An 18-year-old presents with symptoms of delusions, perseverations, feeling low, reduced energy, and a sense of guilt about her symptoms. Select the primary differential diagnosis.

Choice A reason: Schizophreniform disorder is characterized by psychotic symptoms lasting at least 1 month but less than 6 months. While it involves delusions, it does not typically account for the prominent mood symptoms described, such as feeling low, reduced energy, and excessive guilt, which suggest a concurrent major depressive episode. Choice B reason: Schizophrenia requires the presence of psychotic symptoms for at least 6 months with significant functional decline. Although mood symptoms can occur in schizophrenia, they are generally not as persistent or pervasive as the delusions. In this case, the combination of major depressive symptoms and psychosis points more specifically toward a schizoaffective diagnosis. Choice C reason: Delusional disorder is defined by the presence of one or more delusions for at least 1 month in the absence of other psychotic symptoms like hallucinations or disorganized speech. Functional impairment is usually minimal except for the delusion's impact. It does not encompass the pervasive mood symptoms and energy loss reported by this client. Choice D reason: Schizoaffective disorder is the primary differential when a client presents with a concurrent mixture of psychotic symptoms (delusions) and a major mood episode (depressive symptoms like low energy and guilt). This diagnosis requires that psychotic symptoms occur for at least 2 weeks in the absence of a major mood episode during the illness course.