Screening for obstructive sleep apnoea

It took me a little while to get around to opening Sleep Journal from the start of last month, but I have enjoyed reading a study from Japan which validated a simple questionnaire intended to screen a community-based population for obstructive sleep apnoea.

This study group (Sleep Vol 32 No 7 p939-948) created a questionnaire that required only information about a person's gender, body-mass index, snoring history (yes or no) and blood pressure. From this information a score out of 18 was obtained. Scores above 11 were increasingly predictive of the presence of occult obstructive sleep apnoea.

Why did I like this paper?

Firstly, there was no question about sleepiness. Realising that people in the community who have obstructive sleep apnoea may be differentiated from those who go to the doctor with the problem by the absence of sleepiness, this somewhat-nebulous symptom was left out of the mix.

Secondly, a neat combination of two investigations that fall short of a full sleep study was used to evaluate for the presence of obstructive sleep apnoea. A home monitoring device was used which measured only the usual respiratory channels that we measure in the sleep lab - air pressure changes at the nose, thoracic and abdominal elasticated bands as well as pulse oximetery But how did they know when the person was asleep? A wrist actigraph was worn. This is essentially a motion sensor, the size of a wrist watch. When motion stops, sleep is assumed. This sort of device is used in evaluation of people with problems such as shift work sleep disorder, as it is more objective then a sleep diary. The combination of actigraphy and respiratory monitoring is much more simple then a full sleep study. Together they constitute, I think, reasonable way to follow up a community screening questionnaire. There will probably be more of this sort of diagnostic evaluation performed here once medicare agrees to pay for such a test.

Finally, I think we could use something like this here. It should not be difficult to validate for local conditions (our at-risk BMI is likely to be higher than the Japanese). And that has got me thinking ....

OSA and type-2 diabetes - which is the chicken? Or are they both eggs?

A recent round - table expert discussion published in the journal 'Diabetes, Obesity and Metabolism' (11,2009, 733-741) was clearly based on the International Diabetes Federation report on sleep disordered breathing and type 2 diabetes. Each paper attests to a growing interest in the relationship between these two disorders.

Some of the major points were:

1. There is a diabetes epidemic globally. Interstingly the diabetologists are urging the medical community to pay attention to a related epidemic of obstructive sleep apnoea, and to commit to research into how the two may be linked.

2. Obstructive sleep apnoea, some studies have suggested, may contribute to impaired glucose control. And CPAP therapy may reverse the damage. Unfortunately other studies have contradicted this, and the jury is still out.

3. The association between type 2 diabetes and OSA is independent of obesity. Intermittent hypoxia overnight and sleep fragmentation is thought to set off a 'cascade of events' which may contribute to the development of some of the morbidity associated with OSA. Including diabetes. The language is floridly descriptive, but the details are still sketchy!

4. Whether diabetes causes OSA (perhaps via an autonomic neuropathy) or vice versa (chicken or egg), or whether both are simply markers of the same phenotype (both eggs? both chickens? Now that wouldn't be a very productive metaphorical partnership) is open for debate. 40% of patients with OSA have type 2 diabetes, and up to 23% of patients with type 2 diabetes have OSA. So patients in each population group should be evaluated for the possible coexistence of the other condition

5. How to screen patients with diabetes for OSA is not codified. Furthermore, how to evaluate those felt to be at high risk will depend on the local availability of specialist sleep medicine services. The 'expert panel' round table discussion - sponsored by a CPAP company - felt that any patients with a high Epworth Sleepiness Scale or Berlin Questionnaire score should be evaluated with polysomnography. It is worth asking if they snore, or if there have been witnessed apnoeas - as positive answers to these questions significantly heighten the pre-test probability.

6. Treatment of OSA with CPAP may - or may not - help with diabetes control. Weight loss, however, is a clear winner across the board.

Watch this space. If obstructive sleep apnoea hangs on to the coat tails of type 2 diabetes.....

Andrew