Dermatology Flashcards

Question

Species of mite affecting horses

Answer 1

Chorioptes equi Sarcoptes scabei Psoroptes equi Trombicula

Answer 2

Leg mange Very common Consider in all feathered breeds Chewing legs, stomping, kicking

Answer 3

Treat presumptively Skin scrapes if you want to confirm

Answer 4

Clip feathers, especially when using topicals Topical fipronil spray Injectable doramectin (Dectomax®) Selenium shampoo washes (keratolytic) Treat twice at 14 day intervals Advise treat in contacts (even if asymptomatic) Clean the stable/fomites (including disposing of all bedding)

Answer 5

Body mange Very contagious to other horses Biting mites feeding on cellular debris and serum Transmitted by direct contact with infected horses or fomites Affect forelock/mane/tail, may then spread to trunk May show signs of headshaking, alopecia, crusts, but pruritus may be variable Diagnose with skin scrapes Treat as for Chorioptes

Answer 6

Zoonotic Scabies/head mange Highly contagious between horses and will affect humans Burrow into epidermis, preferentially head/ears at first but spread over body Deeper mite, so may be missed on skin scrape Can survive for 3 weeks off host Ivermectin at 14 day intervals for 2-3 repetitions

Answer 7

Chiggers/harvest mites Neotrombicula and Eutrombicula mites that live on small rodents as the natural host Papules/wheals have a central red ‘spot’ which is the mite larva Affect face, muzzle, ventral abdomen/thorax, distal limbs May cause discomfort to horse and can be treated with pyrethrins, may require steroids additionally Self-limiting condition

Answer 8

‘Pinworm’ Primary gastrointestinal parasite (adult lives in colon), but causes skin disease when eggs are deposited Gravid female worms stick eggs to perianal skin Eggs become infective in 4-5 days The sticky substance holding the eggs dries up and flakes off, and the eggs persist in the environment Causes itching, tail rubbing, self-trauma around rump

Answer 9

Tapestrips from perianal skin NOT faecal worm egg counts If suspicious treat anyway, don’t rely on tape strips

Answer 10

Evidence is lacking, and there’s no consensus between clinicians, which causes confusion Suggest starting with ivermectin/moxidectin, but resistance is increasing Pyrantel would be another sensible choice Fenbendazole also licensed as effective but would not be my preference Wash perianal skin to interrupt life cycle Can apply petroleum jelly to prevent eggs sticking Do NOT use anthelmintics around anus/rectally Clean environment

Answer 11

Uncommon in the UK. H. muscae and H. microstoma (house fly intermediate host) and Drashcia megastoma (stable fly intermediate host) Lesions occur when L3 larvae are deposited on a wound or moist areas of skin Cause nodular skin disease or ‘summer sores’, may contain white granular material May be pruritic, may self-traumatise Common sites: periocular, penis/prepuce, lips, any site with a wound Similar appearance to exuberant granulation tissue, sarcoids Spring and summer, partially/completely regress in winter

Answer 12

Oral avermectins May consider topical glucocorticoids +/- DMSO to relieve itching

Answer 13

Onchocerca cervicalis – microfilarial nematode Vector borne (midges), worse in the summer Adult worm can live for 10 years in nuchal ligament Lesion distribution: eyes, muzzle, neck, chest, ventral abdomen Alopecia, scale, self-trauma from scratching Rare in UK Moxidectin and ivermectin are effective, so less common with use of these anthelmintics.

Answer 14

Skin biopsies

Answer 15

Moxidectin/ivermectin May require severeal monthly treatments May have adverse reaction so can give concurrent NSAIDs or steroids

Answer 16

Coital exanthema Viral papilloma

Answer 17

Papillomavirus caballi Two main syndromes - warts or aural plaques

Answer 18

Young: 6mo – 4yrs Muzzle, lips, nose, eyes Spontaneously regress usually within 3-4 months Investigate if persist for >2 years (or if warts spread to atypical areas of the body) Underlying conditions? Consider altered immune status if there’s a failure to clear infection naturally Intervention may actually increase lesion persistence so try to avoid unless necessary Cryotherapy probably best as induces necrosis and possibly viral antigen

Answer 19

> 1 year of age Do not spontaneously regress ‘Cauliflower’ growths inside pinnae Small, then coalesce Treat if causing an issue Imiquimod topically May become sore and head shy

Answer 20

Dermatophytosis (ringworm)

Answer 21

‘Ringworm’ Trichphyton spp. (T. equinum, T. verrucosum) and Microsporum spp. (M. gypseum, M. equinum) are most common in horses Zoonotic/transmissible Hair and epidermis affected Keratolytic enzymes from fungus weaken hair – epilate easily Alopecic regions with surface scale Predilection sites where tack etc. contact skin as skin damage allows for fungal infection to star

Answer 22

qPCR is now best method – results within 24 hours and detects multiple species Fungal culture possible, but takes 2-3 weeks Need to start treatment/barrier nurse in lieu of results

Answer 23

In healthy horses infection is self-limiting and will resolve in 5-10 weeks, but zoonotic/transmission potential too significant to allow this Remove surface scale/bathe to remove debris before applying topical enilconazole washes Ensure all fomites (tack, stable, trailer etc.) are disinfected and not shared between horses

Answer 24

Staphylococcal pyoderma Cellulitis Dermatophilosis

Answer 25

S. aureus, S. pseudintermedia Crusts, papules, pustules May be very pruritic (variable) Can also be very painful potentially Often along dorsum related to tack/rugs

Answer 26

Often treated with antimicrobials based on appearance Culture to confirm, try to get samples from under intact crust

Answer 27

Systemic antimicrobials (e.g. TMPS, penicillin) Topical silver sulphadiazine (Flamazine)

Answer 28

Bacterial infection of subcutaneous tissue/deep dermis Commonly distal limb, but not necessarily Very common, may present as an emergency May be ‘fracture’ lame Heat, pain, swelling May be systemically unwell - pyrexic Commonly Staphylococcus, also Streptococcus Secondary to wounds/puncture injuries, injections, skin trauma? If so, manage the primary cause if it is still presenting an issue

Answer 29

NSAIDs Antimicrobials § systemic – TMPS usually a good first choice (orally), or penicillin (injectable) Some cases may require corticosteroids (evidence poor) § Possibly some conflation with lymphangitis cases Cold hosing Walking in hand Poor consensus between clinicians, treat systematically, if it’s not resolving reconsider the plan and ensure you’ve ruled out any underlying driving factors (e.g. foreign bodies etc)

Answer 30

Dermatophilus congolensis ○ Branching, gram +ve, facultative anaerobe ○ Use this to your advantage when treating – create an AEROBIC environment ‘rain scald’ (dorsum), ‘mud fever’ (limbs) Crusting, forms tufts of hair attached to crusts (’paintbrush’) Carrier animals perpetuate infection Crusts are infective, so clean them up/dispose of them

Answer 31

Send crusts to lab, minced with saline, examined on smear for branching filamentous organism with parallel rows of cocci Treated presumptively usually

Answer 32

Soak and remove crusts Pat dry Topical antimicrobials ○ E.g. fucidic acid gel If severe, systemic e.g. TMPS

Answer 33

Usually described by client as ‘mud fever’, but there are lots of causes beyond Dermatophilus congolensis Often multifactorial, is a syndrome not a single disease entity Often treated symptomatically, and with those concurrent conditions in mind

Answer 34

Manage the environment, prevent from getting wet Barrier creams can be useful, but potential of creating an unhealthy skin environment with thick creams Clip hair to treat skin with topical medications May require antibacterial washes and topical antimicrobial/steroid creams to manage lesions when they flare up

Answer 35

Urticaria 'hives' Insect bite hypersensitivity ('sweet itch', IBH) Atopy (food, environment) Eosinophilic granuloma Pemphigus foliaceus Chronic progressive lymphoedema Photosensitisation

Answer 36

Roughly circular raised wheals - may coalesce Immunological and non-immunological causes May be a one-off event, or may be chronic Investigate causes if recurrent

Answer 37

Insect bites, food allergies, drugs, environmental allergens Type I (and III) immune reaction Type I: characterised by mast cell degranulation, IgE mediated Th2 helper and IgE response -> eosinophils and mast cells

Answer 38

Heat/cold exposure Dermatographism (after twitching the neck, use of whip etc will see focal urticaria) Cholinergic (exercise/heat)

Answer 39

Steroids if severe § May need dexamethasone IV initially before moving onto oral prednisolone § Very severe cases may progress to respiratory tract obstruction Antihistamines may be useful § Hydroxyzine might be useful initially, may cause drowsiness (ridden safety implications) § Chlorphenamine (Piriton) first generation and at useful doses likely to cause drowsiness (implications for ridden safety) Cold hosing may provide some relief

Answer 40

Culicoides spp. hypersensitivity Hypersensitivity to saliva, but also insect mouthparts etc. Type I hypersensitivity response ○ characterised by Th2 helper and IgE response, with subsequent eosinophil and mast cell response Type IV hypersensitivity also implicated ○ Delayed hypersensitivity reaction ○ T-cell and macrophage mediated Association between being affected with asthma and IBH (and vice versa). IBH is associated with airway hypersensitivity Can be a serious welfare issue if not well controlled May necessitate euthanasia in severe cases Onset typically 3-4yrs/age (can be older)

Answer 41

Intense pruritus Alopecia, lichenification, excoriations from self-trauma Lesion distribution: § Common: dorsal distribution. Mane and tailhead are classic, also withers, face, neck (Syndrome I – very common UK) § Ventral chest and abdomen, jaw, (Syndrome II – not common in UK) Both (Syndrome III)

Answer 42

Based on classical lesion appearance and distribution If atypical/does not respond to management may wish to rule out other ectoparasites, other causes of dermatitis, lesions affecting the tail may occur with cases of pinworm etc. To obtain definitive diagnosis may pursue intradermal allergy testing - Expensive and not usually necessary

Answer 43

Revolves around avoiding exposure to midges § Avoid standing water § Stable at dawn and dusk when midges are worse § Use topical insecticides □ Pyrethrins (Deosect, Switch) Permethrin or cypermethrin □ Benzyl benzoate effective, but probably doesn’t persist as long □ Citronella etc. from the tack shop are not sufficient/effective § Fly rugs § Stable with fans if severe (midges are weak fliers) § Move to coastal/exposure pasture May need treatment with systemic/topical glucocorticoids to alleviate itch initially, but management changes are vital § Antihistamines unlikely to be helpful Nicotinamide supplement (Cavalesse) § Poor evidence IL-5 vaccination in occasional use (not licensed) § Switch Th2 response to Th1 response

Answer 44

Multiple allergies stack up to take them over the pruritic threshold Allergen specific IgE to environmental allergens Pruritus, or urticaria, eosinophilic granuloma, secondary pyoderma Commonly see secondary pyoderma Intradermal skin testing: direct management, not a diagnostic tool to label horse with 'environmental allergies' Stop treatments at least 14 days before testing Manage with steroids when required Control secondary bacterial dermatitis- Topical or systemic antimicrobials Essential fatty acids If struggling to control itch consider pentoxyphylline

Answer 45

Trial novel diets, keep it simple, eliminate all supplements and additives Need to try for minimum of 6 weeks before trying something new ○ Can then re-add challenge to see if it was the cause

Answer 46

Intradermal skin testing is useful to direct management, it isn’t a diagnostic tool to confirm environmental allergies Remember to take off of medications at least 14 days before testing Only test relevant allergens! Dermatitis and urticaria

Answer 47

Subcutaneous and sublingual allergen specific vaccinations 65-70% subcut vacc positive response and may achieve long term remission Some respond better to sublingual than subcut and vice versa Response takes several months but aiming for a longer term solution

Answer 48

Can be associated with atopy, but not necessarily Firm nodules associated with collagen degeneration Usually feel like a pea under the skin Usually small, <1cm, can be bigger Usually along dorsum but may be elsewhere Overlying skin/hair normal (unless trauma from tack) Aetiology not understood - ? Hypersensitivity reaction ? ○ Possible association with insect bites? But not well understood Usually left untreated Can surgically excise or use intralesional steroids if large/becoming traumatized

Answer 49

Very uncommon, potentially life-threatening Autoantibodies produced against keratinocyte proteins and disrupt intercellular adhesion -> space fills with fluid -> pustules/blisters Crust and scale, eruptions Coronary band may be only area affected initially May have urticaria first, may become alopecic Weight loss, pyrexia, some may be extremely painful

Answer 50

Often diagnosed late due to similar appearance to other conditions Impression smears of intact pustules/crusts may be useful Biopsy: must include intact crusts attached to skin/hair Acantholytic cells and neutrophilic infiltration

Answer 51

High doses of steroids until no new lesions, then taper Maintenance dose for life Gold salts also reported as useful potentially Azathioprine may be helpful especially if cannot use steroids Generally treatment most successful in younger patients

Answer 52

Progressive limb swelling, chronic severe skin disease Heavy horses (Clydesdales, Shires, Friesians, Cobs etc.) Genetic predisposition, altered lymphatic function and elastin metabolism Significant welfare issue Onset early age, but may not be noticed until much later Skin lesions secondary to poor lymphatic circulation Life long, progressive disease May cause severe lameness Presents often as pastern dermatitis Secondary parasitic/bacterial infection very common

Answer 53

Presumptive § Advanced imaging techniques have been used in studies but not feasible § Biopsies not going to diagnose the problem due to depth of lymphatics from skin § May need diagnostics to rule out secondary/concurrent diseases

Answer 54

Manage secondary infections (bacterial and parasitic) Keep feathers clipped Bandaging (if carefully managed) may help Prognosis fair if carefully managed, otherwise often a significant welfare issue

Answer 55

Lesions caused by UV light exposure after skin is sensitised by photodynamic agent Usually affecting white haired skin

Answer 56

Primary (type I): ingestion/absorbtion of photodynamic agent § Can be through skin contact with substance/plant Hepatogenous (type II): liver cannot excrete phylloerythrin (from chlorophyll) (Porphyria: abnormal pigment synthesis) (Photosensitivity of unknown aetiology)

Answer 57

Ingestion of St John’s wort the most common, also buckwheat, spring parsley Some clovers cause contact photosensitivity and hepatic photosensitivity

Answer 58

Any cause of liver disease – may not show any other clinical signs of hepatopathy Cholestasis, mycotoxin ingestion, pyrrolizidine alkaloid toxicity (Ragwort)

Answer 59

Steroids (dexamethasone - injectable, or prednisolone - oral) Topical steroids (hydrocortisone spray, betamethasone +fusidic acid gel) Antihistamines (results often disappointing) (cetrizine, hydroxyzine, chlorpheniramine) Shampoos and washes (keratolytics, antibacterial/fungal, moisturising)