Introduction and aim:
Peripheral neuropathy affects approximately 8% of the population aged ≥55 years. Nerve conduction studies (NCSs) are used, together with historical and clinical findings, to diagnose this condition. The interpretation of NCS findings depends on the availability of appropriate reference data but there have been surprisingly few robust efforts made to obtain these; most studies involve <250 participants and the data are subject to significant inter-study variation. In current practice a lower normal limit of 10 µV for the sural sensory response is applied. The aim of this study was to determine reference ranges for sural responses in a control population, by age and sex.
A retrospective review was undertaken of 1280 people (men 38,4%, median age 58, range (6-95) years) who attended the Clinical Neurophysiology Department at the Royal Free Hospital, London, between 1 January to 31 December 2017, and underwent sural nerve studies. A total of 381 were excluded for various reasons, including leg oedema and surgical dressings. Of the remaining 899 participants, 314 had clinical and NCS evidence of peripheral neuropathy. The other 585 participants had no findings consistent with a diagnosis of peripheral neuropathy, radiculopathy or myopathy. Receiver operating characteristic (ROC) curve analysis was used to determine thresholds, which distinguished participants with and without peripheral neuropathy, by sex and age.
Significant differences were observed in sural nerve thresholds, by sex and age (Table 1).
Table 1: Sural nerve thresholds in reference population, by sex and age
Age (years), Thresholds (µV) for: Total population, Men, Women
(All), 9, -, -
(≤58), 12, 10, 13
(>58), 8, 7, 9
(>18 to ≤30), 16, 14, 17
(>30 to ≤50), 13, 13, 14
(>50 to ≤70), 8, 7, 10
Sural nerve threshold are influenced by sex and age. Application of the current the NCS threshold of 10 µV could result in under diagnosis of peripheral neuropathy in younger women and over diagnosis in older men. Practitioners should be aware of these factors in the interpretation of NCS results for the diagnosis of neuropathy.