Approach to scale

Explain what scale is

• Desquamated corneocytes on skin and in the hair coat

  • Normal skin physiology: a little scale (dandruff) is normal

What does pathological scaling result from?

• Abnormal desquamation (shedding of corneocytes)

• Abnormal cornification (creation of the outer cornified layer of epithelium)

• Inflammation (increased keratinocyte turnover)

• Bacterial and fungal enzymatic action

Can be adherent or loosely attached

Why may scale be confused with crusts?

• Crusts result from the hardening of pus, serum and/or blood to form a solid material on the skin surface

• Scale can become trapped in skin exudates and form part of crusts

What is the difference between 1° and 2° scaling?

Primary: direct result of disease pathology

Secondary: due to skin inflammation, internal disease or external factors (including environment)

• Much more common than 1°

What causes scale in bacterial infection?

1. Staphylococcus pseudintermedius causes folliculitis (inflammation of hair follicle) and follicular pustule

2. Following rupture of the pustule and central hair loss, a spreading circle of scale is seen (epidermal collarette)

3. Darkening of the skin (hyperpigmentation due to the previously present inflammation

Amount of scale dependent on bacterial toxins

List of Ddxs for scaling

How do you approach a patient where scaling is present?

• If pruritis present most likely parasites, bacterial infection and/or allergic skin disease

1. Check for parasites

2. Check for secondary infections

3. In older dogs perform baseline testing for endocrine/metabolic diseases: urinalysis, haematology & biochemistry

4. Skin biopsy

5. Genetic testing if indicated

• Ichthyosis of the Golden retriever, Great Dane and American Bulldog

• Epidermolytic hyperkeratosis of the Norfolk terrier

• Lethal acrodermatitis of the Bull Terrier & Miniature Bull Terrier (very rare)

List the diseases where scale is a major presenting sign?

• Zinc responsive dermatosis

• Ichytyosis of the Golden Retriever

• Ear margin Seborrhea

• Feline thymoma/non thymoma-associated exfoliative dermatitis

• Feline idiopathic facial dermatitis

• Feline acne

What are the two types of zinc responsive dermatosis?

• Type I: genetically-induced defective intestinal absorption of Zn

  • Siberian huskies, alaskan malmutes, english bull terries predisposed

• Type II: rapidly growing dogs fed a Zn deficient diet (or over-supplemented with substances that interfere with Zn absorption)

  • Juvenile largre/ giant breed dogs

How does zinc responsive dermatosis present?

• Primary: erythema, 50% cases pruritic

• Secondary: scale, alopecia, suppuration & crusting +/- SBI

• Periocular, perioral, chin, ears, occasionally genitals

• May see hyperkeratotic footpads

• Sites of trauma (Zn required for normal keratinisation)

How is zinc responsive dermatosis diagnosed?

Skin biopsy

• Parakeratosis key finding

How is zinc responsive dermatosis treated?

Type I:

• Zn supplementation

• Zinc sulphate traditionally used – may cause vomiting

• Consider prednisolone (increases Zn absorption) and EFAs if poor response

Type II: correct diet

What is the pathogenesis of ichthyosis of the Golden Retriever

• Genetic: mutation in PNPLA1-gene

• Leads to abnormal cleavage of desmosomes between corneocytes during desquamation

How does ichthyosis of the Golden Retriever present?

• Seen from a few weeks old but may be older when scaling noted

• Golden retrievers and goldendoodles

• Non pruritic (unless SBI which is not usually present)

• Variable amounts (can be large) of large flakes of non-adherent scale

• Hyperpigmentation

• Generalised but often more noticeable on ventrum (particularly hyperpigmentation)

How is ichthyosis of the Golden Retriever diagnosed?

• Rule out parasites (unlikely as non-pruritic)

• Skin biopsy

• Genetic testing widely available (part of official UK Kennel Club DNA testing scheme) - if several puppies in litter affected consider skipping biopsy and performing genetic testing

How is ichthyosis of the Golden Retriever treated?

• Skin barrier function not compromised so secondary bacterial infection uncommon, but can get microbial otitis

• Scaling is cosmetic disease: symptomatic treatment only

How does ear margin seborrhea present?

• Mainly adult onset, but can occur in puppies

• Marked breed predilection in Dachshunds

• Non-pruritic (unless SBI)

• White to pigmented, adherent scale +/- follicular casts

  • With chronicity may see fissuring of skin and SBI

• Distribution: pinnal margins (medial and lateral aspects)

How is ear margin seborrhea diagnosed?

• Rule out parasites: particularly demodicosis and sarcoptic mange (unlikely as non-pruritic)

• Skin biopsy (although initial clinical diagnosis and treatment trial acceptable)

How is ear margin seborrhea treated?

• Emollient rinses, Vaseline, propylene glycol

• Surgery to remove pinnal margin (rarely required!)

What are the general features of feline thymoma/nonthymoma-associated exfoliative dermatitis?

• Rare paraneoplastic syndrome

• Middle to older age cats

• Non-pruritic

• +/- signs of respiratory compromise (due to thymoma in thorax)

• No association with thymoma in some cases

• Thymoma and non-thymoma cases are indistinguishable clinically and histopathologically – advanced imaging required

How does feline thymoma/nonthymoma-associated exfoliative dermatitis present?

• Diffuse erythema and scaling (large 1+ cm flakes of skin), +/- alopecia

• Distribution: generalised

How is feline thymoma/ non thymoma-associated exfoliative dermatitis diagnosed?

Skin biopsy

Thoracic radiography / CT

How is feline thymoma/ non thymoma-associated exfoliative dermatitis treated?

• Surgery to remove thymoma may be curative

• Immunomodulatory drugs can be used- more beneficial in nonthymoma associated

• Guarded prognosis

What are the general features of feline idiopathic facial dermatitis?

Disease of unknown aetiology complicated by microbial overgrowth

Young to middle aged cats

Persians and similar breeds (e.g. exotic shorthair), Himalayan cats

Variable pruritus (common with SBI or Malassezia overgrowth)

How does feline idiopathic facial dermatitis present?

Tightly adherent, greasy black scale +/- erosion, ulceration and exudation

Distribution: periocular skin, nasal folds, muzzle, chin

How is feline idiopathic facial dermatitis diagnosed?

• Diagnosis of exclusion: rule out parasites, microbial infection (including dermatophytosis), consider allergic skin disease if generalised disease

• Cytology: Malassezia overgrowth common

How is feline idiopathic facial dermatitis treated?

• Anti-yeast therapy: ideally topical but may need to consider systemic if cat wont permit topicals or concern with proximity to eyes

• Keratolytic shampoos

• Immunomodulation: ciclosporin, prednisolone, topical tacrolimus

What is feline acne?

Common keratinisation disorder of cats

how does feline acne present?

Dark, waxy to dry scale adherent to hair base +/- comedones

Distribution: chin (less commonly lips)

How is feline acne diagnosed?

• Largely clinical diagnosis: rule out Demodex cati

• Cytology: Malassezia overgrowth, SBI

How is feline acne treated?

• Topical antiseptics +/- antimicrobials

• Topical keratolytic

• Prednisolone if significant inflammation present

What are keratoplastic/keratolytic products?

• Reduce scale production . sulphur and coal tar shampoos = keratoplastic

• Or remove scale e.g. salicylic acid shampoos = keratolytic

• Delicate balance between removing scale and causing excessive drying

• Used before moisturizing products

What are moisturizing and emollient products?

• Reduce transepidermal water loss and prevent inflammation e.g. products containing oils, propylene glycol and urea

• Best used after other products have removed scale / treated secondary infections