Psychiatric Disorders: Diagnosis, Differential Diagnosis, and Assessment
Diagnosis, differential diagnosis, and assessment
Start with the mental status examination: appearance, behavior, speech, mood and affect, thought process and content, perception, cognition, insight, and judgment. DSM-5-TR diagnosis requires criteria, duration, impairment, and exclusion of substances or medical conditions. Key thresholds matter: major depressive episode (five of nine symptoms for two weeks), hypomania (four days), mania (one week or hospitalization), generalized anxiety (six months), PTSD (one month), acute stress disorder (three days to one month), and schizophrenia (six months with one month of active symptoms). Screening tools support but do not replace interview: PHQ-9, GAD-7, AUDIT-C, C-SSRS. Always screen for mania before treating depression, ask about substance use, obtain collateral information, and order targeted labs when delirium, thyroid disease, anemia, or drug toxicity is suspected. Delirium is acute, fluctuating attention and awareness; dementia is chronic and progressive. Differential diagnosis also includes adjustment disorder, OCD, trauma-related disorders, personality disorders, and medical mimics. Traps: diagnosing major depression in a patient with past mania; missing delirium because the patient is quiet; labeling grief as major depression too quickly; forgetting that OCD is not an anxiety disorder in DSM-5-TR; and accepting a screening score as a diagnosis. Worked example: a 24-year-old presents with two weeks of low mood, insomnia, anhedonia, and guilt after a breakup. Count five of nine symptoms, confirm impairment, exclude substances and medical causes, and ask about lifetime hypomania. If hypomania is present, the diagnosis shifts toward bipolar disorder. Rule of thumb: before assigning a depressive disorder, screen lifetime mania.