Liquid crystal thermography: quantitative studies of abnormalities in carpal tunnel syndrome

We performed liquid crystal thermography (LCT) in 38 normal hands and in 23 hands with carpal tunnel syndrome (CTS) documented by nerve conduction studies (NCS). Two of the authors unaware of the clinical situation read the 2 palmar thermograms taken at a 5-minute interval. They determined the absolute temperatures of the tip of digit 1 (D1), D2, D3, D4, D5, and of the thenar and hypothenar eminences. We calculated the temperature differences (absolute values throughout) between any 2 of these 7 sites, and computed the median index (MI = [D1 - D2] + [D1 - D3] + [D2 - D3]). Comparison of the control and CTS groups revealed greater temperature differences in CTS between D1 - D3, D1 - D4, D3 - D5, D4 - D5, and MI. There was a marked overlap between the 2 groups. Comparison of individual CTS hands with controls revealed definite thermographic abnormalities in 0 of 9 hands with mild NCS abnormalities, and in 7 of 14 hands with marked NCS abnormalities. These findings indicate that the sensitivity of LCT in CTS is low compared with NCS, and previous favorable reports concerning thermography in CTS may have been due to lack of control series or absence of quantitation.