Effect of therapy on motor cortical excitability in Parkinson's disease.
OBJECTIVE
To assess the impact of the disease stage and therapy on motor cortical excitability in Parkinson's disease (PD).


METHODS
Twenty newly diagnosed and medication-free, early stage patients, 20 late stage patients under antiparkinsonian therapy and 20 normal healthy controls were included. Motor threshold (MT), amplitudes of motor evoked potential (MEP), motor evoked potential amplitude/compound muscle action potential amplitude (MEP/CMAP) ratio, central motor conduction time (CMCT) and cortical silent period (CSP) were measured by stimulation of the motor cortex using a 13.5 cm circular coil and recordings from abductor digiti minimi muscle. Following the first study protocol, early stage patients were given therapy and the same protocol was repeated three months later.


RESULTS
Motor threshold was lower; and the MEP/CMAP ratio was higher in early and late stage patients than normals. In early stage patients after proper therapy, the MTs became higher than before therapy, but still remained lower than normals. In late stage patients, the CMCTs were shorter than the early stage patients before therapy and normals, but there was no difference between the early stage patients and normals. In early stage patients after therapy, the CMCT became longer than before therapy and this difference was significant in both late stage patients and normals. Although more prominent in late stage patients, the CSP duration in both PD groups was found shorter than normals. In early stage patients, after therapy, the CSP durations became significantly longer compared with before therapy.


CONCLUSIONS
These findings suggest that the motor cortical excitability increases in PD because of the impairment of the corticomotoneuronal inhibitory system.
Bakirkoy State Hospital for Psychiatric and Neurological Diseases, I. Neurology Department, Bakirkoy/lstanbul, Turkey.
Aysun
A
Soysal
Ismail
I
Sobe
Turan
T
Atay
Aysu
A
Sen
Baki
B
Arpaci
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D000978:Antiparkinson Agents / Q000627:therapeutic use*; D013181:Cortical Spreading Depression / Q000187:drug effects / Q000502:physiology; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000187:drug effects / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000187:drug effects* / Q000503:physiopathology*; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology; D010300:Parkinson Disease / Q000188:drug therapy* / Q000473:pathology* / Q000503:physiopathology; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology
D000978:Antiparkinson Agents