Infra-red thermography in the assessment of sacro-iliac inflammation.

In a cross-sectional study designed to investigate the sensitivity of infra-red thermography in the detection of sacro-iliac regions were examined by thermography in a group of patients with ankylosing spondylitis and compared with normal volunteers and patients with other causes of low back pain. Thermograms were recorded both quantitatively via profile measurements across the sacro-iliac regions and sacrum and qualitatively via the pattern recorded by photography. Sacro-iliac disease activity was recorded clinically on the same day and was low overall in the patients examined. Thirteen of the 30 ankylosing spondylitis patients were abnormal thermographically either by profile or pattern measurements. None of the 13 patients with other causes of low back pain had increased sacro-iliac activity on thermography. None of four patients without X-ray evidence of sacro-iliitis was abnormal thermographically but there was a trend for increasing thermographic activity to be associated with increasing clinical activity. It was concluded that the thermographic technique examined was of little help in the diagnosis of early sacro-iliitis but might be more helpful in the objective serial assessment of sacro-iliitis in individual patients with active disease.