A 38-year-old woman presents to the psychiatry outpatient clinic with a 3-month history of persistent low mood, loss of interest in her job as a schoolteacher, and difficulty concentrating on routine tasks. She reports waking up at 4 AM daily, unable to return to sleep, and has lost 6 kg unintentionally. She denies suicidal ideation but feels life is not worth living. Her appetite is markedly reduced. Mental status examination reveals psychomotor retardation, depressed affect, and impoverished speech. There is no history of mania or hypomania. Thyroid function tests and vitamin B12 levels are normal. What is the most likely diagnosis?

Explanation

## Diagnostic Criteria Analysis **Key Point:** Major Depressive Disorder (MDD) requires ≥5 symptoms present for ≥2 weeks (here 3 months), causing functional impairment, with no history of manic/hypomanic episodes. ### Symptoms Present in This Case 1. Depressed mood (persistent low mood) 2. Anhedonia (loss of interest in work) 3. Sleep disturbance (early morning awakening at 4 AM) 4. Appetite/weight loss (6 kg unintentional loss, markedly reduced appetite) 5. Concentration difficulty 6. Psychomotor retardation (observed on MSE) 7. Worthlessness/hopelessness (life not worth living) **High-Yield:** This patient meets ≥5 DSM-5 criteria for MDD. The 3-month duration exceeds the 2-week minimum. Absence of manic/hypomanic history rules out bipolar disorder. ### Severity Assessment - **Moderate severity** is indicated by: - Functional impairment (unable to perform job duties effectively) - Multiple neurovegetative symptoms (sleep, appetite, psychomotor changes) - Depressed affect with psychomotor retardation on examination - Symptom duration of 3 months **Clinical Pearl:** Early morning awakening (terminal insomnia) is a hallmark of melancholic features in MDD and suggests more severe, biologically-driven depression. ### Why Organic Causes Are Excluded - Thyroid function and B12 normal → rules out hypothyroidism, pernicious anemia - No substance use history mentioned - Symptoms fit primary psychiatric disorder [cite:DSM-5 Major Depressive Disorder]