Prevalence of attention deficit hyperactivity disorder symptoms in narcolepsy: a systematic review.

OBJECTIVE: Narcolepsy is characterized by excessive daytime sleepiness and cataplexy. Attention deficit hyperactivity disorder (ADHD) is characterized by hyperactivity, inattention, and impulsivity. However, despite their differences, both narcolepsy and ADHD share the symptoms of sleep disturbance and excessive daytime sleepiness. Recent studies have suggested a link between the two disorders. The objective of systematic review was to assess the prevalence of ADHD symptoms in narcolepsy. METHODS: We performed a systematic search of MEDLINE (inception to December 2018) and EMBASE (inception to December 2018) for English publications of human studies using the keywords "narcolepsy" and "ADHD". RESULTS: Five studies examining a total of 328 patients met the eligibility criteria for this study examining the prevalence of ADHD symptoms in narcolepsy. The pooled prevalence of ADHD symptoms in narcolepsy was 33.0%. Two studies using the international classification of sleep disorders, second edition (ICSD-2) observed a pooled prevalence of ADHD symptoms in narcolepsy of 25.0%, while two other studies that relied on the ICSD-3 criteria observed a pooled prevalence of ADHD symptoms in narcolepsy of 36.4%. CONCLUSIONS: The prevalence of ADHD symptoms was >30%, making it an important comorbidity of narcolepsy. Future studies should be performed to better assess the relationship between ADHD and narcolepsy.