Neurology -- Correspondence for Iranzo et al., 58 (6) 911-916

Correspondence published:

Reply to Letter to the Editor: Alex Iranzo, J Santamaria, J Berenguer, M Sanchez and A Chamorro (26 November 2002)

Prevalence and clinical importance of sleep apnea in the first night after cerebral infarction: Thomas E Wessendorf, C Dahm and Helmut Teschler (26 November 2002)

Reply to Letter to the Editor 26 November 2002

Alex Iranzo
Hospital Clinic de Barcelona Spain,
J Santamaria, J Berenguer, M Sanchez and A Chamorro
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Re: Reply to Letter to the Editor

neuro_journal{at}urmc.rochester.edu Alex Iranzo, et al.

We thank Wessendorf et al. for their comments. We agree that performing polysomnography shortly after stroke onset is a difficult task. [1] Both neurologists and sleep laboratory technicians had to be on call 24 hours per day during more than one year to recount patients that met inclusion and exclusion criteria .
Wessendorf et al. are correct concerning our error in table 2 of our paper. A typographical mistake: patients with snoring and AHI<10 were 16 out of 19 instead of 9 out of 19. The statistical analyses in the table, however, were performed based on the correct figures and, patients with or without sleep apnea did not differ in history of snoring before stroke onset (p=0.62 using Fisher’s exact test, two-tail, minimum expected frequency was 1.5) and vascular risk factors. The amended table with the p values using Pearson test when the minimum expected frequency was greater than 5 and two-tail Fisher’s exact test when it was lower than 5. The p- values for the categorical variables remain higher than 0.45; therefore, the results and conlusions of our study are unchanged.
The discrepancy between our results and Wessendorf et al. [2] regarding the association between snoring before stroke and sleep apnea is difficult to explain. A type II error can not be excluded. However, two other studies performed in acute care centers evaluating 128 [3] and 161 [4] patients with acute or recent stroke (mean delay of polysomnography less than 10 days) found on multiple logistic regression analysis that sleep apnea could not be predicted by a history of snoring prior to stroke. Other possible explanations for this discrepancy is that Wessendorf et al. [2] evaluated patients after 46 ± 20 days after stroke onset and not during the acute phase of the disease (the AHI index decreases in the stable phase of the stroke when compared to the acute phase5), and that they studied patients from a rehabilitation center where the most severe stroke patients are usually admitted (altough scales of stroke severity are not provided in their article). The most important points in our study which are that sleep apnea is frequent during the first night after cerebral infaction and, associated with early neurologic worsening and stroke onset while sleeping.
References:
1. Iranzo A, Santamaria J, Berenguer J, Sanchez M, Chamorro A. Prevalence and clinical importance of sleep apnea in the first night after cerebral infarction. Neurology 2002;58:911-916.
2. Wessendorf TE, Teschler H, Wang YM, Konietzko N, Thilmann AF. Sleep-Disordered breathing among patients with first-ever stroke . J Neurol 2000;247:41-47.
3. Bassetti C, Aldrich MS. Sleep apnea in acute cerebrovascular diseases: final report on 128 patients. Sleep 1999;22:217-223.
4. Parra O, Arboix A, Bechich S, et al. Time course of sleep-related breathing disorders in fist-ever stroke or transient ischemic attack. Am J Respir Crit Care Med 2000;161:375-380.
Table 2. Clinical differences between patients with and without AHI ³10 on admission.
AHI <10(n=19) AHI ³10(n=31) P value
Hypertension (n) 13/ 21/ 0.96 *
Smoking (n) 7/ 11/ 0.92 *
Hyperlipidemia (n) 5/ 5/ 0.47 **
Habitual snoring (n) 16/ 28/ 0.62 **
Respiratory pauses(n)9/ 13/ 0.72 *
Somnolence (n) 1/ 4/ 0.63 **
* Pearson test when the minimum expected frequency was greater than 5
** Two-tail Fisher’s exact test when it was lower than 5
First number is AHI <10(n=19)
Second number is AHI 10³(n=31)
Third number is P value

Prevalence and clinical importance of sleep apnea in the first night after cerebral infarction 26 November 2002

Thomas E Wessendorf
Department of Respiratory and Sleep Medicine Essen Germany,
C Dahm and Helmut Teschler
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Re: Prevalence and clinical importance of sleep apnea in the first night after cerebral infarction

thomas.wessendorf{at}uni-essen.de Thomas E Wessendorf, et al.

The article by Iranzo et al. [1] underlines the importance of sleep- disordered breathing for stroke patients, particularly in the acute phase. The performance of full polysomnography within 11 hours after the event must have been a difficult task.
However, we would like to point to several problems in the data analysis: Iranzo et al. divided their patients in two groups (AHI < and >10). They state, “although patients with SA were more often…habitual snorers… the difference did not reach significance”: There were 28 patients with a positive snoring history out of 31 with an AHI >10, and nine patients with a positive snoring history out of 19 with an AHI <10 (table 2). Based on a Chi-Square test (STATISTICA, Version 6) one would have to reject the hypothesis of homogeneity (p=0.0008) given the numbers in the table. Therefore, either the numbers given in the table or the calculations are incorrect.
Apart from this mistake, several comparisons between the groups (e.g. infarct sizes, risk factors) are limited by the relatively low number of patients. However, the power and possibility of a type II error have not been addressed. This is of particular importance because of contradictory results in the literature.
According to other studies including our own the history of habitual snoring prior to stroke is associated with the diagnosis of SDB after stroke. [2, 3] This discrepancy to the authors’ results is of clinical importance and we suggest a correction by the authors.
References
1. Iranzo A, Santamaria J, Berenguer J, Sanchez M, Chamorro A. Prevalence and clinical importance of sleep apnea in the first night after cerebral infarction. Neurology 2002;58:911-916.
2. Wessendorf TE, Teschler H, Wang YM, Konietzko N, Thilmann AF. Sleep-Disordered breathing among patients with first-ever stroke. J Neurol 2000;247:41-47.
3. Bassetti C, Aldrich MS, Chervin RD, Quint D. Sleep apnea in patients with transient ischemic attack and stroke: a prospective study of 59 patients. Neurology 1996; 47:1167-1173.