Review for 10.1186/1471-230X-13-82 (2013)

Reviewer's report
Title:Barrett's esophagus and the risk of obstructive sleep apnea: A case-control
study
Version: 1Date:10 October 2012
Reviewer: Össur Ingi Emilsson
Reviewer's report:
The authors study in a cross-sectional research if Barrett’s esophagus (BE) is
associated with high risk for obstructive sleep apnea (OSA) and if a high risk
status for OSA is associated with nocturnal gastroesophageal reflux (nGER)
symptoms. The study included 54 BE subjects, 62 gastroscopy subjects without
BE, and 171 colonoscopy subjects, a total of 287 subjects. The BE subjects were
older than the colonoscopy controls, and had a higher BMI than the gastroscopy
controls. The authors demonstrate that more than half of BE patients are at high
risk for OSA according to the Berlin Questionnaire, although after adjusting for
age this risk is no longer significantly higher than among controls. They also
show that among all subjects, those at high risk for OSA are more likely to have
symptoms of nGER. They conclude that BE patients should probably be
screened for OSA, as 56% of them are at high risk for OSA, a risk factor in
general anesthesia which BE patients repeatedly require.
The study is generally well-thought and relevant to the field, as data on the
association between BE and OSA seem to be lacking. However, there are some
methodological issues to discuss.
Major Compulsory Revisions
1. All diagnoses except for the diagnosis of BE are based on questionnaires.
There is no objective measurement regarding OSA, nGER or even BMI. The
authors note the lack of OSA measurements as a limitation, but not nGER or
BMI. This should be more clearly stated in the discussion.
2. Questionnaires were sent out via mail to some BE subjects and controls after
they had undergone endoscopy. This might potentially create a recall bias. BE
subjects might also have started anti-acid treatment in the mean-time, making
nGER less common than at the time of diagnosis. Also, the authors do not
explain fully how long after the endoscopy the subjects answered the
questionnaires. This should be more clearly stated, i.e. with median or mean
days from endoscopy to questionnaire.
3. It is unclear why those with a known diagnosis of OSA should be exluded, as
this might confound the results. Most of the subjects excluded on this ground
were from the BE group. Comment please.
4. According to the results, those with BE had more severe nGER symptoms (as
expected), and were more likely to be at high risk for OSA. There is a
disproportionately high number of BE patients in the high risk for OSA group.
Therefore, it would also be of interest to look at the association between high risk
OSA and nGER symptoms within each subgroup. For a more coherent
presentation of the data, the authors might consider to phrase the analysis
differently: “We also aimed to determine if nocturnal gastroesophageal reflux
symptoms affected the relationship between BE and high risk for OSA”.
5. The possible confounding effects of age and BMI should be more clearly
addressed in the Discussion. Higher age and higher BMI are risk factors for OSA,
and could therefore play a significant role in the findings of the study, as the BE
subjects were older than the colonoscopy controls, and had a higher BMI than
the gastroscopy controls.
Minor Essential Revisions
1. As this is a pilot study, it would be appropriate to state so in the background
section of the abstract, for example: “The goals of this case-control pilot study…”
2. The definition of reflux symptoms is based on very mild symptoms, potentially
yielding many false positives. This should be acknowledged in the discussion. It
would be of interest to know how many of the patients had reflux symptoms “at
least twice a week with significant impairment in quality of life”, as GERD is often
defined.
3. It might be interesting to analyze specifically the question on apneas in the
Berlin Questionnaire, which is a very specific symptom for OSA.
4. It would be interesting to see if adjusting for the self-reported BMI affects the
association between BE and high risk for OSA. Even though self-reported BMI is
used in the Berlin Questionnaire, it would still be an interesting and relevant
analysis. There is no reason why this should not be done, as long as it is stated
that self-reported BMI is a part of the Berlin Questionnaire.
5. Presentation of the results is cumbersome. Setting up tables with the statistical
results instead of writing them all into the main text would be of great benefit for
the article.
6. The statistically significant difference between the BE and EGD groups in
snoring could be explained by differences in BMI. Therefore, adjustment
calculations would be appropriate in this context.
7. In the Discussion, it should be added that self-reported BMI can vary
significantly and unpredictably from the true BMI value.
Discretionary Revisions
1. The authors’ might want to reflect more on why BE patients should be at
higher risk for OSA than GERD-patients without BE (i.e. if that is their theory).
2. In “Background”, consider splitting up and rewording the sentence “Other
studies have demonstrated that treatment of OSA … after initiation of continuous
positive airway pressure”. It is too long and could be clearer.
3. As this is a pilot study, a short comment on the following study in the
discussion would be of interest.
Level of interest: An article of importance in its field
Quality of written English: Acceptable
Statistical review: No, the manuscript does not need to be seen by a
statistician.
Declaration of competing interests:
I declare that I have no competing interests.