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

Objective, To investigate the possibility that a hand distal-dorsal differe nce in temperature of greater than 1 degrees C (fingers colder than the dor sum) 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 temperatu res 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 w ater at 15 degrees C for 1 min and thermally imaged the rewarming process f or 15 min. Several variables were derived from the rewarming curve. The pro cedure was repeated within 3 days to assess reproducibility. Results. The best discriminator between PRP and SSc was found to be a dista l-dorsal difference of > 1 degrees C at 30 degrees C (p = 0.005). There is reasonable reproducibility when considering groups of patients. However, th e intra-subject standard deviations were large, indicating that measurement s for the same patient on separate visits may vary considerably. Conclusion. Our results suggest that the finding of a distal-dorsal differe nce of > 1 degrees C (cold fingers) at 30 degrees C in a patient with RP is specific for underlying connective tissue disease.