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Small Animal Medicine > Dermatology - Dermatophytosis > Flashcards

Dermatology - Dermatophytosis Flashcards

1
Q

What is dermatophytosis also known as?

A

Ringworm - Dr. Noxon said don’t call it that

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2
Q

What etiologic agents cause dermatophytosis?

A

Microsporum canis, Microsporum gypseum, Trichophyton mentagrophytes, Epidermophyton and other related organisms

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3
Q

All etiologic agents of dermatophytosis are zoophilic, except what?

A

M. gypseum

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4
Q

How is dermatophytosis transmitted?

A

by contact with infected animals, soil, or through fomites

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5
Q

What age of animals is more commonly affected by dermatophytosis?

A

younger animals

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6
Q

What are the predisposing factors of dermatophytosis?

A

poor nutrition, improper sanitation, immunosuppressive diseases, or use of glucocorticoids, and genetic factors

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7
Q

What is the pathogenesis of dermatophytosis?

A
  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
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8
Q

What are the classical lesions associated with dermatophytosis?

A

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

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9
Q

What classical lesions are associated with chronic dermatophytosis?

A

hyperpigmentation

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10
Q

Where are lesions due to dermatophytosis more frequently located?

A

the head, ears, and extremities

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11
Q

What do lesions of dermatophytosis caused by Trichophyton present as?

A

pustular eruptions

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12
Q

What may lesions may onchomycosis cause?

A

disortion and easily broken claws

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13
Q

What are pseudomycetomas?

A

deep dermal or subcutaneous infections by dermatophytes

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14
Q

How do pseudomycetomas present?

A

as nodules and draining lesions, that histologically are pyogranulomatous to granulomatous panniculitus

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15
Q

What is the causitive agent of pseudomycetomas in cats?

A

M. canis

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16
Q

What is the recommended treatment for pseudomycetomas?

A

surgical excision of the lesion and systemic antifungal therapy

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17
Q

What are the methods of diagnosis for dermatophytosis?

A

Clinical appearance, Wood’s light examination, trichogram, fungal culture, and/or skin biopsy

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18
Q

What differential diagnoses should be considered when considering dermatophytosis?

A

scaling disorders such as familial seborrhea, superficial pyoderma, demodicosis, hypothyroidism, and bacterial hypersensitivity

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19
Q

True or False: Wood’s light examination is a confirmatory test.

A

False, it is only a screening test

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20
Q

What should be examined when doing a Wood’s light examination?

A

the base of the plucked hairs

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21
Q

Which fungi that causes dermatophytosis is the only one that flouresces?

A

M. canis

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22
Q

What is a trichogram?

A

microscopic exam of hair and scrapings

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23
Q

Trichograms are an excellent screening test, ___ specificity, _____ sensitivity.

A

high, moderate

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24
Q

What is the most definitive diagnostic test for dermatophytosis?

A

a fungal culture

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25
Q

What samples should be used for a fungal culture?

A

broken hairs, crusts or scales, and/or individual hairs that fluoresce under the Wood’s light

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26
Q

Can you use alcohol on areas that you want to take a sample from for a fungal culture?

A

yes, it can cut down on contaminants

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27
Q

What is the MacKenzie Brush technique?

A

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

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28
Q

What is the standard fungal culture media?

A

Sabouraud’s dextrose agar

29
Q

What should you be wary of when using dermatophyte test media?

A

Color change is not diagnostic - you should not base the diagnosis of the organism soley on the color change

30
Q

How do M. canis colonies appear?

A

as white, fluffy coloniess

31
Q

How do M. gypseum colonies appear?

A

generally cinnamon-buff in color with some white growth on the periphery

32
Q

How do Trichophyton species colonies appear?

A

Produce a flat thallus that have a cream to yellowish-buff powdery surface

33
Q

How does M. canis appear microscopically?

A

the macroconidiae have terminal knobs and usually have greater than 6 compartments

34
Q

How does M. gypseum appear microscopically?

A

the macroconidiae have no knobs and up to 6 compartments

35
Q

How does Trichophyton appear microscopically?

A

the macroconidiae are club-shaped and often hyphae are spiral shaped

36
Q

What does histopathology from skin biopsies in dermatophytosis patients look like?

A

it shows folliculitis, furunculosis, keratinization abnormalities of the epidermis, fungal elements in keratinized layers

37
Q

What therapies can be used to treat dermatophytosis?

A

Decontamination of the pet, topical therapies, systemic therapies, and decontamination of the environment

38
Q

What is the goal of decontamination of a pet with dermatophytosis?

A

it is done to reduce the number of spores and infective hyphae

39
Q

How is a pet decontaminated from dermatophytosis?

A

The hair is clipped around the lesion and topical disinfectants are used

40
Q

What is Dr. Noxon’s favorite topical disinfectant?

A

miconazole-chlorhexidine shampoo

41
Q

What other topical disinfectants can be used for decontamination of pets with dermatophytosis?

A

2% lime sulfur, 2-4% chlorhexidine rinses or shampoos, enilconazole rinses or spray, povidine-iodine shampoos

42
Q

How often should topical disinfectants be used?

A

weekly if it is the sole therapy, otherwise done initially and then every 7-10 days if possible

43
Q

When is topical dermatophytosis therapy used?

A

only on isolated lesions

44
Q

When is topical therapy best/most effective?

A

when it is used in conjunction with systemic therapy

45
Q

When is topical therapy not recommended as the sole treatment?

A

for multi-focal or generalized dermatophytosis

46
Q

What are some topical therapy commercial products?

A

Conofite, Tinavet, Tresaderm, and Imaverol (in Canada)

47
Q

What systemic treatments can be used to treat dermatophytosis?

A

Griseofulvin, Azoles, and Terbinafine

48
Q

What is the recommended dosage and treatment plan for Griseofulvin?

A

Dosage is 25-50mg/kg of regular formation once daily orally

49
Q

What enhances Griseofulvin absorption?

A

a high fat meal

50
Q

How long should be Griseofulvin be given?

A

It should be given for 2 weeks beyond clinical remission (4-8 weeks is standard)

51
Q

What formulation of Griseofulvin reduces the dosage in half?

A

ultrafine, microsized form

52
Q

What side effects are associated with griseofulvin toxicities?

A

anorexia, vomiting, diarrhea, pruritic dermatoses, leukopenia (more likely in FIV-positive cats), and the drug is highly teratogenic during the first half of gestation

53
Q

What azoles can be used for dermatophytosis treatment?

A

Ketoconazole, itraconazole, and fluconazole

54
Q

What is the recommended treatment plan for ketoconazole?

A

10-30 mg/kg, orally once daily for 30-60 days

55
Q

What adverse effects are associate with ketoconazole?

A

anorexia, alopecia, and increased hepatic enzyme concentrations

56
Q

How is the drug Itraxonazole available?

A

capsules or liquid suspension (in cats)

57
Q

What is the recommended treatment for Itraconazole?

A

Give it orally at 5-10 mg/kg PO daily for 30-60 days

58
Q

Is generic or brand name Itraconazole recommended?

A

brand name - Sporanox

59
Q

What is the recommended dosage for fluconazole?

A

5-10 mg/kg - there is no clear dosage

60
Q

Which azole is the drug of choice for treatment of dermatophytosis in cats?

A

Itraconazole (Sporanox)

61
Q

What is the overall drug of choice for systemic treatment of dermatophytosis in dogs and cats?

A

Terbinafine (Lamisil or generics)

62
Q

What is the recommended treatment plan for Terbinafine?

A

10-30 mg/kg, orally, once daily for 4-6 weeks

63
Q

Just an fyi (flip the card)

A

Terbinafine is not labeled for use in dogs and cats, however it is the drug of choice in dogs and cats…..

64
Q

True or False: It is possible to sterilize the environment to remove all spores and hyphae

A

False - It is virtually impossible, the goal is to reduce the burden of infective agents in the house

65
Q

What is the protocol if an animal tests positive for dermatophytosis in a cattery or a kennel?

A

Separate the infected animal immediately, wear protective clothing, clean and decontaminate the environment, and consider treating all animals with lufenuron (70mg/kg monthly for dogs and 100 mg/kg monthly for cats)

66
Q

How is onychomycosis (infection of the claw) diagnosed?

A

by removing part or all of the claw and culture

67
Q

Which systemic antifungals should not be given during pregnancy?

A

Griseofulvin, itraconazole, and fluconazole

68
Q

What saprophytes are commonly isolated in dermatophytosis cases?

A

Alternaria spp., Mucor spp., Penicillium spp., Aspergillus spp., and Rhizopus spp.

Small Animal Medicine (100 decks)

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