Paradoxical wrist flexion: A new test to detect functional weakness of the upper limb

Positive signs are essential for the diagnosis of functional neurological disorders (FND). The author described a new positive sign to diagnose functional weakness (FW), "paradoxical wrist flexion", and tested its validity.

The test comprised Medical Research Council (MRC) examinations of wrist flexion in two different limb positions, one with the wrist maximally flexed (wrist flexion in the flexed position; WFfl) and the other with the wrist in the neutral position (wrist flexion in the extended position; WFex). In "organic" weakness (OW), WFfl should be stronger than WFex according to the dynamic theory. Paradoxical wrist flexion was judged positive when the MRC score for WFfl was lower than that for WFex. A higher MRC score for WFfl than WFex was considered an "organic sign" for wrist flexion. We retrospectively enrolled patients with FND or other "organic" neurological disorders, who presented with wrist flexor weakness with an MRC score of 4.

Twenty-four patients with FW and 40 patients with OW were enrolled. Paradoxical wrist flexion was positive in 16 patients with FW and in no patients with OW, i.e. 67% sensitivity and 100% specificity. The "organic sign" for wrist flexion was positive in no patients with FW and in 35 patients with OW, i.e. 88% sensitivity and 100% specificity.

Paradoxical wrist flexion is useful for the detection of nonorganic paresis. The background theory is that an active movement is more severely affected in FW than a passive movement when maintaining a limb position.