Introduction
Since Hippocratic times, heat treatment has been popular among people with rheumatic disorders. The evidence for their application is still weak, despite the fact that several studies investigating the effects of heat in rheumatic diseases have been conducted [
1,
2]. Superficial heat can be used in rheumatoid arthritis and low back pain as a palliative therapy and can be recommended for beneficial short-term effects, but these recommendations are limited by methodological considerations such as the poor quality of trials [
3,
4].
Finnish saunas, a well-known form of total-body heating, showed good clinical effects for rheumatic patients [
5,
6].
The so-called whole-body hyperthermia has also been widely used during the last century, especially in Germany and Eastern European countries and was known as “fever treatment” [
7]. Although beneficial effects of total-body hyperthermia have been reported [
8,
9], controlled studies have not been performed, and the method is not often used in Western Europe.
During the past 10 years, a new modality for whole-body hyperthermia, named infrared (IR) sauna, has become available in the Europe. It is a compact and user-friendly IR “whole-body hyperthermia.” Personal experiences of rheumatoid arthritis (RA) and ankylosing spondylitis (AS) patients in our out-patients clinic appeared to be promising. They experienced less pain and improved physical functioning. Despite the theoretical possibility of negative effects on disease activity, in our clinical series, no aggravation of inflammation activity was seen.
The new IR cabin differs from the traditional Scandinavian saunas. The heating effect of a high ambient temperature is comparable, but due to the addition of infrared radiation, some heat penetrates maximally up to 4 mm into the superficial skin [
10]. As this might result in different physiological responses compared to the Finnish sauna, we first studied the physiological effects of infrared whole-body treatment in healthy subjects before starting clinical trials in rheumatic patients [
11]. Fifteen healthy subjects were exposed to total-body heat treatment in an infrared cabin at three different intensities (40°C, 55°C, and 70°C). Mean skin surface temperature (2.6°C, 6.8, and 9.1°C, respectively), core temperature (0.4°C, 0.5°C, and 0.6°C, respectively), and heart rate (+14, +37, and +58 beats per minute, respectively) increased significantly. Significant loss of bodyweight after treatment was also found (0.1, 0.3, and 0.4 kg, respectively). In general, a small decrease of systolic and diastolic blood pressure was shown.
The purpose of this study was to determine whether these previously found physiological changes would also provide beneficial effects in patients with rheumatic disorders. The more explicit research questions, therefore, are:
1.
What is the effect of IR sauna on body functions and structures, such as pain, stiffness, and fatigue (primary outcomes)?
2.
What is the effect of IR on physical activities and (social) participation (secondary outcomes)?
3.
Are there any side effects regarding comfort and tolerance during treatment and disease activity (tertiary outcomes)?
Patients and methods
Patients were recruited consecutively from the rheumatology out-patients clinic (JJR) in a general district hospital in Enschede, The Netherlands.
After oral and written information about the study and the possible clinical effects of IR whole-body hyperthermia, patients were invited to participate. Informed consent was obtained from all patients, according to the Declaration of Helsinki.
The patients were treated for a period of 4 weeks, twice weekly, with eight IR sessions in the IR cabin (30 min at an ambient temperature of 55°C). According to the manufacturers’ recommendation, before treatment, a preheating time of the IR whole-body hyperthermia equipment of 15 min was used. During the whole study period, the dosages of nonsteroidal anti-inflammatory drugs and disease-modifying antirheumatic drugs were not changed; treatments with physiotherapy, when applied, were not changed, and no corticosteroid injection was given
The patient’s perceptions of pain [
14], stiffness [
15], and fatigue [
16‐
18] were measured on a 100-mm visual analog scale and were considered as primary outcomes.
Secondary outcomes for the RA patients were: Escola Paulista de Medicina Range of Motion (EPM-ROM scale) [
19] and activities and participation scales of the Dutch Arthritis Impact Measurement Scales (DUTCH-AIMS) [
20]. For AS patients, Bath Ankylosing Spondylitis Global Score [
21], the Bath Ankylosing Spondylitis Metrology Index (BASMI, a ROM-index) [
22], and the Bath Ankylosing Spondylitis Functional Index [
23] were used. To evaluate possible effects on the disease activity (improvement or exacerbation) for RA patients, the Disease Activity Score using 28 joints (DAS 28) [
24] was calculated, and for AS patients, the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) [
25] and the erythrocyte sedimentation rate (ESR) after 1 h were assessed. The DAS 28, BASDAI, and ESR were considered as tertiary outcomes. These measurements are fairly routine in clinical research and have been proven to be valid, reliable, and of good sensitivity to change [
14‐
25].
Results
One RA and one AS patient dropped out in the pretreatment period due to exacerbation of RA and acute lumbar nerve root compression, respectively, and could not be measured for follow-up. Therefore, the mean group results of 17 RA and 17 AS patients are presented. Functional capacity of RA patients according to Steinbröcker classification [
27] is shown in Table
2.
Table 2
Steinbröcker classification of rheumatoid arthritis patients (n = 17)
Discussion
In all patients, a clinically relevant improvement was seen during the IR sauna treatment with pain and stiffness decreasing 5 to 24 points on the VAS. Pain reduced approximately 40% and 60% and stiffness approximately 50% and 60% for patients with RA and AS, respectively (Table
3). All patients felt well during and after IR treatment, and 30 min after the end of treatment, 88.2% of patients felt “comfortable” or “very comfortable” (Table
6).
In RA patients, a clinically relevant improvement is seen during the 4-week treatment period compared to the pretreatment period, regarding pain and stiffness diminishing 5–10 points on the VAS, while during the previous nontreatment period, there was no noticeable change (Table
4). During the post-treatment period, these effects were lost. These effects are less obvious in AS patients (Table
4).
In RA patients, the physical, affective, and symptoms scales of the DUTCH-AIMS showed a trend of improvement during treatment, persisting during the post-treatment phase on the physical and affective scale (Table
5). It is not surprising that no relevant change was seen on the social scale because it cannot be expected that this period would have any influence on the relationship of a patient with family, friends, and relatives as measured on the social scale.
In the AS patients group, there are no changes on BAS global scores and functional index over time (Table
5). Apparently, IR whole-body hyperthermia does not have major effects on these domains.
No relevant change on EPM-ROM and BASMI in RA and AS patients, respectively, were found, so IR treatment does not seem to have any direct effect on the overall range of motion (Table
5). Probably, the impaired ROM in non-acutely inflamed joints, as was the case in our series, is mainly due to irreversible change in these joints, such as erosions and cartilage damage in RA patients and calcification of joint ligaments or bony outgrowth in AS patients. Therefore, no major improvement could have been expected without adequate additional exercises.
The effect of IR whole-body hyperthermia upon local joint inflammation or disease activity is not clear. The findings of earlier studies were controversial [
9,
28‐
33], and many studies have poor or no optimal quality as summarized in the COCHRANE study [3]. For that reason, we have monitored disease activity as reflected by DAS 28 in RA patients and BASDAI and ESR in AS patients. No relevant change in these disease activity measurements was found, indicating no unwanted side effects of IR treatment (Table
5). This does not exclude that some individual cases may experience increased complaints during or after treatment.
From this study, it appears that IR whole-body hyperthermia has direct beneficial effects. Although in the long-term, there is a tendency toward improvement of clinical symptoms of RA and AS patients, there is no sufficient evidence that the short-term effect will last for several days or weeks. Therefore, further controlled clinical studies with a larger study population are necessary.
Because this was the first study of IR sauna, we had no idea about the mean group effect in RA or AS patients. Comparing the changes on primary outcome variables during treatment with those during the previous nontreatment period, we found an improvement of approximately 10% to 15%. So, from power calculations with 80% power and α of 0.05 for following controlled clinical studies, at least 25 patients per group are required. Furthermore, it is recommended to conduct comparable studies in patients with other types of musculoskeletal disorders such as osteoarthritis, osteoporosis, and fibromyalgia.
The results of this study show that the use of IR sauna as treatment is feasible and well tolerated in patients with inflammatory arthritis.
We would recommend that patients should first experience a couple of trial sessions to see whether they achieve any clinical benefit prior to commencing a course of IR. Based on that experience, continuation of treatment and the appropriate dose and application can be discussed with the physician or physiotherapist. Despite the evidence from this study for positive short-term results and a trend towards beneficial clinical long-term effects, further controlled clinical studies are warranted.