Night Sweating Can Be a Sign of Sleep Apnoea

Have you experienced unexplained sweating at night? This symptom is called nocturnal sweating and it is a common complaint among patients. However, only a few experts have fully evaluated its causes. Night sweating is a bothersome complaint not only to the sufferer but also to the bed partner because of the drenching of bed clothes. Night sweating can be associated with a reduced quality of life.

There are many causes of night sweating, These include malignancy, infections, endocrine and neurological disorders, menopause, gastroesophageal reflux (GER), medications (mainly antidepressants and antipyretics), substance abuse, panic attacks as well as sleep disorders, such as obstructive sleep apnoea (OSA) and insomnia. Other causes include an overheated room or too thick bed clothes. What really matters is that night sweating can cause one to lose sleep and can lead to increased daytime sleepiness.

There are recent reports which have linked untreated obstructive sleep apnoea to night sweating. A recently published study of 98 men with untreated OSA found that 34% reported nocturnal sweating which was reduced to 12% with positive airway pressure (PAP) treatment. Those OSA patients who still reported sweating on CPAP treatment were younger and had higher OSA severity.

Another study found that untreated OSA patients with a higher electrodermal activity index, an objective measurement of sweating that reliably estimate the self-report of sweating. These patients also had higher blood pressure and both sweating and blood pressure decreased objectively with PAP treatment.

A study by Arnardottir ES in May 2013 evaluated the prevalence and characteristics of nocturnal sweating in patients diagnosed with OSA, both before and following PAP treatment, compared with the general population. The primary hypothesis for this study was that OSA patients have an increased prevalence of nocturnal sweating that normalises with PAP treatment. This was a case-control and longitudinal cohort study done in Landspitali—The National University Hospital, Iceland. The Icelandic Sleep Apnoea Cohort consisted of 822 untreated patients with OSA, referred for treatment with PAP. Of these, 700 patients were also assessed at a 2-year follow-up. The control group consisted of 703 randomly selected subjects from the general population.

The results showed that frequent nocturnal sweating (≥3× a week) was reported by 30.6% of male and 33.3% of female OSA patients compared with 9.3% of men and 12.4% of women in the general population (p<0.001). Nocturnal sweating was related to younger age, cardiovascular disease, hypertension, sleepiness and insomnia symptoms. The prevalence of frequent nocturnal sweating decreased with full PAP treatment (from 33.2% to 11.5%, p<0.003 compared with the change in non-users).

The prevalence of frequent nocturnal sweating was threefold higher in untreated OSA patients than in the general population and decreased to general population levels with successful PAP therapy. Nocturnal sweating was more common among younger subjects. Subjects with nocturnal sweating had an increased prevalence of other sleep complaints, specifically, daytime sleepiness and symptoms of insomnia. In the general population, nocturnal sweating may be a marker of increased risk of OSA as well as insomnia.

So what can be deduced from these findings? This study simply confirms the findings of other studies that the prevalence in nocturnal sweating in untreated OSA is three times larger than in a general population cohort and that it is reduced to general population levels with full PAP treatment. This also shows that nocturnal sweating is related to lower sleep quality and more daytime sleepiness. Thus, doctors should include OSA in the differential diagnosis of patients presenting with a complaint of nocturnal sweating and further evaluate that possibility by performing a more complete sleep evaluation. More studies are needed to establish these findings.

Reference:

Arnardottir ES, Janson C, Bjornsdottir E, Benediktsdottir B, Juliusson S, Kuna ST, Pack AI, Gislason T. Nocturnal sweating--a common symptom of obstructive sleep apnoea: the Icelandic sleep apnoea cohort. BMJ Open. 2013 May 14;3(5)

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