Asymmetry of neuroleptic-induced rigidity: development of quantitative methods and clinical correlates.

Twenty-six medicated schizophrenic patients and 14 normal controls underwent laboratory assessment for the presence and asymmetry of neuroleptic-induced rigidity to evaluate the sensitivity, reliability, and validity of a quantitative procedure. Measures of muscle stiffness were made in the upper extremities. Results indicated that 65% of the patients exhibited pathological rigidity. Moreover, 76% of these patients exhibited asymmetric rigidity, while the remaining 24% exhibited bilateral symptoms. Newly treated patients exhibited a greater laterality of rigidity toward the right side compared with patients who were on stable treatment regimens for at least 3 months. Since parkinsonism reflects dopamine receptor blockade by neuroleptic medication, probably in the striatum, we suggest that the lowered susceptibility of the right striatum to drug-induced parkinsonism supports the hypothesis that striatal dopaminergic activity may be asymmetric and more marked in the right striatum among recently treated patients.