Validity of the Drift without pronation sign in conversion disorder

Background: Conversion disorder (CD) is a psychiatric disorder, yet the diagnosis cannot be established without the expertise of a neurologist, as distinguishing a functional from an organic symptom relies on careful bedside examination. Joseph Babinski considered the absence of pronator drift as a 'positive sign' for hysterical paresis but the validity of this sign has never been evaluated. The aim of this study was to examine the sensitivity and specificity of the drift without pronation sign. Methods: Twenty-six patients with unilateral functional upper limb paresis diagnosed with CD (DSM-IV) and a control group of 28 patients with an organic neurological condition were consecutively included. The arm stabilisation test was performed with arms stretched out in full supination, fingers adducted, eyes closed for 10 seconds. A positive drift without pronation sign was defined by the presence of a downward drift without pronation. Results: All CD subjects (100%) displayed a positive sign when only 7.1% of organic subjects did (Fisher's p < 0.001). The sign yielded a sensitivity of 100% (95% CI: 84%-100%) and a specificity of 93% (95% CI: 76%-98%). Conclusion: The observation of a drift without pronation sign is specific for Conversion Disorder and can be of help in making a quick distinction between organic and functional paresis at the bedside.