Flashcards in Dermatology - Dermatophytosis Deck (68)
What is dermatophytosis also known as?
Ringworm - Dr. Noxon said don't call it that
What etiologic agents cause dermatophytosis?
Microsporum canis, Microsporum gypseum, Trichophyton mentagrophytes, Epidermophyton and other related organisms
All etiologic agents of dermatophytosis are zoophilic, except what?
How is dermatophytosis transmitted?
by contact with infected animals, soil, or through fomites
What age of animals is more commonly affected by dermatophytosis?
What are the predisposing factors of dermatophytosis?
poor nutrition, improper sanitation, immunosuppressive diseases, or use of glucocorticoids, and genetic factors
What is the pathogenesis of dermatophytosis?
1. Dermatophytes invade and grow in non-viable keratinized tissue
2. Grow only in hairs in anagen, weakening the hair shaft and causing it to break
3. Incubation period of an average of 2 weeks
4. Growing fungus advances down the hair follicle and releases metabolic by-products to incite an inflammatory reaction (folliculitus
5. Type IV hypersensitivity reaction follows
6. Fungus moves to a follicle nearby (outwards) creating a circular lesion
What are the classical lesions associated with dermatophytosis?
circular areas of alopecia, patchy alopecia with broken and brittle hair, erythema, hyperkeratinization and crusting, nodular hyperkeratotic erythematous lesions, mild-moderate pruritus may be reported
What classical lesions are associated with chronic dermatophytosis?
Where are lesions due to dermatophytosis more frequently located?
the head, ears, and extremities
What do lesions of dermatophytosis caused by Trichophyton present as?
What may lesions may onchomycosis cause?
disortion and easily broken claws
What are pseudomycetomas?
deep dermal or subcutaneous infections by dermatophytes
How do pseudomycetomas present?
as nodules and draining lesions, that histologically are pyogranulomatous to granulomatous panniculitus
What is the causitive agent of pseudomycetomas in cats?
What is the recommended treatment for pseudomycetomas?
surgical excision of the lesion and systemic antifungal therapy
What are the methods of diagnosis for dermatophytosis?
Clinical appearance, Wood's light examination, trichogram, fungal culture, and/or skin biopsy
What differential diagnoses should be considered when considering dermatophytosis?
scaling disorders such as familial seborrhea, superficial pyoderma, demodicosis, hypothyroidism, and bacterial hypersensitivity
True or False: Wood's light examination is a confirmatory test.
False, it is only a screening test
What should be examined when doing a Wood's light examination?
the base of the plucked hairs
Which fungi that causes dermatophytosis is the only one that flouresces?
What is a trichogram?
microscopic exam of hair and scrapings
Trichograms are an excellent screening test, ___ specificity, _____ sensitivity.
What is the most definitive diagnostic test for dermatophytosis?
a fungal culture
What samples should be used for a fungal culture?
broken hairs, crusts or scales, and/or individual hairs that fluoresce under the Wood's light
Can you use alcohol on areas that you want to take a sample from for a fungal culture?
yes, it can cut down on contaminants
What is the MacKenzie Brush technique?
It is a technique that can be used to identify carrier animals - it employs a sterile toothbrush to comb the hair coat of the animal, the bristles are then imbedded or shaken over agar for culture
What is the standard fungal culture media?
Sabouraud's dextrose agar
What should you be wary of when using dermatophyte test media?
Color change is not diagnostic - you should not base the diagnosis of the organism soley on the color change