Accuracy of portable polygraphy for the diagnosis of sleep apnea in multiple system atrophy.

OBJECTIVE: To assess the diagnostic accuracy of portable polygraphy (PG) for the detection of sleep apnea (SA) in multiple system atrophy (MSA).

METHODS: Thirty consecutive patients with probable MSA underwent PG (overnight recording of nasal flow, thoracic/abdominal movements and pulse oximetry), followed 4 weeks later by full polysomnography (PSG) (reference standard). The accuracy of PG was first assessed using the same threshold as for PSG (apnea-hypopnea index [AHI]≥5), then for all possible AHI thresholds using the area under the receiver operating characteristics (AUROC) curve. Inter-rater reliability of PG was assessed using the kappa coefficient.

RESULTS: Among 30 patients enrolled, seven were excluded for technical problems on PG or PSG and 23 were included in the main analysis. Eight out of 23 had an AHI≥5 on PSG. With the same threshold, sensitivity, specificity, positive and negative predictive values of PG for the diagnosis of SA were 87.5% (95% confidence interval: 47-99), 80% (52-96), 70% (35-93) and 92.3% (64-99), respectively. The kappa between PG raters was 0.75 (0.49-1.00) indicating good agreement. The AUROC was 0.93 (0.82-1.00). No association was found between sleep and excessive daytime sleepiness questionnaires and SA.

CONCLUSION: Portable PG seems to be valuable for ruling out SA in MSA.