Sleep Studies For Narcolepsy: How Often Is Necessary?

Sleep studies are often required to diagnose narcolepsy, a sleep disorder characterised by excessive daytime sleepiness (EDS). The two main tests are polysomnography (PSG) and the Multiple Sleep Latency Test (MSLT). PSG is an overnight test that records brain waves, blood oxygen level, heart rate, breathing, and eye and leg movements. MSLT is conducted the following day and measures how quickly a patient falls asleep and enters REM sleep. These tests are typically carried out in a sleep laboratory, and preparation is required to ensure accurate results. Sleep studies are essential for diagnosing narcolepsy, but they may need to be repeated if the results are unclear.

Polysomnography (PSG)

PSG is performed overnight by a technologist who places sensors on the patient's scalp, chest, and legs. The test records the patient's brain waves, blood oxygen level, heart rate, breathing, and eye and leg movements. The data is then analysed by a qualified sleep specialist to determine the presence of a sleep disorder.

PSG is typically performed in a sleep lab, where the patient is assigned a private bedroom. The patient arrives at the lab about two hours before bedtime and is instructed not to change their daily habits. The patient's whole night of sleep is monitored and recorded.

Prior to the test, it is important to obtain sufficient sleep and to discontinue any medications that can affect sleep. The patient may be asked to keep a sleep diary for one to two weeks before the test to ensure that insufficient sleep is not a contributing factor.

In the case of narcolepsy, PSG is used to evaluate the amount and quality of nighttime sleep and to look for any evidence of an additional sleep disorder. PSG, along with the Multiple Sleep Latency Test (MSLT), is necessary for confirming a diagnosis of narcolepsy.

Multiple Sleep Latency Test (MSLT)

The Multiple Sleep Latency Test (MSLT) is a crucial test for diagnosing narcolepsy. It is a full-day test that typically consists of five scheduled naps taken every two hours, starting from the morning after the overnight polysomnogram (PSG). The MSLT measures how long it takes for a person to fall asleep during the day, with people suffering from narcolepsy tending to fall asleep much faster (in less than eight minutes on average). The test also monitors how quickly and frequently the patient enters rapid eye movement (REM) sleep. Entering REM sleep during two or more naps is considered highly suggestive of narcolepsy.

During the test, the patient lies quietly in bed in a dark and quiet environment, designed to be comfortable and to isolate any external factors that may impact their ability to fall asleep. A series of sensors are placed on the patient's head, face, and chin to measure when they fall asleep and to determine their sleep stage. The sensors are connected to a computer and are long enough to allow the patient to move around and turn over in bed. A low-light video camera is also used to observe the patient.

If the patient falls asleep, they will be awakened 15 minutes later. If they do not fall asleep within 20 minutes, the nap trial will end, and they will be asked to stay awake until the next nap trial begins two hours later. This process is repeated for each of the five nap trials.

The results of the MSLT are typically available within two weeks. A sleep technologist will review the data and submit the results to a board-certified sleep medicine physician for interpretation and diagnosis.

Epworth Sleepiness Scale

The Epworth Sleepiness Scale (ESS) is a self-administered questionnaire with eight questions that assess an individual's 'daytime sleepiness'. Respondents are asked to rate their likelihood of dozing off or falling asleep while engaged in eight different activities, using a 4-point scale from 0 (not at all likely to fall asleep) to 3 (very likely to fall asleep). The ESS score, which is the sum of the eight item scores, can range from 0 to 24. Scores of 0-10 are considered normal, while scores of 11 and above generally warrant further investigation.

The ESS was first developed by Dr Johns in 1990 for adults and was subsequently modified in 1997. It is a quick and easy assessment tool, taking no more than 2-3 minutes to complete. The questionnaire is available in multiple languages and is widely used to assess daytime sleepiness in individuals with sleep disorders such as narcolepsy.

The ESS is often used in conjunction with other specialised tests, such as the Multiple Sleep Latency Test (MSLT) and polysomnography (PSG), to confirm a diagnosis of narcolepsy. The MSLT measures how quickly a person falls asleep during the day and monitors their rapid eye movement (REM) sleep patterns. The PSG, performed overnight in a sleep lab, records brain waves, blood oxygen levels, heart rate, breathing, and eye and leg movements.

Together, these tests provide valuable information about an individual's sleep patterns and help doctors make an accurate diagnosis of narcolepsy or other sleep disorders. While the frequency of repeating these sleep studies is not explicitly mentioned, it is recommended to perform them again if the initial results are unclear or if the patient's condition changes.

Lumbar puncture

During a lumbar puncture, a needle is inserted into the lower back, between two lumbar bones, and a small amount of CSF is removed. The procedure is usually performed under local anaesthetic and takes about 30-60 minutes. It is generally safe, but as with any medical procedure, there are some risks, including infection, bleeding, and headaches.

If you are experiencing symptoms of narcolepsy, it is important to consult a medical professional for proper diagnosis and treatment. They will be able to advise you on the best course of action and determine if a lumbar puncture is necessary.

Hypocretin and HLA testing

Hypocretin, also known as orexin, is a chemical that helps people sleep and wake up at the right times. Narcolepsy Type 1 (NT1) is caused by a lack of hypocretin, which results in REM sleep abnormalities and almost always involves cataplexy.

Hypocretin-1 can be measured in the cerebrospinal fluid (CSF) but not in the blood or any other tissue. A lumbar puncture, or spinal tap, is required to collect the CSF. Most patients with narcolepsy and cataplexy have no hypocretin-1 molecules in their CSF.

Stanford Sleep Specialists will commonly perform a blood genetic test for narcolepsy, known as Human Leukocyte Antigen (HLA) DQB1*06:02 typing, if they suspect hypocretin deficiency. Almost 99% of subjects where narcolepsy is caused by a lack of hypocretin are DQB1*06:02 positive, but approximately 25% of the normal US population is also positive, so a negative test is used to exclude hypocretin deficiency.

In some cases, especially if HLA DQB1*06:02 is positive but the case is unclear, a lumbar puncture may be performed to draw CSF and measure hypocretin-1 levels. If CSF hypocretin-1 is below 110 pg/ml, the diagnosis is consistent with narcolepsy caused by hypocretin deficiency.

HLA stands for Human Leukocyte Antigens. HLA antigens are molecules produced by the HLA genes, which are very important for keeping the immune system in check. The best HLA marker for Type 1 narcolepsy is HLA-DQB1*0602. Most (90-95%) patients with narcolepsy-cataplexy carry this marker.

HLA testing cannot be used to diagnose Type 1 narcolepsy. About 20% of the general population carries the same HLA subtypes. Furthermore, many patients without cataplexy do not have this marker. The HLA subtypes are only predisposing factors but are not sufficient on their own to cause narcolepsy.

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