Functional assessment of A delta and C fibers in patients with Fabry's disease

The pathophysiology of neuropathic pain in Fabry's disease (FD) is still largely unknown. Seven FD patients were studied by laser evoked potentials (LEPs) to assess the function of the A delta and C fibers. Laser pulses were delivered on the skin of the hand and perioral region at painful intensity to record LEPs related to A delta-fiber inputs and at nonpainful intensity to obtain LEPs related to C-fiber inputs. When the perioral region was stimulated, a vertex positive component was recorded with a mean latency of 260.3 ms and 376 ms after A delta- and C-fiber stimulation, respectively. The mean A delta-LEP amplitude was significantly lower in FD patients (N1/P1 mean values were 2.8 microV and 4.5 microV after hand and face stimulation, respectively, compared to 4 microV and 8.9 microV for controls; N2/P2 mean values were 8.2 microV and 11.1 microV after hand and face stimulation, respectively, and 16.7 microV and 22.3 microV in controls). Unlike the healthy subjects, 6 FD patients, suffering from neuropathic pain, showed a late positive potential related to C-fiber function (mean latency, 377.1 ms) also after facial stimulation at painful intensity, suggesting a relative overflow of C-fiber input, which may be relevant in the pathophysiology of pain in this disease.