Long-term effect of CPAP in the treatment of nocturnal stridor in multiple system atrophy

Patients and methods.

Between April 1998 and March 2003, 40 subjects fulfilling the criteria for probable MSA5 were referred to our sleep unit for evaluation of suspected stridor (n = 14), difficulties maintaining and initiating sleep (n = 10), and dream-enacting sleep behaviors (n = 16).

Patients underwent fiberoptic laryngoscopy during wakefulness and baseline full polysomnography (PSG) with synchronized audiovisual monitoring allowing detection of stridor when a crowing harsh high-pitched sound occurred during breathing. Subjects with stridor were offered CPAP treatment and underwent a second audiovisual-PSG where CPAP was manually titrated to the minimum pressure required to eliminate stridor, sleep apneic events, and oxyhemoglobin desaturations. Audiovisual monitoring allowed identifying the modification of stridor during CPAP titration. Patients received instructions on how to use CPAP equipment at home and information about possible side effects. They were encouraged to call our sleep unit if difficulties or side effects were encountered. To confirm the elimination of stridor and correct CPAP use, patients returned to the sleep laboratory after 1 month of treatment to undergo an additional audiovisual-PSG using their CPAP machines.

After baseline PSG, all 40 subjects had clinical follow-up evaluations every 3 to 6 months. At the end of the study (December 2003), we assessed in all 40 subjects survival time from disease onset and baseline PSG until death or last follow-up (December 2003).

Comparisons were assessed by the Mann-Whitney U test and χ² test, when appropriate. Survival rates were calculated using the Kaplan-Meier method. The log rank test was used to assess survival differences between patients without stridor and patients with stridor treated only with CPAP.

Results.

Stridor during sleep was detected during audiovisual-PSG in 14 subjects (35%) and excluded in the remaining 26. Patients were unaware of their stridor which was typically described by the bed partners as a “peculiar noise different from snoring.” Two subjects also had mild stridor during wakefulness that had appeared 3 and 6 months after nocturnal stridor. Compared to subjects without stridor, patients with stridor had significantly higher apnea-hypopnea index, oxyhemoglobin desaturations, and vocal cord abductor abnormalities on laryngoscopy (table 1).

Discussion.

This study confirms our previous finding that in MSA, CPAP is an effective therapy for eliminating stridor during sleep.4 Stridor is a condition that indicates obstruction of the upper airway at the level of the larynx. In MSA, the pathophysiology of laryngeal narrowing is thought to be related to either denervation of the vocal cord abductors6,7⇓ or hyperactivation of the vocal cord adductors,8,9⇓ although it probably results from an unbalanced co-activation of both muscles in response to increased upper airway resistance. CPAP presumably abolishes stridor by decreasing this abnormal resistance,9 thereby keeping the glottis open.

Tracheostomy is usually considered an optimal treatment for stridor because it bypasses the vocal cord obstruction. Tracheostomy, however, is a surgical procedure limited by local complications such as infection and tracheal stenosis, and is frequently not accepted by patients.

Our results indicate that CPAP is an effective, safe, and noninvasive long-term therapy for stridor, thereby avoiding tracheostomy in some cases. Long-term follow-up of our patients showed that CPAP tolerance and compliance were high, complication rate was low, and death during sleep did not occur. Nocturnal stridor did not recur and both patients and their spouses noted a marked improvement in sleep quality and considered CPAP a gratifying therapy. Although limited by a relatively small number of patients, our study suggests that the median survival time was not significantly different between subjects without stridor and those with stridor treated only with CPAP.

Optimal CPAP pressures needed to abolish stridor and apneas were similar to those used in subjects with mild to moderate obstructive sleep apnea syndrome. Although one would imagine that CPAP may be difficult to tolerate for subjects with a severe disabling disease such as MSA where initial insomnia and prolonged awakenings are common,4,10⇓ we observed that adequate education, encouragement, and support resulted in a high rate of CPAP compliance. Nevertheless, two subjects did not tolerate CPAP, and in three patients CPAP use was less than 6 months because of death due to pneumonia or respiratory failure secondary to worsening daytime stridor due to progression of disease. It is our impression that stridor during wakefulness follows nocturnal stridor, and that this is a condition that reflects marked laryngeal obstruction and potential severe respiratory impairment. Patients may still benefit from tracheostomy if daytime stridor appears or CPAP is not tolerated or fails to abolish nocturnal stridor.