Normal threshold values for a monofilament sensory test in sural and radial cutaneous nerves in Indian and Nepali volunteers.

Summary Themonofilamenttest(MFT)isareliablemethodtoassesssensorynervefunction in leprosy and other neuropathies. Assessment of the radial cutaneous andsural nerves, in addition to nerves usually tested, can help improve diagnosisand monitoring of nerve function impairment (NFI). To enable the detection ofimpairments in leprosy patients, it is essential to know the monofilament thresholdof these two nerves in normal subjects. The radial cutaneous, sural, ulnar, medianand posterior tibial nerves of 245 volunteers were tested. All nerves were tested atthree sites on both left and right sides. Normal monofilament thresholds werecalculatedpertest-siteandpernerve.Weassessed490radialcutaneousand482suralnerves. The normal monofilament was 2g (Filament Index Number (FIN) 4·31) forthe radial cutaneous and 4g (FIN 4·56) for the sural nerve, although heavy manuallaborers demonstrated a threshold of 10g (FIN 5·07) for the sural nerve. For medianand ulnar nerves, the 200mg (FIN 3·61) filament was confirmed as normal whilethe 4g (FIN 4·56) filament was normal for the posterior tibial. Age and occupationhave an effect on the mean touch sensitivity but do not affect the normal thresholdfor the radial cutaneous and sural nerves. The normal thresholds for the radialcutaneousandsuralnervesaredeterminedasthe2g(FIN4·31)andthe4g(FIN4·56)filaments, respectively. The addition of the radial cutaneous and sural nerve tosensory nerve assessment may improve the diagnosis of patients with impairedsensory nerve function.