A teenager with horizontal purple stripes on the lower back

A boy in his mid teens presented with multiple horizontal linear marks on his lower back that had been there for two months. He was embarrassed about these marks when swimming. His medical and family histories were unremarkable, and he was not taking any medications. His height was 166 cm (10-25^th centile among the Taiwanese population) and weight was 43 kg (5^th centile) and he had a body mass index of 15.6 kg/m² (10^th centile). On examination, multiple horizontal, linear, erythematous-to-purpuric striae, resembling “whipping,” were seen on the lumbosacral region (fig 1a). Wrinkled, atrophic, faint white lines were seen on the knees (fig 1b). The boy had developed axillary and pubic hairs over the past three years. He had no build up of fatty …