delusional disorder

DEFINITION (DSM-5-TR): ≥1 delusion(s) lasting ≥1 month. Criterion A for schizophrenia has never been met (hallucinations, if present, are not prominent and relate to the delusional theme, e.g., smelling foul odor in somatic type). Apart from the delusion's impact, functioning is not markedly impaired and behavior is not obviously bizarre. Manic/depressive episodes, if present, are brief relative to the delusional periods. Not attributable to substances or another medical/psychiatric condition (e.g., body dysmorphic disorder or OCD with poor insight).

KEY CONCEPT: Delusions are NON-BIZARRE, meaning they involve situations that could occur in real life (being followed, poisoned, infected, loved from afar, deceived by a spouse). Bizarre delusions (e.g., aliens removing organs, thought broadcasting) point more toward schizophrenia.

SUBTYPES (specify): - Erotomanic: belief that another person, often of higher status, is in love with the patient (de Clérambault syndrome). Can lead to stalking. - Grandiose: conviction of great talent, insight, wealth, or identity/relationship with a famous figure or deity. - Jealous: belief that the partner is unfaithful (Othello syndrome). Risk of violence and domestic abuse. - Persecutory: most common type. Belief of being conspired against, spied on, poisoned, harassed. Can lead to litigation or violence. - Somatic: belief of a physical defect or medical illness, or infestation (delusional parasitosis, Ekbom syndrome). - Mixed and unspecified types. Specifiers: with bizarre content; first episode vs multiple episodes; current episode acute vs partial/full remission; severity rating.

EPIDEMIOLOGY/RISK FACTORS: Uncommon (lifetime prevalence ~0.2%). Onset typically middle to late adulthood (mean ~40). Slightly more women. Associated with family history of delusional disorder or schizophrenia/schizotypal or paranoid personality traits, immigration, sensory impairment (deafness, vision loss), social isolation, low socioeconomic status, and advanced age.

PATHOPHYSIOLOGY: Not fully understood. Proposed dopaminergic dysregulation (limbic system and basal ganglia), cognitive biases (jumping to conclusions, attribution bias), and limbic/frontal-temporal abnormalities. Distinct from schizophrenia: no marked cognitive decline or negative symptoms.

DIFFERENTIAL DIAGNOSIS (high-yield): - Schizophrenia: ≥6 months, bizarre delusions, prominent hallucinations, disorganized speech/behavior, negative symptoms, functional decline. - Schizophreniform: 1–6 months of schizophrenia criteria. Brief psychotic disorder: 1 day–1 month. - Schizoaffective: mood episode concurrent with psychosis plus ≥2 weeks of delusions/hallucinations without mood symptoms. - Mood disorder with psychotic features: delusions only during mood episodes. - Delusional symptoms from medical/substance causes: stimulants, steroids, dopaminergic drugs, dementia, Parkinson disease, Huntington disease, epilepsy (temporal lobe), brain tumors, stroke, B12 deficiency, hypothyroidism, SLE, HIV. - Paranoid personality disorder: distrust without fixed delusions. - Body dysmorphic disorder, OCD: patient may have poor insight but belief is a preoccupation, with accompanying repetitive behaviors. - Shared psychotic disorder (folie à deux): formerly DSM-IV; in DSM-5 it is classified as delusional disorder (or other specified psychosis) when the delusion is shared by a close individual influenced by a dominant partner. Management includes separating the two individuals.

MANAGEMENT: - Establish a therapeutic alliance (do not collude with or aggressively confront the delusion). Poor insight means patients rarely seek care and often present due to legal or family issues or to non-psychiatric physicians (dermatology for parasitosis, plastic surgery for somatic). - Pharmacotherapy: antipsychotics (second-generation first-line, e.g., risperidone, olanzapine; pimozide historically used for somatic/parasitosis type). Response is variable and often partial. Adherence is a challenge, and long-acting injectables may help. - Cognitive-behavioral therapy and supportive psychotherapy as adjuncts. - Hospitalization for risk of harm to self or others (especially jealous, persecutory, and erotomanic types), including duty-to-warn (Tarasoff) considerations when there is a specific identifiable victim.

PROGNOSIS: Better than schizophrenia. Good prognostic factors: higher functioning, female sex, acute onset, shorter duration, and precipitating stressor. Most patients maintain work and social function if not tied to the delusion. Relapse is common.

BOARD PEARLS: Look for a stem with a previously functional person with a single fixed, plausible false belief for >1 month, normal appearance and behavior, no negative symptoms, and no prominent hallucinations. Always screen for substance use and medical causes before diagnosing a primary psychotic disorder.