The presentation

This 75-year-old man was alarmed by the sudden development of this large lesion. It had started as a small, pink papule but within a few weeks had formed a shiny, dome-shaped nodule before breaking down centrally, leaving a crater filled by a keratin plug.

The management

His GP reassured him that it was a keratoacanthoma, which is a relatively common condition with an excellent prognosis. It was best treated by an excisional biopsy, so the histology could be checked and to ensure that removal had been complete.

The patient was warned that having had such a problem, others could develop at a later date and he should keep a check on any skin that might have had sun damage over the years. In future, he should protect exposed skin with clothing and sunscreen of at least factor 30 when out of doors, particularly in the summer months. He should also look out for other sun-induced problems such as actinic keratoses, Bowen’s disease, basal cell carcinoma, squamous cell carcinoma (SCC), or malignant melanoma, and seek help if they occur.

The discussion

Keratoacanthoma arises in the pilosebaceous glands. On histological examination, it cannot be distinguished from SCC, but has a better prognosis. It most commonly presents in patients over the age of 60. Rarely does it progress to invasive or metastatic disease, but instead, will normally resolve spontaneously within four to six months, leaving a scar.

Sun exposure is important in its development, but other factors have been implicated, such as certain types of HPV, genetic factors and immunocompromised status. Recent research has found chromosomal aberrations in a third of keratoacanthoma.

The presentation in this case was typical of the condition, marked by rapid onset, being sited on the sun-exposed area of the face, and the crater-form appearance with the keratin plug.

Excision of the lesion, with adequate margins of 3-5mm, is normally recommended unless the patient is unsuitable for such a procedure or in patients with multiple lesions. Alternative treatments that may be employed are systemic retinoids, intralesional methotrexate or radiotherapy.

The prognosis is excellent but the patient must be advised to avoid sun exposure in future and taught how to recognise any changes that could develop and require further treatment.

Differential diagnoses

• Actinic keratosis 
• Cutaneous horn 
• Squamous cell carcinoma 
• Metastatic carcinoma of the skin
• Molluscum contagiosum

Dr Watkins is a retired GP in Hampshire