Diagnosis of schizophrenia

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The diagnosis of schizophrenia, a psychotic disorder, is based on criteria in either the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders , or the World Health Organization's International Classification of Diseases (ICD). [1] Clinical assessment of schizophrenia is carried out by a mental health professional based on observed behavior, reported experiences, and reports of others familiar with the person. [2] Diagnosis is usually made by a psychiatrist. [3] Associated symptoms occur along a continuum in the population and must reach a certain severity and level of impairment before a diagnosis is made. [4] Schizophrenia has a prevalence rate of 0.3-0.7% in the United States. [5]

Contents

Criteria

In 2013, the American Psychiatric Association released the fifth edition of the DSM (DSM-5). According to the manual, to be diagnosed with schizophrenia, two diagnostic criteria have to be met over much of the time of a period of at least one month, with a significant impact on social or occupational functioning for at least six months. The DSM diagnostic criteria outlines that the person has to be experiencing either delusions, hallucinations, or disorganized speech. In other words, an individual does not have to be experiencing delusions or hallucinations to receive a diagnosis of schizophrenia. A second symptom could be negative symptoms, or severely disorganized or catatonic behavior. [5] Only two symptoms are required for a diagnosis of schizophrenia, resulting in different presentations for the same disorder. [5]

In practice, agreement between the two systems is high. [6] The DSM-5 criteria puts more emphasis on social or occupational dysfunction than the ICD-10. [7] The ICD-10, on the other hand, puts more emphasis on first-rank symptoms. [2] [8] The current proposal for the ICD-11 criteria for schizophrenia recommends adding self-disorder as a symptom. [9]

Changes made

Both manuals have adopted the chapter heading of Schizophrenia spectrum and other psychotic disorders; ICD modifying this as Schizophrenia spectrum and other primary psychotic disorders. [10] The definition of schizophrenia remains essentially the same as that specified by the 2000 text revised DSM-IV (DSM-IV-TR). However, with the publication of DSM-5, the APA removed all sub-classifications of schizophrenia. [10] ICD-11 has also removed subtypes. The removed subtype from both, of catatonic has been relisted in ICD-11 as a psychomotor disturbance that may be present in schizophrenia. [10]

Another major change was to remove the importance previously given to Schneider's first-rank symptoms. [11] DSM-5 still uses the listing of schizophreniform disorder but ICD-11 no longer includes it. [10] DSM-5 also recommends that a better distinction be made between a current condition of schizophrenia and its historical progress, to achieve a clearer overall characterization. [11]

A dimensional assessment has been included in DSM-5 covering eight dimensions of symptoms to be rated (using the Scale to Assess the Severity of Symptom Dimensions) – these include the five diagnostic criteria plus cognitive impairments, mania, and depression. [10] This can add relevant information for the individual in regard to treatment, prognosis, and functional outcome; it also enables the response to treatment to be more accurately described. [10] [12]

Two of the negative symptoms – avolition and diminished emotional expression – have been given more prominence in both manuals. [10]

First rank symptoms

First-rank symptoms are psychotic symptoms that are particularly characteristic of schizophrenia, which were put forward by Kurt Schneider in 1959. [13] Their reliability for the diagnosis of schizophrenia has been questioned since then. [14] A 2015 systematic review investigated the diagnostic accuracy of first rank symptoms:

First rank symptoms for schizophrenia [15]
Summary
These studies were of limited quality. Results show correct identification of people with schizophrenia in about 75–95% of the cases although it is recommended to consult an additional specialist. The sensitivity of FRS was about 60%, so it can help diagnosis and, when applied with care, mistakes can be avoided. In lower resource settings, when more sophisticated methods are not available, first rank symptoms can be very valuable. [15]

Heterogeneity

Sub-classifications

The DSM-IV-TR contained five sub-classifications of schizophrenia. The sub-classifications were removed in the DSM-5 due to the conditions' heterogeneous nature and their historical insignificance in clinical practice. [16] These were retained in previous revisions largely for reasons of tradition, but had subsequently proved to be of little worth. [7]

The ICD-10 defines seven sub-classifications of schizophrenia. [8] These sub-classifications are:

Sub-classifications of Schizophrenia
ICD-10DescriptionDSM-IV-TR Equivalent
Paranoid (F20.0Delusions and hallucinations are present but thought disorder, disorganized behavior, and affective flattening are not prominent.Paranoid type (295.3)
Hebephrenic (F20.1)Thought disorder and flat affect are present together.Disorganized type (295.1)
Catatonic (F20.2)Psychomotor disturbances are dominant features. Symptoms can include catatonic stupor and waxy flexibility.Catatonic type (295.2)
Undifferentiated (F20.3)Psychotic symptoms are present but the criteria for paranoid, disorganized, or catatonic types have not been met.Undifferentiated type (295.9)
Post-schizophrenic depression (F20.4)A depressive episode arising in the aftermath of a schizophrenic illness where some low-level schizophrenic symptoms may still be present.Not present
Residual (F20.5)Positive symptoms are present at a low intensity and negative symptoms are prominent.Residual type (295.6)
Simple (F20.6)Delusions and hallucinations are not evident and negative symptoms progress slowly.Not present
Other (F20.8)Includes cenesthopathic schizophrenia and schizophreniform disorder NOSNot present

Country-specific versions

The ICD-10 Clinical Modification, used for medical coding and reporting in the United States excludes the post-schizophrenic depression (F20.4) and the Simple (F20.6) sub-classifications. [17]

The Russian version of the ICD-10 includes additional four sub-classifications of schizophrenia: hypochondriacal (F20.801), cenesthopathic (F20.802), childhood type (F20.803), and atypical (F20.804). [18]

Comorbidities

People with schizophrenia often have additional mental health problems such as anxiety, depressive, or substance-use disorders. [19] Schizophrenia occurs along with obsessive-compulsive disorder (OCD) considerably more often than could be explained by chance. [20] An estimated 21% to 47% of patients with schizophrenia have a substance misuse disorder at some time in their life, and the chances of developing a substance misuse disorder is significantly higher among patients with a psychotic illness. [21] [22] [23] All of these factors result in an increased range of clinical presentations and suggest a significant etiological heterogeneity. [19]

Sex differences

Schizophrenia is diagnosed 1.4 times more frequently in males than females, with onset peaking at ages 20–28 years for males and 4–10 years later in females. [24] Females show more psychotic and affective symptoms than males, and have less social impairment. Men present more often with negative symptoms and disorganization. [2] These differences are likely due to the protective effects of estrogen and are correlated with estrogen expression. [25]

Prelingually deaf persons

Usually, psychiatric diagnostics is carried out orally. Thus, the question about schizophrenia in prelingually deaf persons rises. Only few reports exist. A review points out that acoustic hallucinations of normal hearing schizophrenic people correspond to visual and tactile hallucinations of prelingually deaf persons. Also, the structure of the (sign-) language is altered in ill persons. As a follow, “schizophrenia does not depend on the acoustic part of language or the acquisition of spoken language”. [26]

Onset

Early-onset schizophrenia occurs from ages 20–30, late-onset occurs after the age of 40, and very-late-onset after the age of 60. [27] [28] It is estimated that 15% of the population with schizophrenia are late-onset and 5% very-late onset. [27] [28] Many of the symptoms of late-onset schizophrenia are similar to the early-onset. However, individuals with late-onsets are more likely to report hallucinations in all sensory modalities, as well as persecutory and partition delusions. On the other hand, late-onset cases are less likely to present with formal thought disorder, affective symptoms. Negative symptoms and cognitive impairment are also rarer in very-late onset cases. [27] [28]

Etiology

The pathophysiology of schizophrenia is poorly understood. Multiple hypotheses have been put forward, with evidence both supporting and contradicting them. The most commonly supported theories are the dopamine hypothesis and the glutamate hypothesis. [29] Multiple genetic and environment factors have been associated with increased risk for developing schizophrenia. [30] Furthermore, response to treatment with anti-psychotic medication is variable, with some patients being resistant to some therapies. [31] Together, the differences in causes, response to treatment and pathophysiology suggest schizophrenia is heterogeneous from an etiological standpoint. [32] The differences resulting from this in terms of in clinical manifestations make the disorder harder to diagnose. [32]

Genetic

Multiple genetic and environmental factors contribute to the development of the schizophrenic phenotype. Distinct symptomatic sub types of schizophrenia groups show distinct patterns of SNP variations, reflecting the heterogeneous nature of the disease. [33] Studies also suggest there is a genetic overlap between schizophrenia and other psychiatric disorders, such as autism spectrum disorders, attention deficit-hyperactivity disorder, bipolar disorder, and major depressive disorder. [34] These factors complicate the use of genetic tests in diagnosis or prediction of the onset of schizophrenia. [35]

Differential diagnosis

If signs of disturbance are present for more than a month but less than six months, the diagnosis of schizophreniform disorder is applied. [36] Psychotic symptoms lasting less than a month may be diagnosed as brief psychotic disorder, and various conditions may be classed as psychotic disorder not otherwise specified. Schizoaffective disorder is diagnosed if symptoms of mood disorder are substantially present alongside psychotic symptoms.

Psychotic symptoms may be present in several other mental disorders, including bipolar disorder, [37] and borderline personality disorder. [38] Delusions ("non-bizarre") are also present in delusional disorder, and social withdrawal in social anxiety disorder, avoidant personality disorder and schizotypal personality disorder. Schizophrenia cannot be diagnosed if symptoms of mood disorder are substantially present, or if symptoms of pervasive developmental disorder are present unless prominent delusions or hallucinations are also present. Schizophrenia is further complicated with obsessive-compulsive disorder (OCD), and it can be difficult to distinguish obsessions that occur in OCD from the delusions of schizophrenia. [39] In children hallucinations must be separated from typical childhood fantasies. [40]

A urine drug screen must be performed to determine if the cause for symptoms could be drug intoxication or drug-induced psychosis. For example, a few people withdrawing from benzodiazepines experience a severe withdrawal syndrome which may last a long time and can resemble schizophrenia. [41] A general medical and neurological examination may also be needed to rule out medical illnesses which may rarely produce psychotic schizophrenia-like symptoms, [36] such as metabolic disturbance, systemic infection, syphilis, HIV infection, epilepsy, and brain lesions. Stroke, multiple sclerosis, hyperthyroidism, hypothyroidism, and dementias such as Alzheimer's disease, Huntington's disease, frontotemporal dementia, and the Lewy body dementias may also be associated with schizophrenia-like psychotic symptoms. [42] It may be necessary to rule out a delirium, which can be distinguished by visual hallucinations, acute onset and fluctuating level of consciousness, and indicates an underlying medical illness. Investigations are not generally repeated for relapse unless there is a specific medical indication or possible adverse effects from antipsychotic medication.

Biomarkers

A biomarker, as defined by the National Institutes of Health Biomarkers Definitions Working Group, is "a biologic characteristic objectively measured and evaluated as an indicator of normal or pathogenic processes; or of response to a treatment or challenge". [43] Biomarkers of psychosis for use in clinical tests can be diagnostic, prognostic, predictive of conversion, or monitoring of progression. [44] Clinical tests have many benefits: they can provide confidence in a diagnosis, allow clinicians to make better informed choices in regard to treatment, or even make it possible to identify subjects which can benefit from therapy to prevent transition into schizophrenia. [45] Currently, no biomarkers that can be widely used in clinical practice for the diagnosis of schizophrenia have been identified. [44]

Imaging

Brain imaging, such as CT and MRI scans, are currently only used to rule out brain abnormalities, and their benefit is very limited at that. [46] Structural alterations have, however, been identified in schizophrenia, most commonly enlarged ventricles, and decreased grey matter volume in the cortex and hippocampus. [47] Studies using functional MRI have also shown that altered connectivity and activity in present in schizophrenia. [48]

In the last decade interest has grown in the use of machine learning to automatically perform the diagnosis task using brain imaging data. While these algorithms are very robust at distinguishing schizophrenia patients from healthy subjects, they still cannot perform the tasks clinicians struggle the most with – differential diagnosis and treatment selection. [49]

Blood-based

Blood-based biomarkers those are obtained from plasma or serum samples. Since the prevalence of metabolic syndromes is increased in schizophrenia patients, makers of those syndromes have been common targets of research. Differences between patients and controls have been found in insulin levels, insulin resistance, and glucose tolerance. [50] These effects are generally small, however, and often present only in a subset of patients, which results from the heterogeneity of the disease. [50] Furthermore, these results are often complicated by the metabolic side effects of anti-psychotic medication. [50] Serum levels of hormones typically active in the hypothalamic pituitary adrenal (HPA) axis, such as cortisol and acetylcholine, have also been correlated with symptoms and progression of schizophrenia. [50] Peripheral biomarkers of immune function have also been a major target of research, with over 75 candidates having been identified. [51] Cytokines and growth factors are consistently identified as candidates by different studies, but variation in identity and direction of the correlation is common. [50] In recent years, markers of oxidative stress, epigentic methylation, mRNA transcription, and proteomic expression have also been targets of research, with their potential still to be determined. [52] It is likely that no single biomarker will be clinically useful, but rather a biomarker assay would have to be performed, like the well-performing 51 marker assay developed by E. Schwarz and colleagues. [53]

Genetic

Estimates of the heritability of schizophrenia is around 80%, which implies that 80% of the individual differences in risk to schizophrenia is explained by individual differences in genetics. [54] Although many genetic variants associated with schizophrenia have been identified, their effects are usually very small, so they are combined onto a polygenic risk score. [55] These scores, despite accounting for hundreds of variants, only explain up to 6% in symptom variation and 7% of the risk for developing the disease. [35] An example of a well-studied [44] genetic biomarker in schizophrenia is the single nucleotide polymorphism in the HLA-DQB1 gene, which is part of the human leukocyte antigen (HLA) complex. A G to C replacement on position 6672 predicts risk of agranulocytosis, a side effect of clozapine that can be fatal. [56]

Criticisms of classification systems

Spectrum of conditions

There is an argument that the underlying issues would be better addressed as a spectrum of conditions [57] or as individual dimensions along which everyone varies rather than by a diagnostic category based on an arbitrary cut-off between normal and ill. [58] This approach appears consistent with research on schizotypy, and with a relatively high prevalence of psychotic experiences, mostly non-distressing delusional beliefs, among the general public. [59] [60] [61] In concordance with this observation, psychologist Edgar Jones, and psychiatrists Tony David and Nassir Ghaemi, surveying the existing literature on delusions, pointed out that the consistency and completeness of the definition of delusion have been found wanting by many; delusions are neither necessarily fixed nor false, and need not involve the presence of incontrovertible evidence. [62] [63] [64]

Diagnostic criteria

Nancy Andreasen has criticized the current DSM-IV and ICD-10 criteria for sacrificing diagnostic validity for the sake of artificially improving reliability. She argues that overemphasis on psychosis in the diagnostic criteria, while improving diagnostic reliability, ignores more fundamental cognitive impairments that are harder to assess due to large variations in presentation. [65] [66] This view is supported by other psychiatrists. [67] In the same vein, Ming Tsuang and colleagues argue that psychotic symptoms may be a common end-state in a variety of disorders, including schizophrenia, rather than a reflection of the specific etiology of schizophrenia, and warn that there is little basis for regarding DSM's operational definition as the "true" construct of schizophrenia. [57] Neuropsychologist Michael Foster Green went further in suggesting the presence of specific neurocognitive deficits may be used to construct phenotypes that are alternatives to those that are purely symptom-based. These deficits take the form of a reduction or impairment in basic psychological functions such as memory, attention, executive function and problem solving. [68] [69]

The exclusion of affective components from the criteria for schizophrenia, despite their ubiquity in clinical settings, has also caused contention. This exclusion in the DSM has resulted in a "rather convoluted" separate disorder—schizoaffective disorder. [67] Citing poor interrater reliability, some psychiatrists have totally contested the concept of schizoaffective disorder as a separate entity. [70] [71] The categorical distinction between mood disorders and schizophrenia, known as the Kraepelinian dichotomy, has also been challenged by data from genetic epidemiology. [72]

Biological validity

As clinicians and researchers become increasingly aware of the limitations of the current diagnostic systems, calls for new nosology are being made. [73] The National Institute of Health's Research of Domain Criteria (RDoC) research program, launched in 2009, is perhaps the largest combined effort to address the need for a new approach in classifying mental disorders. [74] The European Roadmap for Mental Health Research (ROAMER) funding initiative shares many goals with RDoC. [75] These initiatives encourage researchers to consider diagnosis as dimensional, instead of a clear-cut between patients and healthy subjects, and to cut across diagnostic boundaries. [76] The goal is to develop biologically valid diagnosis by defining nosology based on biological measures instead of symptom profiles, as is done currently. [77] Initial efforts in this area have been able to stratify patients along the psychosis continuum into genetically distinct sub types based on their symptoms, [76] brain measures such as EEG, [78] [79] and serum biomarker profiles. [80]

Related Research Articles

<span class="mw-page-title-main">Catatonia</span> Psychiatric behavioural syndrome

Catatonia is a complex syndrome, most commonly seen in people with underlying mood or psychotic disorders. People with catatonia have abnormal movement and behaviors, which vary from person to person and fluctuate in intensity within a single episode. People with catatonia appear withdrawn, meaning that they do not interact with the outside world and have difficulty processing information. They may be nearly motionless for days on end or perform repetitive purposeless movements. Two people may exhibit very different sets of behaviors and both still be diagnosed with catatonia. Treatment with benzodiazepines or ECT are most effective and lead to remission of symptoms in most cases.

<span class="mw-page-title-main">Dementia praecox</span> Obsolete medical term for the schizophrenia and autism spectrums

Dementia praecox is a disused psychiatric diagnosis that originally designated a chronic, deteriorating psychotic disorder characterized by rapid cognitive disintegration, usually beginning in the late teens or early adulthood. Over the years, the term dementia praecox was gradually replaced by the term schizophrenia, which initially had a meaning that included what is today considered the autism spectrum.

Psychosis is a condition of the mind or psyche that results in difficulties determining what is real and what is not real. Symptoms may include delusions and hallucinations, among other features. Additional symptoms are disorganized thinking and incoherent speech and behavior that is inappropriate for a given situation. There may also be sleep problems, social withdrawal, lack of motivation, and difficulties carrying out daily activities. Psychosis can have serious adverse outcomes.

<span class="mw-page-title-main">Schizophrenia</span> Mental disorder with psychotic symptoms

Schizophrenia is a mental disorder characterized variously by hallucinations, delusions, disorganized thinking and behavior, and flat or inappropriate affect. Symptoms develop gradually and typically begin during young adulthood and are never resolved. There is no objective diagnostic test; diagnosis is based on observed behavior, a psychiatric history that includes the person's reported experiences, and reports of others familiar with the person. For a diagnosis of schizophrenia, the described symptoms need to have been present for at least six months or one month. Many people with schizophrenia have other mental disorders, especially mood disorders, anxiety disorders, and obsessive–compulsive disorder.

Schizoaffective disorder is a mental disorder characterized by symptoms of both schizophrenia (psychosis) and a mood disorder - either bipolar disorder or depression. The main diagnostic criterion is the presence of psychotic symptoms for at least two weeks without prominent mood symptoms. Common symptoms include hallucinations, delusions, disorganized speech and thinking, as well as mood episodes. Schizoaffective disorder can often be misdiagnosed when the correct diagnosis may be psychotic depression, bipolar I disorder, schizophreniform disorder, or schizophrenia. This is a problem as treatment and prognosis differ greatly for most of these diagnoses. Many people with schizoaffective disorder have other mental disorders including anxiety disorders.

<span class="mw-page-title-main">Thought disorder</span> Disorder of thought form, content or stream

A thought disorder (TD) is a disturbance in cognition which affects language, thought and communication. Psychiatric and psychological glossaries in 2015 and 2017 identified thought disorders as encompassing poverty of ideas, neologisms, paralogia, word salad, and delusions—all disturbances of thought content and form. Two specific terms have been suggested—content thought disorder (CTD) and formal thought disorder (FTD). CTD has been defined as a thought disturbance characterized by multiple fragmented delusions, and the term thought disorder is often used to refer to an FTD: a disruption of the form of thought. Also known as disorganized thinking, FTD results in disorganized speech and is recognized as a major feature of schizophrenia and other psychoses. Disorganized speech leads to an inference of disorganized thought. Thought disorders include derailment, pressured speech, poverty of speech, tangentiality, verbigeration, and thought blocking. One of the first known cases of thought disorders, or specifically OCD as it is known today, was in 1691. John Moore, who was a bishop, had a speech in front of Queen Mary II, about "religious melancholy."

Stimulant psychosis is a mental disorder characterized by psychotic symptoms. It involves and typically occurs following an overdose or several day binge on psychostimulants, although it can occur in the course of stimulant therapy, particularly at higher doses. One study reported occurrences at regularly prescribed doses in approximately 0.1% of individuals within the first several weeks after starting amphetamine or methylphenidate therapy. Methamphetamine psychosis, or long-term effects of stimulant use in the brain, depend upon genetics and may persist for some time.

Thought broadcasting is a type of delusional condition in which the affected person believes that others can hear their inner thoughts, despite a clear lack of evidence. The person may believe that either those nearby can perceive their thoughts or that they are being transmitted via mediums such as television, radio or the internet. Different people can experience thought broadcasting in different ways. Thought broadcasting is most commonly found among people who have a psychotic disorder, specifically schizophrenia.

<span class="mw-page-title-main">Psychotic depression</span> Medical condition

Psychotic depression, also known as depressive psychosis, is a major depressive episode that is accompanied by psychotic symptoms. It can occur in the context of bipolar disorder or major depressive disorder. Psychotic depression can be difficult to distinguish from schizoaffective disorder, a diagnosis that requires the presence of psychotic symptoms for at least two weeks without any mood symptoms present. Unipolar psychotic depression requires that psychotic symptoms occur during severe depressive episodes, although residual psychotic symptoms may also be present in between episodes. Diagnosis using the DSM-5 involves meeting the criteria for a major depressive episode, along with the criteria for "mood-congruent or mood-incongruent psychotic features" specifier.

Paraphrenia is a mental disorder characterized by an organized system of paranoid delusions with or without hallucinations and without deterioration of intellect or personality.

A spectrum disorder is a disorder that includes a range of linked conditions, sometimes also extending to include singular symptoms and traits. The different elements of a spectrum either have a similar appearance or are thought to be caused by the same underlying mechanism. In either case, a spectrum approach is taken because there appears to be "not a unitary disorder but rather a syndrome composed of subgroups". The spectrum may represent a range of severity, comprising relatively "severe" mental disorders through to relatively "mild and nonclinical deficits".

The classification of mental disorders, also known as psychiatric nosology or psychiatric taxonomy, is central to the practice of psychiatry and other mental health professions.

<span class="mw-page-title-main">Grandiose delusions</span> Subtype of delusion

Grandiose delusions (GDs), also known as delusions of grandeur or expansive delusions, are a subtype of delusion characterized by the extraordinary belief that one is famous, omnipotent, wealthy, or otherwise very powerful or of a high status. Grandiose delusions often have a religious, science fictional, or supernatural theme. Examples include the extraordinary belief that one is a deity or celebrity, or that one possesses fantastical talents, accomplishments, or superpowers.

Brief psychotic disorder—according to the classifications of mental disorders DSM-IV-TR and DSM-5—is a psychotic condition involving the sudden onset of at least one psychotic symptom lasting 1 day to 1 month, often accompanied by emotional turmoil. Remission of all symptoms is complete with patients returning to the previous level of functioning. It may follow a period of extreme stress including the loss of a loved one. Most patients with this condition under DSM-5 would be classified as having acute and transient psychotic disorders under ICD-10. Prior to DSM-IV, this condition was called "brief reactive psychosis." This condition may or may not be recurrent, and it should not be caused by another condition.

<span class="mw-page-title-main">Persecutory delusion</span> Delusion involving perception of persecution

A persecutory delusion is a type of delusional condition in which the affected person believes that harm is going to occur to oneself by a persecutor, despite a clear lack of evidence. The person may believe that they are being targeted by an individual or a group of people. Persecution delusions are very diverse in terms of content and vary from the possible, although improbable, to the completely bizarre. The delusion can be found in various disorders, being more usual in psychotic disorders.

The word schizophrenia was coined by the Swiss psychiatrist Eugen Bleuler in 1908, and was intended to describe the separation of function between personality, thinking, memory, and perception. Bleuler introduced the term on 24 April 1908 in a lecture given at a psychiatric conference in Berlin and in a publication that same year. Bleuler later expanded his new disease concept into a monograph in 1911, which was finally translated into English in 1950.

Childhood schizophrenia is similar in characteristics of schizophrenia that develops at a later age, but has an onset before the age of 13 years, and is more difficult to diagnose. Schizophrenia is characterized by positive symptoms that can include hallucinations, delusions, and disorganized speech; negative symptoms, such as blunted affect and avolition and apathy, and a number of cognitive impairments. Differential diagnosis is problematic since several other neurodevelopmental disorders, including autism spectrum disorder, language disorder, and attention deficit hyperactivity disorder, also have signs and symptoms similar to childhood-onset schizophrenia.

Simple-type schizophrenia is a sub-type of schizophrenia included in the International Classification of Diseases (ICD-10), in which it is classified as a mental and behaviour disorder. It is not included in the current Diagnostic and Statistical Manual of Mental Disorders (DSM-5) or the upcoming ICD-11, effective 1 January 2022. Simple-type schizophrenia is characterized by negative ("deficit") symptoms, such as avolition, apathy, anhedonia, reduced affect display, lack of initiative, lack of motivation, low activity; with absence of hallucinations or delusions of any kind.

Schizophrenia is a primary psychotic disorder, whereas, bipolar disorder is a primary mood disorder which can also involve psychosis. Both schizophrenia and bipolar disorder are characterized as critical psychiatric disorders in the Diagnostic and Statistical Manual of Mental Disorders fifth edition (DSM-5). However, because of some similar symptoms, differentiating between the two can sometimes be difficult; indeed, there is an intermediate diagnosis termed schizoaffective disorder.

Bouffée délirante (BD) is an acute and transient psychotic disorder. It is a uniquely French psychiatric diagnostic term with a long history in France and various French speaking nations: Caribbean, e.g., Haiti, Guadeloupe, Antilles and Francophone Africa. The term BD was originally coined and described by Valentin Magnan (1835–1916), fell into relative disuse and was later revived by Henri Ey (1900–1977).

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