Equine Dermatology
The RVC Equine Referral Hospital offers a dedicated equine dermatology referral service.
Skin diseases in horses can be difficult to diagnose and frustrating to manage. We investigate and treat the full range of presenting clinical signs such as pruritus (itching), recurrent urticaria (allergic skin reaction), nodular diseases (localised or widespread small lumps), scaling and crusting (scabs and oozing), pigmentary disorders (changes in skin or hair colour) and skin diseases affecting the distal (lower) limb.
Patients can either be seen on an outpatient basis or be admitted to the hospital if further investigations, e.g. intradermal allergy testing, are indicated. Close collaboration with our other equine referral services allow a comprehensive work-up for skin patients where underlying or concurrent disease is suspected. Skin biopsy examination is performed by a pathologist specialising in this area.
Pruritus
The causes of pruritus, or itching, are many and varied and include sweet itch (Culicoides hypersensitivity), chorioptic mange (mite infestation on the legs), Oxyuris (worm infestation causing tail rubbing). In some cases a diagnosis can be reached based on the history and clinical signs, in other cases a more detailed investigation including hair plucks, skin scrapes, skin biopsies and intra-dermal skin testing may be required.
Urticaria
It is important to remember that urticaria is a clinical sign representing many causes rather than a specific diagnosis. Causes can be divided into immunological and non immunological. Most immunological causes involve a hypersensitivity (allergic) response and the allergic stimulus reaches the skin via the blood stream having been injected (drugs), eaten (chemicals, feed) or inhaled (chemicals, pollens, moulds etc). Most non immunologic causes involve a physical trigger including pressure, cold and exercise. However, in the majority of cases the urticaria is idiopathic i.e. no underlying cause can be identified.
The characteristic lesion is a wheal which develops within minutes to hours after exposure to the trigger. The wheal may ooze serum (clear, yellow fluid) resulting in matting of the hair. A diagnosis of urticaria is often made based on the clinical appearance of the skin lesions. Frequently the condition occurs on a single occasion and responds well to medication, with a specific cause never being identified. Further diagnostic tests are required if the condition is recurrent in order to attempt to determine the underlying trigger and most commonly involves intra-dermal skin testing (IDST). The IDST results can then be used to either avoid potential triggers or develop a hyposensitising vaccine.
Nodular Diseases
The development of a nodule (small lump) is a fairly common skin reaction. The most common cause is a simple insect bite. Other causes require further investigations such as a skin biopsy to allow a definitive diagnosis to be made and include collagenolytic granulomas which are small firm nodules which usually occur on the withers, back and neck, axillary nodular necrosis which is characterised by nodules in the armpit region, unilateral popular dermatosis which presents as a large number of nodules on one side of the body and sarcoids (form of skin tumour).
Scaling and Crusting
Causes of scaling and crusting (scabbing and oozing) are many and varied. The lesions may be limited to one area of the body e.g. just around the coronary band and chestnuts in coronary band dystrophy or may be extensive e.g. in the immunologic diseases pemphigus foliaceous. Some causes can be identified by sending hair plucks or skin scrapes to the laboratory e.g. rain scald or ringworm. Other causes will need more extensive investigations.
Pigmentary Disorders
There are several pigmentary disorders of the horse, some of which are inherited conditions related to the breed and other which are acquired. Inherited conditions include reticulated leukotrichia in Quarter horses, juvenile Arabian leukoderma and albinism. Acquired conditions include scarring after trauma and the rare immune-mediated disease cutaneous lupus erythematosus.
Skin Diseases Affecting the Lower Limb
Skin diseases affecting the lower limb are often the most frustrating of all to diagnose and treat as they frequently involve a number of causes. Possible diagnoses include mud fever (bacterial infection), pastern folliculitis (infection by a different bacteria), chorioptic mange (mite infestation), pastern leukocytoclastic vasculitis (immune-mediated disease that may be linked to sunlight) and photosensitisation (affects white legs and linked to liver disease or ingestion of certain plants). A range of further diagnostic tests may be required to pinpoint the underlying cause an individual horse.