Thought disorder
A thought disorder is a multifaceted construct that reflects abnormalities in thinking, language, and communication. Thought disorders encompass a range of thought and language difficulties and include poverty of ideas, perverted logic, word salad, delusions, derailment, pressured speech, poverty of speech, tangentiality, verbigeration, and thought blocking. One of the first known public presentations of a thought disorder, specifically obsessive–compulsive disorder as it is now known, was in 1691, when Bishop John Moore gave a speech before Queen Mary II, about "religious melancholy."
Two subcategories of thought disorder are content-thought disorder, and formal thought disorder. CTD has been defined as a thought disturbance characterized by multiple fragmented delusions. A formal thought disorder is a disruption of the form of thought.
Also known as disorganized thinking, FTD affects the form of thought. FTD results in disorganized speech and is recognized as a key feature of schizophrenia and other psychotic disorders. Unlike hallucinations and delusions, it is an observable, objective sign of psychosis. FTD is a common core symptom of a psychotic disorder, and may be seen as a marker of severity and as an indicator of prognosis. It reflects a cluster of cognitive, linguistic, and affective disturbances that have generated research interest in the fields of cognitive neuroscience, neurolinguistics, and psychiatry.
Eugen Bleuler, who named schizophrenia, said that TD was its defining characteristic. Disturbances of thinking and speech, such as clanging or echolalia, may also be present in Tourette syndrome; other symptoms may be found in delirium. A clinical difference exists between these two groups. Patients with psychoses are less likely to show awareness or concern about disordered thinking, and those with other disorders are aware and concerned about not being able to think clearly.
Content-thought disorder
Thought content is the subject of a person's thoughts, or the types of ideas expressed. Mental health professionals define normal thought content as the absence of significant abnormalities, distortions, or harmful thoughts. Normal thought content aligns with reality, is appropriate to the situation, and does not cause significant distress or impair functioning.A person's cultural background must be considered when assessing thought content. Abnormalities in thought content differ across cultures. Specific types of abnormal thought content can be features of different psychiatric illnesses.
Examples of disordered thought content include:
- Suicidal ideation: thoughts of ending one's own life.
- Homicidal ideation: thoughts of ending the life of another.
- Delusion: A fixed, false belief that a person holds despite contrary undeniable & unfalsifiable evidence and that is not a shared cultural belief.
- Paranoid ideation: thoughts, not severe enough to be considered delusions, involving excessive suspicion or the belief that one is being harassed, persecuted, or unfairly treated.
- Preoccupation: excessive and/or distressing thoughts that are stressor-related and associated with negative emotions.
- Obsessive–compulsive disorder: As obsession, repeated intrusive thoughts that are inappropriate, and distressing or upsetting, and compulsive behavior repeated actions as an attempt to rid the intrusive thoughts.
- Magical thinking: A false belief in a causal link between actions and events. The mistaken belief that one's thoughts, words, or actions can cause or prevent an outcome in a way that violates the laws of cause and effect.
- Overvalued ideas: false or exaggerated belief held with conviction, but without delusional intensity.
- Phobias: irrational fears of objects or circumstances that are persistent.
- Poverty of ideas: abnormally few thoughts and ideas expressed.
- Overabundance of thought: abnormally many thoughts and ideas expressed.
Formal thought disorder
Formal thought disorder, also known as disorganized speech or disorganized thinking, is a disorder of a person's thought process in which they are unable to express their thoughts in a logical and linear fashion. Mild forms of disorganised speech are quite common, and to be considered as a diagnostic criterion for psychosis it must be severe enough to prevent effective communication. Disorganized speech is a core symptom of psychosis, and therefore can be a feature of any condition that has a potential to cause psychosis, including schizophrenia, mania, major depressive disorder, delirium, postpartum psychosis, major neurocognitive disorder, and substance induced psychosis. FTD reflects a cluster of cognitive, linguistic, and affective disturbances, and has generated research interest from the fields of cognitive neuroscience, neurolinguistics, and psychiatry.
It can be subdivided into clusters of positive and negative symptoms and objective symptoms. On the scale of positive and negative symptoms, they have been grouped into positive formal thought disorder and negative formal thought disorder. Positive subtypes were pressure of speech, tangentiality, derailment, incoherence, and illogicality; negative subtypes were poverty of speech and poverty of content. The two groups were posited to be at either end of a spectrum of normal speech, but later studies showed them to be poorly correlated. A comprehensive measure of FTD is the Thought and Language Disorder Scale. The Kiddie Formal Thought Disorder Rating Scale can be used to assess the presence of formal thought disorder in children and their childhood. Although it is very extensive and time-consuming, its results are in great detail and reliable.
Nancy Andreasen preferred to identify TDs as thought-language-communication disorders. Up to seven domains of FTD have been described on the Thought, Language, Communication Scale, with most of the variance accounted for by two or three domains. Some TLC disorders are more suggestive of severe disorder, and are listed with the first 11 items.
Diagnoses
In the diagnosis of a psychotic disorder, the DSM-5 uses the term disorganized thinking over formal thought disorder, used as a synonym. It was thought that formal thought disorder was too difficult to firmly define, and that inferences about a person's thinking can be gained from their speech. Clinical psychologists typically assess FTD by initiating an exploratory conversation with a client and observing their verbal responses.FTD is often used to establish a diagnosis of schizophrenia; in cross-sectional studies, 27 to 80 percent of patients with schizophrenia present with FTD. A hallmark feature of schizophrenia, it is also widespread amongst other psychiatric disorders; up to 60 percent of those with schizoaffective disorder and 53 percent of those with clinical depression demonstrate FTD, suggesting that it is not exclusive to schizophrenia. About six percent of healthy subjects exhibit a mild form of FTD. Less severe FTD may happen during the initial stage, and after psychosis has diminished.
The characteristics of FTD vary amongst disorders. A number of studies indicate that FTD in mania is marked by irrelevant intrusions and pronounced combinatory thinking, usually with a playfulness and flippancy absent from patients with schizophrenia. The FTD present in patients with schizophrenia was characterized by disorganization, neologism, and fluid thinking, and confusion with word-finding difficulty.
There is limited data on the longitudinal course of FTD. The most comprehensive longitudinal study of FTD by 2023 found a distinction in the longitudinal course of thought-disorder symptoms between schizophrenia and other psychotic disorders. The study also found an association between pre-index assessments of social, work and educational functioning and the longitudinal course of FTD.
Possible causes
Several theories have been developed to explain the causes of formal thought disorder. It has been proposed that FTD relates to neurocognition via semantic memory. Semantic network impairment in people with schizophreniameasured by the difference between fluency and phonological fluency predicts the severity of formal thought disorder, suggesting that verbal information is unavailable. Other hypotheses include working memory deficit and attentional focus.FTD in schizophrenia has been found to be associated with structural and functional abnormalities in the language network, where structural studies have found bilateral grey matter deficits; deficits in the bilateral inferior frontal gyrus, bilateral inferior parietal lobule and bilateral superior temporal gyrus are FTD correlates. Other studies did not find an association between FTD and structural aberrations of the language network, however, and regions not included in the language network have been associated with FTD. Future research is needed to clarify whether there is an association with FTD in schizophrenia and neural abnormalities in the language network.
Neurotransmitter dysfunctions that might cause FTD have also been investigated. Studies have found that glutamate dysfunction, due to a rarefaction of glutamatergic synapses in the superior temporal gyrus in patients with schizophrenia, is a major cause of positive FTD.
The heritability of FTD has been demonstrated in a number of family and twin studies. Imaging genetics studies, using a semantic verbal-fluency task performed by the participants during functional MRI scanning, revealed that alleles linked to glutamatergic transmission contribute to functional aberrations in typical language-related brain areas. FTD is not solely genetically determined, however; environmental influences, such as allusive thinking in parents during childhood, and environmental risk factors for schizophrenia also contribute to the pathophysiology of FTD.
The origins of FTD have been theorised from a social-learning perspective. Singer and Wynne said that familial communication patterns play a key role in shaping the development of FTD; dysfunctional social interactions undermine a child's development of cohesive, stable mental representations of the world, increasing their risk of developing FTD.