Seborrhea is characterised by a defect in keratinisation or cornification. This results in increased scale formation, a greasy skin and hair coat and often secondary inflammation and infection.
There are large amounts of free fatty acids and cholesterol and decreased amounts of diester waxes in surface lipids which lead bacterial populations to become pathogenic coagulase positive staphylococci.
It is a chronic disease affecting mainly dogs, but also sometimes cats and horses.
Primary Idiopathic Seborrhea
This is a common inherited skin disorder seen most frequently in Cocker Spaniels. Basal epidermal cells in affected dogs undergo accelerated cellular proliferation and turnover.
There is an increase in the number of actively dividing basal cells, a shortened cell cycle, and a decreased transit time to the stratum corneum (7-8 days compared with 21-23 days). Hair follicles and sebaceous glands are also affected.
Abnormal keratinisation begins from a very early age and tend to worsen with time.
Secondary seborrhea occurs due to an underlying disease predisposing to excessive scale, crusting and oiliness.
The most common causes are endocrinopathies and allergies, but other diagnoses should be considered.
In animals up to five years old, allergy is the most common cause of seborrhea.
In animals over the age of 5 an endocrinopathy or neoplasia become more likely.
Clinical signs are very similar between primary and secondary seborrhea cases.
Mild forms of seborrhea show: greasy scales around the nipples, lips folds and external ear canal.
More severe forms show: more severe and generalised lesions, with multiple coalescent scaly or crusty pruritic patches, digital hyperkeratosis and dry, brittle claws. Otitis can be a prominent feature in some cases.
The degree of pruritus is useful in ruling out certain diseases.
If the pruritus is minimal, endocrinopathies, neoplasia and demodecosis should be considered, and allergies and scabies become less likely.
Seborrheic dogs are prone to developing secondary infections with bacteria and Malassezia and this can have a marked effect on pruritus, which can become severe.
Other systemic signs may be present if a systemic disease is causing the seborrhea, such as polyuria/polydipsia, abnormal oestrous cycles, the influence of diet, the environment or the season.
The diagnosis of primary seborrhea is made by exclusion.
A thorough physical and dermatological examination is made to attempt to identify an underlying cause.
Cytology should be performed on the affected area to determine the bacterial and fungal load. This will help determine the best treatment.
Other tests include: deep skin scrapings, fungal culture, impression smears and coat brushings.
Haematology, biochemistry and urinalysis may be helpful in identifying any systemic problems.
Biopsies are recommended, and for primary seborrhea, will show a hyperplastic superficial perivascular dermatitis. There is usually orthokeratotic or parakeratotic hyperkeratosis, follicular keratosis and apoptosis of keratinocytes.
There may be inflammation, and parakeratotic caps overlie oedematous dermal papillae.
Bacteria and yeast are numerous at the surface and evidence of secondary bacterial infection is common.
Primary seborrhea cannot be cured, but it can be managed in most dogs.
In dogs with secondary seborrhea, the effort should be placed on curing or managing the underlying disease.
In all cases, antibiotics or an antifungal may be necessary at first to cure secondary infections. Cytology can be performed during treatment to check for any recurrence of infection.
Shampoos can also be used to decrease the bacterial load, aid pruritus and normalise the epidermal turnover rate.
The mainstay of therapy is the use of antiseborrheic shampoos and moisturisers:
- Keratinolytic products: salicylic acid, tar, selenium sulfide, propylene glycol, fatty acids, and benzoyl peroxide. These lead to sloughing of surface keratinocytes and reduce the scale.
- Keratinoplastic products: tar, sulfur, salicylic acid, and selenium sulfide. These slow down epidermal basal cell mitosis.
- Emollients: lactic acid, sodium lactate, lanolin and oils. These reduce water loss from the skin and maintain hydration.
- Antibacterial agents: benzoyl peroxide, chlorhexidine, iodine, ethyl lactate.
- Antifungal agents: chlorhexidine, sulfur, iodine, ketoconazole, and miconazole
Shampoos usually combine different agents, and the selection should be made on the basis of the scaliness and oiliness of the coat.
Cleansing and emollient agents are usually sufficient in mild cases.
Sulfur, salicylic acid and benzoxyl peroxide should be used in more severe cases needing agents with keratinolytic, keratinoplastic and antimicrobial effects.
In most cases the prognosis is good, but treatment is usually complex and involves a lot of input from both the vet and the owner.
|Seborrhea Learning Resources|
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|Small Animal Dermatology Q&A 19|
Harvey, R. (2009) A colour handbook of skin diseases of the dog and cat Manson Publishing
Muller, G. (2001) Small Animal Dermatology Elsevier Health Sciences
Merck and Co (2008) The Merck Veterinary Manual Merial
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