The "distal-dorsal difference" as a possible predictor of secondary Raynaud's phenomenon.

OBJECTIVE: To investigate the possibility that a hand distal-dorsal difference in temperature of greater than 1 degree C (fingers colder than the dorsum) at a room temperature of 30 degrees C is a good predictor of secondary Raynaud's phenomenon (RP).
METHODS: We imaged the hands of patients with primary Raynaud's phenomenon (PRP) and systemic sclerosis (SSc) using a thermal camera at room temperatures of 23 and 30 degrees C. From these images we measured the distal-dorsal difference in temperature for all fingers excluding the thumbs. At a room temperature of 23 degrees C we also performed a cold challenge test using water at 15 degrees C for 1 min and thermally imaged the rewarming process for 15 min. Several variables were derived from the rewarming curve. The procedure was repeated within 3 days to assess reproducibility.
RESULTS: The best discriminator between PRP and SSc was found to be a distal-dorsal difference of > 1 degree C at 30 degrees C (p = 0.005). There is reasonable reproducibility when considering groups of patients. However, the intra-subject standard deviations were large, indicating that measurements for the same patient on separate visits may vary considerably.
CONCLUSION: Our results suggest that the finding of a distal-dorsal difference of > 1 degree C (cold fingers) at 30 degrees C in a patient with RP is specific for underlying connective tissue disease.