This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Skin
Which of the following conditions gives a positive Pathergy test? 
Select and explain. 
A. Richter's disease, B. Behcet's disease, C. Ritter's disease, D. Erythema multiforme
B: Behcet's disease
Answer: B: Behcet's disease 
Explanation: The pathergy test is the hyper-reactivity of the skin to trauma. A skin trauma like needle prick will produce a papule or a pustule, surrounded by an erythematous reaction, at the site of the trauma. This curious phenomenon is almost unique to Behcet's syndrome. Behcet's syndrome is a chronic, relapsing, inflammatory disorder of unknown etiology that may involve the mucocuta- neous, ocular, genital, aicular, vascular, CNS, and GI systems.