Excessive Daytime Sleepiness (EDS) is one of the most common presentations of Obstructive Sleep Apnoea (OSA). The Epworth Sleepiness Score (ESS) is the most widely used subjective method to assess sleepiness.


Sleepiness can affect tasks requiring vigilance and has been associated with an increased risk of motor vehicle accidents 1.

One of the main goals of treatment for OSA is to control EDS. Tracheostomy was the first effective treatment for OSA. However, it is rather invasive. In 1981, the introduction of the Continuous Positive Airway Pressure (CPAP) treatment by Sullivan and his colleagues has marked an important milestone in the management of OSA.

CPAP has been proven in many clinical trials to be efficacious in normalising Apnoea-Hypopnoea Index (AHI) in OSA, as well as in controlling EDS 2. CPAP is now the recommended first-line treatment for OSA. However, there are certain groups of OSA patients, who still have persistent sleepiness after a CPAP usage.

PREVALENCE

The prevalence of sleepiness after CPAP was reported as 12% and 6% after exclusion of all possible causes of sleepiness in a French study 3. Another large French study also demonstrated a prevalence of 13% 4.

CAUSES

It is important to establish the underlying cause of persistent sleepiness in OSA patients while on CPAP.

1. INADEQUATELY TREATED OSA

Suboptimal CPAP treatment can lead to the inadequate control of OSA. This can be due to:

  1. Suboptimal CPAP pressure being prescribed
  2. CPAP intolerance, such as a mask leak, claustrophobia, a bloated abdomen, mouth dryness and a nasal congestion
  3. Poor adherence to the CPAP

Adherence to the CPAP is defined as a night use of at least 4 hours, on at least 70% of nights. CPAP adherence is quoted to be around 40% - 83% in many different studies.

The reasons for poor CPAP adherence are complex and often multifactorial, including a CPAP intolerance. Many studies have looked at various strategies to improve the CPAP adherence. Systematic education and supportive care, cognitive behavioural therapy and heated humidification are the few proven effective measures that improve the CPAP adherence.

2. OTHER CO-MORBID SLEEP DISORDERS Periodic Limb Movement Disorder (PLMD)

The co-occurrence of PLMD and OSA varied from 47% to 61.5% in different studies. Periodic Limb Movements in Sleep (PLMS) can disrupt sleep by causing arousals in sleep which in turn result in daytime sleepiness.

Narcolepsy
Classical clinical presentations include cataplexy, excessive daytime sleepiness, hypnagogic hallucination and sleep paralysis. Narcolepsy is divided into Type I (with cataplexy/a CSF hypocretin deficiency) and Type II (without cataplexy/a CSF hypocretin deficiency).

The Multiple Sleep Latency Test (MSLT), a biological test, is used to help with the diagnosis of narcolepsy. In narcolepsy, the MSLT shows a short sleep latency (< 8 minutes) and ≥ 2/4 Sleep-Onset Rapid Eye Movements (SOREMs). OSA is not uncommon in narcolepsy, with a reported prevalence of up to 24.8% in one study 5.

Idiopathic Hypersomnia (IH)
Patients with IH present with excessive daytime sleepiness despite the long hours of sleep (> 11 hours/day) and unrefreshing naps.

IH is diagnosed by the exclusion of the other possible causes of EDS. The MSLT shows short sleep latency (< 8 minutes) and < 2/4 SOREMs.

Behaviourally Induced Insufficient Sleep Syndrome (BIISS)
Patients with BIISS have a shorter habitual sleep episode, than is expected from age-adjusted normative data. When the habitual sleep schedule is not maintained (for e.g., on weekends or during a vacation), they will sleep for longer than is usual. A diagnosis can be made by taking a good history, supported by a sleep diary and an actigraphy.

3. MOOD DISORDERS

Patients with depression can present with daytime sleepiness. Depression is common in OSA.

A study showed that 40% of untreated OSA patients had some depressive symptoms and 2% had moderate to severe depression 6. The presence of depression has been shown to be one of the predictors of persistent sleepiness after a CPAP 4.

4. MEDICATIONS, DRUGS OR ALCOHOL

Many medications have sedative effects, e.g., antihistamines, analgesics, anticonvulsants and certain antidepressants. The use of recreational drugs or alcohol can be the cause of daytime sleepiness.

5. SLEEPINESS DUE TO THE PRETREATMENT OF OSA

Chronic intermittent hypoxia during sleep in untreated OSA may result in permanent damage to brain regions involved in wakefulness. This insult may not be completely reversed with CPAP treatment.

6. OBESITY

Obesity itself is an independent risk factor for hypersomnolence.

APPROACHES

Many patients may perceive fatigue as sleepiness. Fatigue is not associated with the higher propensity to sleep but with a feeling of exhaustion and lethargy and decreased activity.

It is important to take a good history, to differentiate between these two distinct symptoms. A good, detailed and thorough history will help to identify the possible underlying cause for the persistent sleepiness, after CPAP.

TO OPTIMISE THE CPAP TREATMENT
Apart from a detailed history, the CPAP downloads provide useful information on the residual AHI, a mask leak and the adherence.

In some cases, the CPAP downloads appear to be within the normal limits but if there is the clinical suspicion of inadequately treated OSA, attended Polysomnography (PSG) while on CPAP should be considered.

RULE OUT BIISS
BIISS is a common cause of daytime sleepiness. Therefore, it is important to rule out BIISS by taking a good history and by reviewing the sleep diary or the actigraphy.

IDENTIFY AND REVIEW THE INDICATIONS OF ANY MEDICATIONS THAT CAN CAUSE SLEEPINESS
Once the culprit medications that cause the sleepiness are identified, the sleep physician should liaise with the prescribing physician to decide to either stop the medications if there is no clinical indication to continue, or to switch to other non-sedative medications. Any recreational drugs or alcohol should be stopped.

LOOK FOR ANY CO-MORBID ORGANIC SLEEP PATHOLOGY AND TREAT ACCORDINGLY
PLMD, narcolepsy and IH can be diagnosed by taking a good history, and supported by performing a PSG or MSLT, while on a CPAP.

TREAT ANY CO-MORBID MOOD DISORDERS
Treating co-morbid depression can reduce the sleepiness in OSA patients while on a CPAP.

TO CONSIDER THE USE OF MODAFINIL
Modafinil is licensed in the USA, for use in OSA patients who still have persistent sleepiness after the use of a CPAP. It is a stimulant and the exact mechanism of action is yet to be ascertained.

CONCLUSION

Persistent sleepiness in OSA patients while on a CPAP is not uncommon. The possible underlying cause should be looked into and managed accordingly before considering Pharmacotherapy (modafinil).

GPs can call for appointments through the GP Appointment Hotline at 6850 3333 for more information.

By: Dr. Wong Hang Siang, Consultant, Department of Respiratory and Critical Care Medicine, Changi General Hospital; SingHealth Duke-NUS Sleep Centre

Dr. Wong Hang Siang is a Consultant Respiratory and Sleep Physician at the Changi General Hospital. He did his Sleep Fellowship training at the Guy’s Hospital, London and his Chronic NIV training at the Lane Fox Respiratory Unit of St. Thomas’ Hospital, London. His area of clinical interests are in OSA, OHS and Chronic NIV use in Chronic respiratory failure patients.

References

1. Sassani A, Findley LJ, Kryger M, et al. Reducing motor-vehicle collisions, costs, and fatalities by treating OSAS. Sleep 2004; 27: 453-458.
2. Giles TL, Lasseron TJ, Smith BJ, et al. CPAP for OSA in adults. Cochrane Database Systematic Review 2006; Cd001106.
3. Pepin JL, Viot-Blanc V, Escourrou P, et al. Prevalence of residual excessive sleepiness in CPAP-treated sleep apnoea patients: the French multicenter study. Eur Respir J 2009; 33: 1062-1067.
4. Gassa M, Tamisier R, Launois SH, et al. Residual sleepiness in sleep apnoea patients treated by CPAP. J Sleep Res 2013; 22: 389-397.
5. Sansa G, Iranzo A, Samantaria J. OSA in narcolepsy. Sleep Med 2010; 11: 93-95.
6. Vandeputte M, de Weerd A. Sleep disorders and depressive feelings: a global survey with the Beck depression scale. Sleep Med 2003; 4:343-345.