Alopecia areata — SCE Dermatology MCQ

Correct answer: C — Alopecia areata

The correct answer is C, Alopecia areata. The stem describes a solitary, smooth, non-scarring circular patch with no scale, pain or pustulation, which excludes an inflammatory or infective process, and dermoscopy showing exclamation-mark hairs (short hairs tapering proximally) is a classic trichoscopic sign of active alopecia areata. A positive pull test at the margin confirms ongoing follicular shedding at the expanding edge, which is characteristic of this autoimmune, T-cell mediated attack on anagen hair follicles. This combination of clinical morphology and dermoscopic signs is the standard basis for clinical diagnosis without biopsy in primary and secondary care. Why the other options are wrong: D. Tinea capitis: typically shows scale, broken hairs at varying lengths, and sometimes pustules or kerion, with a positive fungal microscopy/culture; the absence of scale here argues against a dermatophyte infection. B. Traction alopecia: results from chronic mechanical tension (tight braiding, ponytails) and characteristically affects the frontotemporal hairline with a fringe sign, not a smooth circular patch elsewhere on the scalp, and lacks exclamation-mark hairs. E. Lichen planopilaris: is a scarring alopecia with perifollicular erythema, scaling and loss of follicular openings on dermoscopy, none of which are present in this smooth, non-scarred patch. A. Telogen effluvium: causes diffuse, generalised hair thinning rather than a discrete circular patch, and does not produce exclamation-mark hairs or a focal positive pull test at a margin. Key point: A well-demarcated, smooth, non-scarring patch with exclamation-mark hairs on dermoscopy and a positive margin pull test is diagnostic of active alopecia areata.

Reference: Primary Care Dermatology Society (PCDS), Alopecia Areata clinical guidance, https://www.pcds.org.uk/clinical-guidance/alopecia-areata