Equine Collagenolytic Granuloma
Also Known As: Equine Eosinophilic Granuloma with collagen degeneration — Nodular Necrobiosis of Collagen
Aetiology
Equine Collagenolytic Granuloma's are the second most common nodular disease in the horse. The underlying cause of the disease is not fully understood but theories include insect hypersensitivity (especially mosquitoes), embedded hairs and trauma. In reality it is likely to be multifactorial. A similar disease can be seen in dogs and cats.
Clinical Signs
The presence of one or more firm, non-pruritic, non-painful nodules. They are normally found on the neck and saddle area but may occur anywhere. Size varies from as small as half a centimeter in diameter to very large nodules. There may be a necrotic plug which appears whitish in colour, but overlying skin can be completely normal. The lesions may become mineralised over time.
Diagnosis
Cytological analysis of FNA's may provide a diagnosis. Smears should show a chronic, active, sterile eosinophilic inflammation. Eosinophils, neutrophils, macrophages and mast cells may all be present. This is common for a non-specific inflammatory response.
Diagnosis can be confirmed by biopsy. Histopathological examination should show a granulomatous eosinophilic inflammation surrounding multifocal areas of collagen degeneration.
Differentials
Any nodular disease may be considered a differential diagnosis. Hypoderma should be considered, but in these cases a breathing pore is normally present.
Therapy
- Surgery — complete surgical excision. Normally only appropriate for single lesions. This is the only effective treatment for mineralised lesions.
- Glucacorticoids — administered systemically or intralesional.
Systemic glucacorticoids are appropriate if there are multiple nodules. Treatment is normally with prednisolone. The other therapies mentioned may be used as adjuncts.
Glucacorticoid administration intralesionally/perilesionally/sublesionally may be effective. Treatment is normally with either triamcinolone acetonide or methylprednisolone acetate. A total dose should be calculated prior to administration to prevent the development of laminitis from exogenous steroids.
If the granulomas are recurrent it may be worth investigating underlying causes such as insect hypersenstivity. This can be achieved by intradermal allergy testing, and management of this using insect control measures and hyposensitisation may be enough to prevent recurrence in the future.
References
Bond, Hendricks, Loeffler (2009) Veterinary Dermatology RVC Intergrated BVetMed Course, Royal Veterinary College
Freeman, KP (2007) Self-Assessment Colour Review of Veterinary Cytology - Dog, Cat, Horse and Cow Manson
Merck & Co (2009) The Merck Veterinary Manual (Ninth Edition), Merial