Pitfalls and pearls in the diagnosis of monilethrix

A 4-year-old girl presented with sparse, brittle hair on her entire scalp and keratosis pilaris on the nape of her neck. Subtle microscopic and macroscopic diagnostic features presented a challenge for physicians. Only repeated, optimized light microscopy revealed the diagnosis of monilethrix, a rare genetic hair shaft disorder with a variable phenotypic expression and inheritance pattern. We provide a short overview of methods that maximize the diagnostic yield in a clinical setting and of light microscopy to reach a rapid and accurate diagnosis in difficult cases. We conclude with essential learning points, including a link to assistance with hair microscopy from a tertiary center.