PHYSIOLOGICAL-STUDIES OF SPINAL INHIBITORY CIRCUITS IN PATIENTS WITH STIFF-PERSON SYNDROME

Objective: To test inhibitory spinal circuits in patients with stiff-p erson syndrome (SPS). Background: Patients with SPS have fluctuating m uscle stiffness and spasms, and most have antibodies against GABAergic neurons. We predicted they would also have abnormalities of spinal GA BAergic circuits. Design/Methods: Physiologic methods using H-reflexes were used to test reciprocal inhibition in the forearm and thigh, vib ration-induced inhibition of flexor carpi radialis and soleus H-reflex es, recurrent inhibition, and nonreciprocal (Ib) inhibition of soleus H-reflexes. Results: Vibration-induced inhibition of H-reflexes was di minished in eight of nine patients tested, but the presynaptic period of reciprocal inhibition was normal in most patients. Bath circuits ar e presumed to involve presynaptic inhibition and GABAergic interneuron s. Presumed glycinergic circuits, including the first period of recipr ocal inhibition and nonreciprocal (Ib) inhibition, showed occasional a bnormalities. Recurrent inhibition was normal in all five patients tes ted. Conclusion: Differences between the two presumptive GABAergic cir cuits may indicate that not all populations of GABAergic neurons are u niformly affected in SPS. The involvement of presumptive glycinergic c ircuits in some patients could point to impairment of nonGABAergic neu rons, unrecognized involvement of GABAergic neurons in these inhibitor y circuits, or, more likely, alterations of supraspinal systems that e xert descending control over spinal circuits.