Abduction finger sign: a new sign to detect unilateral functional paralysis of the upper limb

Objective of this study is testing a new sign to differentiate functional from organic paralysis of the arm. Thirty-six healthy subjects, ten patients with acute functional paralysis of one arm and eleven patients with acute organic paralysis of one arm were enrolled. The test consisted of abduction finger movements of one hand against resistance with a maximal sustained contraction to detect synkinetic abduction finger movements of the contralateral hand. For both hands, contralateral hand synkinesias were observed in healthy subjects. The task performed with the unaffected hand evoked synkinesias of the presumed affected hand in functional patients, but did not evoke synkinesias of the affected hand in organic patients. The abduction finger test had 100% sensitivity and specificity in distinguishing functional from organic paralysis of the upper limb in this cohort of patients. The abduction finger sign may be a reliable bedside test to discriminate functional from organic arm paralysis.