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Oxford Languages defines thought disorder (TD), also known as formal thought disorder, as "a disorder of cognitive organization, characteristic of psychotic mental illness, in which thoughts and conversation appear illogical and lacking in sequence and may be delusional or bizarre in content."
Essentially, formal thought disorder (FTD) is a disturbance or impairment in cognition that can cause disordered thinking and affect the coherence of your speech and writing. While FTD is primarily synonymous with disorganized speech, content thought disorder is characterized as a 'thought disturbance' that can cause you to experience several fragmented delusions.
Thought disorder is often associated with symptoms of psychotic disorders like schizophrenia or depression and mania — although it is not a direct symptom of any disorder.
It's not uncommon for many people to experience some thought disorder symptoms occasionally. A good time to see your doctor is when your symptoms increase in frequency or severity or make it difficult for you to communicate with others.
Thought disorder has been associated with attention-deficit/hyperactivity disorder (ADHD) patients. In fact, several studies have identified a link between ADHD and thought disorder symptoms such as disorganized thinking and distractible speech.¹
Bipolar disorder is another condition widely associated with thought disorder symptoms, often presenting itself in the form of disordered and irrational thinking. According to one study, it is one of several psychotic symptoms a bipolar patient may experience during an episode.²
Obsessive-compulsive disorder (OCD) patients often experience a change in thought patterns, particularly obsessive and recurring thoughts. Fish's classification of thought disorder set out different categories, with one being the "possession of thought."
With that classification in mind, OCD can be comorbid with thought disorders since patients often lose control or 'possession' of their thoughts.
It's important to note that while many of these conditions can be linked to thought disorders, the term itself is not often perceived as a standalone disorder but rather a key feature of some severe mental illnesses.
According to Fish's classification observed in a 2018 study, thought disorders can be divided into these four types or categories:³
Disorders of the stream of thought
Disorders of the possession of thought
Disorders of the content of thinking
Disorders of the form of thinking
You may be having a conversation with someone with a thought disorder if they repeat your conversation back to you, go off on random tangents, mix up their words, make no sense, or lose track of what they are saying.
Like most mental disorders, it is crucial that patients with thought disorders are diagnosed and treated early to see the best results.
Symptoms of thought disorder vary from person to person and by the type of thought disorder you have. However, the primary symptoms are thinking disturbances and disordered speech.
For instance, negative thought disorders are characterized by negative symptoms such as chronic worry and depression. In contrast, positive thought disorders are characterized by positive symptoms such as disorganized thinking, circumstantiality, tangentiality, loose associations, and illogicality.
Using the Thought, Language, and Communication scale, the following are common traits of thought disorder:
Blocking — involves interruptions in speech and persistent pausing while trying to complete a thought (unable to complete it)
Clanging (also referred to as the clang association) — when a person's word choice is governed by the sound of the word rather than its meaning (i.e., stringing words together that rhyme but make no sense)
Derailment — when an individual has a spontaneous speech that is only semi-related to the topic of conversation
Distractible speech — when a patient is easily distracted by nearby stimuli, causing them to shift from topic to topic when talking
Echolalia — when a person repeats back what someone is saying to them
Illogical thinking — exhibiting signs of illogical thinking, which requires the absence of reasoning
Incoherence (also known as word salad) — refers to a person's severe lack of speech cohesion on the basics of sentence/conversation structure
Neologism — when a person creates 'new' words in their vocabulary
Perseveration — when an individual excessively repeats words or ideas
Tangentiality — when a person replies to questions with irrelevant answers
Stilted speech — the use of odd language that may be overly formal or outdated
Self-reference — when a patient references the subject of the conversation back to themselves.
Word approximations — when a person has unconventional and peculiar word use in conversations
The cause of thought disorder is widely debated among experts, with no single underlying cause identified yet. This is likely because thought disorders inhibit a variety of symptoms with no single or definite definition of what is entailed.
While there is no known cure for thought disorder, there are effective treatments for treating associated symptoms. These treatments often target an underlying mental illness such as schizoaffective disorder, autism spectrum disorder, bipolar disorder, or communication disorders. This could mean taking a medication like antipsychotics or participating in psychotherapy (common for patients with schizophrenia).
The Thought Disorder Questionnaire (TDQ) is an assessment your doctor may use to diagnose where you are on the Thought Disorder Index (TDI). TDI assesses the existence and level of severity of different types of thinking disturbances (23 in total).⁴ ⁵
TDI is used by a rater who is unaware of the patient's current diagnosis but fully aware of the education, social class, and ethnic background of the participant since some expressions may be considered acceptable among some groups but abnormal among others.
If you show signs of any thought disorder (particularly severe or frequent symptoms), you should see your doctor to be tested for the condition and properly diagnosed. This is particularly true if you have already been diagnosed with bipolar disorder, schizophrenia, or OCD since they are often associated. Your doctor will be able to get you started with the Thought Disorder Index test to determine if your symptoms are associated with a thought disorder.
You should also consult your doctor if you have already been diagnosed with a thought disorder and suspect that your symptoms are worsening or have become too severe to cope with or communicate properly.
There is still a lot of research required to understand thought disorders in their full complexity. However, they are primarily characterized by speech impairments and disorganized thinking. They have also been strongly associated with mental disorders such as schizophrenia, bipolar disorder, OCD, and others — although they are not mutually exclusive (you can have one without the other).
The single underlying cause of thought disorder has not yet been identified, but many potential problems have been explored (i.e., damage to portions of the brain, although it is not agreed on where).
If you're having any problems with your speech and communication, discuss thought disorder with your doctor to determine if it is the cause of the symptoms you're experiencing. Note, however, that some level of thought disorder can be observed in most of the general population. Every case will not warrant a diagnosis. Diagnosis — assessed via the Thought Disorder Index — will require severe signs or more frequent incidences of thought disorder symptoms (even if they're mild).
Rethinking thought disorder (2017)
Thought disorder | Johns Hopkins Medicine