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Objective: To explore potential differences in motor nerve excitability testing (NET) variables at group levels between patients with a clinical diagnosis of polyneuropathy (PNP), which did not fulfil diagnostic criteria of conventional nerve conduction studies (NCS) and patients without polyneuropathy. Such differences could support a role for NET in increasing the diagnostic sensitivity of NCS in chronic axonal PNP. Methods: Motor NET was performed using the median nerve in patients with a clinical suspicion of PNP in addition to conventional NCS, skin biopsies, corneal confocal microscopy and structured clinical evaluation including scoring of neuropathy symptoms and signs. Results: Of the 57 patients included, 32 had PNP, half of which had NCS, which fulfilled criteria for PNP (NCS+ PNP). There were no significant differences for any of the NET variables between PNP patients with non-diagnostic conventional NCS (NCS− PNP) and patients without PNP. Rheobase was increased, and Ted (undershoot) and subexcitability were decreased in NCS+ PNP. Sural amplitude, peroneal nerve F-wave latency and tibial nerve F-wave-latency were correlated with subexcitability, and tibial nerve motor amplitude was correlated with rheobase. Conclusions: NET was correlated with conventional NCS and no differences were found between NCS− PNP patients and patients without PNP. Significance: NET does not seem to offer any additional diagnostic value in chronic mixed etiology neuropathy.

Abstract Background and aims Polyneuropathy is a common neurological disorder with many potential causes. An essential part in screening, diagnosis, and follow‐up evaluation of polyneuropathy is testing of the sensory function including vibratory sensation. The graduated Rydel‐Seiffer tuning fork and the biothesiometer have been developed to quantify vibratory sensation through detection thresholds. The aim of this study is to compare the vibration detection thresholds determined by the two instruments regarding intraindividual temporal changes, interindividual variation in healthy subjects and comparison of the diagnostic value in patients with a clinical suspicion of polyneuropathy. Methods Ninety‐four healthy subjects, 98 patients with and 97 patients without a diagnosis of polyneuropathy were included. Quantitative sensory testing including biothesiometry, structured clinical examination, and nerve conduction studies were performed three times during 52 weeks in healthy subjects and once in patients. Results There were no significant changes over time for neither the Rydel‐Seiffer tuning fork nor the biothesiometer, and both had larger between‐subject variation than within‐subject variation. Relative intertrial variability was largest for the biothesiometer. Diagnostic value (sensitivity, specificity, positive predictive value, and negative predictive value) was moderate for both methods (Rydel‐Seiffer tuning fork: 58%, 74%, 70%, 64%; biothesiometer: 47%, 77%, 68%, 59%). Interpretation The Rydel‐Seiffer tuning fork and the biothesiometer have a low test‐retest and time dependent variation. They perform almost equally as diagnostic tools in patients with suspected polyneuropathy with a tendency toward better performance of the tuning fork.