Mechanical detection and pain thresholds: comparability of devices using stepped and ramped stimuli.

Quantitative sensory testing is used to assess somatosensory function in humans. The protocol of the German Research Network on Neuropathic Pain (DFNS) provides comprehensive normative values using defined tools; however, some of these may not be feasible in low-resource settings.
Objectives: To compare the standard DFNS devices for assessment of mechanosensory function to a low resource tool, the Sorri-Bauru-monofilaments.
Methods: Mechanical detection thresholds (MDT), pain thresholds (MPT), and suprathreshold pinprick ratings (pain sensitivity: MPS) were measured over cheek, hand dorsum, and fingertip in 13 healthy subjects (7 female, aged 21-44 years). Mechanical detection threshold was assessed with DFNS standard glass monofilaments (0.25-512 mN, 0.5 mm tip) and nylon monofilaments (Sorri-Bauru; 0.5-3000 mN). MPT was assessed with DFNS standard cylindrical probes (8-512 mN, 0.25 mm tip), Sorri-Bauru monofilaments, and with ramped stimuli using an electronic von Frey aesthesiometer (10 mN/s or 100 mN/s, 0.20 mm tip). MPS was measured in response to stepped and ramped pinpricks (128 and 256 mN).
Results: Mechanical detection thresholds were the same for DFNS and Sorri-Bauru monofilaments. For MPT, Sorri-Bauru filaments yielded lower values than PinPricks over face but not hand. Pain thresholds were higher at all test sites for ramped than stepped pinpricks ( P < 0.01). Suprathreshold ratings were lower for ramped than stepped pinpricks ( P < 0.05).
Conclusion: Sorri-Bauru filaments are acceptable substitutes for DFNS standards in estimating tactile sensitivity, but are not consistent with standard probes for pinprick sensitivity because of their nonstandardized tips. Ramped stimuli overestimated MPT and underestimated MPS due to reaction time artefacts and therefore need their own normative values.
Competing Interests: Dr. Lockwood, Dr. Maier, Dr. Schmitter, Dr. Haroun and Dr. Pfau have no conflict of interest to declare. Dr. Rice reports personal fees from Imperial College Consultants, other from Spinifex, outside the submitted work; in addition, Dr. Rice has a patent WO 2005/079771 pending, and a patent WO2013/110945 pending. Dr. Treede reports grants from DFG, during the conduct of the study; grants from European Union and EFPIA companies, grants from Bayer, personal fees from Bayer, Grünenthal, GSK, Sanofi, outside the submitted work; in addition, Dr. Treede has a patent DE 103 31 250.1-35 with royalties paid to MRC Systems. Dr. Vollert reports personal fees from Casquar, outside the submitted work.Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.
(Copyright © 2020 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of The International Association for the Study of Pain.)