Halo Nevus
The halo nevus
phenomenon most often occurs in children and young adults with multiple
melanocytic nevi; it is unusual in adults over 40 years of age. A central
melanocytic nevus is surrounded by a round or oval amelanotic annulus. The
lesions are asymptomatic and the most common site is the trunk, particularly
the back. There are four stages in halo nevus evolution, which occurs over a
period of months to ≥10 years: (1) appearance of the halo; (2) loss of pigment
within the central nevus; (3) disappearance of the nevus; and (4) disappearance
of the halo. Patients often develop multiple halo nevi and some have associated
vitiligo. The exact relationship between halo nevi and vitiligo has been the
subject of controversy.
Both nevus cells and
epidermal melanocytes in the surrounding skin are destroyed, as demonstrated by
histologic and ultrastructural studies. Both CD4+ and CD8+ T cells infiltrate halo nevi.
The clinical diagnosis
of halo nevus is usually fairly straightforward, but Wood’s lamp examination
may occasionally be required to detect the halo. The halo phenomenon can occur
with a variety of types of melanocytic nevi (e.g. neurotized, blue, congenital)
and melanoma. Careful examination of the central lesion is therefore required.
Typical halo nevi require no treatment other than reassurance. Individuals
beyond 40 years of age with new-onset halo nevi should be examined carefully
for melanoma (ocular and cutaneous).
