified and corrected.

2 For mild cases, topical therapy alone is often effective. The patient should be bathed every 2 to 3 days with shampoo that contains 2% ketoconazole, 1% ketoconazole/2% chlorhexidine, 2% miconazole, 2% to 4% chlorhexidine, or 1% selenium sulfide (dogs only). Shampoos that have two active ingredients provide better efficacy. Treatment should be continued until the lesions resolve and follow-up skin cytology reveals no organisms (approximately 4 weeks).

3 The treatment of choice for moderate to severe cases is ketoconazole (dogs) or fluconazole 10 mg/kg PO with food every 24 hours, Treatment should be continued until lesions resolve and follow-up skin cytology reveals no organisms (approximately 4 weeks).

4 Alternatively, treatment with terbinafine 5–40 mg/kg PO every 24 hours or itraconazole (Sporanox) 5–10 mg/kg every 24 hours for 4 weeks may be effective.

5 Pulse therapy protocols using several drugs and a variety of schedules have been published; however, these often take longer to resolve the active infection.

6 The prognosis is good if the underlying cause can be identified and corrected. Otherwise, regular once- or twice-weekly antiyeast shampoo baths may be needed to prevent relapse. This disease is not considered contagious to other animals or to humans, except for immunocompromised individuals.

Author’s Note

Yeast dermatitis is currently the most commonly missed diagnosis in U.S. general practices. Any patient with leathery, elephant skin–like lesions on the ventrum should be suspected of having Malassezia dermatitis.

Cutaneous cytology is not always successful for finding Malassezia organisms, requiring the clinician to rely on clinical lesion patterns to make a tentative diagnosis.

Yeast dermatitis is severely pruritic, with owners reporting an itch level of 10 on a 0 to 10 visual analog scale.

FIGURE 4-1 Malasseziasis.

Severe alopecia, lichenification, and hyperpigmentation on the entire ventrum of a West Highland White Terrier. The yeast infection was secondary to allergic dermatitis.

FIGURE 4-2 Malasseziasis.

Alopecia, erythema, and lichenification on the ventral neck of an allergic dog.

FIGURE 4-3 Malasseziasis.

Pododermatitis caused by a secondary yeast infection demonstrates the alopecia and lichenification typical of Malassezia dermatitis.

FIGURE 4-4 Malasseziasis.

Severe pododermatitis demonstrating the intense inflammatory response caused by the hypersensitivity reaction to the Malassezia organisms. Severe erythema, alopecia, and lichenification are apparent.

FIGURE 4-5 Malasseziasis.

The interdigital dermatitis in this patient was caused by the secondary Malassezia infection. The greasy, alopecic, inflamed skin in between the footpads is typical of yeast pododermatitis.

FIGURE 4-6 Malasseziasis.

The brown discoloration around the base of the nails is a unique change typical of secondary Malassezia infections.

FIGURE 4-7 Malasseziasis.

The brown discoloration caused by the yeast infection is more pronounced at the base of the nail and can be differentiated from normal pigmentation of the nail by its splotchy and interrupted pattern.

FIGURE 4-8 Malasseziasis.

Secondary yeast otitis is a common finding in patients with an underlying primary allergy or endocrine disease. The ear canal and pinnae demonstrate the alopecia, intense erythema, and lichenification typical of Malassezia dermatitis.

FIGURE 4-9 Malasseziasis.

Perianal dermatitis caused by a secondary yeast infection in a food-allergic dog. The alopecia, erythema, and lichenification are characteristic of Malassezia dermatitis.

FIGURE 4-10 Malasseziasis.

Yeast dermatitis can cause lesions typical of feline acne. Alopecia with brown discoloration and comedones is apparent.

FIGURE 4-11 Malasseziasis.

The perioral dermatitis in this cat was caused by a secondary Malassezia infection.

FIGURE 4-12 Malasseziasis.

The secondary yeast infection can cause a seborrhea oleosa in cats. The waxy exudate clumping the base of this cat’s hairs is typical of Malassezia dermatitis in cats.

FIGURE 4-13 Malasseziasis.

Typical “elephant skin” lesion demonstrating the alopecia, erythema, hyperpigmentation, and lichenification caused by Malassezia dermatitis.

FIGURE 4-14 Malasseziasis.

This papular dermatitis on the forearm of an allergic dog was caused by a secondary yeast infection. The papular dermatitis represents an unusual lesion pattern associated with Malassezia dermatitis and is more typical of bacterial Pyoderma.

FIGURE 4-15 Malasseziasis.

More typical yeast dermatitis of the forearm compared with Figure 4-14. The alopecia, hyperpigmentation, and lichenification (“elephant skin”) are highly characteristic of yeast dermatitis.

FIGURE 4-16 Malasseziasis.

This young Beagle demonstrates brown discoloration of the hair on his feet and ventrum. The hair and skin are greasy with a rancid fat odor typical of a yeast infection.

FIGURE 4-17 Malasseziasis.

Close-up of the dog in Figure 4-16. Brown discoloration of the feet is apparent and represents an early change caused by the Malassezia infection.

FIGURE 4-18 Malasseziasis.

Generalized alopecia and lichenification in an adult Collie. The yeast infection was secondary to allergic dermatitis.

FIGURE 4-19 Malasseziasis.

Generalized alopecia and lichenification (“elephant skin”) typical of Malassezia dermatitis in a dog with primary idiopathic seborrhea.

FIGURE 4-20 Malasseziasis.

Generalized alopecia with intense erythema caused by a hypersensitivity reaction to the yeast organisms in a dog with severe Malassezia dermatitis secondary to allergy.

FIGURE 4-21 Malasseziasis.

Cytology of Malassezia organisms, as viewed with a 100× (oil) objective.

FIGURE 4-22 Malasseziasis.

Close-up of the dog in Figure 4-20. Intense erythema and alopecia, with early lichenification caused by the hypersensitivity reaction to the yeast, are apparent.

FIGURE 4-23 Malasseziasis.

Close-up of the dog in Figure 4-20. Intense erythema and alopecia caused by the hypersensitivity reaction to yeast can be seen on the thorax. Note: The skin is beginning to become lichenified, typical of Malassezia dermatitis.

FIGURE 4-24 Malasseziasis.

Severe alopecia and lichenification typical of yeast dermatitis on the ventrum of an allergic dog.

FIGURE 4-25 Brown splotchy discoloration of the nails is a unique symptom of yeast dermatitis.

FIGURE 4-26 Malasseziasis.

Brown discoloration of the nails is a characteristic of yeast dermatitis. If the color was natural pigmentation, the color would extend the entire length of the nail.

FIGURE 4-27 Malasseziasis.

Brown splotchy discoloration of the nails is a unique symptom of yeast dermatitis.

FIGURE 4-28 Malasseziasis.

Severe pododermatitis in a dog with atopy. Note: The yeast infection affects the skin and nails in this dog.

FIGURE 4-29 Malasseziasis.

Severe erythema and alopecia in the axilla of a dog. Note the moist exudate starting to form.

FIGURE 4-30 Malasseziasis.

This papular rash with scaling is more typical of folliculitis, demonstrating the need for routine skin cytology to differentiate the cause of infection.

FIGURE 4-31 Malasseziasis.

Severe erythema and alopecia with erosion formation. This deep lesion is not typical of yeast infections but was diagnosed through cutaneous cytology.

FIGURE 4-32 Malasseziasis.

Generalized seborrhea oleosa (greasiness) of the skin and hair coat is a common symptom of yeast infection.

FIGURE 4-33 Malasseziasis.

Brown, splotchy discoloration of the nails is a unique symptom of yeast dermatitis.

Candidiasis (candidosis, thrush)

Features

Candidiasis is an opportunistic cutaneous infection that results from overgrowth of Candida, a dimorphic fungus that is a normal mucosal inhabitant. Cutaneous overgrowth is usually facilitated by an underlying factor, such as skin damage caused by chronic trauma or moisture, an immunosuppressive disease, or long-term use of cytotoxic drugs or broad-spectrum antibiotics. Candidiasis occurs only rarely in dogs and cats.

Mucosal involvement is characterized by eroded or shallowly ulcerated mucocutaneous junctions, or by single to multiple nonhealing mucosal ulcers covered by grayish white plaques with erythematous margins. Cutaneous involvement is characterized by nonhealing, erythematous, moist, eroded, exudative, and crusty skin or nail bed lesions.

Top Differentials

Differentials include demodicosis, pyotraumatic dermatitis, superficial pyoderma, mucocutaneous pyoderma, other fungal infections, autoimmune disorders, vasculitis, cutaneous drug reactions, and cutaneous lymphosarcoma.

Treatment and Prognosis

1 Any underlying cause must be identified and corrected.

2 For localized cutaneous or mucocutaneous lesions, the affected area should be clipped and cleaned. The patient should be bathed every 2 to 3 days with shampoo that contains 2% ketoconazole, 1% ketoconazole/2% chlorhexidine, 2% miconazole, or 2% to 4% chlorhexidine. Shampoos that have two active ingredients provide better efficacy.

3 A topical antifungal product should be applied until lesions have healed (approximately 1–4 weeks). Effective topical therapies include the following:

1% to 2% miconazole cream, spray, or lotion q 12–24 hours

1% clotrimazole cream, lotion, or solution q 6–8 hours

2% ketoconazole cream q 12 hours

4 For oral or generalized lesions, systemic antifungal medications should be administered (minimum 4 weeks) and continued at least 1 week beyond complete clinical resolution. Effective therapies include the following:

Ketoconazole 10 mg/kg PO with food q 24 hours

Fluconazole 10 mg/kg PO q 24 hours

Terbinafine 30–40 mg/kg PO q 24 hours

Itraconazole (Sporanox) 5–10 mg/kg PO with food q 24 hours

5 The prognosis is good to fair, depending on whether the underlying cause can be corrected. Candidiasis is not contagious to other animals or to humans.

FIGURE 4-34 Candidiasis.

Superficial moist, erosive lesions on the ventrum of the dog.

(Courtesy of A. Yu.)

FIGURE 4-35 Candidiasis.

Close-up of the dog in Figure 4-34. Erythema and crusting on the abdomen.

(Courtesy A. Yu.)

Dermatophytosis (ringworm)

Features

Dermatophytosis is an infection of hair shafts and stratum corneum caused by keratinophilic fungi. It occurs commonly in dogs and cats, with highest incidences reported in kittens, puppies, immunocompromised animals, and long-haired cats. Persian cats and Yorkshire and Jack Russell terriers appear to be predisposed.

Skin involvement may be localized, multifocal, or generalized. Pruritus, if present, is usually minimal to mild but occasionally may be intense. Lesions usually include areas of circular, irregular, or diffuse alopecia with variable scaling. Remaining hairs may appear stubbled or broken off. Other symptoms in dogs and cats include erythema, papules, crusts, seborrhea, and paronychia or onychodystrophy of one or more digits. Rarely, cats present with miliary dermatitis or dermal nodules (see “Dermatophytic Granulomas and Pseudomycetomas”). Other cutaneous manifestations in dogs include facial folliculitis and furunculosis resembling nasal pyoderma, kerions (acutely developing, alopecic, and exudative nodules) on the limb or face, and truncal dermal nodules (see “Dermatophytic Granulomas and Pseudomycetomas”). Asymptomatic carrier states (subclinical infection) are common in cats, especially among long-haired breeds. Asymptomatic disease, although rare in dogs, has been reported in Yorkshire terriers.

Top Differentials

Dogs

Differentials in dogs include demodicosis and superficial pyoderma. If nodular, neoplasia and acral lick dermatitis should be included.

Cats

Differentials in cats include parasites, allergies, and feline psychogenic alopecia.

Diagnosis

1 Rule out other differentials.

2 Ultraviolet (Wood’s lamp) examination: hairs fluoresce yellow-green with some Microsporum canis strains. This is an easy screening test, but false-negative and false-positive results are common.

3 Trichogram (hairs or scales in potassium hydroxide preparation): search for hair shafts infiltrated with hyphae and arthrospores. Fungal elements are often difficult to find.

4 Dermatohistopathology: variable findings may include perifolliculitis, folliculitis, furunculosis, superficial perivascular or interstitial dermatitis, epidermal and follicular orthokeratosis or parakeratosis, or suppurative epidermitis; fungal hyphae and arthrospores in stratum corneum or hair shafts.

5 Fungal culture: Microsporum or Trichophyton spp.

6 Polymerase chain reaction (PCR) analysis, where available, may simplify the diagnosis.

Treatment and Prognosis

2 If response to localized treatment is poor, the animal should be treated for generalized dermatophytosis.

3 For generalized disease: Topical antifungal rinse or dip should be applied to the entire body one or two times per week (minimum 4–6 weeks) until follow-up fungal culture results are negative. Bathing the animal with a shampoo that contains chlorhexidine and miconazole (or ketoconazole) immediately preceding the antifungal dip may be helpful. Dogs with generalized dermatophytosis may be cured with topical therapy alone, whereas cats almost always require concurrent systemic therapy. Effective topical antifungal solutions include the following:

Enilconazole 0.2% solution

Lime sulfur 2% to 4% solution

5 Alternatively, pulse therapy may be almost as effective, and multiple protocols have been published using various drugs. Pulse treatments should be continued until two consecutive follow-up fungal cultures taken 2 to 4 weeks apart are negative.

6 All infected animals, including asymptomatic carriers, should be identified and treated. Exposed, noninfected cats and dogs should be treated prophylactically with weekly topical antifungal rinse or dip for the duration of treatment of the infected animals.

7 The environment should be thoroughly cleaned by removing all contaminated materials, and the area should be disinfected with bleach (vacuums may further contaminate the environment).

8 For endemic infections involving multianimal homes, catteries, or animal facilities, treatment should be provided according to the recommendations outlined in Box 4-1.

9 Lufenuron has not demonstrated consistent efficacy in treating or preventing infection.

10 The prognosis is generally good, except for endemically infected multicat households and catteries. Animals with underlying immunosuppressive diseases also have a poorer prognosis for cure. Dermatophytosis is contagious to other animals and to humans.

BOX 4-1

Treating Dermatophytosis in Multianimal Homes, Catteries, and Animal Facilities

Culture all animals to determine the extent and location of animal infections.

Culture the environment (cages, counters, furniture, floors, fans, ventilation units, etc) to map infected areas to be disinfected.

Treat all infected animals with systemic antifungals until each animal has two negative fungal cultures taken at least 1 month apart.

Treat all infected and exposed animals with topical 2% to 4% lime sulfur solution every 3 to 7 days to prevent contagion and zoonosis. Continue until all animals have two negative fungal cultures taken at least 1 month apart. Do not clip cats, as this contaminates the clippers and facility and worsens the risk of contagion.

Dispose of all infected material. Remove clutter from animal facilities or other infected areas.

Clean and disinfect all surface areas every 3 days. Continue until all animals have two negative fungal cultures taken at least 1 month apart. Enilconazole (Clinafarm EC disinfectant, American Scientific Laboratories, Union, NJ) is a very effective environmental disinfectant, but it is licensed only for poultry farm use in the United States. Household chlorine laundry bleach (5% sodium hypochlorite) diluted 1 : 10 in water is an effective, inexpensive environmental disinfectant.

Author’s Note

Microsporum canis is one of the most common zoonotic diseases in veterinary medicine.

Adopted kittens should be screened for infection during the first veterinary wellness visit.

Chronically infected animals likely have contaminated the home, requiring aggressive cleaning and disinfection of the environment.

Even long-standing and severe infections can be resolved with aggressive and persistent treatment.

Discontinuation of therapy MUST be based on negative cultures.

FIGURE 4-36 Dermatophytosis.

Focal alopecia and crusting on the muzzle of a cat caused by Microsporum canis.

(Courtesy J. MacDonald.)

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Tags: Small Animal Dermatology A Color Atlas and Therapeutic Guide

Sep 10, 2016 | Posted by admin in SMALL ANIMAL | Comments Off

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