Seborrheic keratosis

1 - SEBORRHEIC KERATOSIS

Seborrheic keratoses or seborrheic warts are harmless and common skin lesions which are particularly prevalent in the elderly. They are the most frequently observed form of benign epithelial tumour.

1.1 - DIAGNOSIS

They occur singly or in clusters, sparing the mucosa, palms and soles and most often affect the seborrheic zones of the face, chest and back.

In most cases, they emerge in the fifth decade of life in both men and women but may also affect teenagers.

There are different clinical forms of these benign tumours. Most are coloured and well-defined, with a "pasted-on" appearance; their appearance varies depending on their stage of development, ranging from macula to papules or plaques; some are pedunculated; they are light tan in colour (varying from yellow to blackish brown). The warty surface gradually becomes covered with a thick, squamous, keratotic film. The lesions can vary in size from a few millimetres to several centimetres, but diameters of more than 1 cm are rare.

When several of the lesions are present, they may be distributed along skin folds, the Blaschko lines or in a Christmas-tree pattern.

Some may become inflamed when the pseudocysts they contain rupture, subsequent to trauma or, more rarely, as a result of infection.

It is a chronic, harmless condition. These lesions are frequently asymptomatic but they may become sensitive, itchy, erythematous or scabbed, particularly if rubbed or scratched.

Diagnostic tools : Histologically, they present as epidermal hyperplasia containing abundant basal cells. The hyperplasia is split by invaginations of the horny layer forming the characteristic cyst pockets or "horny pseudocysts". Hyperpigmentation is common. There are various different histological types of seborrheic keratosis: acantholytic, hyperkeratotic, reticulated or adenoidal, irritated or clonal, depending on whether the lesion is mainly acanthotic, papillomatous or hyperkeratotic. The presence of moderate atypia or mitosis is suggestive of irritation or local inflammation. In such cases, a dermal, perivascular, diffuse or lichenoid lymphocytic infiltrate will also be present.

In most cases, this condition is easy to diagnose, simply on the basis of the clinical findings.

Dermoscopy can be a useful means of confirming the clinical diagnosis. Dermoscopic images can be used to confirm that the lesion is not melanocytic (no pigmented network, no globules, striated and regular, parallel, rows). These images also show the presence of horny pseudocysts presenting as round, white to yellowish structures of varying sizes. Comedo-like openings may also be present. These appear as well-circumscribed craters of variable size with a yellowish-brown to blackish-brown colour, corresponding to keratin plugs within the dilated follicular orifices.

Seborrheic keratosis and tumours : Seborrheic keratoses may co-exist with other benign and malignant tumours (collision tumours). Leser-Trélat sign is the explosive onset of multiple, itchy seborrheic keratosis. This can be an ominous indication of an underlying solid tumour, most often stomach cancer or a colon adenocarcinoma, more rarely breast cancer or melanoma.

The aetiology of these tumours is unknown. Solar exposure and heredity have been put forward as possible predisposing factors. There is often an identical family history; these lesions frequently arise in sun-exposed areas. It has also been suggested that there is a link between seborrheic keratosis and HPV infection, owing to the warty appearance of the lesions. While one study found that there was indeed a link between HPV and genital seborrheic keratosis, no such connection has been identified for the extra-genital form of the condition.

1.2 - DIFFERENTIAL DIAGNOSES

The following differential diagnoses must be taken into account: achrocordon, common warts, condylomata acuminata, acrokeratosis verruciformis of Hopf, follicular infundibulum tumours, eccrine poromas, Bowen’s disease, squamous cell carcinoma, lentigo, naevus and even melanoma.

Stucco keratosis and black papular dermatitis are considered to be variants of seborrheic keratosis, the former a hyperkeratotic type and the latter acantholytic; this is further demonstrated by the presence of the PIK3CA and FGFR3 somatic gene mutations also observed in these tumors or in classic seborrheic keratosis.

1.3 - TREATMENT

In most cases, treatment is dictated by aesthetic concerns. Symptomatic lesions may be treated by curetage or cryotherapy. Surgical removal is only recommended when there is doubt about the diagnosis – for example, when a melanocytic tumour has not been ruled out - or when the lesion develops rapidly or has an atypical appearance.

2 - INVERTED FOLLICULAR KERATOSIS

Inverted follicular keratosis or eccrine poroma is also a benign epithelial tumour which some authors consider to be a follicular tumour. It is the main differential diagnosis of an irritated seborrheic keratosis.

This lesion is less common than seborrheic keratosis and is generally seen in adults aged over 60. More men than women are affected (2/1).

Clinically, eccrine poroma presents as a single, firm, white to flesh-coloured or pinkish lesion most often located on the face (cheeks and upper lip). The lesions vary in size: while most measure less than 1 cm, some can reach up to 10 cm in diameter.

Histologically, the lesions are endophytic or exophytic, often symmetrical and well-circumscribed. They are formed by proliferation of medium to large individual keratinocytes with multiple dyskeratotic cells covered by ortho- and parakeratotic hyperkeratosis. Basaloid cells may be observed at the borders.

Patients with inverted follicular keratosis must be screened for Cowden’s syndrome, of which it can be a presenting symptom.

The potential link between inverted follicular keratosis, trichilemmoma, seborrheic keratosis and common warts is the subject of debate.

The treatment is surgical.