Dermatology Flashcards
List 6 differentials for pruritis in a horse.
Mites
Lice
Trombiculids
Dermatophytes
Bacterial infection
Insect bites
Adverse food reaction
Atopic dermatitis
Contact dermatitis
What diagnostic testing could you do if you suspect a horse has ectoparasites?
Superficial skin scraping
Collect superficial debris
Acaricidal trial
How do we do an acaricidal trial?
Ivermectin 0.3mg/kg PO q7d for 4 doses
Fipronil spray 0.25%
What diagnostic testing could you do if you suspect a horse has a dermatophyte infection?
Hair pluck for arthrospores
Impression smear
Fungal culture of Trichophyton equinum
Skin biopsy with Period Acid Schiff stain
Name the infectious organism in dermatophyte infection.
Trichophyton equinum
What are the common bacteria causing pruritis in horses?
Staph. aureus
Staph. psuedintermedius
Staph. hyicus
What diagnostic testing could you do if you suspect a horse has a bacterial skin infection?
Cytology of an impression smear, tape strip
Response to treatment
Biopsy
C&S
Describe the treatment of a bacterial skin infection.
Topical - 3% chlorhexidine shampoo twice a week or spray daily, 2% mupirocin, 1% silver sulfadiazine
TMS 25mg/kg PO q12h for 14d
What are the clinical signs of insect bite hypersensitivity?
Pruritis
Papules/crusts
Alopecia
Urticaria uncommonly
Bacterial folliculitis common
Behavioural changes - anxiety, nervous, restless, aggressive, sensitive to touch
Weight loss
Distribution on the mane, rump, base of tail, face, pinna, neck, shoulder, limbs, dorsal thorax
What diagnostic testing could you do if you suspect a horse has an insect bite hypersensitivity?
Skin scraping for cytology - eosinophilic papules
Response to treatment
Avoidance - stabling and fans, protective rugs, boots
Treat environment
Insect bite trial
List the clinical signs of an adverse food reaction.
Lesions on the face, pinna, and neck
Mild intermittent diarrhoea
Flatulence
What food types have adverse food reactions been reported to?
Wheat, oats, barley, bran, alfalfa, soybean products
Explain the concept of an elimination diet in working up adverse food reactions.
Feed an elimination diet and document the resolution of clinical signs and relapse of clinical signs after the introduction of the previously fed foods. Feed a base food that wasn’t previously fed and withhold all concentrates, additives and supplements.
This process takes 4-8 weeks.
At what point do you evaluate for atopic dermatitis?
If there has been no response to an insect bite trial or elimination diet
If there is a non-contact distribution of lesions
Describe the typical signalment for atopic dermatitis.
TBs and Arabs
1-6 years old
Seasonal or perennial
List the clinical signs of atopic dermatitis.
Pruritis
Urticaria
Alopecia
Papules with crusts
Angiodema
Tail flicking
Stomping
Rubbing
Head shaking
What diagnostic testing could you do if you suspect a horse has atopic dermatitis?
Intradermal testing
Serological testing
Discuss the management of a horse with atopic dermatitis.
Immunotherapy
Avoidance
Dust + mould control
Topical therapy - oatmeal shampoo or 3% chlorhexidine shampoo
Glucocorticoids - prednisolone 1mg/kg q24h; dexamethasone 0.02-0.1mg/kg, maintenance 0.01-0.02 q48h; topical 0.054% hydrocortisone aceponate and mometasone
Antihistamines - hydroxyzine 1-1/5mg/kg q8h; chlorampheniramine 0.25-0.5mg/kg q12h
Fatty acids
List the clinical signs of contact allergic/irritant dermatitis.
Vesicles and papules
Crusting
Hyperpigmentation
Lichenification
Urticaria
Distributed on muzzle, pasterns, fetlocks, girth, generalised, white haired areas at risk
List 4 causative agents for contact allergic dermatitis.
Plants
Bedding
Topical shampoo, insecticides
Hoof paint
Topical medications
What diagnostic testing could you do if you suspect a horse has contact allergic/irritant dermatitis?
Localisation of Cx raises suspicion
Medication reactions at site of application
Avoidance
Patch testing
Define pastern dermatitis.
Skin lesions that affect the lower limbs of horses.
Name 3 differentials for clinical presentations in the pastern area.
Scratches
Greasy heel
Mud fever
Mud foot
Foot rot
Cracked heels
What are the prediposing factors for pastern dermatitis?
Feathers on pasterns
White skin and hair
Environmental - climate, moisture, stabling and pasture hygiene, sand
Iatrogenic - topical products, training devices, poor grooming habits
Name 4 primary causes of pastern dermatitis.
Mites - chorioptes, trombiculids
Dermatophytes
Contact allergy/irritants
Food/atopic dermatitis
Photosensitisation
Vasculitis
Pemphigus foliaceus
Name 2 perpetuating causes of pastern dermatitis.
- Secondary bacterial infection - Staph, Strep, Dermatophilus
- Chronic inflammation - fibrosis, exuberant granulation, cheloids
List the clinical signs of chorioptic mite infestation.
Pruritis
Stomping
Irritation of lower limbs
Crusting
Scaling
Exudation
Self-trauma
Alopecia
Excoriation
Name the causative agent of chorioptic mite infestation.
Chorioptes bovis
Name the causative agent of trombiculid infestation.
Neotrombicula autumnalis - larval stage
List the clinical signs of trombiculid infestation.
Pruritis
Papules and crusting
Alopecia
Discuss the preparation of cytology slides from crusting lesions.
- Take a small crust
- Place on slide with saline, macerate with blade
- Leave for 15-20 mins in warm place
- Knock off large clumps of debris
- Heat fix over a flame or with a hair dryer
- Stain with Quick-Diff or Gram stain if possible
If a skin scraping for pastern dermatitis came back positive for dermatophytosis what is the treatment?
Ivermectin 0.3mg/kg PO q7d for 4 doses
Topical selenium sulphide shampoo
2% lime sulphur dips q5d for 4 weeks
Fipronil spray 0.25%
Discuss the treamtent plan for pastern dermatitis caused by bacterial infection.
Clip
3% chlorhexidine shampoo q24h for 7d and taper off
Silver sulfadiazine cream
2% mupirocin cream
TMS 15-30mg/kg PO for 14-21d
Procaine penicillin G 22,000 IU/kg IM BID for 7-10d (if dermatophilosis)
Discuss your initial treatment plan for a case of pastern dermatitis.
Dry leg wraps - padded water repellent bandages, avoid ointments, avoid previously used topical products
Avoid pastures/paddocks with mud/water or sand for Arabs
Stable during wet weather and until morning dew has dried
Clip hairs especially feathers to avoid moisture retention
Then can address predisposing management factors, primary (mites and dermatophytes) factors, and perpetuating factors (infection)
Next step is usually biopsy for histopathology to identify the underlying disease - contact irritant, photosensitisation, vasculitis, photoactivated leukocytoclastic vasculitis, pemphigus foliaceus
List the clinical signs associated with photosensitization and photoactivated vasculitis in pastern dermatitis.
Erythema
Crusts
Superficial erosions on white haired and skinned areas
Oedema
Lameness
Define the term nodule.
Solid elevated lesion greater than 1cm in diameter.
List the systemic signs that may present alongside nodular dermatitis.
Pyrexia
Cough
Rhinitis
Anorexia
Lethargy
List 1 cause of nodular dermatitis from each of the following categories - bacterial, fungal, parasitic, inflammatory, neoplastic, sarcoid.
BACTERIAL - Staph, Actinomycosis, Nocardiosis, Corynebacterium
FUNGAL - Phaeohyphomycoses, zygomycoses, pythiosis, sporotrichosis, cryptococcosis
PARASITIC - tick bite granulomas, hypodermiasis, habronemiasis
INFLAMMATORY - axillary nodular necrosis, haematoma, sterile nodular panniculitis, FB granuloma, calcinosis circumscripta, eosinophilic granuloma
NEOPLASIA - SCC, melanoma, malignant melanoma, melanomatosis
SARCOID - fibroblastic, occult, nodular, verrucose, mixed, malignant
Explain the diagnostic testing options for nodular dermatitis.
FNA + skin cytology
Single or multiple incisional or excisional skin biopsies –> histopathologic evaluation
Aseptic biopsy for tissue maceration, bacterial + fungal cultures
Immunophenotype staining to identify cell types
PCR to identify DNA from potential infectious agents
Tumour staging - CBC, clinical chemistry, urinalysis, rads, LN aspiration for cytology review, US, CT
Describe the geographical distribution of fungal nodular dermatitis.
Humid areas of US, South America, and Australia
Name the causative agent of equine sporotrichosis.
Sporothrix schenckii
List the clinical signs of equine sporotrichosis.
Nodules causing cutaneous lesions
May progress to lymphadenitis (ulcerative lymphatic cording)
Discuss the diagnosis and treatment of equine sporotrichosis.
Diagnose with cytology, histopathology (pyogranulomatous inflammation, round or oval organisms surrounded by a clear halo resembling a capsule), immunofluorescent antibody testing on tissue and/or culture
Treatment with fluconazole
Name the causative agents of Habronemiasis.
Larvae of 1 of 3 species
Habronema muscae
H. microstoma
H. megastoma (Draschia)
Discuss the diagnosis of equine habronemiasis.
Tissue sulphur granules, cytology, histopathology, immunofluorescent antibody testing on tissue and/or culture
Describe the expected histopathology signs of equine habronemiasis.
Granulomatous inflammation with focal to diffuse infiltration of eosinophils + areas with coagulation necrosis surrounding a centrally located larva
Explain the treatment plan for a case of equine habronemiasis.
Oral ivermectin or moxidectin paste
Prednisolone 1mg/kg PO q24h for 14d then taper off AND/OR topical corticosteroids
In severe cases may need to surgically remove or debulk lesion
Strict attention to fly control + wound management
Describe the reaction pattern, clinical signs and lesion distribution of eosinophilic granuloma.
Insect hypersensitivity is the most common
Single or multiple lesions between 1-10cm, well circumscribed, round, firm
No hyperpigmentation, alopecia or ulceration
Mineralisation in chronic lesions
Distribution on neck, withers, saddle and girth areas
Explain the treatment plan for eosinophilic granuloma.
Glucocorticoids
For single lesions - intralesional or sublesional injection of triamcinolone actonide, surgical excision or CO2 laser ablation
For multiple lesions - prednisolone 1-2mg/kg/d for 7-10d, then taper off completely within 3-4 weeks, ectoparasite control, dietary trial and ASIT
Name the most common skin tumour in horses.
Equine sarcoid
What is equine sarcoid and how is it transmitted?
A locally invasive non-metastatic fibroblastic tumour, which rarely regress spontaneously.
It has strong association with bovine papillomavirus (BPV)-1.
Transmitted via flies, shared grooming equipment, common rubbing posts
There is also a genetic predisposition and familial tendency
Name 7 differential diagnoses for equine sarcoid.
Proud flesh (excessive granulation tissue)
Dermatophytosis
Linear hyperkeratosis
Blisters
Burns
Rub marks
Papillomatosis
Hyperkeratosis
SCC
Fibroma
Neurofibroma
Equine eosinophilic granuloma
Melanoma
Pythiosis
Fibrosarcoma
Lymphosarcoma
How do we get a definitive diagnosis of equine sarcoidosis?
Histologic examination of the affected tissue
Discuss the treatment options for equine sarcoidosis.
Benign neglect may be appropriate to monitor small lesionsin areas not interfering with tack, but any change or signs of growth should initiate intervention
En bloc resection of the entire tumour
Cryotherapy with or without prior debulking
Laser surgical excision
Radiation therapy
Intralesional therapy using cytotoxic agents - mitomycin, cisplatin or immunomodulation with BCG vaccine
Topical therapy - immunomodulation with imiquimod or cytotoxic agents (liverpool sarcoid cram, blood root ointments)
Describe the average signalment and distribution of squamous cell carcinomas.
12yo horses, males overrepresented, no breed predisposition
Distribution - mucocutaneous junctions (periocular, perioral, perinasal), unpigmented sparsely haired skin, penile + preputial lesions
Discuss the treatment and prognosis for a case of squamous cell carcinoma.
Wide surgical excision, cryotherapy, laser surgery
Radiotherapy
Cytotoxic chemotherapy - intralesional cisplatin, topical 5 fluorouracil
Prognosis - locally aggressive + may spread to local LNs, distant metastasis is possible, penile + preputial lesions are more aggressive
What is the average signalment and distribution for melanoma?
Grey and white coated older horses
Distribution on ventral tail, perineum, vulva, dorsal prepuce, lips, periocular and parotid gland regions
