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Overview
Formal thought disorder (FTD), or simply thought disorder, is also known as disorganized speech – evident from disorganized thinking, and is one of the hallmark features of schizophrenia. Formal thought disorder is a disorder of the form of thought rather than of content of thought that covers hallucinations and delusions. FTD, unlike hallucinations and delusions, is an observable objective sign of psychosis. FTD is a common, and core symptom of a psychotic disorder and may be seen as a marker of its severity, and also as a predictor of prognosis. It reflects a cluster of cognitive, linguistic, and affective disturbances, that has generated research interest from the fields of cognitive neuroscience, neurolinguistics, and psychiatry.

FTD is a complex, multidimensional syndrome characterized by deficiencies in the logical organizing of thought needed to achieve goals. FTD can be subdivided into clusters of positive and negative symptoms, as well as objective versus subjective symptoms. Within the scale of positive and negative symptoms they have been grouped into positive formal thought disorder (posFTD) and negative formal thought disorder (negFTD). Positive subtypes were those of pressure of speech, tangentiality, derailment, incoherence, and illogicality. Negative subtypes were those of poverty of speech and poverty of content. The two groups were posited to be at either end of a spectrum of normal speech. However, later studies showed these to be poorly correlated. A comprehensive measure of formal thought disorder is the Thought and Language Disorder (TALD) Scale.

Nancy Andreasen preferred to call the thought disorders collectively as thought-language-communication disorders (TLC disorders). Within the Thought, Language, Communication (TLC) Scale up to seven domains of FTD have been described with most of the variance accounted for by just two or three domains. Some TLC disorders are more suggestive of a severe disorder and given priority by listing them in the first 11 items.

Diagnoses
The DSM V categorises FTD as “a psychotic symptom, manifested as bizarre speech and communication.” FTD may include incoherence, peculiar words, disconnected ideas, or a lack of the unprompted content we would expect from normal speech. Clinical psychologists typically assess FTD by initiating an exploratory conversation with patients and observing the patient’s verbal responses. FTD is often used to establish a diagnosis of schizophrenia, as such, in cross-sectional studies 27–80% of patients with schizophrenia present with FTD. FTD, although a hallmark feature of schizophrenia, is also widespread amongst sufferers of other psychiatric disorders; up to 60% of those with schizoaffective disorder, and 53% of those with clinical depression show FTD, suggesting FTD is not pathognomonic of schizophrenia. Around 6% of healthy probands show a mild form of FTD. The characteristics of FTD vary amongst disorders. Multiple studies show that FTD in mania is marked by irrelevant intrusions and pronounced combinatory thinking, usually with playfulness and flippancy lacking in Schizophrenic patients. The FTD present in schizophrenic patients, however, was characterised by disorganisation, neologism, and fluid thinking; as well as confusion with word-finding difficulty. There is limited data on the longitudinal course of FTD. The most comprehensive longitudinal study of FTD done to date 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.

Speculative Causes
Several theories have been developed to explain the causes of formal thought disorder. It has been proposed that formal thought disorder relates to neurocognition via semantic memory. Semantic network impairment in people with schizophrenia—measured by the difference between fluency (number of animals' names produced in 60 seconds) and phonological fluency (number of words beginning with "F" produced in 60 seconds)—predicts severity of formal thought disorder, suggesting that verbal information (through semantic priming) is unavailable. Other hypotheses include working memory deficit (being confused about what has already been said in a conversation) and attentional focus. FTD in schizophrenia has been found to be associated with structural and functional abnormalities in the language network. Structural studies have found bilateral grey matter deficits in the language network, in particular, the bilateral inferior frontal gyrus, bilateral inferior parietal lobe and bilateral superior temporal gyrus to be FTD correlates. However, there are studies that did not find an association between FTD and structural aberrations of the language network and regions not included in the language network have been associated with FTD. Thus, future research is needed to clarify whether there is an association with FTD in schizophrenia and neural abnormalities in the language network. There has also been investigation into the transmitter systems that might cause FTD. Studies have found that glutamate dysfunction due to a rarefication of glutamatergic synapses in the superior temporal gyrus in patients’ schizophrenia is a major cause for positive FTD. The heritability of FTD has been demonstrated in myriad 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. However, FTD is not solely genetically determined: environmental influences, such as allusive thinking in parents during childhood, and general environmental risk factors for schizophrenia (neurodevelopmental, childhood abuse, migration, social isolation, cannabis, etc) also contribute to the pathophysiology of FTD. The origins of FTD have also been conceptualized from a social-learning perspective. Singer and Wynne contended that familial communication patterns play a key role in shaping the development of FTD— believing that dysfunctional social interactions undermine a child’s development of cohesive, stable mental representations of the world, therefore increasing their risk of developing FTD.

Treatments
Antipsychotic medication is often utilised to treat FTD. The vast majority of studies examining the efficacy of antipsychotic treatment do not report the effects on syndromes or symptoms. Nevertheless, there are six older studies reporting on the effects of antipsychotic treatment on FTD. From these studies and from clinical experience, we know that antipsychotics are often an effective treatment for patients with positive or negative FTD. There is, however, a subgroup of patients with treatment refractory FTD. Cognitive Behavioural Therapy is an another example of a treatment for FTD. There is currently very little research exploring the effectiveness of CBT for individuals with FTD. Large randomised controlled trials evaluating the effectiveness of CBT for treating psychosis often exclude individuals with high levels of FTD due to FTD reducing therapeutic alliance which is associated with key outcomes in therapy. However, there is some provisional evidence suggesting that FTD may not preclude the effectiveness of CBT. Kircher and colleagues have suggested the following methods should be used in Cognitive-behavioural therapy for treating patients with formal thought disorder:

• Practise structuring, summarising, and feedback methods

• Repeat and clarify the core issues and main emotions that the patient is trying to communicate

• Gently encourage patients to clarify what they are trying to communicate

• Ask patients to clearly state their communication goal

• Ask patients to slow down and explain how one-point leads to another

• Help patients identify the links between ideas

• Identify the main affect linked to the thought disorder

• Normalise problems with thinking

• Model clear and precise communication for patients

• Introduce the idea of “pressing the buzzer” to let patients know when they are getting off track

• Use diagrams to demonstrate disruptions in the flow of thinking—contrast these with diagrams of effective patterns of communication

• Review audiotape or videotape to clarify the main themes.