Aetiology

Not understood fully: some cases of multiple seborrhoeic warts are inherited in an autosomal dominant pattern^[1] and sunlight appears to play a role in causation given the typical distribution of keratoses.^[2]

Epidemiology

• Presence and frequency increases with age: almost all elderly patients have some. An Australian study found 100% of the over 50 year olds in their sample had at least one seborrhoeic wart (median number of 23 warts in the 51-75 year range and 69 in the over 75 year olds).^[2]
• Onset usually in middle age although common finding in younger patients - found in 12% of 15-25 year olds making the term 'senile keratosis' redundant.^[3]
• No sex difference exists.
• Less common in dark skinned races.

Visual appearance

• A flat-topped or warty-looking lesion that appears to be 'stuck on' to the skin.
• They are usually pigmented, sometimes deeply and may even be black. Others can be paler in colour.
• The surface is usually pitted and irregular with visible keratin dots giving a granular and rough appearance.
• They tend to have a well-circumscribed border.

Less common variants of seborrhoeic keratoses include:

• Stucco keratoses - multiple skin-coloured or white, dry, scaly lesions often seen on the extremities (dorsa of hands, forearms, ankles and feet).
• Dermatitis papulosa nigra - multiple small, brown or black pedunculated lesions seen on the face of dark-skinned individuals. Often have an earlier onset than typical seborrhoeic keratoses.
• Melanoacanthoma- very deeply pigmented seborrhoeic keratoses.^[4]

Presentation

• Start as hyperpigmented macule and progress to characteristic plaque.
• Start small (2 mm) and grow in size, up to 3 cm in diameter. Rarely they can become very large.
• Initially lesions are velvety and soft in texture, before developing a warty surface and becoming uneven, with multiple plugged follicles.
• The surface may become covered by adherent greasy scale.
• The trunk is the most common site for seborrhoeic keratoses but also found on all sun-exposed areas (extremities, face and scalp).
• Multiple lesions may align along skin folds.
• Usually asymptomatic but may become irritated, itchy or inflamed spontaneously or after minor trauma.

Differential diagnosis^[5]

• Malignant melanoma
• Verruca vulgaris
• Condyloma acuminatum
• Fibroepithelial polyp
• Epidermal naevus
• Melanocytic naevus
• Pigmented basal cell carcinoma
• Squamous cell carcinoma

One American study found that 6.4% of a series of histopathology specimens, from both dermatologists and non-specialists, sent with a clinical diagnosis of seborrhoeic keratosis were in fact malignant tumours.^[6]

Associated diseases

Rarely a sudden onset or increase in number of seborrhoeic keratoses can herald an underlying malignancy (usually adenocarcinoma of the stomach, colon or breast). It can be associated with acanthosis nigricans. This is known as Leser-Trélat sign.^[7][8]

Primary care management^[4]

• Reassurance: most often no treatment is required.
• Remove where cosmetic dislike, repeated irritation or chafing from clothes or diagnostic uncertainty.
• Removal by cryotherapy (may require repeat treatments), curettage and cautery or shave excision are effective and produce a better result than excision and suture, although a pale white scar can be left.
• Excisional biopsy should be reserved for lesions that are suspicious for melanoma.

When to refer

Usually can be managed in primary care. Reserve referral for help with diagnosis or removal of difficult lesions.

Complications

• Repeated irritation and inflammation where lesions catch on clothing.
• Aesthetic dislike.
• Concerns regarding malignancy:
  • Harder to notice a malignant melanoma arise amongst multiple seborrhoeic keratoses.
  • Rare for a 'compound' malignant lesion to develop within or contiguous to a seborrhoeic keratosis.^[9][10]

Prognosis

While seborrhoeic keratoses are benign, they do not spontaneously resolve and become larger and thicker with time.