Psychiatric Differential Diagnosis of Psychosis

Essential Concepts

Delusional disorder is a psychotic disorder with the hallmark of nonbizarre delusions in an otherwise unremarkable person.
Mood disorders can be accompanied by psychosis, including Schneiderian First-Rank Symptoms. In textbook cases, mood disorders are episodic (i.e., have periods of illness clearly delineated from normal), and psychosis is only present during mood episodes, not in the interepisode period.
Catatonia has an extensive differential diagnosis that includes medical causes and mood disorders. Catatonic schizophrenia is but one diagnostic consideration.
Schizotypal and schizoid personality disorders are nonpsychotic disorders that share attenuated positive and negative symptoms with schizophrenia, respectively. Dissociative phenomena can be confused with psychosis.

“Sometimes paranoia’s just having all the facts.”

—William S. Burroughs, 1914-1997, of the Beat Generation

Once you have excluded drug-induced psychosis and secondary schizophrenia as the cause for psychotic symptoms in a patient, you can then (and only then) turn your attention to primary psychiatric reasons for the psychosis; Table 6.1 presents a comprehensive list of primary psychiatric disorders that can be accompanied by psychosis. These psychiatric disorders are all diagnosed based on clinical features (cross-sectionally and longitudinally) alone, so to diagnose them you must know what they look like in the clinic—there are no laboratory tests that will help you.

DELUSIONAL DISORDER (PARANOIA)

Delusional disorder, the paranoia of late, is a disorder of midlife, with the hallmark of nonbizarre delusion(s) in the absence of
other prominent psychotic symptoms; only minimal formal thought disorder or hallucinations are allowed. Patients’ personalities are intact: In casual conversation you do not suspect a psychiatric disorder unless you happen to come upon the delusion. You are usually able to fit your patient, based on the content of the delusion, into one of these subtypes: persecutory, grandiose, jealous (Othello syndrome), erotomanic (de Clérambault syndrome), and somatic (e.g., Ekbom’s syndrome). Some degree of depressive overlay can be present leading to a mistaken diagnosis of psychotic depression.

TABLE 6.1. Psychiatric Differential Diagnosis of Psychosis

Schizophrenia^a	Catatonia
Schizophreniform disorder, brief psychotic disorders, (ATPD)^a	Posttraumatic stress disorder (PTSD), dissociation, trance states
Schizoaffective disorder^a Delusional disorder Bipolar disorder Psychotic depression Late paraphrenia (late-life psychosis) Postpartum psychosis Obsessive-compulsive disorder (if severe with no insight) Pfropfschizophrenia (schizophrenia “grafted upon” mental retardation)	Personality disorders Paranoid personality disorder Schizoid and schizotypal personality disorder Borderline and histrionic personality disorder Autism Other pervasive developmental disorders Asperger’s syndrome Heller’s syndrome Rett syndrome Nonpathologic psychotic symptoms in general population
Folie á deux	Malingering
ATPD, acute and transient psychotic disorders
^aSometimes referred to as “schizophrenia-spectrum disorders.”

The degree of social impairment depends on the nature of the delusion, the degree of encapsulation (to which degree patients function normally outside their delusion), and the degree of systematization (i.e., the extent to which the ramifications of a delusional system are connected to a common theme). Grandiose and persecutory delusions are very impairing once these delusions spread and extend into all spheres of life.

Patients with delusional disorders are notoriously difficult to treat, to the point of being untreatable. This is not due to antipsychotic unresponsiveness (they are an effective first-line treatment) but because patients tend to categorically
reject psychiatric treatments, as they do not feel ill. Despite great efforts on your part, “insight” is often not forthcoming, and patients come mainly to convince you that they are right and you are wrong. In less severe cases, cognitive-behavioral therapy might lead to some improvement. Sometimes you can provide symptomatic relief with ancillary treatments, e.g., benzodiazepines or antidepressants.

CLINICAL VIGNETTE

An engineer in his 30s lost his job after repeatedly accusing his co-workers of spreading rumors about his sexual orientation. When he confronted an innocent bystander about a perceived insult, he was arrested. He never actually heard anyone talk about him or insult him, but merely had the impression, deduced from gestures, that people were conspiring against him. He had an excellent response to antipsychotics, with complete resolution of persecutory delusions. However, he never acknowledged the possibility that his experiences might have been the result of a psychiatric illness, and only took antipsychotics under duress as part of court-imposed probation.

The management of patients with delusional disorder is further complicated by the real possibility of violence, particularly in patients who feel persecuted or harassed (which can lead to self-defense or preventive action) or loved (which can lead to stalking). A good risk assessment and risk plan is an important part of treatment.

PSYCHOSIS IN MOOD DISORDERS

Psychotic symptoms (i.e., delusions and hallucinations) can occur in primary mood disorders like unipolar depression or bipolar disorder (manic-depressive illness). Unfortunately, there are no pathognomonic psychotic symptoms that allow you to decide if psychosis is part of a mood disorder or schizophrenia.