Background/Aims: The occurrence of psychotic symptoms in narcolepsy type 1 (NT1) has been reported as responsible for delayed diagnosis due to the misdiagnosis of schizophrenia. This study aimed to identify shared and distinctive clinical characteristics between NT1 and schizophrenia, with the focus on psychotic symptoms. Methods: A total of 28 NT1 and 21 schizophrenia patients were included. Hallucination characteristics and PANSS (Positive and Negative Syndrome Scale), HRSD (Hamilton Rating Scale for Depression), DES (Dissociative Experiences Scale), and STAI (State-Trait Anxiety Inventory) scores were collected. Symptom overlap was investigated by χ2, Fisher's or t tests and multiple logistic regression models. Results: Hallucinations and illusions frequently occurred in both diseases. Unimodal hallucinations were more common in schizophrenia (p = 6.30e-07) and multimodal hallucinations in NT1, but no clear difference was identified in their sensory modality. Hypnagogic/hypnopompic hallucinations were typical of NT1 (p = 5.22e-07), and 25% of NT1 patients exhibited some degree of insight deficit. Hypnagogic/hypnopompic hallucinations, unimodal hallucinations and PANSS score were the most distinctive clinical characteristics. Clinical overlap was found in the dissociative and anxiety domains, while higher depressive scores were observed in schizophrenia. Conclusion: The overlap between NT1 and schizophrenia should be further investigated under a clinical and pathogenetic point of view to improve diagnostic and therapeutic approaches.

Keywords:
Narcolepsy, Schizophrenia, Differential diagnosis, Sleep, Hallucination, Psychosis, Delusion, Anxiety, Dissociation
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2015
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