11.1 Major Depressive Disorder & Medical Mimics

Psychiatric and behavioral health disorders represent one of the most common reasons for primary care visits and internal medicine hospital consultations. Over 20% of primary care patients meet criteria for a depressive or anxiety disorder. For the ABIM Internal Medicine examination, internists must master the diagnostic criteria, rule out organic medical and pharmacologic mimics, select initial pharmacotherapy based on patient comorbidity profiles, execute structured treatment algorithms for inadequate response, manage mood stabilizers and their toxicities in bipolar disorder, and treat anxiety and trauma-related conditions.

1. Major Depressive Disorder (MDD): Diagnostic Criteria & Medical Mimics

DSM-5 Diagnostic Criteria

Major Depressive Disorder is diagnosed when a patient experiences at least 5 of the 9 diagnostic symptoms during the same 2-week period, representing a clear change from previous functioning. At least one of the symptoms must be either (1) Depressed mood or (2) Loss of interest or pleasure (anhedonia).

DSM-5 Diagnostic Mnemonic: "SIG E. CAPS"
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S — Sleep changes (insomnia [initial, middle, or terminal] or hypersomnia)
I — Interest lost (anhedonia — markedly diminished pleasure in almost all activities)
G — Guilt (excessive, inappropriate feelings of worthlessness or guilt)
E — Energy loss (persistent fatigue or loss of energy nearly every day)
C — Concentration impairment (diminished ability to think, concentrate, or make decisions)
A — Appetite / Weight changes (significant weight loss/gain [>5% in a month] or appetite shifts)
P — Psychomotor agitation or retardation (observable by others, not merely subjective restlessness)
S — Suicidal ideation (recurrent thoughts of death, passive ideation, or specific suicide plan/attempt)
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Requirement: >= 5 symptoms for >= 2 consecutive weeks, including depressed mood or anhedonia.
Exclusions: Not attributable to physiological effects of a substance or another medical condition.

Clinical Screening Tools

• PHQ-2 (Patient Health Questionnaire-2): Ultra-brief 2-question initial screening tool assessing depressed mood and anhedonia over the past 2 weeks (scored 0-6). A score of >=3 has a sensitivity of 83% and specificity of 92% for MDD and mandates immediate full evaluation with the PHQ-9.
• PHQ-9 (Patient Health Questionnaire-9): Validated 9-item diagnostic and severity tool (scored 0-27):
  • 1 to 4: Minimal depression (no pharmacotherapy required)
  • 5 to 9: Mild depression (supportive counseling, lifestyle modification, watchful waiting)
  • 10 to 14: Moderate depression (psychotherapy and/or first-line antidepressant pharmacotherapy)
  • 15 to 19: Moderately severe depression (pharmacotherapy +/- psychotherapy)
  • 20 to 27: Severe depression (immediate pharmacotherapy + psychotherapy; evaluate for hospitalization / suicide risk)

Organic Medical Mimics & Required Diagnostic Evaluation

Before diagnosing primary MDD, secondary medical and pharmacologic etiologies must be systematically evaluated and excluded:

4. Other Mood Disorders in the Blueprint

The mood disorders subsection explicitly names other mood disorders (psychogenic erectile dysfunction, premenstrual dysphoric disorder) alongside depression and bipolar disorder.

Premenstrual dysphoric disorder

A severe, functionally impairing mood disorder confined to the luteal phase, distinct from ordinary premenstrual syndrome by the severity of the affective symptoms and the degree of impairment.

Diagnostic requirements:

• At least five symptoms in the final week before menses, improving within a few days of onset of menses and minimal or absent in the week after menses
• At least one core affective symptom: marked affective lability, marked irritability or anger, markedly depressed mood, or marked anxiety or tension
• Plus additional symptoms such as anhedonia, difficulty concentrating, lethargy, appetite change, hypersomnia or insomnia, a sense of being overwhelmed, and physical symptoms including breast tenderness and bloating
• Confirmation by prospective daily symptom ratings over at least two cycles — this is the requirement most often omitted, and retrospective recall substantially over-diagnoses the condition
• Significant interference with work, school or relationships

The essential differential is premenstrual exacerbation of an underlying disorder. In premenstrual dysphoric disorder the symptom-free interval after menses is genuinely symptom-free; in premenstrual exacerbation of major depression, bipolar disorder, an anxiety disorder or a personality disorder, symptoms are present throughout the cycle and merely worsen premenstrually. Prospective charting is what distinguishes them, and treating a premenstrual exacerbation as premenstrual dysphoric disorder leaves the underlying illness untreated.

Treatment:

• Selective serotonin reuptake inhibitors are first-line and are unusually effective here: unlike in major depression, the response occurs within a day or two, which permits luteal-phase-only or symptom-onset dosing as an alternative to continuous therapy.
• Combined oral contraceptives, particularly continuous or extended-cycle regimens, are an option.
• GnRH agonists with add-back therapy are reserved for refractory cases.
• Cognitive behavioral therapy, exercise and calcium supplementation have supporting evidence.

Psychogenic erectile dysfunction

Also named in this subsection. It is suggested by preserved nocturnal and early-morning erections and by situational rather than global loss of function, with abrupt onset often tied to a relationship or life event. Organic causes produce gradual, global loss. Because depression, anxiety and antidepressant therapy all contribute, the evaluation should assess mood, medications and relationship factors alongside the vascular, neurologic and endocrine causes covered under male reproductive health.