At which stage of sensory recovery can a tingling sign be expected? a review and proposal for standardization and grading

The phenomenon of paresthesia elicited by percussion of regenerating axons is usually associated with Tinel and Hoffmann, who both described it separately in 1915, although the same phenomenon had been described previously, in 1909, by Trotter and Davies. This sign is used widely, but its standardization is almost completely lacking, its grading is seldom used, and its reliability or validity is scarcely mentioned in the literature. The authors present a method of standardization and grading of the tingling response by means of a vibrostimulator, which permits precise localization of the trigger point and uniform stimulation. The tingling response may then be classified according to its location and to the magnitude threshold at which the response is triggered. In the distal part of the nerve, after neurotmesis repair, the tingling sign is graded T++ (tingling after a weak stimulus) and T+ (tingling only after a strong stimulus). At the site of the injury, the initial tingling sign is graded T0. The sign is graded T00 if, independent of recovery, a slight positivity persists at the initial site of injury. Grading of sensory recovery is poorly standardized, since different authors use different variations and modifications of existing classifications. The authors of this paper present a cross-matching of these classifications and propose to use Dellon's modification of Zachary's classification in eight stages, from S0 to S4. A discussion of the probability of eliciting a tingling sign during axonal regeneration concludes that the clinician can expect to trigger a T+ + sign when sensory recovery evolves from stage S0 to stage S1 and should no longer expect to trigger one when sensory recovery improves from stage S2+ to stage S3.