• stridor
• sleep apnoea syndrome
• multiple system atrophy

We read with interest the article by Hirayama et al¹ in which the authors, using an original imaging method, low field magnetic resonance fluoroscopic study, proposed that upper airway obstruction precedes laryngeal occlusion causing the stridor in patients with multiple system atrophy (MSA). This issue of nocturnal stridor in MSA is of great importance since it is a common cause of sudden death and a recognised prognostic factor in this disease.² It affects about 19% of patients as shown in our series and by others.³ We feel that the relationship proposed between obstructive apnoeic respiratory events and stridor is not as simple as suggested by the authors and must be considered in light of classical standardised polysomnographic (PSG) data.

In our own series, 18 consecutive patients with MSA were assessed for night-time disturbances by all-night standard PSG with continuous synchronised audiovisual recording. Nocturnal stridor occurred in 10 patients and, except in one patient, was always accompanied by breathing disorders, mostly apnoeic, with or without significant oxygen desaturation. In four patients, obstructive sleep apnoeas (OSA) occurred without stridor, and one of these patients presented predominantly with central apnoea that also occurred while awake. Among the patients with stridor, four presented predominantly OSA and one mainly central apnoea. Mixed and prolonged apnoea, up to 53 s, was seen along with stridor in five patients and was isolated in two others. Episodes of mixed apnoea were typical in …