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18 April 2012, by RICHARD M.-A.



Keratoacanthoma is a skin tumour that is believed to originate from the hair follicle. The tumour typically emerges very suddenly (even brutally), grows rapidly and then regresses spontaneously through various morphological stages and changes.

Clinically, a keratoacanthoma presents as an erythematous, scaly papule which is often overlooked in its initial stages ; then, within the space of a few days, it suddenly develops into a symmetrical, well-defined, purple, nodular tumour that sits on the surface of the skin. The nodule consists of a peripheral ring covered with smooth and telangiectasic epithelium surrounding a central crater filled with a keratin plug. The keratoacanthoma involutes spontaneously within two to 12 weeks, as the raised peripheral ring flattens out and the contents of the central crater are eliminated, leaving a sometimes unsightly puckered scar, often scattered with milia. Widespread ulceration may develop, mainly on the nose and eyelids.

Several variants of keratoacanthoma have been reported on the literature but since their biological and histological profiles are similar, keratoacanthoma is considered to be a separate histoclinical entity, irrespective of the conditions under which it arises or the number of lesions observed. 

• The single or solitary form is most common, particularly in men, most often after the fifth decade of life. The tumour is most often located on sun-exposed and hair-covered areas such as the face, leg below the knee and forearm. It generally measures less than 3 cm in diameter and regresses spontaneously within two to three months.

• The extensive and ulcerative form, or keratoacanthoma centrifugum marginatum, is rare. This is a single centrifugally-growing keratoacanthoma characterised by peripheral growth which can be very destructive since it has a very active polycyclic border despite concomitant central healing. It has been described on the lips, nose and eyelids.

• The giant forms which are probably actually the result of confluence of several keratoacanthomas ; these are found mainly on the forearms.

• Multiple keratoacanthomas may also arise. These have been reported in three different contexts :

— familial keratoacanthomas (Ferguson-Smith type) are seen in young patients with an autosomal dominant genodermatosis who will present with rapidly-regressing keratoacanthomas affecting all parts of the body throughout their lives ;

— generalised eruptive and sporadic keratoacanthomas (Grzybowski type) which are mainly seen in patients with a cell immune deficiency (lymphomas, etc.) and who develop hundreds of tiny keratoacanthomas on the skin and mucosa ;

— Muir-Torre syndrome is another genodermatosis in which multiple keratoacanthomas combine with sebaceous tumours to become cutaneous markers of primary visceral (colon) or larynx carcinomas.

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