Thermal imaging has been applied to detect possible temperature variations in various rheumatic disorders. This study sought to determine whether rheumatoid arthritis (RA) patients without active synovitis in their hands exhibit different baseline thermographic patterns of the fingers and palms when compared to healthy individuals. Data from 31 RA patients were compared to that of 51 healthy controls. The RA patients were recruited upon confirmed absence of synovitis by clinical examination and musculoskeletal ultrasound.
Participants underwent medical infrared imaging of the regions of interest (ROIs). Significant differences were found between the mean temperatures of the palm regions (29.37 °C (SD2.2); n = 306) and fingers (27.16 °C (SD3.2); n = 510) of the healthy participants when compared to the palm regions (31.4(SD1.84)°C; n = 186) and fingers (30.22 °C (SD2.4); n = 299) of their RA counterparts (p = 0.001), with the latter group exhibiting higher temperatures in all ROIs.
Logistic regression models confirm that both palm and finger temperature increase significantly in RA without active inflammation. These innovative findings provide evidence that baseline thermal data in RA differs significantly from healthy individuals. Thermal imaging may have the potential to become an adjunct assessment method of disease activity in patients with RA.
Thermography is an emergent technology that has the potential to become an important clinical tool in various fields of medicine, since disease processes can vary the magnitude and pattern of emitted heat in the afflicted person1. Besides the obvious effects that vascular perfusion, or sometimes the lack of it, through human tissue may have on body heat emissivity, inflammation also has the potential to alter such heat patterns and magnitude since warmth and localised hyperaemia, are two important components of the inflammatory process2.
Persistent synovitis is the hallmark manifestation of RA. Clinical signs of RA include pain and swelling3, which often progress to produce deformity unless early aggressive therapy is initiated4. Structural damage is associated with irreversible pain and functional impairment5, with synovitis being one of the most important predisposing factors preceding structural damage6.
In the early stages of the disease, patients may present without apparent joint swelling, making timely detection difficult. Although wider availability of musculoskeletal ultrasound has enabled earlier detection of synovitis, it still has limitations such as access, time required to perform the investigation and being operator dependent3. Nonetheless, to date ultrasound has been proven to have the capacity to predict subsequent progression of structural damage following diagnosis of synovitis7.
The application of thermography to quantify the effect of disease processes on heat emissivity has been studied in a wide range of conditions ranging from assessment of the diabetic foot to breast cancer1. However, evidence of its role in the assessment of inflammation in RA is lacking. Published research to date is characterised by small sample sizes and a lack in methodological consistency. Furthermore, there is conflicting evidence in literature regarding the applicability of thermography in RA.
Whilst a study reports that while there may be a role for thermography in assessment of larger joints, it does not appear to be an effective modality for the small joints of the hand8, another study reported that the authors demonstrated that infrared can identify the presence of rheumatoid arthritis and the best joints to measure were the metacarpals of the hand, and more specifically the 2nd and 3rd joints3. This creates an anomalous situation in this imaging field and, more importantly, currently there is no description of the thermographic characteristics of rheumatoid hands and wrists, which would form the basis on which such studies can be built upon.
The aim of the study was to determine whether patients with established RA but no clinical signs and symptoms of inflammation including pain, swelling and tenderness, would exhibit different thermographic patterns when compared to healthy controls. Consequently this would permit the development of an innovative, noninvasive, inexpensive and more reproducible method to detect the presence of inflammation in RA.
The RA group consisted of 29 females and 2 males (mean age 60.19years (SD = 12.38); mean height 1.57 m (SD = 0.09); mean weight 75.7 kg (SD = 21.53)). The Healthy group consisted of 51 participants (12 males and 39 females with a mean age of 36years (SD = 12.24), mean weight 70.5 kg (SD = 14) and mean height of 164.5 cm (SD = 9.7)).
Mean duration of RA amongst the study group was 15.2years (SD = 11.9). 29 participants were on Disease Modifying Drugs (DMARDS); out of these, 5 were also on Biologics, 4 were also on glucocorticoids, 2 were also taking NSAIDs, whilst 4 were on DMARDS + glucocorticoids + biologics. 13 were on DMARDS alone. Another participant was on DMARDS + NSAIDs + analgesics. Another participant was on Biologics alone whilst another was on Biologics + Glucocorticoid treatment.
Univariate statistical tests
No significant differences in mean temperatures were found in the 3 ROIs of the palms of both the healthy and RA group when analyzed individually, both for left and right when imaged from the palmar regions; also between the 5 fingers, of both left and right when imaged from palmar regions, of both groups (Table 1).
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