Diagnostic yield by testing small fiber function in patients examined for polyneuropathy

We assessed the diagnostic yield of adding quantitative sensory testing to the standard work-up for polyneuropathy in unselected patients. All patients aged 18 to 70 years referred to our department for electrodiagnosis with a tentative diagnosis of polyneuropathy and symptoms complying with predefined criteria were included in the study. We performed near nerve conduction studies in 4 nerves and determined heat and cold detection thresholds on hand and foot with a Thermotest (Somedic AB, Sweden). In order to uncover CNS diseases, somatosensory-evoked potentials were recorded in patients with abnormal quantitative sensory testing and normal nerve conduction studies. A total of 198 patients completed the study and 149 were considered to have polyneuropathy. Twenty-five patients remained undiagnosed and in 24 patients, other diseases were responsible for the symptoms. Of the patients with either polyneuropathy or no other diagnosis, 76% (n = 174) had abnormal nerve conduction. Abnormal cold sensation, heat sensation or abnormality in at least 1 of these and normal nerve conduction were found in 14, 12 and 17 patients. Of the 174 patients, 86% (95% CI 80-90%) had an abnormality in at least 1 of the tests (i.e. abnormal nerve conduction and/or abnormal quantitative testing of temperature sensation). In conclusion, quantitative testing of temperature sensation improves the diagnostic yield in patients examined for chronic polyneuropathy.