Sleep apnea is frequently associated with foramen magnum stenosis in patients with achondroplasia and considered a cause of sudden death. The aim of this study was to evaluate the results of respiratory polygraphy (RPG) before and after surgery in patients who underwent foramen magnum decompression (FMD) to elucidate the effectiveness for treatment of sleep apnea.

The findings of RPG, MRI, and otolaryngological fibroscopy were retrospectively reviewed in 22 children with achondroplasia who underwent FMD at a single institution from 2016 to 2022. The Mann-Whitney U-test was used to assess the association of sleep apnea to age at FMD; preoperative upper airway stenosis (UAS); preoperative Achondroplasia Foramen Magnum Score (AFMS); concomitance of endoscopic third ventriculostomy, ventriculoperitoneal shunt placement, or adenotonsillectomy after FMD; and type of predominant apnea as determined at the preoperative RPG evaluation. The Wilcoxon signed-rank test was used for comparisons of RPG results.

Of 22 patients (median age 8 months) included in the study, the RPG-determined respiratory event index (REI) was within the reference range (REI < 5) for 8 patients and indicated mild sleep apnea (REI 5-15) in 10 patients, moderate sleep apnea (REI 15-30) in 3 patients, and severe sleep apnea (REI ≥ 30) in 1 patient. Postoperatively, 21 patients (95.4%) showed REI improvement. Of the 14 patients with preoperative sleep apnea (REI of ≥ 5), 12 patients (85.7%) had at least 1 level of improvement in sleep apnea. In comparisons between pre-FMD and post-FMD indexes, the REI (p = 0.0009, p < 0.01) and Central Apnea Index (p = 0.03, p < 0.05) showed significant improvement, while the Obstructive Apnea Index (OAI) did not show significant differences. However, the type of predominant apnea according to preoperative RPG had no significant effect on the extent of improvement in the postoperative REI. In 7 patients for whom the predominant type of apnea was obstructive, the OAI improved during the follow-up period.

FMD was effective for improving sleep apnea in patients with achondroplasia associated with foramen magnum stenosis. Regardless of the type of sleep apnea, the decompressive surgery could be indicated when the patient has no significant UAS.