Throwing Light onto the Core of a Halo Nevus: A New Finding.

Sir,

A melanocytic nevus is a benign melanocytic cell proliferation that develops due to unhindered growth of melanoblasts during embryogenesis.[1]

A 27-year-old male presented with an asymptomatic dark flat lesion over the right cheek since birth which had gradually increased in size over the years, associated with diminished pigmentation and central loss of pigmentation since 3–4 years. The patient gave no history of using any topical agents over the lesion.

Examination revealed a 3 cm × 3 cm hyperpigmented macule with a central area of hypopigmentation which comprised gray-white hair [Figure 1]. The surrounding skin was normal. There was seen a patch of gray hair over the frontal aspect of the scalp.

Figure 1

Nevus with central hypopigmentation and leukotrichia

Dermoscopy of the lesion showed an ill-defined demarcation line within which hypopigmented whitish spots and bicolored areas of brown and pink were seen [Figure 2].

Figure 2

Dermoscopic image showing hypopigmented whitish spots and leukotrichia (×40)

Histopathology of the lesion revealed orthokeratotic epidermis, scattered lymphocytic infiltrate, and the absence of nevus cell proliferation in the dermis [Figure 3].

Figure 3

Histopathology showing lymphocytic infiltrate and absence of nevus cell nest (H and E, ×10)

Melanocytic nevi are given importance due to its potential to develop into malignant melanoma; the risk ranges between 5% and 10% for a giant melanocytic nevus. In addition, there are reported associations with central nervous system malformations and skeletal defects.

Congenital melanocytic nevus (CMN) is classified according to the largest diameter as: Small (<1.5 cm), medium (1.5–19.9 cm), and large (or giant: ≥20 cm). The lesion discussed here would conform to the medium sized category.[1]

Dermoscopy of CMN shows a brownish homogeneous background with islands of darker pigmentation within. Other findings include hypertrichosis, perifollicular hypo- or hyper-pigmentation, pseudomilia and vascular structures.[2] The hypopigmented whitish spots and bicoloured areas seen under dermoscopy for our patient is in agreement with CMN.[3]

Halo nevus (HN) is a rare finding characterized by a hypopigmented peripheral lining around the melanocytic nevus due to an autoimmune lymphocytic response which simulates a halo. In 1916, Sutton described HN as a “leukoderma acquisitum centrifugum.” Happle termed the entity as “Grünewald nevus.”[4]

Halo nevi undergo specific changes in sequence. In Stage I, the central nevus remains brown, or its pigment can disappear leading to a pink-colored papule (Stage II). The central papule disappears, leading to a circular area of depigmentation (Stage III). Finally, the depigmented area may repigment (Stage IV), leaving no trace of its existence.[5]

The halo phenomenon may be the result of an immune response leading to nevus cell destruction which explains the histopathological absence of nevus cells alongside lymphocytic infiltrate. The dermoscopic findings include the globular pattern with blue pepper-like granules and/or white-scar areas.[5]

There are four histologic forms of halo nevi described: (a) Inflammatory (b) noninflammatory (c) HN without HN phenomenon diagnosed by histopathology and (d) halo dermatitis around a melanocytic nevus.[6]

Unusual finding have been reported by Zack et al.,[7] and Kageshita et al.,[8] who described the resolution of congenital nevi without the halo phenomenon. Sotiriadis et al. reported one case of an HN without the halo phenomenon which developed on the trunk of a 5-year-old girl.[5]

This case is reported to demonstrate a phenomenon of inverse halo phenomenon. The dermoscopic findings confirm a melanocytic nevus and histopathology is consistent with the halo phenomenon with the destruction of nevus cells. Here, the depigmentation commences within the lesion evidenced by a lighter hue in the central aspect which is associated with overlying leukotrichia.

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Conflicts of interest

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