Background: Obstructive sleep apnoea (OSA) and subclinical hypothyroidism are relatively frequent disorders that may be causally linked. However, discordant results exist on the prevalence and severity of OSA in subclinical hypothyroidism. The aim of this study was to compare the prevalence and severity of sleep-disordered breathing in individuals with or without subclinical hypothyroidism, and to investigate the possible effect of levothyroxine treatment on these patients.
Patients and methods: One hundred and eight subjects were consecutively enrolled and divided in 3 groups, according to the TSH levels and levothyroxine therapy. The first group (Group A) was represented by 63 subjects with normal TSH and thyroid function. The other two groups included patients affected by subclinical hypothyroidism; one group (Group B) treated with levothyroxine, while the other group (Group C) was never treated with levothyroxine. Anthropometric, respiratory and polysomnographic data were evaluated in all individuals.
Results: The percentage of OSA, neck circumference, and body mass index (BMI) were not statistically different among the 3 groups. Respiratory disturbance index (RDI) as well as the percentage of the total number of events (apnoea-hypopnoea) by total sleep time (TST) with <90% oxyhemoglobin saturation (TSTSaO2 <90%) were not different among the groups. When we observed OSA patients, the only significant difference between groups B and C was represented by the Epworth Sleepiness Scale (ESS) (p=0.005).
Conclusion: This study shows that subclinical hypothyroidism and treatment with levothyroxine do not influence the prevalence and severity of OSA, while sleep propensity is increased by untreated subclinical hypothyroidism.