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Difficulty: MediumSchizophrenia and Psychotic Disorders

A 54-year-old man is brought to the clinic by his adult daughter. She states that over the last 4 months, her father has been repeatedly filing police reports claiming that local teenagers are entering his garage at night to rearrange his tools. He has installed multiple padlocks and a security system, but he claims the intruders "know how to bypass the sensors." The daughter notes that aside from this specific fixation, his behavior is completely normal. He continues to run his successful landscaping business, maintains his personal hygiene, and enjoys spending time with his grandchildren. He denies hearing voices or seeing things, and his mood has been normal. His medical history is significant only for hypertension, for which he takes lisinopril. A physical examination and medical workup are unremarkable. Which of the following is the most likely diagnosis?

  1. Delusional disorderAnswer
  2. B
    Schizophreniform disorder
  3. C
    Brief psychotic disorder
  4. D
    Schizophrenia
  5. E
    Schizoaffective disorder

Answer

Delusional disorder
The correct answer is delusional disorder because the patient presents with a persistent, isolated delusion (persecutory type) that has lasted for more than 1 month (4 months total). Crucially, he does not meet Criterion A for schizophrenia, as he denies hallucinations and lacks disorganized speech, disorganized behavior, or negative symptoms. Furthermore, his overall psychosocial functioning is not markedly impaired, which is highly characteristic of delusional disorder.

Step-by-Step Solution

1
Analyze the patient's presenting symptoms and their impact on daily functioning.
The patient exhibits a fixed, false belief (delusion) about teenagers rearranging his tools, but he lacks hallucinations, disorganized speech, or negative symptoms. His occupational and social functioning remains well-preserved.
Identifying the specific types of psychotic symptoms present and the patient's functional status is necessary to differentiate among schizophrenia spectrum disorders.
2
Determine the duration of the symptoms.
The patient's delusions have been present for exactly 4 months.
Duration is a critical differentiator for psychotic disorders, distinguishing brief psychotic disorder (<1 month) from schizophreniform disorder (1-6 months) and schizophrenia (>6 months).
3
Synthesize the clinical findings to confirm the most appropriate diagnosis.
The presence of an isolated delusion for greater than 1 month, without meeting the criteria for schizophrenia and with relatively preserved daily functioning, confirms delusional disorder.
This rules out schizophreniform disorder and schizophrenia, both of which require multiple psychotic symptoms and generally involve functional impairment.

Key Concept

Delusional disorder is characterized by one or more delusions lasting at least 1 month, without meeting Criterion A for schizophrenia, and with psychosocial functioning that is not markedly impaired.
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Topics

Schizophrenia and Psychotic Disorders

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