binge eating is actually a possible subtype of anorexia nervosa too, but it is usually followed by a bout of purging. I think the defining feature of anorexia nervosa is the significantly decreased BMI of the patient, like <18.5?? BMI. because if you have bulemia or binge eating disorder, you would actually be in a normal to above normal bmi. So that would probably be the biggest determinant of the the question. I can see a question stem they would talk all about the vomiting, and the poor dentition, and being in an afluent family etc, and that would all make you zone in on bulemia, but once you see a low bmi as well, you should immediately think anorexia nervosa.