Hair-Shaft Abnormality in a 7-Year-Old Girl—Quiz Case

A 7-year-old girl presented with complaints of hair loss and a known partial biotinidase deficiency since birth. Biotin supplementation was discontinued after the first year of life because clinical manifestations were absent, and laboratory findings were normal. At age 2 years, hair loss and eczema occurred. Owing to low biotinidase activity, biotin supplementation, 20 mg/wk, was restarted, but it was again discontinued at age 3 years because normal biotin levels had been achieved once more. The patient showed a normal physical and mental development, but hair loss continued. Clinical examination revealed dense but short and brittle terminal hairs of different lengths with white nodes along the lengths of hair shafts (Figure 1). No other pathologic findings were seen on the scalp, and results of the hair-pull test were negative. Light microscopy analysis of the longitudinal embedded hair was carried out (Figure 2). The biotin supplementation dose at last follow-up was 5 mg/wk. What is your diagnosis?