Seborrhea in horses
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Seborrhea is a term that indicates scaling and crusting – this can be dry (seborrhea sicca) or oily (seborrhea oleosa). Seborrhea can be due to a primary disease of keratinization, which is a rare condition, or secondary to a disturbance in the process of epidermal proliferation, differentiation and desquamation. Primary diseases are evident at a very young age, while secondary conditions develop later in life. Predisposing factors include bacterial, fungal, parasitic, nutritional, malabsorption/maldigestion, chemicals, immunological and neoplasticetiologies.
Clinical signs
Affected horses present with scaling and crusting. Alopecia and pruritis may also develop. If primary seborrhea is present, crusting and/or scaling is the first change noticed, if it is a secondary condition, then other lesions may be noted first, eg initial papular eruption, and crusting develops later. There may be a rancid odor in oily forms.
Crusting and scaling may be localized or more generalized, depending on the cause. In primary seborrhea, the distribution may be symmetrical, sparing the extremities.
Diagnosis
Diagnosis is based on clinical signs and diagnostic investigation. Cytology will highlight thepresence of a secondary infection and/or Malassezia overgrowth. Scrapings, brushings or acetate tape impressions can be performed to investigate parasites. Hair examination and fungal culture will help to rule out dermatophytosis. Biopsy is required if all other tests are negative.
Treatment
Topical treatment with keratolytic and keratoplastic agents is required, eg sulphur, benzoyl peroxide, salicylic acid. Emollients and moisturizers can be used in cases of dry seborrhea, egoils, propylene glycol, colloidal oatmeal. Any secondary infections need treating and re-assessing. Most cases have a secondary bacterial component or Malassezia overgrowth, although they may have other diseases as underlying cause, thus elimination of the secondary infection is important to be able to assess the triggering disease. Generally, shampoo should be left to stand for 15 min then thoroughly rinsed, twice weekly until control is reached then followed by weekly or biweekly washing.
Prognosis
Prognosis depends on the underlying cause. For there to be improvement, there needs to be at least a few weeks of treatment. Treatment failure is usually due to inadequate control of an underlying disease. Primary seborrhea is incurable.
References
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