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Abstract
Background SLE arthritis is difficult to evaluate because of the sometimes-evanescent nature of the symptoms and limitations of physical exams and imaging studies. Dynamic diffuse optical spectroscopy (dDOS) can be used to assess changes in light absorption through tissues during transient venous occlusion. The optical signal reflects changes in blood perfusion and has diagnostic value in rheumatoid arthritis. The current study explored the use of dDOS in SLE arthritis.
Methods 12 SLE patients (ACR criteria) with active arthritis and 5 controls were evaluated. A dDOS sensor module was developed (figure 1a). Hemodynamic effects were obtained by inflating a BP cuff to 40 mmHg ×60 s. Light at 3 wavelengths (lambda=530, 655, 940 nm) was used to illuminate joints at 8 different points. Transmitted light intensities were measured with Si-photodetectors at 8 other positions (total 8×8×3=192 signal traces). Swollen, tender and healthy joints were examined by the same assessor.
Results SLE patients and normal controls dDOS data were available for analysis from 66 and 24 proximal interphalangeal (PIP) joints, respectively (PIPs 2–4). Best results were obtained at 530 nm with cuff inflation at 40 mmHg. A representative measurement of 3 SLE arthritis and 3 normal joints is shown in figure 1b, highlighting differences in rise and plateau time. Given the pronounced effects at lambda=530 nm, we speculate that altered vessel physiology paired with already-increased blood pooling in the affected inflamed joints resulted in quicker increase in light absorption (rise time) that is maintained longer (plateau time) compared to normal joints. The AUC for dDOS was consistent with excellent discrimination, AUC=0.8639, sensitivity=76.19, specificity=88.57 (figure 1c).
a) Two dDOS sensor module bands (1a) wrapped around a PIP joint for measurement (1b). Each band contains 4 measurement heads (black dots). Each of the measurement heads includes 3 light-emitting diodes at three different wavelengths (λ = 530 nm, 655 nm, and 940 nm, power = 2 mW) and one Si-photodetector.
Representative raw data for one healthy subject (blue) and one SLE arthritis subject (red). (1) and (2) are respectively the rise and the plateau times for a SLE patient, while (3) and (4) are respectively the rise and the plateau times for a healthy patient. It can be seen that SLE arthritis joints display a faster rise time (time needed to increase from 10% to 90% of the maximum value) and a longer plateau time than healthy joints.
Discriminant and ROC analysis which demonstrate the high specificity and sensitivity of dDOS when taking into account the rise time and the plateau time of the absorption signal (see Fig. 1b).
Conclusions dDOS can evaluate SLE arthritis with high sensitivity and specificity. Rise and plateau time of the optical traces correlate strongly with swollen and tender joint count. The advantages of dDOS are non-invasiveness, objectivity (eliminates inter-rater variability and operator dependency), low cost, and high speed of performance (~5 min per area of scanning) compared to US and MRI. dDOS has the potential to bring much-needed objectivity to the quantification of SLE arthritis.
Funding Source(s): N/A