Send letter to journal:
Re: Down syndrome with OSA may not snore

Dear Editor,

We read with interest the article “Severity of obstructive apnoea in children with Down syndrome who snore” by Fitzgerald et al. ¹ Fitzgerald et al reported that 97% of Down syndrome (DS) children who snored had obstructive sleep apnea. In light of the limited access to sleep polysomnography (PSG) in children, ² it would seem appropriate for DS children who snore together with tonsil hypertrophy to be offered tonsillectomy and adenoidectomy without the need for PSG if the findings by Fitzgerald et al are confirmed by other studies. However, other existing studies not quoted by Fitzgerald et al reported a much lower prevalence. The study by De Miguel-Diez et al ³ assessed 108 consecutive 1-18 years Down syndrome (DS) children and showed that the prevalence of PSG confirmed obstructive sleep apnea (OSA) in DS children was 54.6%. Another study by Shott et al ⁴ enrolled 56 younger DS children and showed that the prevalence of OSA was 57%. The case controlled study conducted in our department ⁵ showed that the prevalence of OSA in a group of 22 DS children recruited from the community was 59%. The above three studies showed a much lower prevalence than that demonstrated in Fitzgerald et al's study. It is probably due to the fact that the patients from Fitzgerald et al's series was enrolled from a sleep clinic and all DS patients enrolled were snorer. In our study,⁵ we showed that out of 13 DS children with OSA, only 5 of them were habitual snorer. Hence, we agree with Shott et al that routine baseline PSG should be provided to all DS children and not just snoring DS children as suggested by Fitzgerald et al. in light of the poor correlation between parental perception of symptoms during sleep and PSG abnormalities. Another problem in the study by Fitzgerald et al1 was the inappropriate use of the normal value of arousal index of 5 for the whole study group aged from 0.2 to 19-year when the normal values of arousal index change with age, i.e. infants: 7-9 per hour, prepubertal children: 7+/-2 per hour, adolescents: 14+/-2 per hour and young adults: 16-18 per hour.^6,7 The authors should also report the wake time after sleep onset (WASO) that may be related to daytime symptoms.

References:

1. Fitzgerald DA, Paul A, Richmond C. Severity of obstructive apnoea in children with Down syndrome who snore. Arch Dis Child 2007;92:423-5.
2. Ng DK, Kwok KL, Chow PY, Cheung MY. Diagnostic access for sleep apnea in Hong Kong. Am J Respir Crit Care Med 2004; 170: 196.
3. de Miguel-Diez J, Villa-Asensi JR, Alvarez-Sala JL. Prevalence of sleep-disordered breathing in children with Down syndrome: polygraphic findings in 108 children. Sleep 2003;26:1006-9.
4. Shott SR, Amin R, Chini B, Heubi C, Hotze S, Akers R. Obstructive sleep apnea: Should all children with Down syndrome be tested? Arch Otolaryngol Head Neck Surg 2006;132:432-6.
5. Ng DK, Hui HN, Chan CH, Kwok KL, Chow PY, Cheung JM, Leung SY. Obstructive sleep apnoea in children with Down syndrome. Singapore Med J 2006;47:774-9.
6. Traeger N, Schultz B, Pollock AN, Mason T, Marcus CL, Arens R. Polysomnographic values in children 2-9 years old: additional data and review of the literature. Pediatr Pulmonol 2005;40:22-30.
7. Marcus CL. Sleep-disordered breathing in children. Am J Respir Crit Care Med 2001; 164:16-30.