Skin Moles

Skin moles
The term ‘mole’ refers to a lesion, often present at birth, which has a local excess of one or more normal constituents of the skin. Skin moles (nevi) are localized benign proliferations of melanocytes. Their classiflcation is based on the site of the aggregations of nevus cells.

Causes of skin moles.
The cause is unknown. A genetic factor is likely in many families, working together with excessive sun exposure during childhood.

Classiflcation of skin moles.
Congenital melanocytic skin moles
Acquired melanocytic skin moles
Junctional mole
Compound mole
Intradermal mole
Spitz mole
Blue mole
Atypical melanocytic mole

With the exception of congenital skin moles, most appear in early childhood, often with a sharp increase in numbers during adolescence. Further crops may appear during pregnancy, oestrogen therapy or, rarely, after cytotoxic chemotherapy and immunosuppression, but new lesions come up less often after the age of 20 years. Skin moles in childhood are usually of the junctional’ type, with proliferating melanocytes in clumps at the dermo-epidermal junction. Later, the melanocytes round off and ‘drop’ into the dermis. A ‘compound’ mole has both dermal and junctional components. With maturation the junctional component disappears so that the melanocytes in an intradermal’ mole are all in the dermis.

Presentations of skin moles.
Congenital skin moles.
These are present at birth or appear in the neonatal period and are seldom less than 1 cm in diameter. Their color varies from brown to black or blue-black. With maturity some become protuberant and hairy, with a cerebriform surface. Such lesions
can be disflguring, e.g. a ‘bathing trunk’ mole, and carry an increased risk of malignant transformation.
Junctional skin moles.
These are roughly circular macules. Their color ranges from mid to dark brown and may vary even within a single lesion. Most skin moles of the palms, soles and genitals are of this type.
Compound skin moles.
These are domed pigmented nodules of up to 1 cm in diameter. They may be light or dark brown but their colour is more even than that of junctional skin moles. Most are smooth, but larger ones may be cerebriform, or even hyperkeratotic and papillomatous; many bear hairs.
Intradermal skin moles.
These look like compound skin moles but are less pigmented and often skin-coloured.
Spitz moles (juvenile melanomas).
These are usually found in children. They develop over a month or two as solitary pink or red nodules of up to 1 cm in diameter and are most common on the face and legs. Although benign, they are often excised because of their rapid growth.
Blue moles.
So-called because of their striking slate grey-blue colour, blue skin moles usually appear in childhood and adolescence, on the limbs, buttocks and lower back. They are usually solitary.
Mongolian spots.
Pigment in dermal melanocytes is responsible for these bruise-like greyish areas seen on the lumbosacral area of most Down’s syndrome and many Asian and black babies. They usually fade during childhood.
Atypical mole syndrome (dysplastic nevus syndrome).
Clinically atypical skin moles can occur sporadically or run in families as an autosomal dominant trait, with incomplete penetrance, affecting several generations. Some families with atypical skin moles are melanoma-prone. Genes for susceptibility to melanoma have been mapped to chromosomes 1p36 and 9p13 in a few of these families. The many large irregularly pigmented skin moles are most obvious on the trunk but some may be present on the scalp. Their edges are irregular and they vary greatly in size, many being over 1 cm in diameter. Some are pinkish and an inflamed halo may surround them. Some have a mamillated surface. Patients with multiple atypical melanocytic or dysplastic skin moles with a positive family history of malignant melanoma should be followed up 6-monthly for life.

Differential diagnosis of skin moles.
* Malignant melanomas. This is the most important part of the differential diagnosis. Melanomas are very rare before puberty, single and more variably pigmented and irregularly shaped.
* Seborrhoeic keratoses. These can cause confusion in adults but have a stuck-on appearance and are warty. Tell-tale keratin plugs and horny cysts may be seen with the help of a lens.
* Lentigines. These may be found on any part of the skin and mucous membranes. More profuse than junctional skin moles, they are usually grey-brown rather than black, and develop more often after adolescence.
* Ephelides (freckles). These are tan macules less than 5 mm in diameter. They are confined to sun-exposed areas, being most common in blond or red-haired people.
* Hemangiomas. Benign proliferations of blood vessels, including hemangiomas and pyogenic granulomas, may be confused with a vascular Spitz mole or an amelanotic melanoma.

Histology of skin moles.
Most acquired lesions are orderly nests of benign nevus cells that are seen in the junctional region, in the dermis, or in both. However, some types of skin moles have their own distinguishing features.
In congenital skin moles the nevus cells may extend to the subcutaneous fat, and hyperplasia of other skin components (e.g. hair follicles) may be seen.
A Spitz mole has a histology worryingly similar to that of a melanoma. It shows dermal oedema and dilatated capillaries, and is composed of large epithelioid and spindle-shaped nevus cells, some of which may be in mitosis.
In a blue mole, nevus cells are seen in the mid and deep dermis.
The main features of clinically atypical (‘dysplastic’) skin moles are lengthening and bridging of rete ridges, and the presence of junctional nests showing melanocytic dysplasia (nuclear pleomorphism and hyperchromatism). Fibrosis of the papillary dermis and a lymphocytic inflammatory response are also seen.

Complications of skin moles.
* Inflammation. Pain and swelling are common but are not features of cancerous transformation. They are caused by trauma, bacterial folliculitis or a foreign body reaction to hair after shaving or plucking.
* Depigmented halo. So-called ‘halo moles’ are uncommon but benign. There may be vitiligo elsewhere. The mole in the centre often involutes spontaneously before the halo repigments.
* Malignant change. This is extremely rare except in congenital skin moles, where the risk has been estimated at between 3 and 6% depending on their size, and in the atypical skin moles of melanoma-prone families. It should be considered if the following changes occur in a skin mole:
* itch;
* enlargement;
* increased or decreased pigmentation;
* altered shape;
* altered contour;
* inflammation;
* ulceration; or
* bleeding.
If changing lesions are examined carefully, remembering the ‘ABCDE’ features of malignant melanoma, few malignant melanomas should be missed.

Treatment of skin moles.
Excision is needed when:
1- a mole is unsightly;
2- malignancy is suspected or is a known risk, e.g. in a large congenital mole; or
3- a mole is repeatedly inflamed or traumatized.

The ABCDE of cancerous transformation in a skin mole
Asymmetry
Border irregularity
Colour variability
Diameter greater than 0.5 cm
Elevation irregularity