Eosinophilic granuloma complex is a hypersensitivity reaction that has been reported in cats, dogs and horses. It is most commonly seen in cats. Sensitivities to insects, foods, bacteria and other environmental factors have been documented. There is a genetic predisposition to this disease although the cause of many cases remains undetermined (idiopathic).
Canine eosinophilic granuloma is most commonly reported in Arctic Circle breeds, and is most often seen on the inner thighs or in the mouth. Erythematous to yellow raised nodules with papillated surfaces are typical. Pruritus is variable. Diagnosis is by histology which shows eosinophils and granulomatous inflammation around eosinophilic
debris coated collagen. Treatment is with prednisone at 1 mg/kg q12h for one week, then tapering down over the course of four to six weeks. Occasionally, higher initial dosages are necessary.
Canine eosinophilic furunculosis is probably a related disease. It has been reported in many breeds, but typically is seen in long-nosed large breeds or curious small breeds (i.e., terriers) with potential access to wasps, bees, ants, spiders, etc. It is thus felt to be due to arthropod bites or stings. Consistent with this, the disease may be very rapid in onset, leading to nasal/muzzle swelling, exudation and pain. Large, swollen, erythematous lesions on the muzzle are the most common lesions, but in some dogs similar lesions may be seen on the head, periocularly and around the pinna. Impression smears will often show eosinophils. While diagnosis is usually done on a clinical basis, histologic confirmation will show lesions similar to that of the canine eosinophilic granuloma, but with more eosinophilic infiltration into the epidermis and follicular wall, a furunculosis, and fewer areas of eosinophilic debris-coated collagen. Treatment is as reported for the canine eosinophilic granuloma.
In dogs, the lesions reported as eosinophilic granulomas histologically resemble the eosinophilic granuloma of cats, with marked collagen degeneration surrounded by a granulomatous and eosinophilic infiltrate. These lesions may be seen as ulcerated or vegetative masses in the oral cavity or, less commonly, as plaques, nodules, or papules on the lips and other areas of the body. Any breed may be affected, but Siberian Huskies may be at greater risk.
In dogs, antibiotics should also be tried initially. Many lesions seem much more responsive to corticosteroids, and therapy is usually oral prednisone or prednisolone (0.5-2 mg/kg/day initially, tapering the dosage over 20-30 days). Lesions recur in some dogs, in which case low-dose, every-other-day corticosteroid therapy is indicated.