Gina Johnson
Non-24-hour sleep-wake disorder (N24SWD) is a chronic circadian rhythm sleep disorder that is more common in blind people, affecting up to 70% of the totally blind, but it can also affect sighted people. The disorder is characterised by a sleep-wake cycle that is longer or shorter than 24 hours, resulting in a misalignment with the natural light-dark cycle. While N24SWD is rare among sighted individuals, it is challenging to diagnose and treat due to limited data and understanding of the underlying causes. The disorder can have a significant impact on social and occupational functioning, leading to negative perceptions and challenges in maintaining a regular schedule.
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N24SWD is a rare sleep-wake disorder, more common in blind people
Non-24-hour sleep-wake disorder (N24SWD) is a rare sleep-wake disorder that is more common in blind people. It is a chronic circadian rhythm sleep disorder (CRSD) characterised by a chronic steady pattern of daily delays in sleep onset and wake times. Individuals with N24SWD have a circadian rhythm that is slightly longer than 24 hours, which causes sleep and wake times to be pushed back by one or two hours at a time. This results in a desynchronisation from regular daylight hours, leading to inappropriate fluctuations in appetite, mood, and alertness.
The prevalence of N24SWD in blind individuals is attributed to the lack of light input reaching their internal clock. Without light to the retina, the suprachiasmatic nucleus (SCN) in the hypothalamus is not cued to synchronise the circadian rhythm to the 24-hour social day. This results in a non-24-hour sleep-wake cycle for many totally blind individuals. It is estimated that N24SWD affects 50-70% of completely blind people, while being rare among visually impaired patients who retain some light perception.
In sighted individuals, N24SWD is considered a rare disorder, with limited data available on its management. The largest study of sighted people with N24SWD found that the majority were male, with symptoms often appearing in the teens or twenties. Additionally, a significant percentage of sighted people with N24SWD have a prior diagnosis of a mental health disorder, such as major depression, bipolar disorder, or schizophrenia. The etiology of N24SWD in sighted individuals is less well understood, and the disorder can go unnoticed for some time due to its fluctuating nature.
The diagnosis and management of N24SWD pose challenges, regardless of the individual's visual status. An adequate duration of sleep diary or actigraphy monitoring is necessary to detect the non-24-hour pattern. Treatment options include timed melatonin and bright light therapy, but the long-term effectiveness is limited due to the behavioural and environmental factors required to maintain stable entrainment. Furthermore, N24SWD can have a significant impact on social and occupational obligations, as individuals struggle to meet the demands of a conventional schedule.
In summary, N24SWD is a rare sleep-wake disorder that is more prevalent in blind individuals due to the absence of light input affecting their internal clock. The disorder results in a desynchronisation of the circadian rhythm, causing a range of symptoms and disruptions to daily life. While treatment options are available, the management of N24SWD remains challenging, and increasing awareness about this rare disorder is important to provide support and understanding for those affected.
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The disorder is characterised by a delay in the sleep-wake cycle
Non-24-hour sleep-wake disorder (N24SWD) is a chronic circadian rhythm sleep disorder (CRSD) characterised by a delay in the sleep-wake cycle. This delay is caused by a misalignment between an individual's endogenous circadian rhythm and the light-dark cycle in nature. The disorder is considered rare, especially in sighted individuals, but it is prevalent in people with total blindness, affecting up to 50-70% of the totally blind population.
The core feature of N24SWD is a gradual delay in the sleep-wake cycle, resulting in bedtimes that get progressively later each day. This delay can be as little as minutes per day or as much as one to two hours. Over time, the circadian rhythm becomes desynchronised from regular daylight hours, leading to a cycle that is longer than the standard 24-hour day. The sleep cycle of individuals with N24SWD typically ranges from just over 24 hours to as many as 28-30 hours in extreme cases.
The delay in the sleep-wake cycle causes significant disruptions to daily life. Individuals with N24SWD experience inappropriate fluctuations in appetite, mood, and alertness. They may also face challenges in maintaining a regular schedule, including difficulties with work, school, social obligations, and everyday tasks. The erratic sleep schedule associated with N24SWD can lead to social isolation and negative perceptions from others, who may view those with the disorder as lazy or not trying hard enough to maintain a normal sleep schedule.
The delay in the sleep-wake cycle can result in severe sleep deprivation, as individuals with N24SWD attempt to fight against their body's natural rhythm and adhere to a conventional sleep schedule. This sleep deprivation can contribute to various psychiatric and health issues, including depression, anxiety, and an increased risk of obesity, diabetes, and cardiovascular disease. The cyclical nature of N24SWD means that individuals may experience temporary relief from symptoms during periods when their body's rhythm aligns with societal norms for sleep and wakefulness.
The underlying cause of N24SWD is not fully understood, particularly in sighted individuals. In blind individuals, the disorder is attributed to the lack of light input reaching the internal clock, resulting in a failure to entrain the circadian rhythm to the 24-hour social day. In sighted individuals, the disorder may have a genetic component or be associated with prior mental health diagnoses or head injuries.
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It is challenging to diagnose and treat N24SWD
Non-24-hour sleep-wake disorder (N24SWD) is a chronic circadian rhythm sleep disorder (CRSD) that is often overlooked and can be challenging to diagnose and treat. The disorder is characterised by a sleep-wake cycle that is longer or shorter than the conventional 24-hour cycle, typically ranging from just over 24 hours to as many as 28-30 hours in extreme cases. This desynchronisation from regular daylight hours results in individuals experiencing inappropriate fluctuations in appetite, mood, and alertness, as well as insomnia and fatigue.
The diagnosis and management of patients with N24SWD pose several challenges. Firstly, the disorder is relatively rare, especially among sighted individuals, which leads to limited data and public awareness. As a result, N24SWD is often misdiagnosed or goes unnoticed for extended periods, with many sighted people living with the disorder for years before receiving a diagnosis. The cyclical nature of the disorder, with periods of symptomatic and asymptomatic phases, further complicates the diagnosis.
To establish a diagnosis of N24SWD, an adequate duration of sleep diary or actigraphy monitoring is necessary to detect the non-24-hour pattern. However, this can be challenging as the progressive delay of the circadian rhythm makes it difficult to determine the optimal timing for melatonin and bright light therapies. Additionally, the effectiveness of these therapies is limited by the behavioural and environmental factors required to maintain stable entrainment.
The treatment of N24SWD is also challenging due to the complex nature of the disorder. While melatonin and bright light therapies can be used to entrain the sleep-wake schedule, the timing of these interventions is crucial. The phase angle from dim light melatonin onset (DLMO) to sleep onset varies, and the administration of melatonin relative to DLMO must be carefully calculated to achieve the maximum phase advance. Furthermore, even with successful entrainment, maintaining stable entrainment over the long term can be difficult due to behavioural and environmental factors involved.
In summary, N24SWD presents diagnostic and therapeutic challenges due to its rarity, especially in sighted individuals, the complexity of the disorder, and the limited understanding and treatment options currently available. While melatonin and bright light therapies offer some hope, further research and awareness are needed to improve the diagnosis and management of N24SWD.
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The disorder can cause severe sleep deprivation
Non-24-hour sleep-wake disorder (N24SWD or N24) is a rare disorder that affects the circadian rhythms of 55%–70% of the totally blind population and a small proportion of the sighted population. The exact number of sighted people with the disorder is unknown. The disorder is considered rare in sighted individuals, with blindness being the most well-understood cause of N24SWD.
The disorder is characterised by a chronic steady pattern of daily delays in sleep onset and wake times. This occurs when the endogenous circadian rhythm drifts out of alignment with the light-dark cycle in nature. The circadian rhythm is controlled by the suprachiasmatic nucleus (SCN) in the brain via a hormone called melatonin. Without regulation, the cycle of the SCN lasts slightly longer than 24 hours, leaving it out of sync with the 24-hour day.
The internal circadian clock, located in the hypothalamus of the brain, generates a signal that is on average slightly longer than 24 hours. This slight deviation is usually corrected by exposure to environmental time cues, especially the light-dark cycle, which reset the clock and synchronize it to the 24-hour day. Morning light exposure resets the clock earlier, and evening light exposure resets it later.
For people with N24SWD, their sleep time gradually delays by minutes to hours every day. They will sleep at later and later clock times until their sleep periods go all the way around the clock. This results in a pattern of excessive daytime sleepiness and nighttime insomnia. The disorder can cause severe sleep deprivation, as individuals with N24SWD attempt to fight against their internal rhythm and sleep on a typical schedule.
The accumulation of sleep deprivation can lead to various physical and psychological complaints during waking hours, including sleepiness, fatigue, headache, decreased appetite, depressed mood, and difficulty concentrating. The disorder can severely impair an individual's ability to function in school, employment, and their social lives. It can cause extreme difficulty in maintaining social and career obligations, leading to issues such as isolation and loneliness.
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N24SWD can co-occur with other sleep disorders and mental health issues
N24SWD, or Non-24-Hour Sleep-Wake Disorder, is a chronic circadian rhythm disorder characterised by a delay in the sleep-wake cycle. This disorder is often comorbid with other sleep disorders and mental health issues.
Firstly, N24SWD can co-occur with other sleep disorders. For instance, it is common for those with N24SWD to also experience Obstructive Sleep Apnea and Delayed Sleep-Wake Phase Disorder (DSWPD). In fact, a history of DSWPD may even precede the onset of N24SWD. As N24SWD progresses, individuals may experience additional symptoms of sleep deprivation, including fatigue, abnormal melatonin levels, and general weakness.
Secondly, N24SWD is also associated with various mental health issues. Psychiatric symptoms are especially prevalent, caused by both sleep loss and the significant impact of the disorder on social schedules. One notable study found that 34% of sighted N24SWD patients developed major depression after the onset of sleep symptoms, with their depressive symptoms worsening when sleep habits misaligned with a regular day/night schedule. This study also concluded that the cause of depression symptoms is likely twofold, with both sleep loss and the isolating nature of the disorder to blame. Furthermore, a significant percentage of sighted people with N24SWD also have a prior diagnosis of a mental health disorder such as bipolar disorder, obsessive-compulsive disorder, and schizophrenia or schizoid personality. For these individuals, N24SWD may develop as a result of social isolation and other side effects of their disorder.
In addition, N24SWD is also linked to traumatic brain injuries in sighted people. In one case, a patient diagnosed with the disorder was later found to have a "large pituitary adenoma that involved the optic chiasma". This suggests that the disorder may be neurological in nature, involving abnormal functioning of the suprachiasmatic nucleus (SCN) in the hypothalamus.
Overall, N24SWD is a complex disorder that often co-occurs with other sleep disorders and mental health issues, making it a challenging condition to manage and treat effectively.
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Frequently asked questions
Non-24-hour sleep-wake disorder (N24SWD) is a chronic circadian rhythm sleep disorder (CRSD) in which an individual’s biological clock fails to synchronize with the 24-hour day.
N24SWD is rare among the general population, but relatively common among blind people, affecting an estimated 50-70% of totally blind people. The prevalence among sighted people is unclear.
The cause of N24SWD is not well understood, but it is thought to involve abnormal functioning of the suprachiasmatic nucleus (SCN) in the hypothalamus. The disorder may have a genetic component, but it rarely runs in families.
The most common symptoms of N24SWD are nighttime insomnia and excessive daytime sleepiness. Other symptoms include fatigue, grogginess, malaise, disrupted sleep, abnormal melatonin levels, and general weakness. Psychiatric symptoms are also common, including depression, anxiety, and problems with attention, memory, and mood.
