Summary: Despite recent advances in the understanding of gait disorders in the elderly, little is known about the precise neurochemical mechanism that underlies such conditions. To determine the neurochemical basis of freezing, an apomorphine test was carried out in 21 patients with freezing associated with Parkinson's disease (11 patients) or with a higher level gait disorder (10 patients). The test was positive in parkinsonian patients with freezing exclusively during "off" periods ([nu] = 9). In these cases, there were a parallel improvement in motor function. The remaining 12 patients (two with Parkinson's disease and unpredictable freezing, eight with subcortical dysequilibrium, and two with isolated gait-ignition failure) failed to improve throughout the test period. We conclude that freezing may be the consequence of different neurochemical disturbances, although a common neural substrate cannot be excluded.
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