Halo naevus (Sutton's naevus) — Viva

Q1: Definition and clinical presentation (2 min)

A 14-year-old girl is referred with three round white patches on her back, each surrounding a small brown mole. What is the diagnosis, and what are the four clinical pillars that support it?

Model answer: This is a halo naevus (Sutton's naevus). The four clinical pillars are: (i) a benign-appearing central naevus (regular, small, symmetric brown mole); (ii) a symmetric, uniform-width depigmented halo encircling it completely; (iii) asymptomatic course (no pain, itching, bleeding); and (iv) the right demographic — typically a child or adolescent. Lesions are often multiple and favour the trunk. The diagnosis is clinical.^[1]

Q2: Pathophysiology (3 min)

Explain the immunology of the halo. Which cells, which antigens, and why is the halo symmetric?

Model answer: The halo is produced by a CD8+ cytotoxic T-cell response directed against melanocyte differentiation antigens expressed by BOTH the naevus cells and the surrounding normal epidermal melanocytes, so the T-cells destroy both, producing depigmentation (the halo). The effector mechanism includes perforin/granzyme-induced apoptosis, with granulysin upregulated (shared with vitiligo). The halo is symmetric because the antigen load is highest at the naevus and falls off concentrically into the surrounding epidermis. As the naevus cells are themselves destroyed, the antigenic stimulus fades, the T-cell response subsides, and the halo may repigment over time.

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Q3: Differential diagnosis (3 min)

A 50-year-old man presents with a single round white patch on his back, 9 mm across, with no central pigmented lesion. Walk me through your differential and your next step.

Model answer: The principal differential is melanoma with regression — a fully regressed melanoma can leave a depigmented halo with no visible residual tumour. Unlike a halo naevus, this lesion is solitary, in an adult, and has no central naevus — three red flags. Other considerations: vitiligo (but this is a single lesion, not a generalised pattern), post-inflammatory hypopigmentation (preceding inflammation, ill-defined, off-white), naevus depigmentosus (congenital stable off-white patch). The next step is a full skin examination for a primary melanoma elsewhere (the halo may be a paraneoplastic immune response) and an excisional biopsy of the depigmented lesion for histology. Never reassure a solitary adult halo without histology.

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Q4: Management (3 min)

How do you manage a typical halo naevus in a child? When would you intervene, and what are the options?

Model answer: For a typical lesion, reassure, observe, photograph, and sun-protect. Explain the benign natural history (four-stage evolution — halo forms, naevus fades, naevus disappears, halo repigments over months to years). Photograph at baseline and review at 6 to 12 months. Sun protection is essential (high-protection sunscreen, clothing) because the depigmented skin burns easily. Screen for vitiligo (full skin examination) and autoimmune thyroid disease (TSH, anti-TPO) when lesions are multiple. Active treatment is reserved for cosmetic concern about persistent depigmentation: topical calcineurin inhibitor (tacrolimus, pimecrolimus), topical corticosteroid, 308 nm excimer laser, narrowband UVB for widespread depigmentation, or cosmetic camouflage — the same therapies used for localised vitiligo. Biopsy is mandatory for any atypical feature (asymmetric/irregular/changing halo, ABCDE features, symptoms, solitary adult halo).

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Q5: Associations and prognosis (2 min)

What systemic associations should you ask about, and what is the long-term outlook?

Model answer: Halo naevus shares its autoimmune mechanism with vitiligo (a proportion of patients have vitiligo elsewhere) and autoimmune thyroid disease (Hashimoto's thyroiditis, anti-TPO; less often Graves'). Take a focused autoimmune history — vitiligo, thyroid disease, type 1 diabetes, Addison's disease, pernicious anaemia, alopecia areata — in the patient and first-degree relatives. The prognosis is uniformly benign: the central naevus regresses and disappears over months, and the halo repigments over months to years, sometimes incompletely or not at all. No halo naevus itself undergoes malignant transformation. New halo naevi may continue to appear through adolescence.^[1]

References3ShowHide

1. [1]Ko E, Panchal N. Pigmented Lesions Dermatol Clin, 2020.PMID 32892857
2. [2]Langford MA, Al-Ghazal SK. Halo naevus or malignant melanoma: A case report JPRAS Open, 2018.PMID 32158818
3. [3]Hlača N, Vičić M, Kaštelan M, et al. Analysis of granulysin expression in vitiligo and halo-nevus Sci Rep, 2024.PMID 39020008