Keywords

1 Introduction

Rheumatologic disorders comprise various conditions having different etiologies and pathogeneses. The leading clinical symptoms are chronic joint pain and musculoskeletal impairment. With regard to pathogeneses, systemic autoimmune inflammatory diseases can be categorized as rheumatoid arthritis (RA), spondyloarthritis (e.g., axial spondyloarthritis, axSpA), connective tissue diseases and vasculitides. Rheumatic conditions such as osteoarthritis (OA) and fibromyalgia (FM) have no associated systemic inflammation.

The optimal treatment and management of rheumatologic disorders consist of non-pharmacological and pharmacological strategies. Physical therapy plays an important role in treatment algorithms and is therefore implemented in the relevant care guidelines [1,2,3]. The use of hyperthermia (HT) in physical therapy is a classical and developing therapeutic approach which can be applied in different forms. An established variant of HT is water-filtered infrared A (wIRA) therapy, which can be applied locally or systemically (whole-body). To date, local wIRA application has been tested in the context of rheumatological disorders in different entities (RA, axSpA, OA and FM), with whole-body wIRA treatment leading to pain reduction in patients with axSpA or FM [4, 5].

This chapter reviews the current state of research into the clinical effects of locally applied wIRA (using a wIRA radiator) in the field of rheumatism.

2 wIRA: Clinical Experiences in Rheumatology

2.1 Axial Spondyloarthritis (axSpA)

In 1996, Falkenbach et al. [6] published a clinical trial investigating the impact of wIRA on the cervical rotation mobility and sensation of pressure pain in the neck region of subjects with axSpA (n = 11) and subjects with degenerative disorders of the spine (n = 11). wIRA irradiation was applied as a monotherapy over 20 min with the irradiation field focused on the vertebrum prominens. Data were collected before, during and 10 min after the intervention. In both cohorts, the range of motion in transverse plane increased significantly. Using a pressure algometer, pain was quantified bilaterally on defined (trigger)-points of musculus (m.) trapezius superior, m. supraspinatus, and m. infraspinatus. Although significant changes in the sensitivity of pain during the intervention were not detected in either group, a trend towards an augmented level of sensitivity was described. The authors assumed that the improved cervical mobility was due to a modified elasticity of collagen in tissue triggered by wIRA irradiation and not an alleviation of pain.

In 2019, Xu et al. [7] investigated the effects of wIRA treatment on sacroiliitis in patients with active axSpA. The pharmacological therapy of the exclusively male probands (n = 120) consisted of methotrexate and non-steroidal anti-inflammatory drugs (NSAIDs). The patients were split randomly into two groups. The interventional group received regional wIRA therapy focused on the sacroiliac joints twice daily for 20 min each in a sequence of 5 days. After an interval of 24 hours, wIRA therapy was switched to the control group (crossover design). Significant decreases in morning stiffness and pain, as measured with VAS (visual analogue scale) scores (0–100 mm) and the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), a validated questionnaire to assess disease-specific disease activity, were observed after the intervention. The following blood serum data were additionally assessed: levels of C-reactive protein (CRP) declined significantly under wIRA treatment and increased after completion. Levels of vascular endothelial growth factor (VEGF) only showed a slight downward trend. An increase in the resistance index of sacroiliac joint assessed by ultrasonography may be interpreted as a sign of attenuated inflammation.

In 2020, a prospective randomized controlled trial evaluating the effects of serially applied wIRA irradiation on patients with an active axSpA was reported by Klemm et al. [8], allowing only pharmacological therapy with NSAIDs. In the context of a 7-day multimodal rheumatologic treatment, the intervention group (n = 36), in comparison with the control group (n = 35), also received wIRA irradiation twice daily for 30 min (a total of 12 applications). The radiation field encompassed the lower thoracic and lumbar area. A numeric rating scale (NRS) demonstrated a significant reduction of pain (primary outcome parameter) in the intervention group, with about 75% of the treated cohort reducing their pain medication after the completion of the trial. Approximately one-third of the treated patients discontinued their NSAID medication. The authors related these findings to a significant reduction of the levels of tumour necrosis factor α (TNFα) in the wIRA group after the intervention. As secondary outcome parameters, BASDAI and Bath ankylosing spondylitis disease functional Index (BASFI), a validated questionnaire to assess disease-specific functionality, were suggestive of beneficial effects. However, no statistically significant differences in these indices were found between the groups. According to the authors, the design of the trial could have influenced this outcome in terms of a bias due to the multimodal rheumatologic treatment for all probands. Furthermore, BASDAI and BASFI are regarded as tools detecting differences particularly in longer time periods. No adverse or severe adverse events were documented.

2.2 Osteoarthritis (OA)

Osteoarthritis (OA) was one of the first rheumatologic disorders for which the analgesic effects of wIRA were tested. In 1992, the first experiences of locally applied wIRA in patients with gonarthrosis (n = 52) or coxarthrosis (n = 63) with pain as leading symptom were reported by Goltermann (extracted from [9]). This study also included subjects with non-rheumatological disorders such as lumbago. Therapy with anti-rheumatic agents, glucocorticoids or painkillers was exclusion criteria. For the study, patients were treated for 20–35 min on a total of 10 occasions at intervals of 1 or 2 days. About one-third were regarded as responders, as defined as at least considerable reduction of pain post-interventional. Worsening pain under therapy was reported by one patient with gonarthrosis and two patients with coxarthrosis.

In the same year, positive effects of wIRA (for 20 min three to five times per week on 10–20 occasions) in reducing pain for patients (n = 26) with degenerative musculoskeletal alterations such as gonarthrosis were presented by Scherf et al. (extracted from [9]). Subjects with non-rheumatological disorders were also included, analogous to Goltermann. Outcomes and findings were based on the subjective assessment of the investigators.

In 1995, Merle et al. reported two case series of patients with osteoarthritis of the knee (n = 10) and hand (n = 10) treated with wIRA therapy (extracted from [9]). A control group received conventional, unfiltered infrared irradiation. A defined exclusion criterion was secondary OA caused by, for example, inflammatory rheumatologic diseases. The knee irradiation in both groups was applied twice weekly for 30 min on 10 occasions. The treatment regime of the hands was approximately twice weekly for 20 min on 12 occasions. NSAIDs could be taken as required. The intensity of pain, which was measured using a rating scale (0 = no pain to 6 = unbearable pain), reduced in the treated group in comparison to the control group. The requirement for painkillers also declined in the treated group. However, the low number of cases in this study requires that its findings are regarded as explorative.

To re-evaluate and confirm the effects of wIRA on gonarthrosis, Schuester et al. [10] designed a randomized controlled trial, the results of which were published in 2020. In this study, patients (n = 54) were required to irradiate their predominant knee at home for 30 days for at least 60 min per day. The control group (n = 54) continued their standard therapy. The wIRA intervention significantly reduced pain under stress and improved quality of life, as quantified using the VAS score (VAS 0–100 mm), with twice as many subjects in the intervention group (20 vs. 10) stating that they could walk pain-free for an unlimited distance post-intervention. The Knee Injury Osteoarthritis Outcome Score (KOOS) in all its categories showed a trend to improvement, albeit without being statistically significant. No substantial changes in additional outcome parameters, such as the range of motion and the length of one leg stand, were observed. The intake of analgesics (NSAIDs) was not monitored. Two female subjects undergoing wIRA therapy stopped therapy because of increasing pain. Chronic venous insufficiency (CVI), one of their common comorbidities, was reported as the trigger for pain. The discontinuation of treatment led to rapid recovery without consequences. This adverse event is remarkable and was discussed as an exclusion criterion by the authors.

2.3 Fibromyalgia

In a controlled observational study, Krüger et al. [11] addressed the effects of serial exercise plus wIRA therapy in patients with fibromyalgia (FM), with the control group undergoing exercise therapy alone. Patients received 12 treatment sessions of 30 min each over 4 weeks. Clinical effects were measured using the Fibromyalgia Impact Questionnaire (FIQ), a validated measurement of health status in FM. wIRA irradiation significantly reduced pain and increased overall well-being.

2.4 Current Research Activities

We are currently investigating the effectiveness of applying wIRA to both hands of patients with osteoarthritis, non-inflammatory arthralgia and recent-onset arthritis in an observational study. In this study, adult subjects received wIRA for 30 min, three times a week (15 min from palmar and dorsal, respectively) over 4 weeks. Anti-inflammatory therapy (e. g., glucocorticoids) is one of the exclusion criteria. The following outcome parameters are evaluated: patients’ global, physicians’ global, patients’ pain (each VAS 0–100 mm), duration of morning stiffness, tender joints, swollen joints, clinical disease activity index (CDAI) and the self-reported functional score HAQ (Health Assessment Questionnaire). Musculoskeletal ultrasound in grey-scale and power Doppler are also being performed. Preliminary data on patients with hand OA (n = 14), and non-inflammatory arthralgia (n = 2), predominantly females, reveal a reduction of mean (SD) patients’ global from 52 mm (25) to 36 mm (27; p = 0.003), physicians’ global from 16 mm (9) to 12 mm (8; p < 0.001), and patients’ pain from 46 mm (26) to 32 mm (24; p = 0.008) from baseline (BL) to week 4. No positive effect of wIRA on the duration of morning stiffness has been detected {mean (SD) 21.8 min (29.5) at BL, 22.2 min (31.5) after 4 weeks}. The number of tender/swollen joints only tends to be reduced. CDAI was significantly reduced from 13.0 (7.7) at BL to 9.8 (8.0) after 4 weeks (p = 0.001). In addition, HAQ was significantly reduced from 0.7 (0.5) at BL to 0.5 (0.4) at week 4 (p < 0.001) (Abstract submitted to DGRh, 2021). The study and further inclusion of eligible subjects is on-going. The researchers intend to compare the effects of wIRA in the three different aforementioned conditions.

3 Discussion and Summary

Rheumatologic diseases are predominantly chronic with potential progressive courses which cover a broad field of different conditions. Joint pain is a leading symptom and the core therapeutic effects to deliver include pain reduction, functionality improvements and a deceleration of disease progression. A multimodal therapy including pharmacological and non-pharmacological treatment options is favoured. The chronic aspect of rheumatologic diseases often requires long-term therapies. Therefore, compliance and therapy adherence are required. In this context, the easy handling (portable wIRA irradiator), safety aspects and lack of adverse events upon wIRA treatment should be considered.

Referring to the above studies and considering the aforementioned aspects, locally applied wIRA reveals therapeutics benefits in the field of rheumatologic disorders, and thus can be recommended as an additive treatment option. Especially in patients with axSpA, OA and FM, wIRA therapy applied locally and serially leads to a strong relief of pain.

wIRA significantly reduces lower back pain in axSpA and sacroiliitis. The findings of Klemm et al. [8] that NSAID intake is reduced after wIRA therapy suggests it might help to minimize the side-effects of long-term NSAID therapy, and be especially appropriate for patients with contraindications for NSAIDs. Locally applied wIRA also reduces levels of the acute-phase protein CRP and the proinflammatory cytokine TNFα. These findings confirm those of Tarner et al. [12] who have reported decreasing TNFα levels after mild whole-body HT induced by wIRA. Taken together, these findings indicate that a disease modifying capacity on its own is at play, and that wIRA could act as a useful complement to TNFα-inhibitors for treating axSpA.

In OA of the hands, knees and hips, the first explorative studies that were already performed in the 1990s reported pain reduction after wIRA treatment. More recently, Schuester et al. [10] confirmed these findings and also demonstrated an increased quality of life after wIRA therapy. Merle et al. (extracted from [9]) reported on a reduced demand for analgesic medication after wIRA treatment; however, these findings need to be validated in a larger study. As worsening pain temporally related to wIRA was reported occasionally in patients with OA of the knee/hip [9, 10]; it is necessary to be careful with patient selection. In two cases, retrospective chronic venous insufficiency has been considered as a causative trigger.

Irradiation with wIRA was also an effective therapy in patients with FM and pain, a key symptom in this disease. Multimodal combination therapies are necessary as FM is difficult to treat. The good safety and good tolerability of wIRA makes it an excellent candidate for combination therapies with standard approaches.

4 Limitations

The number of trials investigating the effects of locally applied wIRA in rheumatologic disorders is limited so far, and their level of evidence differs. Additional limitations are the lack of standardization in the treatment protocols (optimal intensity, e.g., frequency, duration and course of treatment for each disorder need to be defined), and the lack of follow-ups make it difficult to assess beneficial effects of wIRA in the longer term. Additionally, head-to-head studies of local wIRA therapy and other thermal interventions are necessary in order to generate robust comparative evidence.

5 Outlook

Other rheumatologic disorders should be considered for wIRA therapy. Beneficial effects on patients with secondary Raynaud’s phenomenon (RP) in the context of systemic sclerosis could be possible and the value of wIRA as adjuvant therapy to help reduce the frequency, duration or intensity of Raynaud attacks could be envisioned. Foerster et al. [13] found positive effects of mild whole-body hyperthermia induced by wIRA irradiation on scleroderma-associated RP. Furthermore, positive trends for skin manifestation and arthralgia have been reported. A case study of a 6-year-old girl with progressive linear morphea affecting the left upper extremity by von Felbert et al. [14] demonstrated therapeutic success after wIRA therapy in terms of softening sclerotic skin lesions and reducing functional impairment. The capacity to deliver wIRA locally with a radiator in children underlines the tolerability of the treatment. Evaluating the effects of wIRA on patients with sclerosing skin changes requires further research. Raynaud’s phenomenon also occurs in other connective tissue diseases, such as systemic lupus erythematosus (SLE) or dermatomyositis (DM), which might increase photosensitivity of the skin as a potential contradiction to wIRA therapy. The possible influence of local and whole-body hyperthermia on proven and possible influences on the network of the mucosal and systemic immune system has been considered [15], but needs to be further evaluated.