Dermal Joint Temperature to Screen For Radiographic RA Joint Damage

Elevations in dermal temperature appear to accurately identify patients with rheumatoid arthritis (RA) who are at increased risk of developing radiographic joint damage. Furthermore, increased joint temperature was shown to have both high sensitivity and specificity for predicting new joint damage in the next year after screening.  These findings were recently published in Arthritis Care & Research. 

The recognition that outcomes are improved with early, targeted treatment has prompted a search for cost-effective, accurate tools to identify patients who are at high risk for progressive disease. The dermal thermometer was identified as a relatively low cost tool that is simple to administer and provides objective data, thereby being a good screening tool candidate if validated. 

“This study was a proof-of-concept design, not to compare multiple scoring systems evaluating RA but to determine if joint skin temperature identifying individuals with active inflammation had prognostic significance,” the authors stated.

An observational, parallel-group study was designed, analyzing data from patients with seropositive (rheumatoid factor-positive and/or cyclic citrullinated peptide antibody-positive) RA who were being treated at a single outpatient rheumatology clinic between 2009 and 2014. In these patients, RA was diagnosed according to the 1987 American College of Rheumatology (ACR) revised criteria and the 2011 and the European League Against Rheumatism criteria.   

Patients were eligible for inclusion into the study if they were receiving stables doses of methotrexate (MTX, 20-25 mg/week) for at least 3 months. Use of another biologic or disease-modifying antirheumatic drug (DMARD) prior to enrollment into the cohort or during the year of observation precluded inclusion into the study. MTX was continually administered through the observation year. Patients eligible for the study could also be on up to 5mg/day of prednisone and nonsteroidal antiinflammatory drugs. 

Twenty-five healthy patients were recruited to serve as normal temperature controls. All patients underwent a physical examination, review of medical history, determination of erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) levels, and hand/wrist radiographs. The forehead was selected as representative of central body temperature since less variations are seen at that site as compared to the ear.  A digital thermometer was first placed on the forehead and then on either the left wrist (selected as default) or the joint identified by patients as being most painful. 

Those patients with RA who did not receive further biologics or other DMARD therapy within the year were eligible for comparative follow-up hand/wrist radiographs. If joint dermal temperatures were above central body temperature measured at the forehead they were included sequentially into the “hot-joint cohort” (n=104).  If joint temperatures were below forehead temperatures, patients were sequentially included into the “cool-joint cohort” (n=104).

A total of 208 patients with RA were included in the data analysis. Those patients with hot joints were more likely to have statistically significant increases in modified Sharp/van der Heijde scores (SHS, 8.7 ± 6.2; 95% CI 6.6–10.8) when compared to patients with cool joints (2.5 ± 1.4, 95% CI 2.0–3.0; P < .001).  This corresponded with an almost 4-fold greater risk of new radiographic joint damage when compared to those with cool joints.

These patients were also more likely to be younger at baseline and had high ESR levels than those with cool joints (P < .001 for both).  Patients taking MTX were also more likely to have cool joints than those not taking MTX. 

New radiographic joint damage (SHS ≥5). was detected in 77 out of 104 patients (74%) in the hot-joint cohort. In comparison, only 7 out of 104 patients in the cool-joint cohort had bone or cartilage damage. The hot-joint cohort had a 1.06 ± 0.69 ºF (mean ± SD) increase in dermal temperature above forehead central body temperature.  The calculated sensitivity of joint temperature was 92% and the specificity was 78%.

These findings suggest that “dermal temperature can quickly and accurately identify individual, specific RA patients at high risk for further destructive change… [as patients] with hot joints had a nearly 4-fold higher risk of new radiographic damage than those with cool joints, and more than 70% of patients with hot joints had clear radiographic evidence of new destructive radiographic joint damage 1 year later,” the authors concluded.  

It was further suggested that cytokine production may be causing increases in dermal temperature over inflamed joints with radiographic progression.

Summary and Clinical Applicability

Dermal temperature may accurately specify patients with RA who are increased risk of developing radiographic joint destruction.  

“Using a simple clinical tool to identify patients… may also positively impact patient understanding, acceptance, and adherence, and, unlike other tools, can quickly and easily be used to ascertain joint temperature as part of standard vital signs in less than 1 minute, with no added cost,” the authors concluded.

Limitations and Disclosures

• This study was a smaller pilot study conducted at a single center and findings need to be replicated across different settings
• A single hot joint measurement was selected in this study; the clinical utility of measuring temperatures at multiple joints should be investigated as there may be an increase in screening specificity
• A predetermined cut-off temperature point, created using receiver operating characteristic curves to determine sensitivity and specificity, that provides a discreet numerical value that clinicians can use to easily classify patient risk should be investigated

Reference

Greenwald M, Ball J, Guerrettaz K, Paulus H. Using dermal temperature to identify rheumatoid arthritis patients with radiologic progressive disease in less than one minute. Arthritis Care Res (Hoboken). 2016;68(8):1201-5.

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