The literature pertinent to the pathological anatomy subserving dementia in Parkinsonian patients is reviewed. Mechanisms discussed include cerebral cortical atrophy; hydrocephalus; Lewy body inclusions; neocortical lesions of the Alzheimer type; depletion of cholinergic, dopaminergic or noradrenergic transmitter systems; ‘subcortical’ dementia; and neuronal depopulation of the basal forebrain.

New autopsy data are presented to confirm that, contrary to published reports, most patients with parkinsonism who exhibit dementia do not have concomitant Alzheimer’s disease, and that some different pathogenetic mechanism must be sought to account for this increasingly common cause of cognitive decline in the sufferers of Parkinson’s disease.

We have studied the concentrations of taurine and of 6 other amino acids in platelets from 12 patients with Friedreich's disease and 12 age sex-matched normal control subjects. No significant differences could be demonstrated between the two groups. The glycine/serine ratio was lower in all the patients but this change did not reach statistical significance. From these and other data, we conclude that the taurine retention deficit observed previously in Friedreich's disease cannot be the primary causal defect.

According to their mental status, patients with Parkinson’s disease can be subdivided into three groups: (1) mentally normal patients; (2) patients with severe cognitive impairment and Alzheimer-type brain pathology (neuritic plaques, neurofibrillary tangles, granulovacuolar changes); and (3) demented patients without any evidence of Alzheimer changes. Neurochemically, irrespective of the presence or absence of Alzheimer-type brain pathology, demented Parkinson patients seem to have the same disturbance of cortical cholinergic neuron function as patients with Alzheimer-type dementia (Alzheimer’s disease), namely, reduced levels of cortical acetylcholine esterase and choline acetyltransferase activity. At present, the question whether the “cortical cholinergic deficiency” is the only (or sufficient) neurochemical basis for the cognitive impairment in Parkinson patients with dementia cannot be answered with certainty; the additional role of other neurotransmitter changes known to occur in the Parkinson brain, especially loss of cortical, hippocampal and subcortical noradrenaline and/or dopamine cannot be ruled out.

Effective control of parkinsonian symptoms can be achieved in a substantial number of patients by the judicious use of dopaminergic agents. To a considerable extent these drugs produce optimal therapeutic effects during the first 3–5 years of their use. Subsequently, efficacy diminishes with reemergence of parkinsonian symptoms as well as a number of untoward responses. The nature, frequency and mechanisms underlying the limitations of long term use of presently available anti-parkinson agents are discussed in this presentation.

New studies were undertaken to verify the previous findings of increased urinary excretion of taurine, in the basal state and after challenge with a taurine load, in Friedreich's disease. Particular attention was paid to possible causes of error such as weight, muscle mass, creatine and creatinine excretion, variability with time and appropriate control groups. Although the overall findings were confirmed, their interpretation is open to question because of all these factors of error. Many possibilities must still be further explored to account for the apparent taurine retention defect observed in many cases of Friedreich's disease.

Clinical and experimental evidence suggests that, in Parkinson’s disease, the late-occurring fluctuations in response to levodopa therapy are due to progression of the disease rather than to the therapy. Therefore, treatment with carbidopa/levodopa should be started early, because postponement does not provide patients with added benefits but deprives them of the most satisfying period of the therapeutic response.

Free amino acid levels and zinc, magnesium and calcium content have been determined in autopsy samples of 9 areas of the brain, two skeletal muscles, and the right ventricle, left ventricle and septum of the heart of a Friedreich's ataxia subject.