Dysplastic naevi syndrome

Dysplastic naevi syndrome (also known as atypical mole syndrome (AMS)) is otherwise known as heritable melanoma syndrome; it refers to a group of patients who appear to inherit a tendency to develop dysplastic naevi. This inheritance appears to follow an autosomal dominant pattern.

Many hundreds of naevi may form in sun-exposed as well as unexposed areas, distinguishing these naevi from ordinary moles.

Dysplastic naevi tend to be larger than common acquired naevi, with diameters between 5 and 10 mm. Typically they have fuzzy, indistinct borders and are multicoloured in shades of tan, brown, pink and black. The naevi vary from macules to papules surrounded by a lighter macular component. Persistence of a macular component in a naevus larger than 6 mm is strong evidence of dysplasia. The best indicator of early malignant change may be the appearance of a new area of black pigmentation in a dysplastic naevus.

Patients have an implied increased risk of developing a malignant melanoma, and this may arise either from a naevus or even apparently unaffected skin. In children with dysplastic naevi, melanoma has been documented as early as the age of 10 years.

There is an increased incidence of multiple malignant melanomas in patients with a positive family history and/or dysplastic nevi.

In the general UK population, individuals with multiple moles (the atypical mole syndrome (AMS)) are at increased risk of MM and this is thought to be genetic, probably due to low-penetrance susceptibility genes

• phenotype is common and patients with the AMS require education about prevention, both primary (sun avoidance) and secondary (signs and symptoms)
  
  
• patients with AMS have a relative risk of MM of around 10 compared with those who have very few moles (lifetime risk of MM in the UK is approximately 1 in 150; patients with AMS have an estimated 1 in 20 lifetime risk compared with a person with an average number of moles. Their risk is lower when compared, for example, with those with xeroderma pigmentosum, but as 2% of the general population have the AMS these patients 'explain' a significant proportion of the disease (4)
  
  

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Reference:

1. Murphy, GF & Mihm, MC. in Robbins Pathologic Basis of disease, ed. Cotran, Kumar & Robbins, 1989, 4th edition, Pub. WB Saunders, 1280-1281.
2. Ceballos PI et al. Melanoma in children. NEJM 1995;332: 656-62
3. Ferrone CR et al. Clinicopathological features of and risk factors for multiple primary melanomas. JAMA 2005; 294:1647-54
4. Bataille V, de Vries E. Melanoma--Part 1: epidemiology, risk factors, and prevention. BMJ. 2008;337:a2249.