Veterinary Medicine - December 2007 - (Page 774)

Clinical Exposures PEER-REVIEWED greater risk of dermatophytosis than do older dogs, but mild or localized disease may be self-limiting in some young dogs.1 Older dogs may be at increased risk for disseminated disease if they have concurrent immune system dysfunction (secondary to endocrinopathy, autoimmune disease, or neoplasia) or if they are receiving chemotherapy or immunosuppressive therapy. No sex or breed predilection has been reported,1-3 but the coats of longhaired breeds may trap arthrospores, promoting infection.1,3 Diagnostic testing A Wood’s lamp examination is a commonly used in-house diagnostic test for dermatophytosis. The lamp uses an ultraviolet light to detect hair shafts presumably contaminated with certain strains of M. canis. Test results are positive if the characteristic greenish fluorescence is noted. Unfortunately, this test has poor sensitivity and only detects 50% of M. canis infections.4 False positive results may be caused by cellular or acellular debris, scales, or some topical medications.1,4 Microscopic examination of the fluorescing hairs may be confirmatory, but using a clearing agent (e.g. potassium hy- (e.g. orange to red) of the dermatophyte test medium with concurrent visible colony growth supports the presence of fungal infection.1,4 Histologic examination is especially valuable in diagnosing nodular or granulomatous disease. Fine-needle aspiration of the nodules may reveal fungal hyphae, but histology is often needed for a definitive diagnosis. Treatment overview Treatment may involve topical or systemic therapy, depending on the type and distribution of lesions. It is possible for some dogs to spontaneously resolve mild disease, but most dogs will need medical intervention.1,3 Topical therapies may include clipping the coat and using lime sulfur dips or miconazole shampoos. Systemic therapy is most often used with generalized infections, and the most commonly used medications are griseofulvin and azole antifungals (e.g. itraconazole, ketoconazole).1,3 Because dermatophytosis lesions can be pruritic, bacterial infections secondary to self-trauma are common and may require antibiotic therapy. Treating dermatophytosisassociated pruritus with corticosteroids is contraindicated.1,3 To deter the spread of infection to other animals and people in the household, isolation of the affected animal and environmental decontamination of bedding and other potential fomites may be necessary.1-3 O REFERENCES 1. DeBoer DJ, Moriello KA. Cutaneous fungal infections. In: Greene CE, ed. Infectious diseases of the dog and cat. 3rd ed. St. Louis, Mo: Saunders/Elsevier, 2006;530-538. 2. Gross TL, Ihrke PJ, Walder EJ. Diseases of the hair follicles. Veterinary dermatopathology: a macroscopic and microscopic evaluation of canine and feline skin diseases. St. Louis, Mo: Mosby-Year Book, 1992;243-244. 3. Scott DW, Miller WH, Griffin CE. Fungal skin diseases. Muller and Kirk’s small animal dermatology. 6th ed. Philadelphia, Pa: WB Saunders, 2001;339-357. 4. Noli C. Practical laboratory methods for the diagnosis of dermatologic diseases. In: Bonagura JD, ed. Kirk’s current veterinary therapy XIII. Philadelphia, Pa: WB Saunders, 2000;528-530. Presentation The classic dermatophyte lesion is a ring of alopecia expanding from an erythema- Using a clearing agent on the hairs may increase the probability of finding fungal hyphae. tous border that surrounds a central area of healing. The lesions are often pruritic. Other possible dermatologic changes associated with infection include scales, crusts, and hyperpigmentation.1-3 Although dermatophyte lesions may occur anywhere on the body, the face and forelimbs are most commonly affected. Dogs infected with M. gypseum or T. mentagrophytes may have symmetrical facial lesions with marked exfoliation and crusting. Trichophyton mentagrophytes may cause onychodystrophy or paronychia.2,3 Other possible presentations include nodular and granulomatous forms. The nodular form, which was seen in this case, is characterized by wellcircumscribed nodules called kerions. Kerions occur on the face and extremities and may develop draining tracts. Kerions are often associated with M. gypseum or T. mentagrophytes infection.1-3 droxide, chlorphenolac) on the hairs may increase the probability of finding fungal hyphae.4 Microscopic examination of skin scrapes by using a mineral oil suspension is not an effective screening test.1,4 Definitive diagnosis Fungal culture and histologic examination are considered the gold standards for definitively diagnosing dermatophytosis. Both tests are good for screening and confirming disease, but neither test has 100% sensitivity or specificity.1,3,4 The fungal culture medium or dermatophyte test medium (Fungassay— Synbiotics, InTray DM—BioMed Diagnostics) contains inhibitors of bacterial and saprophytic growth and phenol red as an indicator of colony growth. The plates are observed for at least seven to 14 days, and an incubating temperature warmer than room temperature may be necessary for optimal growth. A color change 774 December 2007 VETERINARY MEDICINE

Table of Contents Feed for the Digital Edition of Veterinary Medicine - December 2007

Veterinary Medicine - December 2007 Contents Letters Editors' Guest Thanking Our Valued Reviewers The Veterinary Medicine Interview: Dr. Joseph Harari Clinical Exposures Idea Exchange Answers to Three Commonly Asked Questions About Lyme Disease Practical Ideas for Managing Common Internal Medicine Problems A Tip for Interpreting Leptospira Species Titers Investigating Proteinuric Kidney Disease Counseling New Puppy Owners: Normal Play vs. Aggressive Tendencies 11 Guidelines for Conservatively Treating Chronic Kidney Disease CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller Merial Insert

Veterinary Medicine - December 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.