<s>[INST] <<SYS>> This is a medical question of type : information <</SYS>> What is (are) Prurigo nodularis ? [/INST] Prurigo nodularis is a skin condition characterized by hard crusty lumps that itch intensely.  The exact cause of the condition is unknown. However, it can occur in isolation or as a result of repeated trauma to chronic pruritus (itching). Treatment for the condition can be challenging. </s>