The term eosinophilic granuloma complex (EGC) refers to a group of inflammatory skin problems in cats.
Different clinical forms of the disease are recognised, although the underlying inflammatory response often appears very similar.
It appears that EGC is a form of ‘reaction pattern’ seen in the skin of cats that may potentially be initiated by a number of underlying disorders, but it is thought that most, if not all, cases represent some form of allergic (hypersensitivity) disorder.
The skin lesions are often highly pruritic (itchy) and can be exacerbated by the cat licking them.
Different forms of eosinophilic granuloma complex
- Eosinophilic ulcer, or indolent ulcer
These lesions occur on the edge of the upper lip of the cat (on one or both sides, usually towards the front of the lip). The lip develops a clearly demarcated ulcer that can have a raised border and there may be marked swelling of the lip in the region of the ulcerated area. The ulcer can get large and very extensive in some severe cases.
Eosinophilic ulcer in a cat with
allergic skin disease
- Eosinophilic plaque
These lesions can occur anywhere on the body but are commonly seen on the ventral abdomen (‘tummy’ area). They usually appear as well demarcated, flat swellings of the skin with a reddened appearance. Hair is usually lost from the affected skin and the lesions can be very pruritic (itchy). Ulceration is common.
Severe pruritus and eosinophilic
plaques associated with flea allergy
– note matting of the fur with saliva
- Eosinophilic granuloma
These lesions can again occur anywhere on the body, and common sites include the mouth (on the tongue or palate), hind legs and foot pads. The lesion appearance is variable but usually there is a nodular or linear area of raised, thickened skin that may be reddened. Hair loss and ulceration are again common findings although pruritus may be more variable.
Pedal eosinophilic granuloma on
the paw of a cat with allergic disease
Diagnosis of EGC lesions
The lesions of EGC have to be differentiated from other skin diseases such as: fungal, bacterial or viral infections; skin or oral tumours; abscesses; and other causes of swellings. To confirm the diagnosis and rule out other causes, microscopic examination of tissues (cytology of a needle aspirate or preferably a biopsy) is required. Histological examination of tissue by a pathologist will typically show inflammation and ulceration and the presence of a large number of eosinophils (a type of inflammatory cell often associated with allergic reactions). The histological appearance is quite typical for EGC, although differentiating between the different forms of EGC can be difficult (and is not really necessary).
Investigation of EGC
When an EGC lesion is diagnosed, it is important to search for possible underlying causes, especially potential underlying allergies. Your vet will probably want to evaluate your cat carefully for common potential allergies such as flea bite allergy, mosquito bite allergy and food allergy. These investigations may include response to trial treatments or food trials. Trial treatments (for flea eradication) or food trials using a special diet may take time (e.g., 6-8 weeks) but are important and worthwhile to avoid unnecessary prolonged use of symptomatic treatments such as steroids, which can have side effects. Some cases of EGC may be associated with atopy (reaction to environmental or inhaled allergens), and these may be more difficult to investigate and manage.
Treatment of EGC lesions
Although there is no evidence that bacteria actually cause EGC lesions in cats, it is very common to have secondary bacterial contamination and infection of the tissues involved. Where this is the case, a course of antibiotics may help the the condition, and in some cases this can produce quite a dramatic improvement (although it will not resolve the lesion).
Treatment depends on the extent of the problem and trying to find the underlying cause of the reaction (see above). If no underlying cause is evident, or if an underlying cause is identified but cannot be controlled, symptomatic treatment of the lesions may be required. Small single lesions which do not seem to bother the cat may be left, and some of these will spontaneously resolve. If disease is more extensive, treatment will be required.
Glucocorticoids (steroids) are the most common form of therapy (usually given as tablets, oral liquid, or injection), and in many cases the lesions respond very well (and pruritus will rapidly subside). The duration and dose of steroids needed will vary between cats, but in some recurrent treatment or continuous therapy may be needed to control the disease.
If long-term (or high doses) of steroids are needed, additional or alternative therapies may also be tried to help reduce the dose of steroids needed to help minimise the risk of long-term side effects. Other treatments include:
- Anti-histamines, which may help in some cases
- Immunosuppressive drugs such as ciclosporin or chlorambucil
- Topical steroids such as hydrocortisone aceponate spray (that should have minimal systemic side effects)
In the past, progestagens (progesterone-like drugs such as megoestrol acetate, and medroxyprogesterone acetate) have been used to treat EGCs. However, these drugs work because they have extremely potent glucocorticoid (steroid)-like activity and they have a high frequency of significant side effects. These drugs should NOT now be used to treat allergic skin disease in cats as other safer alternatives are available.