SEPs N30 amplitude in Parkinson's disease and in pharmacologically induced rigidity: relationship with the clinical status

The frontal N30 wave amplitude of somatosensory evoked potentials (SEPs) has been studied in 41 Parkinson's disease (PD) patients (pts) in a basal condition and compared to that of 30 normal subjects; moreover the N30 amplitude and clinical motor score have been evaluated in a subgroup of 30 PD pts before and during apomorphine infusion and in a second subgroup of 22 PD pts also during levodopa chronic therapy. The data show that N30 amplitude is decreased in PD pts in basal condition and increased following both treatments by a percentage proportional to the clinical improvement Analysis by non parametric correlations showed that the increase is well correlated to the clinical score amelioration induced by apomorphine in the more affected side. The best correlation was to rigidity score amelioration in the group of PD pts in medium stage (Hohen and Yahr stage between 2 and 3), suggesting a relationship between the rigidity and N30 amplitude decrease. Non parkinsonian subjects, treated with low (11 aged normal subjects) and high (eight young psychotic pts) doses of antidopaminergic drugs, were studied. N30 amplitude decreases were only found in the group of eight psychotic pts showing clinical extrapyramidal signs, produced by the high dose of drug administered, but not in the group treated with the lower dose not producing extrapyramidal side effects, although this dose was efficacious on different modalities of evoked potentials. We conclude that N30 amplitude decrease in PD reflects the dopaminergic lack paralleled by clinical symptoms. We propose that N30 amplitude variations by dopaminergic agonists may be useful in the clinical evaluation of dopamine related and non related tone alterations.