Circadian Rhythm Disorders
‘Circadian rhythm’ refers to the body’s natural cycle of sleep and wakefulness. It is now known that each cell of the body has such a cycle, and that complex control mechanisms keep everything co-ordinated so that the body functions as a whole.
Our natural sleep/wake cycle is actually around 25 hours, but light and darkness play an essential role in keeping the timing of the cycle corrected to 24 hours. As darkness ensues, the centre of the body’s internal clock called the Supra Chiasmatic Nucleus (SCN) sends messages to the Pineal Gland which then secretes Melatonin. Melatonin is a chemical which is often compared to the conductor of an orchestra, where the musicians are the individual hormones that actually produce sleep and wakefulness, and Melatonin co-ordinates their actions. Melatonin causes the sleep hormones (including GABA) to switch on and combined with tiredness, this leads to non-REM sleep commencing soon after. As daylight ensues, the SCN causes melatonin to switch off, and this resets the body clock locking it into the day-night cycle and giving the internal time clock a cue for the next 24 hours. At the same time, the hormones that wake us and maintain daytime function switch on and keep us awake.
If we remove the light cue at rise time, and put a subject into a neutral environment where they do not know the time, sleep onset gradually delays as the days progress, because the body clock is now working on its natural 25 hour cycle without the light to reset it each day. This has been shown to be a cause of sleep problems in subjects with certain types of blindness by the researchers at the Surrey Sleep Research Centre. I am always struck by the speed with which birdsong ceases as dusk proceeds in the summer when I am in the garden. Within 15 minutes, the noise of the birds dies away to virtually nothing as they go to roost. This also happened during the last total eclipse of the sun just after midday the UK in 1999, when the sudden silence was striking and rather eerie.
Mankind has generally done his best to disrupt this well developed mechanism. When it gets dark, instead of trying to go to sleep, we put all the lights on, watch TV and begin to socialise. We also watch TV at bedtime, and use iPhones, iPads and laptops in bed. This is a particular problem because the blue light emitted from these devices suppresses the production of Melatonin and this can make it harder to fall asleep (parents take note!). We also live in a 24/7 society – we can spend all night shopping on-line, and even visit supermarkets in person in the middle of the night. Night shifts are now the norm in all walks of life, and cities ‘never sleep’. It is not surprising that our circadian rhythms are beginning to find it hard to cope!
Several disorders of circadian rhythm can occur, and the most common are Delayed Sleep Phase Syndrome (DSPS) and sleep disorders related to shift working.
DSPS is common and sufferers turn up in outpatient clinics regularly. It is generally a condition seen in teenagers and young adults.
Typically, a teenager will be brought to clinic by an anxious parent because school performance is beginning to suffer due to tiredness and lack of concentration. The story is one where the subject cannot fall asleep until late into the night, typically 3.00 am to 5.00 am, and then has difficulty rising in the morning due to lack of sleep. I often refer to this as
‘I can’t go to sleep at night and wake up for school in the morning syndrome’
In all other ways, sleep is normal and, left to their own devices, the sufferer will sleep until midday or longer, and then feel refreshed and wide awake. However, if they don’t sleep until 4.00 am and then have to get up for school or work at 7.00 am, they will have had only four hours of sleep and are very tried as a result. Getting the sufferer up for school is a nightmare, and I saw one mother recently who went to the lengths of pouring cold water over her daughter in an attempt to get her out of bed! The problem is that the internal body clock is out of synchronisation with the normal social clock, and Melatonin is secreted later than it should be. There is a genetic predisposition to this in the ‘period clock-genes’ that control the response of Melatonin secretion to darkness.
DSPS is often referred by GPs as 'difficulty getting to sleep' or 'insomnia'. Whilst there are some similarities in that insomnia patients may also have difficulty getting to sleep, there are fundimental differences between insomnia and DSPS that are present in the history. DSPS patients have normal sleep, but it comes at the wrong time, and they therefore do not get enough of it if they have to rise early. This makes them sleepy in the daytime and they usually have raised Epworth Sleepiness Scores. In contrast, insomnia patients cannot get to sleep, but never experience daytime sleepiness and have unusually low Epworth Sleeiness Scores.
Investigations for DSPS are centred around Actigraphy. The subject wears a watch-like device called an Actiwatch for about two weeks to delineate their sleep wake cycle. When we are awake, we tend to move around, and when we are asleep, we tend NOT to move around. The Actiwatch responds to movement by recording onto a tiny hard-disk, and the data can be downloaded and displayed graphically for the time of the study.
Time of the day is displayed across the top of the graph, and day of the week is displayed down the side. The higher the spike, the more the movement recorded at the time.
Normal Actigram shown below
Normal sleep is shown here, and sleep onset is around midnight with waking at 7.00 am. Midnight is represented by the vertical line 'M' down the centre of the graph. The vertical lines are spaced one hour apart.
Delayed Sleep Phase Syndrome shown below
Sleep onset is now around 4.00 am, with sleep continuing until midday, because the recording was made during the school holidays, and the subject was allowed to get up when they wished.
Free Running Circadian Clock shown below
Sometimes the delay is not fixed, and there is a tendency for sleep onset to become progressively later each night, demonstrating a so-called Free Running Circadian Clock shown below. Sleep onset progressively delays each day. There are good and bad phases for sleep through the month.
It should be remembered that there is a tendency for youngsters to want to stay up late and continue activity into the night anyway. As we age, there appears in practice to be a tendency for the clock to advance. Children are difficult to persuade to go to bed or to get up in the mornings, whilst elderly parents probably retire before 10.00 pm and get up at 6am. Provided daytime performance is adequate, it is not essential to administer treatment, because the condition is harmless enough, and just an extreme of the ‘owl’ mentality that many people exhibit. I tell parents that the condition will tend to self correct at university, where no-one goes to bed until the middle of the night, and no-one bothers to get up until late in the morning anyway! However, if daytime performance is suffering, then treatment is necessary to maintain quality of life.
The first line of treatment is to correct sleep hygiene. For teenagers, this involves getting all electrical gadgets out of the bedroom, including phones and text devices, TVs and laptops, and putting the lights off to give the required darkness which helps to produce Melatonin. Whilst this may cause extreme annoyance and distress to the teenager, there is no gain without pain!
In the morning, flooding the room with light, either by opening all the curtains to let the sun in, or by purchasing a light box commonly used in Seasonal Affective disorder, will provide the circadian rhythm cue and reset the body clock.
If these measures do not work, then treatment with Melatonin may help. Bio-melatonin is preferable to the sustained release product, and given at least two hours before the desire time of sleep onset, because it needs time to work. Melatonin is NOT a sleeping tablet and does NOT cause sedation in itself, but works by turning on the hormones that then initiate sleep. Quite high doses may be required (6-12mg) and this may need to be negotiated with the GP because it is used off licence and needs to be prescribed on a shared care basis. Sometimes, it is necessary to progressively and deliberately delay sleep onset round the clock by three to four hours per day until the desired time of sleep onset is reached, and then lock the subject into that timing with Melatonin. Gradual tolerance may develop, in which case stopping the drug for a while to allow the body to clear the system may help.
Information to follow shortly.
Information to follow shortly.