Posterior interosseous syndrome in acute Guillain-Barré syndrome.

Four cases presenting with posterior interosseous nerve syndrome (PIS) in the early period of acute Guillain-Barré syndrome (GBS) are described. The characteristic signs of PIS, consisting of finger extension inability, partial loss of power in wrist extension, and radial deviation during attempted wrist extension were demonstrated bilaterally. Radial nerve conduction study revealed a fall in of compound muscle potential amplitude after proximal stimulation. The signs of PIS became indistinguishable during the course of the illness; this was due to further progression of the forearm weakness veiling the syndrome in some patients, or recovery following plasmapheresis in others. Three of them were amateur sportsmen, in whom active supination-pronation of the forearm was probably responsible for this particular presentation.