Paediatric Hypotrichosis: A Clinical and Algorithmic Approach to Diagnosis.

Paediatric hypotrichosis is the clinical feature of paucity of hair arising congenitally or in early life with the presentation being that of the child whose hair is growing insufficiently. It is a hallmark finding of a diverse group of genodermatoses and sporadic disorders, presenting as either an isolated symptom or in association with syndromic features. Hypotrichoses are rare, with numerous possible differentials requiring a thorough clinical assessment, additional investigations for hair shaft abnormalities and occasionally genetic counselling to reach a diagnosis. We propose a clinical algorithm for the investigation and diagnosis of paediatric hypotrichosis, designed to aid the clinician by utilising key clinical findings in conjunction with the forced hair pull test and trichoscopy to differentiate groups of hair shaft and hair loss disorders. We also discuss in further detail the pathogenesis, phenotypical features and microscopy findings of various types of hypotrichosis.