This short paper demonstrates that the Finkelstein's test in De Quervain's tenosynovitis is based on an incorrect assumption. The correct basis for a pathognomic manoeuvre in De Quervain is the provocation of tendons attrition of the first wrist dorsal compartment against their pulley which elicits pain. The Brunelli's test induces this friction and pain by asking the patient to hardly adduct the thumb with the wrist in radial deviation.