A 67-year-old-woman, whose husband died 18 months ago, is admitted to the hospital because of severe headaches for 4 weeks. She is quiet and seems sad. She believes that she has brain cancer, deserves to be punished for her sins, and is being punished by God for past mis-deeds. She has had fatigue and a 6.8-kg (154 lb) weight loss over the past 4 months. Physical and neurologic examinations show no abnormalities. Which of the following is the most likely diagnosis?
A) Bipolar disorder.
B) Cyclothymic disorder.
C) Major depressive disorder with psychotic features.
D) Schizo affective disorder.
E) Schizophrenia.