Sympathetic skin response in primary Raynaud's phenomenon

The pathogenetic hypotheses of Raynaud's phenomenon include increased activation of sympathetic noradrenergic nerves controlling muscle tone of digit arteriolar walls. Because acral sympathetic fibres contain vasoactive adrenergic and cholinergic fibres for sweat glands, we tested cholinergic sympathetic fibre function in primary Raynaud's phenomenon (PRP) patients by sympathetic skin response (SSR).

Twenty-six consecutive patients (19 women, 7 men, mean age 37.8 years) with PRP were enroled prospectively. SSR was obtained by random electrical stimulation of the left ulnar nerve at the wrist recording from the palm (PSSR), third (M3SSR) and fifth fingers (U5SSR) on the right side. For each subject latency of shortest response, area of largest response and grand mean latencies and areas of 12 consecutive responses were calculated. The differences between patients and a control group (15 women, 6 men, mean age 38.9 years) were calculated. SSR habituation was also compared between patients and controls.

PSSRs were recorded in all patients and no difference in any PSSR parameter was found between patients and controls. U5SSRs and M3SSRs were absent in two patients. Grand mean area and mean of largest M3SSRs and U5SSRs were significantly lower in patients than in controls. Grand mean latency and mean of shortest M3SSRs and U5SSRs were significantly slower in patients than in controls. M3 and U5SSRs habituated less in patients than in controls.

Dysregulation of cholinergic sympathetic fibres innervating the fingers was found in PRP. Abnormal peripheral mechanisms may be the cause. Since SSR habituation was also not normal, even central mechanisms may be implicated.