Understanding and Assessing Delusions | CASC Article and Video

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If you establish a possibly delusional belief, gently inquire as to whether this belief is shared by others, and how fixed the belief is.

Key Knowledge

What Are Delusions?

What are delusions?
Delusions have been defined as fixed, false beliefs held with strong conviction, not shared by others in the same culture and resistant change despite conflicting evidence.

Types of delusion
● Persecutory: Belief of being targeted, spied on, or harmed.
● Grandiose: Belief in special powers, status, or identity.
● Referential: Belief that neutral events or comments refer specifically to oneself.
● Control: Belief that thoughts are controlled, inserted, withdrawn, or broadcast by external forces.
● Religious: Belief of having a special relationship with God or gods, or claims of a special religious identity
● Somatic: Belief of having a physical illness or abnormality, e.g. of parasitic infestation – known as Ekbom syndrome
● Delusional/Morbid Jealousy: The thought that one’s partner is being unfaithful – known as Othello Syndrome
● Delusional misidentification disorder:
– The belief that one is dead or has lost their internal organs (Cotard syndrome, or a ‘nihilistic’ delusion)
– The belief that different people are in fact a single person in disguise – ‘the postman, the nurse and my neighbour are all the same person just wearing different outfits’ (Fregoli syndrome)
– The belief that a familiar person has been switched with a lookalike – ‘that looks like my wife but it’s not really her’ (Capgras syndrome)

Differential Diagnosis for Delusions

● Primary psychotic disorders e.g. schizophrenia, delusional disorder
● Mood disorders with psychotic features e.g. bipolar disorder, major depressive disorder
● Drug-induced psychosis
● Organic psychosis e.g. brain tumours, Huntington’s disease, autoimmune encephalitis, delirium.

Essentially, delusions can be present in any condition with psychotic features. The type of delusion might give you a clue about the diagnosis, for example grandiose delusions are more typical of manic states, whereas Cotard syndrome is a classic presentation for psychotic depression. A fixed delusional belief for longer than 3 months, without other mood disturbance or schizophrenia-like symptoms (e.g. hallucinations, thought disorder, disorganised behaviour and negative symptoms), may be consistent with delusional disorder.

Communication Tips

● Ask open questions, for example “Has anything new been happening to you?”, “Do you have any new ideas or beliefs that are really important to you?’’
● Be curious and non-judgmental, “Tell me more about that…when did you first start believing this?”
● Do not dismiss their experiences, but gently challenge their beliefs to determine how ‘fixed’ they are, for example, “Have you considered any other explanations?”
● Roll with resistance. If the patient is defensive, gently redirect or focus on their feelings and impact, for example “I can see this is really distressing for you.” Avoid arguing about the delusion, it rarely changes the belief and can increase distress.

CASC Practice Scenarios

Scenario 1: Assessing Strange Beliefs

Candidate Instructions
You are the liaison psychiatry SHO in the emergency department. Mr. Peter Evans, a 48-year-old accountant, has been brought in by his wife due to strange, persistent beliefs.
 
Take a focused psychiatric history to clarify the nature of his beliefs, and evaluate risk.

Actor Instructions
You are Peter Evans, a 48-year-old man who has worked as an accountant at the same firm for over 15 years. Over the past six months, you have become absolutely convinced that several of your colleagues—particularly your line manager and two team members—are conspiring to get you fired. You are certain it is true, despite your wife’s reassurances and the lack of any direct evidence.
 
You believe these colleagues are spreading malicious rumours about you, both in the office and via email. You are convinced they have access to your work emails and are monitoring your computer activity. You have noticed that sometimes your computer seems “slower than usual,” and you interpret this as evidence that someone is remotely accessing your files. You have also overheard colleagues laughing in the break room and are sure they were talking about you, even though you did not hear your name mentioned.
 
You have started keeping a detailed notebook at home, recording every incident you think is suspicious—such as people glancing at you, whispering, or sending emails at odd times. You have even considered recording conversations at work to gather proof, but have not done so yet because you are worried about being caught and making things worse. You sometimes search your emails for keywords or phrases that could be about you, and occasionally print out emails to “build a case.”
 
You have not told anyone at work about your suspicions, fearing it would make things worse. You have confided in your wife, hoping she would understand, but she does not believe you. This makes you feel isolated and misunderstood. You are frustrated that others cannot see what is happening and feel let down by your wife’s lack of support.
 
You do not believe you are mentally unwell. You are certain that your colleagues’ behaviour is deliberate and targeted. When the doctor asks about your beliefs, you become slightly defensive if you sense disbelief, but you are willing to explain your reasoning in detail.
 
You have not noticed any changes in your mood, appetite, or sleep, although you admit to feeling more stressed and sometimes irritable, especially in the evenings before work. You continue to go to work but have become more withdrawn, avoid the staff kitchen, and no longer join colleagues for lunch or after-work drinks. You have not lost interest in your hobbies; you still enjoy reading and gardening, and these activities help you relax.
 
You do not hear voices or see things that others cannot. You have never felt that your thoughts are being controlled or broadcast, and you do not think you have any special powers or abilities. You do not drink alcohol excessively (a glass of wine with dinner, occasionally) and do not use recreational drugs. You have no previous psychiatric history, have never seen a psychiatrist before, and have no significant medical problems.
 
If asked about risk, you deny any thoughts of harming yourself or others. However, you admit you have become increasingly anxious about going to work and sometimes dread Monday mornings, but you have not taken any sick days. You are married, have two adult children (both at university), and live at home with your wife.
 
If the doctor gently probes, you may reveal that you sometimes check social media to see if colleagues have posted anything about you, but you have not found anything concrete. You occasionally worry that your reputation is being damaged beyond repair and have considered looking for a new job but feel “trapped” because you worry the rumours might follow you.
 
If the interviewer is patient and non-judgmental, you will describe your experiences in detail. However, if you feel challenged or dismissed, you may become defensive and guarded. 
 

Feedback for Scenario 1

Scenario 2: History Taking around Fixed Beliefs

Candidate Instructions: 
You are the psychiatry registrar on-call. Ms. Angela Browning, a 51-year-old woman, has been referred by her GP due to persistent, fixed beliefs about having a serious illness despite multiple normal investigations.
 
Take a psychiatric history, assess risk, and consider differential diagnoses.

Actor Instructions: 
You are Angela Browning, a 51-year-old woman who previously worked as a librarian. For the past eight months, you have become absolutely convinced that you have a severe, undiagnosed parasitic infection in your intestines. You believe you can feel the parasites moving inside you, especially at night, and sometimes see “evidence” in the toilet—though doctors have told you all your tests are normal.
 
You have seen your GP, two gastroenterologists, and an infectious diseases specialist, but none have found anything wrong. You believe they are missing something or not taking you seriously. You have spent hours online researching rare parasites and have ordered herbal cleanses and anti-parasitic medications from abroad.
 
You have stopped eating most foods, convinced that anything you eat will “feed the parasites.” You now only drink water and herbal teas. You have lost over a stone in weight in the past three months and feel weak and dizzy much of the time. You have started refusing your prescribed blood pressure medication, believing it “makes the parasites stronger.” You have begun to avoid family and friends, feeling they don’t understand and are siding with the doctors.

You live alone, but your adult daughter visits daily. She is very worried about your weight loss and that you might collapse at home. You have no history of mental illness, but your mother had depression. You do not drink alcohol or use drugs.
 
If asked, you deny hearing voices or seeing things others cannot. You do not believe your thoughts are being controlled, and you do not have any special powers. You are not worried about being harmed by others (except doctors not taking you seriously), but you are preoccupied with the idea that your health is deteriorating due to this infestation.
 
If asked about risk, you admit you have thought about ending your life before parasite kills you anyway, but you have not made any plans or tried to harm yourself. You feel hopeless and desperate for someone to believe you. Aside from drinking herbal tea advertised as ‘cleansing’, you have not attempted any other ‘self-treatment’. You have considered buying anti-parasite medication on the internet and going to a different country for treatment.
 
You have no significant medical history other than hypertension. Your appetite is poor, you feel cold all the time, and you have not slept well for weeks.
 
If the interviewer is patient and nonjudgmental, you will describe your symptoms and beliefs in detail. If you feel challenged or dismissed, you may become defensive, frustrated, or withdraw from the conversation.
 

Feedback for Scenario 2

Authors/Reviewers

Dr Damir Rafi is a psychiatry speciality registrar in forensics, currently working in London.
Dr Sarah Barber is a Psychiatry Registrar, currently taking time out of clinical work to complete a PhD in psychiatric epidemiology.

References and Resources

1 World Health Organization (2022). ICD-11: International classification of diseases (11th revision).
2 Collin, S., Rowse, G., Martinez, A. P., & Bentall, R. P. (2023). Delusions and the dilemmas of life: A systematic review and meta-analyses of the global literature on the prevalence of delusional themes in clinical groups. Clinical Psychology Review, 104, 102303.

Disclaimer:

This article is intended for use as a learning resource for doctors training in Psychiatry in the UK. It is not intended for patients. If you are looking for information about mental health conditions, please visit www.rcpsych.ac.uk/mental-health to find readable, user-friendly and evidence-based information on mental health problems, treatments and other topics written by qualified psychiatrists, with help from patients and carers. If you are looking for help for a mental health condition, please visit https://www.mind.org.uk/ for information about where help is available.
 
The article was written by UK doctors and cross-checked against various published sources (see Reference list). We endeavour to keep information up to date, but it should not be relied on for clinical decision making. Consult local guidelines and senior colleagues whenever you are not sure.

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