Trichogram — SCE Dermatology MCQ

Correct answer: E — The ratio of anagen to telogen hairs — normal is approximately 85% anagen and 15% telogen; an increased telogen percentage (>25%) indicates telogen effluvium

The correct answer is E: the ratio of anagen to telogen hairs, with a normal distribution of approximately 85 percent anagen and 15 percent telogen, and an increased telogen percentage above 25 percent indicating telogen effluvium. A trichogram is performed by plucking 40 to 60 hairs and examining the root morphology under light microscopy to classify each hair as anagen (growing, with an intact pigmented root sheath) or telogen (resting, with a club-shaped depigmented bulb). This quantitative anagen:telogen ratio is the diagnostic basis for distinguishing telogen effluvium, in which excessive follicles are prematurely shifted into telogen, from other causes of hair loss such as androgenetic alopecia or anagen effluvium. The diagnosis can be made histologically by hair pluck trichogram or trichoscopically by demonstrating an increased ratio of hairs in telogen to hairs in anagen, which is the accepted diagnostic principle in UK dermatology practice. Why the other options are wrong: C. Hair growth rate only: the trichogram assesses follicular cycle phase (anagen versus telogen) by root morphology, not linear growth rate, which requires other techniques such as sequential clipping or trichoscan. A. Only the causative organism: identifying fungal or bacterial pathogens requires microscopy with potassium hydroxide preparation or culture, not root phase analysis of plucked hairs. D. Only hair thickness: shaft diameter variability is assessed by trichoscopy or hair shaft microscopy, not by the anagen:telogen classification that defines a trichogram. B. Only hair colour: pigmentation is a visual feature unrelated to follicular cycle staging and plays no role in trichogram interpretation. Key point: A trichogram quantifies the anagen:telogen ratio from plucked hair roots, and telogen exceeding roughly 25 percent confirms telogen effluvium.

Reference: British Association of Dermatologists, Telogen Effluvium patient information leaflet, 2020; and Oxford Academic, Clinical and Experimental Dermatology, 'You cannot go bald without first losing your hair', 2024, https://academic.oup.com/ced/article/51/2/220/8220667