Melasma — SCE Dermatology MCQ

Correct answer: E — Melasma

B, melasma, is correct. This 34-year-old presents with symmetrical, light-brown macular pigmentation of the cheeks and upper lip appearing after pregnancy and darkening with sun exposure, the classic distribution and behaviour of melasma (chloasma), driven by pregnancy-related hormonal change and ultraviolet light stimulating melanocytes. The absence of scale, erythema or textural change excludes an inflammatory or infective process, and there is no antecedent rash to explain post-inflammatory change. Melasma is a clinical diagnosis based on the typical symmetrical facial distribution, flat macular quality and seasonal fluctuation, exactly as described here. Why the other options are wrong: A. Post-inflammatory hyperpigmentation: this follows a preceding inflammatory dermatosis, acne, eczema or injury to the skin; there is no history of prior rash or trauma here, and the pattern would usually reflect the distribution of the original lesion rather than a symmetrical malar pattern. D. Lentigo maligna: this is a solitary, irregular, asymmetric pigmented macule on chronically sun-damaged skin (typically face) in an older patient, not symmetrical bilateral macules linked to pregnancy. C. Acanthosis nigricans: this produces velvety, thickened, hyperpigmented plaques in body folds (neck, axillae), not flat macules on the cheeks and lip, and reflects insulin resistance rather than hormonal pigmentation. B. Pityriasis versicolor: caused by Malassezia yeast, it produces scaly, hypo- or hyperpigmented patches typically on the trunk, and the stem explicitly excludes scale. Key point: symmetrical, non-scaly facial macular pigmentation that worsens with pregnancy and sun exposure is melasma, distinguished from other pigmentary and inflammatory skin conditions by its distribution, flat texture and hormonal/UV triggers.

Reference: British Association of Dermatologists, Patient Information Leaflet: Melasma (reviewed 2024), https://www.bad.org.uk/pils/melasma