Associations Between Night Sweats and Other Sleep Disturbances: An OKPRN Study

As I said below, stay tuned. We now have data from a sleep laboratory and have objective evidence regarding whether there is an association between the subjective complaint of night sweats is related to the apnea/hypopnea index and actual periodic leg movements. However, we won't be able to say anything about whether actual night sweats are associated with OSA. You're right that there is no other hard evidence available about this so I'd be cautious about what you think ought to be true. I am fascinated by the "anatomy" of this very common symptom. Some people notice sweating more that others and some seem to be more willinging to report them. Then there are issues related to underlying sympathetic tone, sympathetic nervous system discharges, and end organ sensitivity, not to mention increases in core body temperature and endogenous pyrogens and other mediators of peripheral vasodilatation. It is much more complicated that I had imagined. Has anyone actually shown that there is increased sympathetic nervous system stimulation during apneic episodes? If so is this from the adrenergic portion of the sympathetic nervous system or the cholinergic portion of the sympathetic nervous system? Do you have a reference?

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Night sweats are frequently associated with Obstructive sleep apnea/hypopnea syndrome (OSAHS). In my experience, they more commonly occur in morbidly obese patients, and in patients with the most severe blood oxygen desaturations during sleep. I have seen no consistent association between night sweats and periodic limb movement disorder, chronic insomnia, or other sleep disorder. Though little direct research has been done between the OSAHS\night sweats association in adults, there are numerous studies demonstrating autonomic (sympathetic) hyperactivity in patients with untreated OSAHS. Interestingly, night sweats was found to be on of two factors highly correlated with the presence of obstructive sleep apnea in infants (the other is noisy breathing), and it is frequently seen in school-age children with untreated OSAHS.

Night sweats almost always resolve completely in OSAHS patients after successful treatment with CPAP.

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Like many of us, I was taught as a medical student that night sweats are a symptom of tuberculosis (TB) and lymphoma. Undoubtedly, medical students today are taught the same thing. And it is true: night sweats can be a predominant symptom in patients with TB or lymphoma. That these two diseases are probably still at the top of a physician’s differential diagnosis when evaluating a patient with night sweats reflects the facts that medical students are taught predominantly in tertiary care centers and that there has been relatively little research on night sweats. The ongoing work by Dr. Mold and colleagues continues to shed light on what turns out to be a very common symptom. In this recently published study, Mold, Woolley, and Nagykaldi found that 34% of adults being seen in primary care practices report having had night sweats in the past month.

When controlling for several variables, this preliminary work demonstrated an association between night sweats and several sleep-related symptoms: daytime tiredness (OR 1.99), gastroesophageal reflux (OR 1.94), awakening with pain (OR 1.87), and legs jerking during sleep (OR 1.78). Because night sweats were so common, these odds ratios will overestimate the actual “risk.” People who are asked about (screened for) night sweats are also likely to be different than people who bring it up as a complaint. Nevertheless, this work demonstrates the importance—and the necessity—of research conducted in primary care settings. TB and lymphoma are not going to be the top diagnoses in patients with night sweats in primary care. Common disorders, such as gastroesophageal reflux and other conditions associated with poor sleep, need to be high on the differential.

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I agree that our study is purely exploratory. It is now time to do a more dfinitive study in. There are two problems: 1. How should such a study be designed? and 2. Who will fund such a study?

My preliminary answer to the first question is that we should identify a representative group of patients with night sweats, work them up to the hilt trying to identify contributing factors, then try to reduce or elimninate contributing factors and see if their night sweats improve. Because of the placebo effect, we would probably have to do some sort of cross-over (multiple N of 1) study of the interventions. Isn't it interesting that we have no standard research design for determining the cause or causes of symptoms?

I don't know the answer to the second question or we would have already gotten started with a more definitive study. Any suggestions?

Competing interests:   None declared