Plasma exchange in stiff-man syndrome

Stiff-man syndrome (STS) is a rare neurological disorder characterized by involuntary axial and proximal limb rigidity and continuous motor unit activity on electromyography (EMG). Autoantibodies to glutamic acid decarboxylase (GAD) present in 60% of the patients are implicated. We report on the use of plasma exchange (PE) in 2 patients with STS whose serum and cerebrospinal fluid were negative for GAD autoantibodies. One patient showed minimal clinical improvement following PE while the second reported subjective improvement, but not any different from that with medications. Based on the results of PE in our patients, it seems that those who are autoantibody negative are less likely to respond. Whether a more aggressive approach to PE will be beneficial remains speculative.