[The "off-on" phenomenon during treatment of parkinson's disease with levodopa (author's transl)]

The fluctuation in daily performance of Parkinson patients on long-term L-dopa therapy is known as the so called "off-on" phenomenon. Cotzias et al. found that a low protein diet is able to control this phenomenon in patients taking L-dopa alone but not in those receiving a combination of L-dopa and decarboxylase inhibitor. The author's hypothesis was based on the competition between the alimentary aminoacids and L-dopa for transport to the brain ganglia. In our attempt to prove the findings of Cotzias group we tested the influence of a low protein diet on 23 Parkinson patients manifesting the "off-on" phenomenon. All had been pretreated with L-dopa for 5--8 years and taking dopa DI for a minimum of 3 years. The protein intake was limited to 25 g/day (which is less than 0.5 g/kg body weight) for 1--4 months. In 6 cases there was a marked improvment with reduction of the "off-on" effect, and in one it disappeared completely. A distinct improvment of general capability was seen in the other 5 cases, and an objective improvment of the symptoms was noted, except during the "off" period. No response could be observed in the remaining 12 cases. All cases with hyperkinesia showed an augmentation of this symptom during the use of the diet. The diet restriction was not found to be correlated with age, stage, duration of illness or duration of dopa treatment. The possible mechanism of the "off-on" phenomenon and some suggestions to influence it, are presented.