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Hypothyroidism is common ; it constitutes the most common variety of thyroid disorder in some reports (Sridhar, 1991). Higher intellectual functions, often blunted in hypothyroidism, could be related to associated sleep disorders often seen in thyroid deficiency (VanDyck P et al, 1989). Most recent studies have focussed on sleep apnea syndrome associated with hypothyroidism (Lin CC et al 1992). There is little information about sleep in young subjects with untreated hypothyroidism (Hayashi M et al, 1988). We have studied the pattern of sleep in untreated hypothyroid patients aged 30 years or less at presentation.
The data was collected from our prospective computerised database at our Centre. One hundred and forty one consecutive subjects with untreated hypothyroidism aged 30 years or less form the subject of this presentation. Goitre was graded according to Stanbury's criteria (Stanbury JB and Hetzel BL, 1980). Body weight was measured using a lever-and-arm balance, with the subjects wearing light indoor clothing.
154 subjects having euthyroid goitre, aged 30 years or less were taken as controls (ie, those with goitre, and normal levels of serum T4 and/or TSH).
Sleep was categorised as normal, difficulty in initiating sleep, difficulty in maintaining sleep and excessive daytime somnolence (Sridhar GR and Madhu K, 1994). Difficulty in initiating sleep (DIS): difficulty in falling asleep at least three times a week, for two weeks or more. Difficulty in maintaining sleep (DMS): interruption of sleep two or more times per night, resulting in problems going back to sleep again. Excessive daytime somnolence (EDS): desire to sleep during daytime that was affecting his or her daily functioning, in the absence of other contributing factors. . Pearsons product moment correlation was calculated, and z-test for differences in percentages was employed. P values of <0.05 were taken as significant.
Among 141 hypothyroid subjects, 29 were aged 15 years or less (Group I) and 112 between 16 and 30 years (Group II). Comparisons were made within each group, and across both groups (Table 1). A significantly lower number of hypothyroid subjects in the older age group had normal sleep compared to the younger age (55.55% vs 68.97%; p<0.01). The most common variety of sleep disorder was excessive daytime somnolence (DMS) in both groups with hypothyroidism. None of the younger hypothyroid subjects complained of DIS or DMS, as compared to 4.5 -16% in the older age group.
Hypothyroid subjects with EDS were younger and weighed less than the corresponding group with euthyroid goitre (Table 1). However there was no similar association in the older age group (16-30 years).
In the younger group with euthyroid goitre, subjects with EDS were older and heavier than those with normal sleep. Such associations were not present in the older age group, among subjects with both hypothyroid and euthyroid goitre.
Detailed comparisons are given in Table 1.
Sleepiness is a prominent presenting feature in most patients with hypothyroidism (Kales A et al, 1967).Sleep apnea syndrome (SAS), where excessive daytime somnolence is often present, (Okada T et al, 1993) has been well studied in patients with untreated hypothyroidism. Hypothyroid patients with SAS tended to be younger than those without SAS (Lin CC et al, 1992), comparable to our group, if EDS can be taken as a surrogate of SAS.
Unlike other causes where SAS is often causally responsible for EDS, hypothyroidism might be associated with daytime sleepiness, independent of SAS. This results in clinical overlap of symptoms between apneic and non-apneic causes of daytime sleepiness in hypothyroidism.
Though SAS/ EDS is the most common form of sleep disturbance in untreated hypothyroidism, other forms of sleep disorders such as DIS and DMS may also occur, especially in the post-adolescent age group. These disturbances should be identified and looked for after thyroxine replacement, so that other forms of treatment may have to be considered, should the sleep disturbances persist. Besides affecting the quality of life, uncorrected sleep disorders contribute to having a sensation of low energy and make it difficult to cope with the disease (Sridhar GR, Madhu K, 1994).
Table 1. Sleep in young untreated hypothyroid subjects ( contact the author for a copy )
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