Characterization of Neuropathic Pain in Primary Sjogren's Syndrome with Respect to Neurophysiological Evidence of Small-Fiber Neuropathy

Objective. To determine whether clinical features of neuropathic pain differ with respect to the presence of small-fiber neuropathy (SFN) in patients with primary Sjogren's syndrome (pSS). Methods. We compared the clinical presentation of neuropathic pain between 15 patients with pSS and SFN detected by neurophysiological tests (laser-evoked potentials, cold and warm detection thresholds, sympathetic skin responses, and electrochemical skin conductance) and 15 patients with pSS but no neurophysiological evidence of SFN. Results. The patients with SFN had more intense squeezing and pressure sensations and more frequent dynamic mechanical allodynia (pain provoked by brushing) than the patients without SFN. Restless leg syndrome was also more frequently observed in patients with SFN, who had pain aggravated at rest that improved by moving. Conclusions. These findings are in favor of the sensitization of relatively spared large A beta-fibers and second-order nociceptive neurons in patients with SFN. On the other hand, burning sensations, which rather reveal sensitization of small nociceptive fibers, were observed whether SFN was present or not. Thus, some discriminating clinical features may help to suggest the presence of SFN in patients with pSS and chronic neuropathic pain.