Psychiatric comorbidity in Danish patients with narcolepsy type 1, narcolepsy type 2, and idiopathic hypersomnia: a case-control study

Study objectives: To examine the difference in psychiatric comorbidity of Danish patients with Narcolepsy type 1 (NT1), Narcolepsy type 2 (NT2), and idiopathic hypersomnia (IH).

Methods: Polysomnography (PSG), Multiple Sleep Latency Test (MSLT), and lumbar puncture were performed on 505 patients referred to a sleep clinic for diagnostic evaluation of hypersomnia. Diagnosis, clinical characteristics, electrophysiologic data, and cerebrospinal fluid hypocretin-1 (Csf-Hcrt-1) results were retrieved. Subsequently, the patients were identified in the Danish national health registers to collect information on psychiatric diagnoses and psychotropic medication use 10 years before the sleep disorder diagnosis. The prevalence of psychiatric comorbidities per hypersomnia group was compared to a 1:4 general population control group matched on age, gender, and educational level.

Results: A diagnosis of NT2 and IH was significantly associated with total psychiatric comorbidity compared to the matched controls but not NT1 (NT1: OR = 1.5; NT2: OR = 6.1; IH: OR = 5.2). NT1 was not significantly associated with any psychiatric disorder. NT2 was significantly associated with schizophrenia spectrum disorders (OR = 8.5), mood disorders (OR = 6.7), neurotic disorders (OR = 3.8), personality disorders (OR = 3.1), and behavioral and emotional disorders (OR = 4.3). IH was significantly associated with schizophrenia spectrum disorders (OR = 3.3), mood disorders (OR = 5.9), neurotic disorders (OR = 3.0), and behavioral and emotional disorders (OR = 4.0).

Conclusions: NT2 and IH had a close relationship to psychiatric disorders before diagnosis of their sleep disorder, while NT1 did not. This supports previous studies finding higher rates of psychiatric illness in patients with hypersomnia; however, it highlights the similarity between NT2 and IH. We believe this link to psychiatric disorders could play a role in the pathophysiology. Future studies evaluating the relation between hypersomnias of central origin and psychiatric diseases should include hypersomnia subclassifications to further the understanding of the differences in these disorders.