Relation between changes in long-latency stretch reflexes and muscle stiffness in Parkinsonʹs disease – comparison before and after unilateral pallidotomy

Objective: To study the effects of posteroventral pallidotomy on both the size of long-latency stretch reflex (LLR) and the muscle stiffness in the wrist flexor muscles. Patients and methods: Eleven consecutive patients (right-handed, 6 men and 5 women) underwent left-side microelectrode-guided pallidotomy. The LLR of the contralesional forearm was studied at baseline and 2–3 months after surgery while patients continued to take their optimal medical regimens (‘on’ period). Patients were instructed not to respond to the perturbation (passive mode) or to oppose the mechanical extensor perturbation (active mode). Results: The stretch reflex evoked by extension perturbations of the wrist consisted of a short-latency reflex (M1) and an LLR (M2). Pallidotomy had no effects on the size of M1 components in both passive and active mode and on that of M2 component in the passive mode, however, it significantly reduced M2 component in the active mode (P<0.05). The inherent muscle stiffness over 60 ms period of mechanical stretch was not influenced by pallidotomy in any experimental condition (preoperative vs. postoperative or passive mode vs. active mode). The hand displacement following M2 component increased significantly after pallidotomy in both passive (P<0.005) and active mode (P<0.05). The inverted value of the displacement following M2 component correlated with the size of M2 component (r=0.60, P<0.001). Conclusions: Pallidotomy decreased the transcortical reflex gain, probably at cortical level, and consequently reduced muscle stiffness.