344 Feeding and Eating Disorders
Differential Diagnosis
Other possible causes of either significantly low body weight or significant weight loss
should be considered in the differential diagno sis of anorexia nervosa, especially when the
presenting features are atypical (e.g., onset after age 40 years). 
Medical conditions (e.g., gastrointestinal disease, hyperthyroidism, occult malignan-
cies, and acquired immunodeficiency syndrome [AIDS]). Serious weight loss may oc-
cur in medical conditions, but individuals with  these disorders usually do not also mani-
fest a disturbance in the way their body weig ht or shape is experienced or an intense fear
of weight gain or persist in behaviors that interfere with appropriate weight gain. Acute
weight loss associated with a medical condition can occasionally be followed by the onset
or recurrence of anorexia nervosa, which can initially be masked by the comorbid medical
condition. Rarely, anorexia nervosa develo ps after bariatric surgery for obesity. 
Major depressive disorder. In major depressive disorder, severe weight loss may occur,
but most individuals with major depressive diso rder do not have either a desire for exces-
sive weight loss or an inte nse fear of gaining weight. 
Schizophrenia. Individuals with schizophrenia may exhibit odd eating behavior and oc-
casionally experience significant weight loss, but they rarely show the fear of gaining
weight and the body image disturbance requir ed for a diagnosis of anorexia nervosa. 
Substance use disorders. Individuals with subs tance use disorders may experience low
weight due to poor nutritional intake but gene rally do not fear gaining weight and do not
manifest body image di sturbance. Individuals who abuse substances that reduce appetite
(e.g., cocaine, stimulan ts) and who also endorse fear of weight gain should be carefully