Quantitative thermal imaging in rheumatology

Inflammatory joint diseases, generally referred to as `arthritis´, are commonly indicated by increased temperature. Modern rheumatology now recognises a wide range of diseases and syndromes, which require completely different methods of treatment. Heat is one of the oldest clinical signs of inflammation, and is efficiently recorded by infrared imaging techniques. Peripheral joints of the upper and lower limbs, e.g. knees, ankles, elbows and fingers, are subject to large changes in temperature from inflammatory conditions, i.e. up to 5°C. They are easily identified when the subject is examined in an ambient of 20°C, when the normal skin surface cools, increasing the temperature contrast from the persistent hot areas. Standardisation protocols are used to derive a thermal index T.I. from a region of interest in the thermal image. The author has shown that anti-inflammatory treatment will reduce this index to near normal levels (from 7.0 to 2.0), while analgesic (pain receiving agents) will not. Since many clinical tests for arthritis show improvement after pain relief, the T.I. is a valuable objective additional test to show the effectiveness of a drug treatment. Controlled trials of steroid injection and oral non-steroid drugs have been conducted with this standardised technique. In Paget´s disease, osteitis deformans, diseased bone near the skin surface can be used to monitor the required drug treatment using calcitonin and newer drugs such as bisphosphonates. The latter is used in intermittent treatment, so the T.I. can indicate the optimum time for starting and stopping an individual course of the drug in difficult cases. Present day thermal imaging systems are reliable, and used under standardised conditions provide objective data for clinical trials in arthritis and locomotor diseases