Muscular pain is the most frequent kind of nondystonic pain associated with Parkinson's disease (PD). It might be related not only to peripheral factors but also to an abnormal nociceptive input processing in the central nervous system. To test this hypothesis, we recorded CO(2) laser-evoked potentials (LEPs) in response to shoulder stimulation (skin over deltoid muscle) in 11 hemiparkinsonian PD patients complaining of muscular pain in the shoulder (ipsilateral to motor symptoms) and compared the results with those obtained in 12 pain-free PD patients with hemiparkinson and in 11 normal subjects. N2/P2 LEP, which is thought to originate from the cingulate cortex and insula, was significantly lower in amplitude in both groups of PD patients than in controls, regardless of the clinically affected body side. In both groups of PD patients, no significant correlation was observed between the severity of motor symptoms and N2/P2 amplitude abnormalities. In PD patients with muscular pain, the N2/P2 amplitude obtained following stimulation of the painful shoulder was significantly reduced compared with that obtained in response to nonpainful shoulder stimulation and compared with the values obtained in pain-free PD patients. No significant correlation was observed between the intensity of muscular pain and N2/P2 amplitude abnormalities in this group of PD patients. These results suggest abnormal nociceptive input processing in PD, which appears to be independent of clinical expression of parkinsonian motor signs. These alterations are more evident in the presence of muscular pain.

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Objective of this study is testing a new sign to differentiate functional from organic paralysis of the arm. Thirty-six healthy subjects, ten patients with acute functional paralysis of one arm and eleven patients with acute organic paralysis of one arm were enrolled. The test consisted of abduction finger movements of one hand against resistance with a maximal sustained contraction to detect synkinetic abduction finger movements of the contralateral hand. For both hands, contralateral hand synkinesias were observed in healthy subjects. The task performed with the unaffected hand evoked synkinesias of the presumed affected hand in functional patients, but did not evoke synkinesias of the affected hand in organic patients. The abduction finger test had 100% sensitivity and specificity in distinguishing functional from organic paralysis of the upper limb in this cohort of patients. The abduction finger sign may be a reliable bedside test to discriminate functional from organic arm paralysis.