Halo Naevus
Sutton's naevus.
A halo naevus on the cubital fossa. Note the pale area surrounding the central naevus. This change often worries patients, but is usually a sign of impending regression of the lesion. Image used courtesy of Stuart Waterston and the Unviersity of Aberdeen.
Features
A Halo naevus is defined as a melanocytic naevus surrounded by a depigmented halo of otherwise normal skin. It occurs when a pre-existing melanocytic naevus develops a ring or "halo" of depigmentation around it. This depigmentation has a regular margin and is particularly noticable when the unaffected surrounding skin is tanned (ie. during the summer months). Some Malignant melanomas also display this depigmented area, sometimes causing diagnostic confusion. In Malignant melanoma, however, the depigmented area is usually very irregular.
The back is the most commonly affected site. Lesions tend to be multiple, although not all existing melanocytic lesions develop a halo. Over the next few months, the central melanocytic lesion gradually regresses, leaving the depigmented lesion. It may take several years for the depigmented area to regain normal skin colour.
Incidence
Halo naevi are fairly common with the incidence being estimated at 1% of the population in the US. It has no sexual or racial prediliction. The average age of first onset is 15.
Aetiology
The aetiology is unknown. Various theories have been proposed, some centered around the presence of anti-melanoma antibodies in those who have developed Halo naevi. Lymphocytic infiltration of the depigmented areas is also thought to be significant.
Differential Diagnosis
Superficial spreading melanoma. Atypical mole. Lichen planus. Vitiligo.
Treatment
Usually none is required. In areas which will be exposed to the sun, sun screen should be recommended as the depigmented areas burn very easily. If in doubt about the diagnosis, an excision biopsy should be performed.
