Non-24-hour sleep-wake rhythm disorder
Non-24-hour sleep-wake rhythm disorder (
Non-24-Hour Sleep-Wake Rhythm Disorder (N24SWD) Overview
N24SWD is characterized by a misalignment between the individual's circadian rhythm and the external 24-hour environment. This results in shifting sleep-wake patterns, often leading to periods of insomnia at night and excessive sleepiness during the day. It commonly affects blind individuals lacking light perception and can also occur in sighted individuals. (1, 2, 3)
Treatment Strategies for N24SWD
Melatonin and Melatonin Receptor Agonists
Melatonin, taken one hour before the desired bedtime or at a fixed time, is the primary treatment to align the circadian rhythm with the 24-hour day. The standard starting dose is 0.5 mg. For those who don't respond to over-the-counter melatonin, melatonin receptor agonists like tasimelteon (20 mg at a fixed time, one hour before target bedtime) can be beneficial. Achieving circadian adjustments and synchronization may take up to two and a half months. (5)
Behavioral Modifications
Maintaining a regular sleep-wake schedule and reinforcing daily time cues, such as social interactions, physical activities, and meal timings, are important behavioral strategies. These help to strengthen the body’s natural circadian rhythm. (6)
Timed Bright Light Therapy
For sighted individuals, timed bright light therapy can be effective in shifting the circadian clock. Light exposure after the core body temperature nadir, typically about two hours before waking, helps move the circadian clock earlier. Light boxes emitting 10,000 lux, positioned around 5 feet away, are typically recommended for this therapy. (6)
Symptomatic Therapy
While symptomatic therapies such as sleep aids for insomnia and stimulants for daytime sleepiness may offer short-term relief, they don't provide a long-term solution and do not effectively synchronize the circadian rhythm with the external environment. (4)
References
1-American Academy of Sleep Medicine. International Classification of Sleep Disorders, 3rd ed, American Academy of Sleep Medicine, Darien, IL 2014.
2- Dubocovich ML, Delagrange P, Krause DN, Sugden D, Cardinali DP, Olcese J. International union of basic and clinical pharmacology. LXXV. Nomenclature, classification, and pharmacology of G protein-coupled melatonin receptors. Pharmacol Rev (2010) 62(3):343–80.
3- Lockley SW, Dressman MA, Licamele L, Xiao C, Fisher DM, Flynn-Evans EE, et al. Tasimelteon for non-24-hour sleep-wake disorder in totally blind people (SET and RESET): two multicentre, randomised, double-masked, placebo-controlled phase 3 trials. Lancet (2015) 386(10005):1754–64.
4-Auger RR, Burgess HJ, Emens JS, et al. Clinical Practice Guideline for the Treatment of Intrinsic Circadian Rhythm Sleep-Wake Disorders: Advanced Sleep-Wake Phase Disorder (ASWPD), Delayed Sleep-Wake Phase Disorder (DSWPD), Non-24-Hour Sleep-Wake Rhythm Disorder (N24SWD), andIrregular Sleep-Wake Rhythm Disorder (ISWRD). An Update for 2015: An
American Academy of Sleep Medicine Clinical Practice Guideline. J Clin Sleep Med 2015; 11:1199.
5- Lewy AJ, Emens JS, Sack RL, Hasler BP, Bernert RA. Low, but not high, doses of melatonin entrained a free-running blind person with a long circadian period. Chronobiol Int (2002) 19(3):649–58.
6-Malkani RG, Abbott SM, Reid KJ, Zee PC. Diagnostic and Treatment Challenges of Sighted Non-24-Hour Sleep-Wake Disorder. J Clin Sleep Med 2018; 14:603.
