Hair diagnoses and signs: the use of dermatoscopy

Background. Hair-shaft examination is diagnostically useful in a range of adult and paediatric conditions. Objective. To evaluate the usefulness of dermatoscopy in hair-shaft microscopy. Methods. Typical examples of selected conditions from an extensive collection of scalp hair were examined using a dermatoscope and a light microscope with paired cross-polarizing filters. Hair-shaft characteristics were photographed using a digital camera. Results. Dermatoscopy was helpful in detecting tapered hairs, weathering, monilethrix, pediculosis capitis, peripilar casts, 'exclamation-mark' hairs of alopecia areata, bubble hair and pili torti. It was less helpful in pili annulati and unhelpful in detecting 'tiger-tail' banding in trichothiodystrophy. Light microscopy provided greater detail in almost all cases; it was necessary for detection of cuticle changes and added significant information in detecting characteristic features of trichothiodystrophy, pili annulati, bubble hair and pili torti. Conclusions. Dermatoscopy is most revealing in conditions resulting in gross changes in shaft outline and colour, where reflected light is valuable. It is unhelpful for detection of features within the shaft or at higher levels of resolution. When added to its ability to aid evaluation of scalp surface characteristics, dermatoscopy provides an excellent first-line method of assessment in clinics. In vivo it may aid screening and selection of hairs of greatest diagnostic yield for further assessment. In some instances, it may obviate the need for obtaining hair specimens and have implications for public health screening. Where detailed or cortical hair-shaft features need assessment, transmitted light microscopy remains the standard tool.