[Etiologic diagnosis and behaviour when confronted with abnormal hair growth in a child]

Knowledge of the physiology of hair follicle growth and its relationship to the endocrine and the metabolic system is essential in understanding abnormalities in hair development or hirsutism. Although there is no sexual dysmorphism in the distribution of hair follicles, there are many factors that induce hair growth. The first clinical measure is to differentiate all the intrinsic causes from auxologic and normal psychomotor development related to ethnic, racial and hereditary differences (generalized congenital or idiopathic hypertrichosis) and congenital causes within the context of a multi-malformation syndrome in which hirsutism is associated with mental retardation (Cornélia de Lange's syndrome), major hypotrophy (leprechaunism) or with abnormalities of the limbs (Rubinstein Taybi's syndrome or mucopolysaccharidosis). In these cases, the hormone balance is normal and genetic and/or metabolic explorations are required. Secondly, virilism may occur with hirsutism combining pubis and axillary hair growth, hypertrophy of the clitoris, and android characteristics. This results from hyperandrogenia with increased circulation of plasma androgens. Dynamic hormone tests (ACTH test and dectanyl suppression test), together with sonography help to determine the adrenal (hyperplasia, more frequent than tumors), gonadic (tumors, cysts or gonadic dysgenesis) or paraneoplastic origins (choriocarcinoma). In practice, most hirsutism is considered as idiopathic.