Approach to common dermatological presentations Flashcards
How does pruritus present in different species?
Dogs: Licking feet, scratching, chewing
Cats: Overgrooming (self-induced alopecia)
Horses: Stamping, rubbing
Small furries: Barbering (must differentiate from normal grooming)
What are the major causes of pruritus?
Hypersensitivities (atopic dermatitis, food allergy)
Parasites (fleas, mites, lice)
Microbial infections (bacterial pyoderma, Malassezia)
Other causes (neoplasia, immune-mediated diseases)
What tests help rule out parasitic and microbial causes of pruritus?
Parasites: Coat brushing, skin scraping, trichogram, acetate tape strips
Microbial Infections: Cytology (bacteria, Malassezia), Wood’s lamp, fungal culture
Consider treatment trials if test sensitivity is low (e.g. fleas, scabies)
What should be done if parasites and infections are ruled out as causes of pruritus?
- Elimination diet trial:
- 6-8 weeks with novel or hydrolysed protein (dogs/cats)
- Limited forage diet (horses)
- Challenge with old foods to validate results
- If diet works: diagnose with food-induced allergy - If diet trial fails: Diagnose environmental atopic dermatitis by exclusion
- Treatment options:
- Anti-pruritics &/or anti-inflammatory drugs
- Prophylactic treatments to control secondary infections
- Allergen-specific immunotherapy (ASIT) if IgE tests confirm environmental triggers
What is the step-by-step systematic approach to pruritus?
- Signalment, history & clinical signs → Make ranked d/d list
- Investigate & rule out parasites & infections first
- If pruritus remains → Conduct elimination diet trial
- If pruritus still persists → Diagnose environmental atopic dermatitis
Biopsies used for rare conditions or when presentation is unusual.
Client communication is essential – Process takes time!
What are some important considerations when assessing the signalment in pruritic animals?
Species:
- Diseases affect different species with different frequency
- e.g. Farm animals: Environmental atopy rare; ectoparasites more important
- e.g. Prion disease (scrapie) important in sheep
Age:
- Consider not only age, but age of ONSET of first signs of pruritus
- e.g. Parasites → Any age (Demodex in young/old)
- e.g. Atopy → Environmental (young adults); Food-induced (<1 year)
- e.g. Older animals → Rule out neoplasia & secondary infections
Sex:
- e.g. (older) ME dog: Sertoli cell tumour → secondary pyoderma
Breed predispositions:
- Care that these don’t have unconsidered effect on diagnosis
What questions would you ask/what would you want to find out for the history of the pruritic animal?
Animal background, details of husbandry (eg housing, bedding, diet)
Routine medical care & when administered (esp re parasites)
History of contagion/zoonosis
Details of skin condition – age of onset/duration, initial clinical signs/progression, seasonality
Evidence of systemic disease
What are the key considerations in eliminating parasites and microbial infections in dermatological cases?
Use wide range of tests
Choose effective anti-parasiticides
Consider antibiotic stewardship
Combine parasite control & microbial testing for:
- Better welfare
- Easier interpretation of results
- Clear communication with owners
In large animals, parasite control is main focus due to economic impact
What are the next steps if a pruritic animal improves with parasite control?
Continue parasite control
Reassess need for ectoparasitic therapy based on:
- Parasite type
- Environment
- Cost
What are the next steps if a pruritic animal improves with antimicrobial treatment?
If pruritus resolves after stopping treatment → monitor closely
If pruritus returns after stopping treatment → investigate further (consider other signs, owner wishes & antibiotic stewardship)
How should parasite control and antimicrobial therapy be assessed in a pruritic animal?
If both treatments were given & animal improved → stop antimicrobials first & observe response before deciding on further interventions
Are pustules and papules primary or secondary lesions?
Always primary
Define papule
Small solid elevation of skin <1cm diameter
Often erythematous
May → crusts of serum, pus or blood
Define pustule
Small (<1cm) skin elevation, filled with pus
Often start as papule
Depth in epidermis varies with disease
Fragile, short-lived so often see as crusts/ epidermal collarettes
What are some common causes of pustules & papules?
Infections
- Superficial bacterial pyoderma/folliculitis! (dog, horse)
- Dermatophytosis (cat)
- Malassezia dermatitis (dog)
Ectoparasites
- Fleas (dog, cat)
- Surface mites
- Burrowing mites (e.g. Sarcoptes)
- Demodicosis (dog)
Hypersensitivities
- Fleas (dog, cat)
- Environmental/food (dog, cat, horse)
- Insect bites (horse, farm animal)
Autoimmune disease (rare)
- Pemphigus foliaceus (dog, cat)
What key factors should be assessed during a dermatological clinical examination of lesions?
Follicular lesions? Suggests bacterial folliculitis, demodicosis, dermatophytosis
Lesion distribution:
- Caudal/dorsal trunk (dog) → Fleas
- Ventral abdomen, pinnal margins, elbows, hocks (dog) → Sarcoptic mange
- Lesions on face/pinnae/head? Consider autoimmune disease
- Lesions at different stages? Suggests superficial pyoderma
- Lesions appearing in waves? Consider pemphigus
Describe the diagnostic approach for pustules/papules
Are scale and crust primary or secondary lesions?
Usually secondary, rarely primary
(Where scale occurs in diseases, its secondary to underlying primary cause: secondary keratinisation disorders)
Define scale
Rafts of immature keratinocytes which accumulate at skin surface
Due to hyperkeratosis (increased depth of cornified layer)
Caused by increased or disrupted epidermal turnover
Loose or tightly adherent
Form scurf when desquamate
Define crust
exudates (serum, pus or blood) that dried on skin surface
Often also involves surface squames, hair, topical medications
Can be associated with:
- scaling diseases
- pustular/papular diseases
- ulcerative/erosive diseases
Very non-specific finding
What are some common infectious causes of scale and crust?
Bacterial
- Pyoderma/folliculitis! (dog, horse)
- Dermatophilosis! (farm, horse)
Fungal
- Dermatophytosis! (cattle, horse, cat)
- Malassezia dermatitis (dog)
Viral
- Viral papillomas (cattle, horse)
- Occult sarcoids (horse)
What are some common parasitic causes of scale and crust?
Ectoparasites
- Fleas (dog, cat)
- Lice (farm, horse)
- Surface mites
* Chorioptes (horse, cattle)
* Cheyletiella (rabbit)
* Psoroptes (sheep, rabbit)
- Burrowing mites
* Sarcoptes (dog)
* Trixacarus (guinea pig)
* Cnemidocoptes (bird)
- Demodicosis (dog, hamster)
Endoparasites (horse)
What are some common hypersensitivity causes of scale and crust?
Flea (dog, cat)
Environmental/food (dog, cat, horse)
Insect bites (horse, farm)
What are some common nutritional/metabolic causes of scale and crust?
Photosensitisation (cattle, horse)
Hypothyroidism (dog)
What are primary keratinisation disorders?
Defects in normal keratinisation process
- Abnormal formation of keratinocytes
- Abnormal sebaceous gland function
Often breed-related & tend to occur in younger animals
Diagnosis of exclusion
Describe the diagnostic approach for scale/crust
What lesion is this?
Crust
What lesion is this?
Scale
What lesion is this?
Papule
What lesion is this?
Pustule
Give examples of swellings of non-dermatologic origins
Hernias
Oedema
- E.g. due to right sided heart failure, hypoalbuminaemia
Bursitis
Emphysema
Mammary tumours
How does oedema (swelling of non-dermatologic origin) present?
Ill-defined, soft, painless swelling from, e.g. R sided heart failure, hypoalbuminaemia
Pits on pressure
Clear fluid on FNA
What is emphysema and what causes it?
gas in subcutaneous tissue
crepitant without pain or swelling
caused by:
- Severe respiratory disease or lung puncture
- Introduction of air through cutaneous wound
- Rumenotomy or rumen cannulisation
- Clostridial infections
How can skin masses be classified?
Give examples of infectious inflammatory skin masses
Abscess/ cellulitis
- e.g. post trauma/FB/ bite (farm animal, cat, also rabbit secondary to dental disease)
Furunculosis
- e.g. staphylococcal deep pyoderma
- e.g. Demodex
Bacterial granulomas
- e.g. Mycobacteria
- e.g. Actinobacillus, Nocardia, Actinomyces
Deep/subcutaneous or systemic fungal granuloma
Give examples of non-infectious inflammatory skin masses
Urticaria, angioedema (horse>dog>cat)
Seroma
Haematoma
Others
- e.g. eosinophilic granulomas, tick/insect bite granulomas, sterile panniculitis
What is urticaria/angioedema?
Degranulation mast cells –> oedema (painless, pit on pressure)
Can be allergic (type I or III) or non-immunologic cause
Urticaria –> wheals (+/- pruritus)
Angioedema –> large oedematous swelling, usually involving head – can be fatal
- same process but bigger area
What is a seroma?
Accumulation of serum under skin
Painless, non-pitting
Frequently occurs post-surgery
What is a haematoma?
Loss of blood from damaged/ruptured blood vessels under skin; painless, non-pitting
Usually due to trauma, occasionally due to clotting problems
Give examples of common neoplastic causes of cutaneous skin masses in different species
Most common in older animals –> uncommon in farm animals
Horse – esp. melanomas (grey horses), sarcoids
Dogs – skin neoplasms common - e.g. lipomas, sebaceous adenomas, mast cell tumours
Cats – neoplastic skin masses less common
What is a cyst?
Epithelial-lined cavity, containing fluid or solid material produced by cells of cyst lining
Smooth, well-circumscribed
Fluctuant/solid – dependent on nature of contents
What key factors influence the differential diagnosis for skin masses?
Species
- e.g. abscess in cat, cattle, rabbit; skin neoplasm in old dog
Breed/colour
- e.g. Melanomas in grey horse, mast cell tumours in boxers
Age
- e.g. neonate: umbilical abscess
- e.g. old animal: neoplasia
General & dermatologic history
What are examples of history findings that suggest specific conditions in cutaneous skin masses?
Recent trauma, fight, surgery → Abscess, haematoma, seroma
Recent injection → Abscess, panniculitis
Systemic signs (e.g. weight loss, respiratory signs) → Neoplasia, systemic fungal infections
What are key factors to look for in a general clinical examination of a patient with a cutaneous skin mass?
Pyrexia → Often seen with systemic or severe cutaneous microbial infections & abscesses
Peripheral Lymphadenopathy → Lymph node enlargement due to metastatic neoplasia or reaction to infection/inflammation
Other Systemic Abnormalities → May influence diagnostic/treatment choices or directly relate to mass
- Animals with lung metastases may have no clinical signs
Non-Dermatological Swelling? → Consider bursa, joint swelling, or hernia
What are we assessing in a dermatological examination of a patient with a cutaneous skin mass?
Solitary/multiple lesions?
Area of body? Size?
Well-defined? Ill-defined?
Freely moveable?
Draining tracts/sinuses?
Pits on pressure?
Painful/painless?
Inflammatory?
What cytology investigations can be done to a cutaneous skin mass?
Fine needle aspirate
1. ‘Needle only’ with no suction
2. ‘Continuous suction’
3. ‘Intermittent suction’
Impression smear of surface
Smears/touch impressions of sinus contents
How can cytology help differentiate types of inflammatory cutaneous masses?
Sterile vs. Septic – Presence of organisms suggests septic inflammation
- may be difficult to detect, esp. in pyogranulomatous inflammation
- Some organisms (e.g. mycobacteria) require special stains
Chronic vs. Acute – Chronic inflammation may show macrophages & fibrosis, while acute inflammation is often neutrophilic
What are the three main categories of neoplastic cells in cutaneous cytology?
Round cell
Epithelial cell
Spindle cell
How does cytology help identify cystic skin masses?
Cyst contents are produced by epithelial lining, leading to different aspirates:
- Sebaceous material, keratinised debris, cholesterol crystals
Granulomatous inflammation may be present if cyst has ruptured
Often amorphous appearance
What are the limitations of cytology?
Not all cell-types shed easily, so not always representative
May take unrepresentative sample
Gives no info re tissue architecture thus can’t grade neoplasm
- Requires subsequent histopathology if grading required
When is tissue biopsy recommended?
When FNA is inconclusive, for histopathology confirmation, and for tissue culture if needed
What skin mass is this?
Urticaria
What skin mass is this?
Angioedema of muzzle
What skin mass is this?
Seroma
What skin mass is this?
Aural heamatoma
What skin mass is this?
Eosinophilic granuloma (horse)
What skin mass is this?
Melanoma of perineum
What is alopecia, and what are the two main types?
Partial or complete hair loss, can be:
- Primary – Failure of normal hair growth
- Secondary – Hair grows normally but is later damaged or lost
What is the difference between true and apparent alopecia?
True alopecia – Direct damage to hair follicle unit –> loss of whole hair follicle
Apparent alopecia – Hair shafts damaged but not lost from follicle –> hair cropped short
What are the key mechanisms leading to primary alopecia?
Lack of stimulation of anagen phase → Hair fails to enter growth phase
Abnormal growth factors → Leads to miniaturised/dysplastic hairs that break off or shed
Elongation of telogen phase → Hair remains in resting phase indefinitely, preventing new growth
What are the major categories of alopecia causes?
Folliculitis!/furunculosis/bulbitis – Inflammatory damage to hair follicle unit
Hair cycle abnormality – Hair stops growing (e.g. endocrinopathy)
Hair morphology defects – Hair is malformed and breaks off
Congenital aplasia (rare) – Hair never grows
What factors should be considered when creating a differential diagnosis list for alopecia?
Species:
- Ringworm → Cattle, horses, cats, hedgehogs.
- Demodicosis, pyoderma → dogs
- Occult sarcoids → Horses
Age:
- Young → Infections (e.g. demodicosis, dermatophytosis, superficial pyoderma)
- Older → Endocrinopathies, neoplasia, chronic demodicosis
Breed:
- Terriers & Boxers → hyperadrenocorticism
- Staffies → demodicosis
- Dachshunds → Pattern baldness
- Jack Russell Terriers → Trichophyton infections from rodents/hedgehogs
Sex:
- Entire female guinea pigs → Ovarian neoplasia
- Entire male dogs → Sertoli cell tumours
How can history help identify the cause of alopecia?
Contagious/Zoonotic Causes → Consider dermatophytosis (ringworm) or ectoparasites
Systemic Signs:
- PUPD, polyphagia → HAC? (dog)
- Weight gain, lethargy → Hypothyroidism?
Pruritus?
- If present, investigate as self-trauma (pruritic alopecia), not true alopecia
In what cases can alopecia be normal?
Preauricular/pinnal alopecia of cats
Sphinx cats
Irish water spaniels
Flank scent glands on hamsters
What differentials do different distributions of alopecia suggest?
Localized or Multifocal/diffuse patchy alopecia → Dermatophytosis, pyoderma, demodicosis
Symmetrical alopecia → Dermatophytosis, pyoderma, demodicosis, Endocrinopathies, pattern alopecie, follicular dysplasias (+- colour linked), trace element deficiency (cattle)
How can we investigate whether an animal has true or apparent alopecia?
Trichogram
- Ease of epilation at periphery
- Easily epilated → true
- Requires some effort → apparent
- Broken distal tips → apparent
* NB often seen with trauma/pruritus so if pruritic investigate as per pruritus protocol
What lesion is seen here (alongside alopecia) and what condition is it suggestive of?
Calcinosis cutis –> Hyperadrenocorticism (dog)
What lesion is seen here (alongside alopecia) and what condition is it suggestive of?
Comedones, skin thinning –> Hyperadrenocorticism (dog)
What lesion is seen here (alongside alopecia) and what condition is it suggestive of?
Epidermal collarettes, papules –> pyoderma (dog)
What lesion is seen here (alongside alopecia) and what condition is it suggestive of?
Draining sinuses, furunculosis –> demodicosis (dog)
What tests help differentiate causes of alopecia?
Skin scrapings
- esp. Demodex mites
Dermatophyte testing
- Direct microscopy, culture
- Wood’s lamp for ringworm
Trichogram (hair analysis):
- Telogen dominance → endocrinopathies
- Melanin clumps → colour dilution alopecia (dog)
- Arthrospores/hyphae → dermatophyte infection
- Follicular casts → sebaceous adenitis (dog)
- Broken hair tips → trauma/pruritus
If no definitive diagnosis is reached in a alopecia case following skin scrapings, dermatophyte testing & trichogram, what further tests can be done?
Cytology – Helps diagnose secondary bacterial pyoderma
Endocrine testing
Skin biopsy to see:
- Folliculitis – e.g. bacterial, demodicosis, dermatophytosis
- Atrophic changes - e.g. endocrinopathy
- Follicular dysplasias
- Autoimmune cause - e.g. sebaceous adenitis or alopecia areata
What lesion is this?
Palatine lesion
What lesion is this?
Plaque
What lesions are these?
Plaques & ulceration
What lesion is this?
Lip ulcer
What lesion is this?
Excoriation on face
Fred is 11-month-old cat with 3-month history of severe pruritic skin disease. He is systemically well & lives in a multi-cat household.
Based on the history, what test would you want to do?
Wet paper tests (fleas) and thorough testing for other parasites
Label the cells and what condition does it suggest?
11-year-old Cavalier King Charles Spaniel with severe pruritus & redness of skin. He has mild cardiac disease, but this is adequately treated & he is generally well. He is receiving monthly afoxolaner & has good appetite & normal thirst.
Owner has googled allergic skin disease & considers this most likely diagnosis.
Why is cAD unlikely:
Based on history?
Based on lesions?
Based on the history?
- Age of onset very late for allergic disease (75% of cases start between 6m & 3y of age)
Based on the lesions?
- Distribution – esp. nose leather & top of head would be very unusual in cAD
- Nature of lesions – erosions, depigmentation, scale, alopecia & small hyperpigmented macules suggestive of disease attacking basement membrane
What test is best for diseases of basement membrane?
biopsy or cytology from exudative lesions
What are examples of diseases of the basement membrane?
Epitheliotropic lymphoma, cutaneous lupus, vitiligo
Describe these lesion. Are the lesions suggestive of endocrine alopecia?
Well demarcated, irregular alopecia affecting lateral flank with hyperpigmentation of exposed skin
Distribution appears geographical rather than generalised, indicating localised process rather than widespread telogenisation
Lesions don’t suggest endocrine alopecia, where hair loss occurs due to wear & tear, often presenting with diffuse & poorly demarcated edge
2½ year old MN mastiff cross has 4-month history of alopecia affecting sides. He is non-pruritic & owner reports that he has had no other lesions & is fit & well. His weight is normal & static. Its March at time of consultation.
What history points would you consider helpful in considering endocrine problems?
Age
- very young dog for neoplastic endocrinopathy (e.g. HAC or hyperoestrogenism due to Sertoli cell tumour)
- Immune-mediated endocrine problem (e.g. hypothyroidism) more likely, but dog is still quite young for this disease
Normal behaviour is noted & no weight gain
Problem started in winter, if it resolves in summer it would be strong hint that endocrine disease isn’t present
What basic tests can help investigate hormonal alopecia?
Haematology & Biochemistry:
- Stress leukogram, increased ALP → Hyperadrenocorticism
- Raised cholesterol → Hypothyroidism
Urine Tests:
- high USG → HAC unlikely
- Urine Creatinine:Cortisol: Useful as rule-out test for HAC
Thyroid Function Tests:
- T4 & TSH → Used to rule out hypothyroidism
Give examples of primary causes of feather loss in parrots
Hypovitaminosis A
Allergies
Hypothyroidism
Feather cyst
Giardia
Give examples of secondary causes of feather loss in parrots
Fungal/parasitic
Mites (Knemidocoptes)
Ringworm
Systemic illness
Give examples of behavioural causes of feather loss in parrots
Stress
Self mutilation
Boredom
Mating behaviours
Overbonding with owner
Give examples of primary causes of feather loss in chickens
Dermayssus Gallinae (red mite)
Nutritional deficiencies
Give examples of behavioural causes of feather loss in chickens
Feather pecking (hierarchy)
Poor enrichment
Stress
Overmating
Brooding
Give examples of causes of hair loss in guinea pigs
Cystic ovarian disease
Ectoparasites
Pyoderma
Post partum alopecia
Overgrooming
Endocrine disease
Vit C deficiency
Dermatophytes!
What are the 3 most common equine skin neoplasia?
Melanoma
- Black, spherical or plaque like, common around perineum & parotid region of grey horses
Sarcoid
- Multiple types, usually hairless, sometimes ulcerative, common in groin, axilla & around eyes
Squamous cell carcinoma
- Raised, irregular, pink, locally invasive, common around genitals & eyes
What are equine sarcoids?
Most common skin tumour in horses, caused by Bovine Papillomavirus
What are key characteristics of equine sarcoids?
Locally invasive, fibroblastic & wart-like
Can be single or multiple lesions
Six different types exist
How are equine sarcoids diagnosed?
Based on visual appearance, but confirmed by biopsy
Histologically, they show dense dermal fibroblasts in interlacing bundles
How are equine sarcoids (Bovine Papillomavirus) transmitted?
Flies act as vectors, spreading virus between horses
Common in areas where flies frequently bite (e.g. groin, axilla & around eyes)
What type of equine sarcoid is this?
Occult
What type of equine sarcoid is this?
Verrucose
What type of equine sarcoid is this?
Nodular
What type of equine sarcoid is this?
Fibroblastic
What type of equine sarcoid is this?
Malignant
What type of equine sarcoid is this?
Mixed
What are the treatment options for equine sarcoids?
Laser surgical removal
Cryotherapy
Caustic cream application
Elastrator band application (causes hypoxic necrosis in nodular sarcoids)
Radiotherapy (particularly for periocular sarcoids)
How can melanomas around the perineum be treated?
Removed with a surgical laser
What are the key features of Squamous Cell Carcinoma (SCC)?
Locally invasive, pink, irregular, sometimes ulcerated lesions
Can grow rapidly
Often affects genitals, eyes, penis & third eyelid
What is the standard treatment for SCC?
Complete surgical excision is recommended as SCC can progress & spread rapidly
Histological confirmation ensures complete removal
Early intervention is curative in most cases
What are eosinophilic granulomas?
Small, firm, non-itchy, non-painful raised nodules with normal hair covering
Commonly found on withers & back
Not neoplastic; their exact cause is unknown
How are eosinophilic granulomas diagnosed?
Based on clinical appearance
Confirmed via fine needle aspirate or biopsy
What is the treatment for eosinophilic granulomas?
Often not required unless interfering with tack
Can be treated with surgical excision or corticosteroid injections if necessary
What are juvenile papillomas?
Multiple, small, irregular, verrucose (wart-like) grey proliferative lesions
Commonly found on muzzle, face & sheath of young horses
Caused by equine papillomavirus
What is the typical progression and treatment of juvenile papillomas?
They are usually self-limiting, so treatment is not required
Cryotherapy may be considered for severe cases
What are the key characteristics of equine melanomas?
Typically benign, black, nodular & slow-growing
Most common in grey horses, esp. in perineum, sheath & parotid region
