Clinical rheumatology, 1989, 8, N ~ 2 225-230 Infra-red surface thermography. Evaluation of a new radiometry instrument for measuring skin temperature over joints M.H. ARNOLD, S.J.L. PRESTON, E.M. BELLER, W.W. BUCHANAN* The Florance and Cope Professorial Department of Rheumatology and Sutton Re- search Laboratory, The Royal North Shore Hospital of Sydney, St. Leonards, New South Wales, 2065, Australia, *On sabbatical leave from McMaster University, Hamilton, Ontario, Canada. SUMMARY A study is reported of the evaluation of a new portable, light-weight, infra- red thermometer, for the measurement of the skin temperature over joints. A high degree of reproducibility was observed, but no increase in heat was found over selected rheumatoid joints. The instrument wilt prove useful in detecting temperature changes in disease states where the changes are considerable, and where the ambient temperature can be strictly con- trolled. Key words : Infra-Red Thermography, Radiometry, Rheumatoid Arthritis, Clinical Trials. INTRODUCTION Although calor is one of the four cardinal signs of inflammation as described by Celsus (35BC-7AD), its quantitation in inflammato- ry joint disease has proven difficult. A variety of methods have been employed including in- fra-red thermography (1) and contacting skin sensors, such as thermistors and thermocou- ples (2) with varying degrees of success. These methods have the advantage of being free of subjective bias(l), and infra-red thermogra- phy can be quantitated (3) to produce a ther- mographic index for a number of joints (4). Infra-red thermography has also been shown Received 29 September 1988, Revision-accepted 20 Decembre 1988 Correspondence to : Dr. M. H. ARNOLD The Florance and Cope Professorial Department of Rheumatology, The Royal North Shore Hospital of Syd- ney, St. Leonards, New South Wales, 2065 Australia. to correlate with the anatomical localisation of synovial hyperaemia (5), cathepsin D re- lease (6), volume and protein content (7) and number of inflammatory cells in synovial fluid (8) and synovial blood flow as measured by radioactive xenon and plethysmography (1). There is no correlation, however, with ar- throscopic appearances (9). Infra-red ther- mography has been shown to be sensitive to changes occurring with nonsteroidal anti-in- flammatory drug therapy (10,11), intra-artic- ular corticosteroids (1,12,13), and radioac- tive Yttrium (14,15). The major disadvantages of thermo- graphy are that it requires expensive equip- ment (16), rigid control of ambient temper- ature (1,17), a period of patient equilibration to the ambient temperature (18), and standar- dised positioning of the patient (1). Further- more, the initial cost, lack of portability of the equipment, and the expense of operating