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: Psychiatry
"Russel sign" is 
Select and explain. 
A. Hyperpigmented patch over nose, B. Development of callus over knuckles, C. Inverted tree shaped rash over the back, D. Loss of buckle pad of fat
B: Development of callus over knuckles
Answer: B: Development of callus over knuckles 
Explanation: Development of callus over knuckles because of repeated episodes of purging is called "Russel sign".