Delusional disorder: a therapist's manual

1. The programme at a glance

Indication. Delusional disorder in adults, as outpatients, diagnosed or strongly suspected by a psychiatrist, with the risk to others and to self assessed and organised.

Reference model. Cognitive behavioural therapy for delusions (Chadwick, Birchwood and Trower, 1996; Kingdon and Turkington, 2005), adapted to a disorder in which the conviction is isolated and the rest of functioning preserved: engagement through distress, a shared formulation of what maintains the conviction — emotion, worry, sleep, reasoning under strain, safety behaviours (section 5) — the search for alternative explanations and behavioural experiments (sessions 9 and 11), and direct work on the behaviours the conviction leads the patient to adopt.

Format. Sixteen key sessions over six to nine months, often longer; weekly, then spaced out. 50-minute sessions. A session with a relative, usually following session 13, when the patient agrees and safety allows. Booster sessions after session 16, for example at one, three and six months: their timing has not been studied, and this schedule is a clinical rule of thumb.

Targeted mechanism. Reducing distress and the place the conviction takes up in the day, introducing a tolerable doubt, reducing the behaviours that maintain the conviction and those that damage life — surveillance, complaints, confrontations, repeated consultations, dangerous treatments — and restoring relational and social functioning.

Phase	Session	Topic	Session output
I. Engaging	1	Starting from what hurts	Reason for coming stated in the patient's words
	2	A transparent framework	Goals chosen, link with the psychiatrist in writing
	3	Assessment, and risk by theme	Risks assessed, history gathered
II. Understanding	4	The history of the conviction	Timeline drawn with events
	5	What the conviction costs and protects	Written balance sheet
	6	The maintaining cycle	Cycle drawn from a real episode
III. Loosening	7	Worry and sleep	Worry time measured, sleep plan
	8	Thinking under strain	Reasoning style identified, delay rule before concluding tried
	9	Other explanations	At least three explanations other than the patient's, for two events
	10	Mid-point review	Measures repeated, plan revised
IV. Living	11	Safety behaviours	Two behaviours reduced, outcome recorded
	12	Complaints, proceedings and consultations	A delay rule before acting in place
	13	Relationships	One behaviour that damages a relationship changed
V. Consolidating	14	What lies underneath	An issue recognised, an action under way, if the patient wishes
	15	A life that does not revolve around it	Two activities outside the theme under way
	16	Vigilance, relapse, next steps	Written plan, measures repeated, booster sessions scheduled

In this table, the "balance sheet" in session 5 is the written review of what the conviction brings the patient and what it costs them (worksheet 2); the "cycle" in session 6 is the loop that maintains the conviction, described in section 5; the "delay rule before concluding" in session 8 consists in waiting before drawing a conclusion from a new clue (section 23), and the "delay rule before acting" in session 12, in waiting before taking any new action (section 27).

What the patient takes away. Seven printable worksheets, listed in section 40: what I want to achieve, what my conviction costs me, my circle, other explanations, the steps I take and my waiting times, the corner for family and friends, my plan for what comes next.

What sets this programme apart from the other manuals on this site. Three things. A patient who almost never comes for what we think they have. A risk that is read through the theme of the conviction. And a goal that is not the disappearance of the belief, but the return of doubt and of a life that no longer revolves around it.

2. Before you begin

The patient who does not think they are ill

This is the usual situation. The patient does not come because they think they are deluded, but because they are suffering, because someone asked them to, or because they hope you will confirm what they are experiencing. This programme does not begin by announcing a delusion. It begins with what the patient themselves recognises as a problem: anxiety, insomnia, exhaustion, loneliness, conflict, the complaint that goes nowhere, the skin that does not heal.

The four preliminary decisions

1. Does the risk allow outpatient care? For others and for self. Section 9.

2. Has the diagnosis been made, and has a medical cause been ruled out? Especially if the conviction appeared late, suddenly, or with problems of memory, alertness or perception. Sections 7 and 11.

3. What link is there with the psychiatrist? If there is none, building one is a goal in itself, often a slow one. Section 10.

4. What is the theme, and who is involved? A partner, a designated person, a neighbour, an administration. The theme shapes the risk, the possible joint sessions and the work on actions. Section 33.

What this programme does not treat

The delusions of schizophrenia, schizoaffective disorder, a manic episode or depression with psychotic features, which have their own manuals.

Delusions due to a substance, a medication or an illness, which call first for medical treatment.

Delirium and dementia, in which delusions are part of a cognitive impairment.

Situations of imminent danger to others, which call for immediate action.

How to use it

First read sections 3 to 15, then sections 32, 33 and 34 before the first session: engagement, themes and risk come into play from the first meeting. The sessions described are key sessions; some take up several, particularly phase I, which can last months with a mistrustful patient. Section 41 says what must not be let go.

3. The clinical picture

What defines the disorder

An unshakeable conviction that resists what other people of the same culture regard as evidence to the contrary, and that lasts. It is isolated: no pervasive hallucinations, no disorganisation of thought or behaviour, no marked negative symptoms. Apart from what the conviction leads the patient to do, functioning is often preserved (Munro, 1999).

What distinguishes it from a strong belief

An ordinary belief, even an unusual one, is shared by a group, revisable in principle, and does not take over life. A delusion is personal, incorrigible by experience, central — it organises attention, the interpretation of events and actions — and it comes with a certainty that nothing seems able to shake. None of these features taken alone is enough: it is their combination, and their impact, that count.

What patients describe

Something that became obvious one day, often after a period of strain. Clues everywhere, which fit together. Incomprehension and anger at those who do not see. Exhaustion from checking, watching, gathering evidence. A loneliness that sets in as those around them grow weary or move away. And often a real suffering that has nothing delusional about it: fear, humiliation, a sense of injustice, shame.

What you see in the consulting room

A coherent, organised person, often convincing, sometimes charming, who can talk at length about other things without letting anything show. Then, on the theme, a tension, a precise, detailed, circumstantial account, backed by documents, photos, recordings, samples. Possible mistrust of the therapist if they do not seem convinced. And great sensitivity to the slightest sign of scepticism or condescension.

Epidemiology and course

Delusional disorder is rare in psychiatric services, a few per cent of admissions, and its lifetime prevalence in the general population is estimated at about 0.2% (American Psychiatric Association, 2022), probably an underestimate because many patients never see a psychiatrist. It most often begins in middle or late adulthood. The persecutory theme is the most common.

The course is variable. Some patients reach remission, complete or partial; in others, the conviction persists for years, with periods when it takes up more or less space. The social impact comes mainly from behaviour: break-ups, neighbour disputes, legal proceedings, job losses, spending. Some diagnoses are revised over time, particularly towards schizophrenia or a mood disorder, which justifies regular reassessment.

4. Delusional themes

The classifications describe the disorder by its dominant theme. The theme changes the risk, the people involved and the work on behaviour. Section 33 covers them in detail.

Persecutory. Being spied on, followed, poisoned, harassed, slandered, prevented from obtaining what one is owed. The most common. It is often accompanied by anger and by actions: complaints, letters, proceedings.

Jealous. The conviction that one's partner is unfaithful, based on minimal clues. More often described in men, often associated with alcohol. It exposes the partner to surveillance, control and violence.

Erotomanic. The conviction that a person, often of higher status or inaccessible, is in love with the patient. It exposes the designated person to harassment.

Somatic. The conviction of being infested with parasites, of giving off a bad smell, of having an organ that does not work, a deformed body part. Delusional infestation is seen mainly in dermatology; it exposes the patient to skin lesions and dangerous treatments.

Grandiose. The conviction of having an exceptional talent, discovery, mission or connection. It exposes the patient to financial losses and conflicts.

Mixed, when no theme predominates.

5. The model

The model that guides this programme is borrowed from cognitive work on delusions (Chadwick, Birchwood and Trower, 1996; Garety and Freeman, 1999; Garety et al., 2001; Freeman and Garety, 2014), and presented to the patient in plain language, without ever saying that their conviction is false. We explain not why they are wrong, but what makes any conviction, whatever it may be, become all-consuming and costly.

A starting point that is often real

A troubling experience — a skin sensation, a noise, a look, an ambiguous message, a change in the partner's behaviour — occurs in a context of vulnerability: isolation, sensory impairment, migration, loss, conflict, a feeling of humiliation, a mistrustful or sensitive temperament. The meaning the person gives it answers a question they are already asking.

Emotion that steers

Anxiety directs attention towards threat and makes one remember what confirms it. Repeated worry — hours spent imagining what is happening or might happen — makes the threat more present and more plausible. Fragile self-esteem makes some explanations more likely than others: being targeted, being deceived, being rejected, or on the contrary being exceptionally loved or chosen.

Reasoning under strain

Under the influence of emotion, each of us tends to jump to conclusions on little evidence, not to consider other explanations, and to hold on to our first idea. These tendencies, measured in research on delusions, are not a logical fault peculiar to the patient: they are human ways of thinking, simply more marked and more constant.

Behaviours that prevent checking

To protect or prepare themselves, the patient watches, checks, avoids, collects evidence, stays silent, accuses, withdraws. These are called safety behaviours. They bring relief in the moment, but they prevent the discovery that the feared danger does not happen, and they change how others behave — a partner questioned every evening ends up lying about details, a neighbour under surveillance ends up hostile — which provides new clues.

Sleep and isolation

Lack of sleep increases mistrust and troubling perceptions. Isolation removes the conversations that, in everyone, correct interpretations. Both worsen along with the conviction.

The cycle

These elements link together into a cycle of seven links, which the patient learns to draw in session 6:

1. An ambiguous event. 2. An already primed vigilance that spots it. 3. A quick interpretation, in line with the theme. 4. A strong emotion. 5. A protective or evidence-gathering behaviour. 6. A reaction from others, or an absence of checking. 7. A strengthened conviction, and heightened vigilance.

What the model explains to the patient

That what they are going through is gruelling, and that their anxiety, exhaustion and anger are understandable. That, whatever the truth of their conviction, some things make it more all-consuming and more painful — worry, sleep, isolation, vigilance, checking — and that these can be acted on. And that we will work together on what they themselves want to change.

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