Keratoacanthoma is a skin tumour which arises from the hair follicle. It is a low-grade skin tumour, which is more likely to occur on parts of the skin regularly exposed to the ultraviolet rays of the sun. This leads to DNA damage in that portion of the skin and subsequently to the development of a skin tumour in the form of a keratoacanthoma.

In a typical keratoacanthoma, there is a single skin lesion, which appears as a well-defined nodule in the upper epidermal layer of the skin. It is usually found on areas such as the face, neck, arms and legs, which are commonly exposed to the sun. In rare cases the keratoacanthoma may be multiple. This condition is known as multiple keratoacanthomas.

Four Variants of Multiple Keratoacanthomas

There are different causes for multiple keratoacanthomas. The predominant four variants are mentioned below:

Ferguson-Smith

This form of multiple keratoacanthomas attributed to a chromosomal defect. Identified in 1934 in a Scottish family by Dr. Ferguson Smith, it generally appears in the individuals after the age of 30 years. Also known as Familial Keratoacanthomas and Ferguson-Smith disease, this is a genetic abnormality transmitted as an autosomal dominant trait. The skin lesions are larger and generally appear on those body parts which are exposed to the sun. The mucous membrane is not affected. The lesions tend to heal on their own without medical intervention.

Grzybowski

The Grzybowski variant of multiple keratoacanthomas was first described in 1950. These have no known etiology. The skin lesions are smaller and are found in large numbers. The size of a typical nodule is about 2-3 mm and thousands of them may be found on the individual. They have a tendency to occur on the eyelids, palms of the hand, soles of the feet and oral mucous membrane. The nodules are very pruritic. The condition is very rare, and to date only thirty cases have been recorded in medical journals. There is no successful treatment for the condition.

Witten and Zak

This form of multiple keratoacanthomas is a combination of the Ferguson-Smith and Grzybowski forms of the skin condition. They are genetically inherited in an autosomal dominant manner and manifest in childhood. The nodules are a combination of the larger and smaller varieties. They do not affect the mucous membranes for the most part. They do not affect lymph nodes or other internal organs.

Muir-Torre Syndrome

This is caused by a genetic mutation of the MLH1 or MSH2 gene. It is a form of Lynch syndrome and is associated with internal cancers, especially of the gastrointestinal tract. One of the symptoms of Muir-Torre syndrome is the formation of multiple keratoacanthomas, often accompanied by sebaceous epitheliomas, sebaceous carcinomas and tumours at other sites on the skin. Sebaceous carcinomas tend to form on the eyelids and often metastasize, i.e., spread to other areas. They are very aggressive and can prove to be fatal.

Treatment Options for Multiple Keratoacanthomas

Since the underlying causes for multiple keratoacanthomas are different, it stands to reason that the form of treatment will also vary, based on the cause.

Ferguson-Smith

The skin lesions are self-healing in Ferguson-Smith disease. Even if the individual develops hundreds of nodules, they will clear up over a period of about two months. Medication helps to hasten the process. Oral retinoids such as acitretin and isotretinoin are prescribed to individuals as standard care. In most cases the treatment results in the prevention of any new skin lesions as well as the gradual reduction in size of the existing skin lesions. Anti-itching ointments may be used as a topical aid to help with the skin irritation.

Grzybowski

The skin lesions do not have a self-healing trigger in Grzybowski disease. Only one case of spontaneous healing has ever been recorded for the condition. If left untreated, the condition may persist indefinitely. As the skin lesions do not clear up spontaneously, they are treated with medications such as acitretin, isotretinoin, 5-fluorouracil, methotrexate and cyclophosphamide. Emollients are suggested to keep the skin moist, so that the itching may be controlled.

Witten and Zak

The treatment is a combination of oral and intravenous medication. 5-fluoroucil given intravenously for a period of five days helps achieve the reduction of small skin lesions. The medication cycle may be repeated to help deal with the larger skin eruptions. Oral retinoids may also be prescribed to help control the emergence of new skin lesions. Keeping the skin moist helps mitigate the itching.

Muir-Torre Syndrome

Multiple keratoacanthomas are one of the clinical symptoms of Muir-Torre syndrome. The benign skin tumours formed on the skin in this condition can be surgically removed. The tumors may be treated by excision or cryotherapy. Oral retinoids like acitretin and isotretinoin may be prescribed. Interferon injections may be added as adjuvants to the oral medication.