Possible confusion between primary hypersomnia and adult attention-deficit/hyperactivity disorder

Abstract

We explored the possibility of diagnostic confusion between hypersomnias of central origin (narcolepsy and idiopathic hypersomnia, IH) and the adult form of attention-deficit/hyperactivity disorder (ADHD). We included 67 patients with narcolepsy, 7 with IH and 61 with ADHD. All patients completed the Epworth Sleepiness Scale and the ADHD Rating Scale. We found that 18.9% of the hypersomnia patients fulfilled the self-reported criteria for ADHD in adulthood, compared with 77% of the ADHD patients. A score ≥ 12 on the Epworth Sleepiness Scale (usually regarded to indicate excessive daytime sleepiness) was found in 37.7% of the ADHD patients compared 95.9% of the hypersomnia patients. In ADHD patients, inattention scores correlated with the excessive daytime sleepiness score. We conclude that one should be aware of possible diagnostic confusion between narcolepsy or IH and adult ADHD when using self-report questionnaires. The high percentage of symptom overlap found in our study raises questions about possible misdiagnosing of both conditions, comorbidity with sleep problems in adult ADHD, and the validation of the used scales. It remains unclear whether our findings indicate pathophysiological overlap.

Introduction

Adults referred to a sleep-disorders clinic may sometimes be diagnosed with attention-deficit/hyperactivity disorder (ADHD) and treated accordingly. Recently, we encountered the opposite situation. A patient previously diagnosed with ADHD in a psychiatric outpatient clinic was treated with psychostimulants with good effect on the ADHD symptoms. However, a residual complaint of involuntary sleep episodes during the day was reported and the patient was referred to our narcolepsy clinic. Additional sleep registrations confirmed the presence of excessive daytime sleepiness (EDS), and a diagnosis of idiopathic hypersomnia was made (American Academy of Sleep Medicine, 2005).

Until recently, ADHD was only recognised as a disorder affecting children. However, follow-up studies among children revealed that in approximately 50% of affected children, ADHD persists into adulthood (Weiss et al., 1985, Biederman et al., 2000). Recent epidemiological studies show prevalence rates of ADHD among adults of up to 4.7% (Murphy and Barkley, 1996a, Murphy and Barkley, 1996b, Kessler et al., 2005, Kooij et al., 2005). ADHD in adults is diagnosed by assessment of lifetime inattentive, hyperactive and impulsive symptoms with childhood onset, leading to impairment. To obtain the information, the patient, the partner and, if available, the parents are interviewed. In addition, information on school reports is examined to build the diagnosis in childhood. ADHD is a clinical diagnosis, since no objective diagnostic tests are yet available.

To be given a full diagnosis of adult ADHD according to the clinical assessment, subjects must have (1) met six of nine DSM-IV criteria of inattention and/or hyperactivity/impulsivity for a diagnosis of ADHD in childhood and at least five of nine criteria in adulthood, (2) described a chronic persisting course of ADHD symptoms from childhood to adulthood, and (3) endorsed a moderate to severe level of impairment in work and relationships, attributed to the ADHD symptoms. A cutoff point of five of the nine criteria was set for adult diagnosis of ADHD based on literature and epidemiological data using the same DSM-IV ADHD-Rating Scale (Murphy and Barkley, 1996a, Murphy and Barkley, 1996b, Biederman et al., 2000, Kooij et al., 2005).

Sleep problems are common in children with ADHD. Until now, the most frequently mentioned sleep problems have been restless legs syndrome (Wagner et al., 2004), sleep apnea (Owens, 2005), and circadian rhythm disorders (Gruber et al., 2000, Van der Heijden et al., 2005). Data on sleep complaints and/or sleep studies in adults diagnosed with ADHD are limited. Questionnaire studies in adults with ADHD report in around 70% serious sleep problems, consisting of sleep onset problems, restless sleep, and difficulty getting up in the morning (Dodson and Zhang, 1999). There is one study using sleep registrations in adult ADHD patients, which mainly found increased nocturnal motor activity (Philipsen et al., 2005).

Narcolepsy and idiopathic hypersomnia (IH) are hypersomnias of central origin, characterized by excessive daytime sleepiness. Clinically, narcolepsy can be distinguished by the presence of cataplexy, a bilateral muscle weakness triggered by emotions without loss of consciousness (Overeem et al., 2001). However, there is no diagnostic test for cataplexy, and it may occur years after EDS onset. Narcolepsy and IH can be objectively diagnosed using sleep registrations, particularly the Multiple Sleep Latency Test (MSLT), although the sensitivity and specificity of these tests are not optimal (Overeem et al., 2001). Of note, hypersomnia patients frequently complain about concentration difficulties and inattention.

The fact that symptoms like inattention and sleepiness are sometimes expressed in a similar manner in patients may pose problems in the diagnostic process. In this exploratory study, we aimed to look further at the possibility of diagnostic confusion between EDS and ADHD in adults.