Lecture 21 4/15/25 Flashcards by Danika Boltz

What are the characteristics of folliculitis/furunculosis?

-most commonly caused by Staph. aureus and Staph. intermedius group
-secondary to cutaneous trauma
-can see papules, crusts, and circular alopecia
-draining lesions can be seen on trunk, pastern, and tail

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What are the characteristics of truncal folliculitis/furunculosis?

-occur in saddle area
-associated with poor grooming and trauma from tack

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What is pastern folliculitis?

crusts and papules around the pasterns and fetlocks

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What causes tail pyoderma?

secondary to tail rubbing

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How is folliculitis/furunculosis diagnosed?

-cytology
-skin scrapings
-possible biopsy
-possible culture and sensitivity

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What is the treatment for folliculitis/furunculosis?

topical +/- systemic antibiotics (TMS, doxy) for a 10 to 14 day minimum

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What are the characteristics of contact dermatitis?

-very common
-occurs with irritant or allergic etiology
-trigger type determines lesion location
-triggers include pasture, bedding, topical meds, and fly sprays
-causes erythema, alopecia, scaling, and crusting
-pruritus is variable

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How is contact dermatitis diagnosed?

-history and physical exam
-cytology
-environmental elimination
-biopsy possible but not often needed

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How is contact dermatitis treated?

-discontinue/avoid allergen or irritant
-gentle cleansing
-antibacterial agents
-steroids

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What are the important differentials for scaling and crusting?

-actinic/solar-induced
-nutritional

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What are the types of photosensitivity?

-primary: photodynamic agent is ingested
-hepatogenous: associated with liver disease and increases in phylloerythrin
-congenital: aberrant porphyrin or heme synthesis
-photocontact photosensitivity: lesions only in depigmented areas

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What are the clinical signs of of photosensitivity?

-sun burn, typically in white or lightly haired areas
-erythema
-scaling
-necrosis
-ulceration
-photo-activated vasculitis (white areas only)

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Why can horses get thermal burns in darker areas of hair?

the dark coat wicks heat into the follicle and causes a thermal burn

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How is photosensitivity diagnosed?

-history and physical exam
-chem panel/liver function tests
-biopsy
-possible porphyrin studies

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What is the treatment for photosensitivity?

-avoid sunlight
-stop intake of photo-sensitizers or hepatotoxins
-topical antimicrobial creams/ointments
-glucocorticoids to reduce inflammation in cases of vasculitis
-possible systemic antibiotics

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What are the causes of true nutritional deficiencies that can lead to dermatoses?

-poor food storage; esp. towards end of winter
-endoparasitism
-poor teeth

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What does it mean for nutritional dermatoses to be “responsive” dermatoses?

respond to vitamins or minerals as therapeutics in most cases

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What are the characteristics of demodectic mange?

-rare
-causes scaling and alopecia
-nodular presentation is most common

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What are the characteristics of cutaneous onchocerciasis?

-dermatitis associated with microfilaria of Onchocerca cervicalis nematode
-microfilaria found in skin of ventral midline, face, and eyelids
-microfilaria is ingested by Culicoides vector
-many horses in the southeast are infected without cutaneous lesios

What causes lesions in cutaneous onchocerciasis?

hypersensitivity to microfilariae

What are the clinical signs of cutaneous onchocerciasis?

-lesions of face and periorbital region
-scaling
-alopecia
-depigmentation
-permanent scarring and depigmentation
-non-seasonal with seasonal flares

What are some helpful hints regarding cutaneous onchocerciasis and culicoides?

-depigmentation is NOT associated with culicoides
-tail pruritus is NOT associated with onchocerciasis

How is cutaneous onchocerciasis diagnosed?

-histopathology
-response to treatment

What is the treatment for cutaneous onchocerciasis?

-one dose of ivermectin
-re-treat in 3 to 12 months to kill adults

What are the adverse effects of cutaneous onchocerciasis?

-facial and/or abdominal edema -uveitis

What are the characteristics of pemphigus foliaceus?

-autoimmune dz with autoantibodies to intercellular cement of epidermis -causes sub-corneal separation with acantholysis -may have a vasculitic component -uncommon cause of scaling and crusting -predisposed in Appaloosas

What are the clinical signs of pemphigus foliaceus?

-pustules, crusts, and alopecia -lesions involving head, ears, lower extremities, and genitalia -depression -edema -fever

What are the two unusual forms of pemphigus foliaceus?

*foals -may not require life-long treatment *coronary band only -all 4 feet -causes scaling, crusting, and ulceration -hooves may slough

What is the main differential for pemphigus foliaceus?

dermatophilosis

How is pemphigus foliaceus diagnosed?

-cytology showing acantholytic keratinocytes -biopsy showing sub-corneal pustules with acantholytic cells +/- vasculitis

What is the treatment for pemphigus foliaceus?

-prednisolone or dexamethasone -foals may go into permanent remission, adults require treatment for life

What are the characteristics of cutaneous vasculitis?

-immune complex dz -can occur with: *infections *solar exposure *drugs *allergies *autoimmune dz

What are the characteristics of cornification disorders?

-can be localized or generalized -can be primary or secondary -secondary disorders can occur with any of the crusting or pruritic disorders

What are the characteristics of mane and tail seborrhea?

-moderate to heavy scaling in mane and tail -no pruritus

What are the differentials for mane and tail seborrhea?

-pyoderma -culicoides -lice -nutritional

What is the treatment for mane and tail seborrhea?

anti-seborrheic shampoos

What are the characteristics of cannon hyperkeratosis?

-seborrhea affecting dorsal surface of cannon bone -occurs in middle aged to older horses -cause is unknown -treated symptomatically

What is important regarding pastern dermatitis?

-NOT a diagnosis -must have microtrauma that damages skin barrier

What can cause pastern dermatitis?

-folliculitis -dermatophilosis -dermatophytosis -chorioptic mange -contact irritant/allergy -contact photosensitivity -habronemiasis -rhabditic dermatitis -anaerobic infection

What is the "grapes" variant of pastern dermatitis?

form of the syndrome in which the lymphatic system gets involved that is harder to manage

How is pastern dermatitis diagnosed?

-history and physical exam -skin scraping -cytology -biopsy -culture -contact elimination

What is the treatment for pastern dermatitis?

-depends on diagnosis -clip and clean -topicals, including chlorhexidine and anti-inflammatories -ivermectin -systemic treatment -surgery if severe and proliferative

What are the characteristics of eosinophilic granuloma?

-most common nodular skin dz of horses -likely a type 4 hypersensitivity to insect bites -more common in the summer

What are the clinical signs of eosinophilic granuloma?

-one to several firm nodules in the dermis -overlying skin usually normal but surface may ulcerate -typically on sides of neck, withers, and back -no pruritus or pain

What are the differential diagnoses for eosinophilic granuloma?

-Staph. furunculosis -sarcoid -tick bite reaction -neoplasia -hypoderma -amyloid

How is eosinophilic granuloma diagnosed?

-aspirate cytology showing eosinophils, macrophages, and lymphocytes -biopsy

What is the treatment for eosinophilic granuloma?

may regress spontaneously over time -if a few lesions, can be treated with sublesional triamcinolone or dexamethasone -if many lesions, treated with systemic corticosteroids -mineralized lesions may not completely disappear -insect control very important