Halo naevus (Sutton's naevus) — SAQ

Stem

A 13-year-old boy is brought by his mother, who has noticed four round white patches on his back, each with a small brown mole at the centre. The lesions appeared over the last three months and are not itchy or painful. His aunt has vitiligo and his mother has hypothyroidism.

Questions

a) What is the most likely diagnosis, and which four clinical features support it? (2 marks)

b) What is the underlying pathophysiology, and which antigens are targeted? (3 marks)

c) Outline your management plan for this patient, including any screening you would perform. (3 marks)

d) What feature in the history or examination would prompt you to biopsy one of these lesions, and why? (2 marks)

Model answer

^[1]a) Diagnosis (2 marks) — Halo naevus (Sutton's naevus). Supporting features: (i) symmetric, well-demarcated depigmented halo around a central brown naevus; (ii) multiple lesions; (iii) child/adolescent (age 13); (iv) asymptomatic (no itching, pain, bleeding).

b) Pathophysiology (3 marks) — CD8+ cytotoxic T-cell-mediated autoimmune destruction of melanocytes, directed against melanocyte differentiation antigens expressed by BOTH the naevus cells and the surrounding normal epidermal melanocytes, producing the symmetric centrifugal halo. Effector mechanism: perforin/granzyme apoptosis, with granulysin upregulated (shared with vitiligo). Same antigens as vitiligo — hence the association.^[1]

^[1]c) Management (3 marks) — Reassure the patient and mother (benign, self-limiting, staged evolution). Photograph the lesions at baseline and review over the coming months. Sun protection (high-protection sunscreen, clothing) of the depigmented areas. Screen for vitiligo (full skin examination) and autoimmune thyroid disease (TSH, anti-TPO) given the family history of vitiligo and hypothyroidism. No active treatment needed unless cosmetic concern.^[1]

d) Biopsy trigger (2 marks) — Any atypical feature would prompt biopsy: an asymmetric, irregular, or changing halo; a central naevus with ABCDE features (asymmetry, irregular border, colour variegation, over 6 mm, evolution); any symptom (pain, itching, bleeding); or a solitary halo without a central naevus (in an adult). The reason is to exclude melanoma with regression, which can mimic a halo naevus — the immune system may have destroyed the melanoma, leaving only the depigmented halo.^[1]

References1ShowHide

1. [1]Hlača N, Vičić M, Kaštelan M, et al. Analysis of granulysin expression in vitiligo and halo-nevus Sci Rep, 2024.PMID 39020008