Atypical nevi are moles with unusual features. There are basically two types of atypical nevi, sporadically occurring atypical moles and familial (inherited) atypical moles. The term atypical nevus is sometimes used to mean any funny-looking mole. However, strictly speaking, an atypical nevus is defined as a mole with at least 3 of the following features.
- Size >5 mm diameter
- Ill-defined or blurred borders
- Irregular margin resulting in an unusual shape
- Varying shades of color (mostly pink, tan, brown, black)
- Flat and bumpy components
Clinically atypical nevi are sometimes called dysplastic nevi, but this is term is best used for a specific microscopic appearance. Only a minority of clinically atypical nevi fulfill microscopic criteria for dysplastic nevus. Dysplasia may be mild, moderate or severe. People with atypical nevi have a slightly higher risk than the general population of developing a skin cancer called melanoma, particularly if they have five or more atypical nevi. In general, atypical nevi are actually harmless and do not need to be removed. However, it is not always easy even for an experienced dermatologist to tell whether a lesion is an atypical nevus or a melanoma. A suspicious or changing atypical nevus should be biopsied, and a pathologist will usually make the correct diagnosis. If you have numerous moles you should visit your dermatologist regularly for a thorough skin check.
It is often helpful to keep photographic records of the moles with digital photos using a technique called mole mapping. The close-up photographs should be repeated from time to time. Dermoscopic views with a special hand held microscope enables your dermatologist to detect change early. Careful sun protection, sun protective clothing, avoiding excessive sun exposure and using at least a SPF 30+ sunscreen is recommended. Patients with numerous moles should also perform a monthly self skin exam.