<s>[INST] <<SYS>> This is a medical question of type : exams and tests <</SYS>> How to diagnose Lichen planus pigmentosus ? [/INST] How is lichen planus pigmentosus diagnosed? A diagnosis of lichen planus pigmentosus is usually suspected based on the presence of characteristic signs and symptoms. A skin biopsy may then be ordered to confirm the diagnosis. </s>