Fatigue or Daytime Sleepiness?

Abstract

Daytime sleepiness is one of the criteria for daytime impairment (section-C of ICSD-2) for the diagnosis of insomnia as stipulated by International Classification of Sleep Disorders, 2nd edition.1 Similarly, in the proposed DSM-V criteria2 for primary insomnia, daytime sleepiness has been included as one of the criteria to indicate associated impairment. At our Sleep Research and Treatment Center, Penn State University College of Medicine, we have seen hundreds of patients with chronic insomnia. Most of these patients were referred by other providers for their chronic sleep complaints. Patients with chronic insomnia present with complaints of sleep difficulty for several months and often for more than a year.3 Along with nocturnal sleep disturbances, most of them report several daytime symptoms. Notable among the daytime symptoms are excessive fatigue and exhaustion during the day. However, most of the patients with chronic insomnia deny daytime sleepiness. In our clinical practice to differentiate daytime fatigue/tiredness from sleepiness we use a clarifying question; “Since you feel tired/fatigued, if given a chance would you be able to sleep during the day” and almost all of the patients with chronic insomnia report inability to sleep during the day despite having an opportunity and feeling excessively tired or fatigued. When a patient answers “yes” to the above mentioned question, i.e., ability to sleep during the day, we found that such patients often will have an underlying other primary sleep disorder of excessive daytime sleepiness or chronic sleep deprivation. The differentiation of daytime sleepiness and fatigue as clinical criterion has been suggested earlier by us4,5 and has been adopted by 25 leading investigators in the field of insomnia research convened in Pittsburgh, Pennsylvania on March 10-11, 2005.6 Our clinical experiences are further supported by the data from objective measures of daytime sleepiness using MSLT (multiple sleep latency tests) in insomnia. Mean sleep latency during MSLT have been consistently found to be increased in insomniacs compared to normal controls.7–10 The mean sleep latency on MSLT in insomniacs were longer despite significantly decreased nocturnal sleep efficiency.7 Recent data by Randall and colleagues10 found that more than 70% of the patients with primary insomnia had mean sleep latency on MSLTs of more than 10 minutes in comparison to only 47% in general population controls. Considering the subjective reports of inability to sleep during the day and the supporting MSLT data indicating decreased propensity to fall asleep during the day in insomniacs, it is prudent to consider deleting the “daytime sleepiness” criteria from the impairment section of proposed DSM-V criteria for primary insomnia. In fact, insomniacs endorsing daytime sleepiness may actually be suffering from other primary sleep disorders or sleep deprivation and may lead to misdiagnosis of insomnia.