6.3 Psychological Disorders: DSM-5 Categories & Models

6.3 Psychological Disorders: DSM-5 Categories & Models

Mastering psychological disorders for the MCAT requires synthesizing clinical diagnostic criteria from the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR) with underlying biological mechanisms. Disorders are conceptualized via the biopsychosocial model, which integrates genetic vulnerability, neurochemical dysregulation, cognitive-behavioral patterns, and environmental stressors.

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Diagnostic Framework & The Biopsychosocial Model

The DSM-5-TR classifies mental disorders based on categorical criteria while incorporating dimensional measures of symptom severity. The biopsychosocial model emphasizes that psychiatric disorders rarely stem from a single origin:

• Biological Domain: Genetic susceptibility, monoamine neurotransmitter alterations, neuroanatomical anomalies, and endocrine HPA-axis dysregulation.
• Psychological Domain: Learned helplessness, maladaptive cognitive schemas, coping mechanisms, and emotional dysregulation.
• Social Domain: Socioeconomic status, acute trauma, environmental stressors, isolation, and systemic cultural factors.

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Schizophrenia Spectrum & Psychotic Disorders

Schizophrenia is a severe chronic psychotic disorder characterized by distorted perception, thought, emotion, and behavior. Diagnosis requires at least two diagnostic symptoms present for a significant portion of time during a 1-month period (with continuous signs of disturbance for at least 6 months), and at least one symptom must be a positive symptom (delusions, hallucinations, or disorganized speech).

Clinical Presentation

Symptoms are partitioned into three domains:

1. Positive Symptoms (Behaviors Added to Normal Cognition):

   • Delusions: Fixed, false beliefs resistant to contradictory evidence. Subtypes include persecutory (belief that one is being harassed or spied on), referential (belief that environmental cues, such as TV broadcasts, contain special messages for oneself), grandiose (belief in holding exceptional power or identity), and control/passivity (belief that thoughts are inserted or controlled by external forces).
   • Hallucinations: Perceptual experiences occurring without external sensory stimuli. Auditory hallucinations (hearing voices) are the most common in schizophrenia.
   • Disorganized Thought / Speech: Loose associations, derailment (slipping off topic), word salad (incoherent speech), and neologisms (invented words).
   • Disorganized or Catatonic Behavior: Inappropriate affect, motor immobility (waxy flexibility), or purposeless excessive motor activity.

2. Negative Symptoms (Absence of Normal Behaviors):

   • Flat / Blunted Affect: Reduced emotional expression in face and voice.
   • Avolition: Severe reduction in goal-directed motivation and initiative.
   • Alogia: Poverty of speech and thought content.
   • Anhedonia: Inability to experience pleasure.
   • Asociality: Apparent lack of interest in social interactions.

3. Cognitive Symptoms: Deficits in working memory, executive function, and sustained attention.

Neurobiological Etiology of Schizophrenia

+-------------------------------------------------------------------------+
|                    DOPAMINE HYPOTHESIS OF SCHIZOPHRENIA                 |
|                                                                         |
|    MESOLIMBIC PATHWAY:  VTA ===> Nucleus Accumbens                      |
|    -- DOPAMINE HYPERACTIVITY (Excess D2 Receptor Activation)            |
|    -- Clinical Outcome: POSITIVE SYMPTOMS (Delusions, Hallucinations)   |
|                                                                         |
|    MESOCORTICAL PATHWAY: VTA ===> Prefrontal Cortex                     |
|    -- DOPAMINE HYPOACTIVITY (Deficient D1 Receptor Activation)          |
|    -- Clinical Outcome: NEGATIVE & COGNITIVE SYMPTOMS (Avolition, Flat Affect)|
+-------------------------------------------------------------------------+

• Dopamine Hypothesis: Posits that schizophrenia involves pathway-specific dopamine dysregulation. Hyperactivity of dopaminergic transmission in the mesolimbic pathway generates positive symptoms (antipsychotic D2 blockers reduce positive symptoms). Conversely, hypoactivity of dopamine in the mesocortical pathway to the prefrontal cortex underlies negative and cognitive symptoms.
• Neuroanatomy: Structural neuroimaging shows enlarged lateral ventricles, reduced total cortical volume, and decreased volume in the hippocampus and temporal lobes.
• Genetic Predisposition: Concordance rates are approximately 40% to 50% in monozygotic twins, compared to 10% to 15% in dizygotic twins and 1% in the general population, demonstrating high genetic heritability combined with environmental trigger interaction (diathesis-stress model).

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Depressive & Bipolar Disorders

Major Depressive Disorder (MDD)

Major Depressive Disorder is characterized by persistent low mood and a loss of interest in activities. Diagnosis requires at least 5 out of 9 symptoms present during the same 2-week period, representing a change from previous functioning. At least one symptom must be either (1) depressed mood or (2) loss of interest/pleasure (anhedonia).

The high-yield MCAT mnemonic SIG E CAPS captures the diagnostic criteria:

• Sleep disturbances (insomnia or hypersomnia)
• Interest loss (anhedonia)
• Guilt or feelings of worthlessness
• Energy decrease (fatigue)
• Concentration impairment or indecisiveness
• Appetite or weight changes (increase or decrease >5% in a month)
• Psychomotor agitation or retardation
• Suicidal ideation or recurrent thoughts of death

Persistent Depressive Disorder (Dysthymia): A milder but chronic depressed mood present for most of the day, for more days than not, for at least 2 years.

Neurobiology of Depression

• Monoamine Hypothesis: Posits that depression results from functional deficits in monoamine neurotransmitters—specifically serotonin (5-HT), norepinephrine (NE), and dopamine (DA)—in synaptic clefts. (Antidepressants such as SSRIs, SNRIs, and MAOIs elevate monoamine availability).
• Endocrine Dysregulation: Hyperactivity of the Hypothalamic-Pituitary-Adrenal (HPA) axis, resulting in elevated baseline cortisol levels and loss of negative feedback inhibition.

Bipolar Disorders

Bipolar disorders are marked by dramatic oscillations between emotional poles (depression and mania).

• Manic Episode: A distinct period of abnormally and persistently elevated, expansive, or irritable mood and abnormally increased activity/energy, lasting at least 1 week (or any duration if hospitalization is necessary). Must include at least 3 symptoms from the DIG FAST mnemonic:
  • Distractibility
  • Indiscretion / Impulsivity (excessive involvement in risky activities)
  • Grandiosity or inflated self-esteem
  • Flight of ideas or racing thoughts
  • Activity increase (goal-directed) or psychomotor agitation
  • Sleep requirement decrease (e.g., feels rested after only 2 hours)
  • Talkativeness (pressured speech)

+-------------------------------------------------------------------------+
|                    BIPOLAR I vs. BIPOLAR II DIAGNOSTIC SPECTRUM        |
|                                                                         |
|   BIPOLAR I DISORDER:                                                   |
|   Requires: At least ONE MANIC Episode (>=1 week duration, severe)      |
|   Note: Major Depressive Episodes common, but NOT strictly required.    |
|                                                                         |
|   BIPOLAR II DISORDER:                                                  |
|   Requires: At least ONE HYPOMANIC Episode (>=4 days, no severe impairment)|
|   AND: At least ONE MAJOR DEPRESSIVE Episode (>=2 weeks duration)       |
|                                                                         |
|   CYCLOTHYMIC DISORDER:                                                 |
|   Requires: Chronic fluctuating hypomanic & depressive symptoms for >=2 yrs|
|   Without meeting full criteria for major depressive or manic episodes. |
+-------------------------------------------------------------------------+

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Anxiety, OCD & Trauma-Related Disorders

Anxiety Disorders

• Generalized Anxiety Disorder (GAD): Excessive, uncontrollable worry about multiple everyday domains occurring more days than not for at least 6 months, accompanied by autonomic tension, fatigue, and irritability.
• Panic Disorder: Recurrent, unexpected panic attacks (sudden surges of intense fear reaching a peak within minutes), leading to persistent apprehension about future attacks or maladaptive behavioral changes. Often associated with Agoraphobia (fear of places where escape might be difficult during a panic attack).
• Specific Phobia: Irrational, intense fear and avoidance of a specific object or situation.
• Social Anxiety Disorder: Severe fear or anxiety regarding social or performance situations where the individual faces potential scrutiny by others.

Obsessive-Compulsive Disorder (OCD)

OCD is defined by the presence of obsessions, compulsions, or both:

• Obsessions: Recurrent, intrusive, unwanted thoughts, urges, or images that cause marked anxiety or distress (e.g., contamination fear, harm impulses).
• Compulsions: Repetitive behaviors (handwashing, checking) or mental acts (counting) that an individual feels driven to perform in response to an obsession to neutralize anxiety. OCD is typically ego-dystonic (the individual recognizes the thoughts/behaviors are irrational).

Trauma and Stressor-Related Disorders

• Post-Traumatic Stress Disorder (PTSD): Triggered by exposure to actual or threatened death, serious injury, or sexual violence. Symptoms must persist for more than 1 month across four clusters:
  1. Intrusive Symptoms: Flashbacks, distressing dreams, emotional reactivity.
  2. Avoidance: Avoiding trauma-related thoughts, feelings, or external reminders.
  3. Negative Alterations in Cognition/Mood: Amnesia for trauma details, persistent negative emotional states, detachment.
  4. Alterations in Arousal/Reactivity: Hypervigilance, exaggerated startle response, insomnia.
• Acute Stress Disorder: Similar symptom presentation to PTSD, but symptoms resolve between 3 days and 1 month post-trauma.

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Dissociative & Somatic Symptom Disorders

Dissociative Disorders

Dissociative disorders involve disruptions of memory, consciousness, identity, or perception:

• Dissociative Amnesia: Inability to recall important personal information, usually of a traumatic nature, unexplainable by ordinary forgetfulness. May present with Dissociative Fugue (sudden, unexpected travel away from home accompanied by amnesia for identity).
• Dissociative Identity Disorder (DID): Disruption of identity characterized by two or more distinct personality states (alters) that alternately control behavior, accompanied by memory gaps.
• Depersonalization / Derealization Disorder: Recurrent experiences of feeling detached from one's own mental processes or body (depersonalization) or feeling that surrounding objects/environment are unreal or dreamlike (derealization), with intact reality testing.

Somatic Symptom Disorders

• Somatic Symptom Disorder: Presence of one or more physical symptoms that cause distress, accompanied by excessive, disproportionate thoughts, anxiety, and time devoted to these symptoms.
• Illness Anxiety Disorder: Preoccupation with having or acquiring a serious, undiagnosed medical illness despite absent or minimal somatic symptoms ("hypochondriasis").
• Conversion Disorder (Functional Neurological Symptom Disorder): Sudden, unexplained loss of voluntary motor or sensory function (e.g., blindness, paralysis, seizures) incompatible with known neurological pathophysiology, typically preceded by acute psychological stress. Historically associated with la belle indifférence (an unexpected lack of concern regarding the severe disability).

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Personality Disorders: Cluster A, B & C

A Personality Disorder is an enduring, inflexible pattern of inner experience and behavior that deviates markedly from cultural expectations, is pervasive across situations, has an onset in adolescence or early adulthood, and leads to distress or impairment. The DSM-5 categorizes ten personality disorders into three Clusters:

+-------------------------------------------------------------------------+
|                        DSM-5 PERSONALITY DISORDER CLUSTERS              |
|                                                                         |
|   CLUSTER A (Odd / Eccentric - "Weird"):                                |
|   -- Paranoid | Schizoid | Schizotypal                                 |
|                                                                         |
|   CLUSTER B (Dramatic / Emotional / Erratic - "Wild"):                  |
|   -- Antisocial | Borderline | Histrionic | Narcissistic                |
|                                                                         |
|   CLUSTER C (Anxious / Fearful - "Worried"):                            |
|   -- Avoidant | Dependent | Obsessive-Compulsive Personality Disorder  |
+-------------------------------------------------------------------------+

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Neurodegenerative Disorders (Parkinson's & Alzheimer's)

Parkinson's Disease

Parkinson's disease is a progressive neurodegenerative motor disorder caused by the loss of dopaminergic neurons in the substantia nigra pars compacta, which projects to the striatum in the basal ganglia.

• Motor Symptoms (TRAP Mnemonic):
  • Tremor at rest (classic "pill-rolling" tremor)
  • Rigidity ("cogwheel" muscular stiffness)
  • Akinesia or Bradykinesia (slowness of voluntary movement)
  • Postural instability (impaired balance and shuffling gait)
• Histopathological Hallmark: Presence of Lewy bodies—intracellular aggregates composed primarily of misfolded alpha-synuclein protein.

Alzheimer's Disease

Alzheimer's disease is the most common cause of dementia in older adults, characterized by progressive memory loss, executive dysfunction, and neurobehavioral decline. Pathophysiology involves the loss of cholinergic neurons in the nucleus basalis of Meynert.

• Histopathological Hallmarks:
  1. Extracellular Amyloid-Beta (A-beta) Plaques: Misfolded peptide aggregates derived from abnormal cleavage of amyloid precursor protein (APP).
  2. Intracellular Neurofibrillary Tangles (NFTs): Hyperphosphorylated tau protein aggregates that disrupt the neuronal microtubule transport system.
• Gross Pathology: Marked diffuse cortical atrophy, widening of sulci, and compensatory enlargement of lateral ventricles (hydrocephalus ex vacuo).

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Rates of Psychological Disorders

The AAMC names rates of psychological disorders as a subtopic in its own right, because epidemiology is what turns a diagnostic category into a population-health claim. Two measures must be distinguished: prevalence (existing cases in a population at a point in time or over a window) and incidence (new cases per unit time). Passages that describe a treatment lengthening survival with a disorder are describing rising prevalence without rising incidence.

Approximate United States adult figures from national epidemiological surveys — quoted as ranges because estimates shift with the survey instrument and the diagnostic edition:

Patterns the exam expects you to recognize:

• Sex differences run in opposite directions by disorder. Anxiety disorders, major depression, and eating disorders are roughly twice as common in women; substance use disorders and antisocial personality disorder are more common in men. Schizophrenia has similar overall risk by sex but earlier onset in men (early-to-mid twenties versus late twenties).
• Onset is age-patterned. Anxiety disorders typically begin in childhood and adolescence, mood disorders in adolescence and early adulthood, and schizophrenia in late adolescence through the early thirties.
• Prevalence is not the same as treatment. About half of US adults with any mental illness receive any mental health treatment in a given year, and the shortfall is concentrated by sex and by race and ethnicity (roughly 42% of men versus 57% of women; lowest among Asian, Black, and Hispanic adults). That pattern belongs to health care disparities (Section 12.4), not to biology.
• Reported rates are partly artifacts of measurement. Broadened criteria, screening in primary care, and reduced stigma all raise measured prevalence without any change in underlying risk. Whenever a passage reports that a disorder is "increasing," the first question is whether the case definition changed.