Sympathetic Skin Response: Normal values evoked by stimulation at the supraorbital nerve

The Sympathetic Skin Response (SSR) is used to quantify autonomic disturban ces. Its value in diagnosing pathology of the efferent pathways is often li mited by loss of afferent conduction distorting the response. This problem does not occur with stimulation at the supraorbital nerve, as the supraorbi tal nerve rarely is affected by polyneuropathy or transverse syndromes. The article describes normal values evoked by stimulation at the supraorbital nerve in 36 subjects aged 49.9 +/- 12.0 years. In 26 subjects, the response to stimulation at the tibial nerve was evaluated as well. The literature c oncerning normal values evoked by stimulation at the supraorbital nerve is summarised in a table. With stimulation at the supraorbital nerve and recor ding from the hands, onset latency was 1473 +/- 276 ms and peak latency 249 1 +/- 510 ms. The amplitudes did not follow a normal distribution; the medi an amplitude was at 0.91 mV with a minimum of 0.19 mV and a maximum of 5.74 mV. The side-to-side quotient of the amplitudes was 78 +/- 10% (expressed as the smaller amplitude in percentage of the larger). With stimulation at the tibial nerve, onset latency was at 1571 +/- 333 ms and peak latency at 2783 +/- 741 ms. Variability was slightly higher with stimulation at the ti bial nerve: 21% (onset latency) and 26% (peak latency) vs. 19% and 21% with supraorbital stimulation. Criteria for abnormal SSR are in order of their reliability: (1) absence of response, (2) onset latency > mean + 2,5 SD, an d (3) side-to-side quotient of the amplitudes < 50%. Stimulation at the sup raorbital nerve is a reliable method of central stimulation which excludes the influence of afferent disturbances and thus allows better localisation of pathology of the efferent sudomotor pathways.