Keratoacanthoma

Also known as: Intracutaneous Cornifying Epithelioma — Infundibular Keratinising Acanthoma

Introduction

A keratoacanthoma is a benign nodular neoplasm of the skin of dogs. It is a follicular tumour with adnexal differentiation, evolving from the epithelium of the infundibulum or isthmus of the hair follicle. The central portion of the tumour is filled with keratin.

The incidence of the tumour is higher in purebred dogs, with a particular predisposition in the Norwegian Elkhound. Other predisposed breeds include: Lhasa Apso, Pekinese, Yorkshire Terrier and German Shepherd Dog. The Norwegian Elkhound and the Lhasa Apso are the breeds most at risk of developing generalised lesions.

It is seen most frequently in dogs between 4 and 9 years of age.

Clinical signs

Keratoacanthomas develop most commonly on the back, tail and neck.

The neoplasm generally appears as a well-circumscribed dermal or subcutaneous mass ranging in size from 0.4 to 4 cm in diameter, with a pore that opens to the skin surface. The pore may be filled with inspissated keratinous material which can be expulsed by appying digital pressure to the mass. A keratinised plug may protrude from the pore and, if large, may appear as a cutaneous horn.

If the neoplasm does not communicate with the skin surface it appears as an encapsulated intradermal mass. If the tumour wall becomes disrupted, keratin leaks into the surrounding tissues, evoking a foreign body reaction and a severe inflammatory response.

The condition usually presents as a solitary lesion, however it may be generalised in which case a large number of nodules can be found.

Diagnosis

Diagnosis is based on excisional biopsy and subsequent histopathologic examination.

The pore is lined by stratified squamous epithelium with intracytoplasmic keratohyalin granules. From the base of the pore, the tumour extends into the dermis and subcutis. There is central aggregation of keratin.

The wall of the tumour consists of large, pale-staining keratinocytes. Compression of the surrounding dermal collagen produces a pseudocapsule.

No evidence of malignancy is seen, the tumour is benign.

Treatment

Surgical excision is the treatment of choice for solitary lesions. The tumour does not usually recur, however dogs can be prone to developing additional tumours over time.

In generalised forms, surgical excision is often not possible.

Topical or systemic antimicrobials might be necessary if secondary bacterial infection occurs.

Oral retinoids such as isoretinoin or acitretin can prevent the development of new lesions and cause regression of small lesions. Larger lesions can be pretreated with cryotherapy to give better results. Lifelong administration might be necessary.

Retinoids have numerous side-effects including: conjunctivitis, hyperactivity, pruritus, vomiting, diarrhoea, stiffness, erythema at the mucocutaneous junction and teratogenic effects. These should be monitored for, although they are usually self-limiting and disappear when the drug is stopped.

References

Meuten, D. (2002) Tumours in domestic animals Wiley Blackwell

Harvey, R. (2009) A colour handbook of skin diseases of the dog and cat Manson Publishing

Kahn, C. (2005) Merck Veterinary Manual Merck and Co