Sparing of the thumb in Raynaud's phenomenon

To conduct a prospective study to determine which digits are affected (and whether the thumb is spared or not) in a cohort of patients with RP as assessed by symptoms and thermography and to determine whether the degree of thumb involvement differs between primary (PRP) and secondary Raynaud's phenomenon (SRP).

This was a cross-sectional study of 44 patients with RP. The following characteristics were recorded to allow comparisons between digits: symptoms of RP in each digit (graded on a scale of 'never', 'sometimes' and 'always' affected during an attack of RP) and thermography at 23 degrees C. A distal-dorsal difference (DDD) in temperature at 23 degrees C of -1 degree C or less was considered to be clinically relevant.

Symptom scores in the thumb were significantly better, i.e. less severe than in each finger (P < 0.001). As only three participants had any finger better than the thumb, there was no power to compare whether the thumb was spared more in PRP compared with SRP. Mean DDD was significantly higher (i.e. better) in the thumb compared with each finger (P < 0.001). Although DDD scores were higher in PRP compared with SRP (P = 0.01), there was no evidence that the relative effect of the thumb differed between the two groups (P = 0.26).

Our findings confirm that the thumbs are spared in RP, both primary and secondary, as demonstrated by both symptoms and thermography. The reasons for sparing of the thumb were not addressed in this study but raised questions regarding pathophysiology.