Abnormal contingent negative variation in writer's cramp.
OBJECTIVE
To investigate the physiological abnormality in writer's cramp, a focal dystonia which specifically affects writing.


METHODS
We recorded brain potentials that precede hand and neck movements (contingent negative variation or CNV) in 11 patients and 11 age-matched normal subjects. A 1000 Hz tone burst (S1) was delivered to the right or left ear in random sequence, and 2 s after, a 2000 Hz tone burst (S2) was delivered to both ears simultaneously. For the response task to S2, the subjects were instructed to extend their fingers ipsilateral to the ear to which S1 was given in one experiment or to rotate the head to the side of the S1 presentation in another. All the patients had symptoms in the right hand only, and performed both tasks normally. CNV amplitudes were compared between normals and patients using unpaired t test.


RESULTS
They showed normal CNV for neck movement but significantly decreased CNV amplitudes for movements both in the affected and unaffected hands.


CONCLUSIONS
Our findings suggest that motor programming is specifically abnormal for the affected body part, including the asymptomatic contralateral limb, and that the clinical symptom may result from a deficient compensatory mechanism for abnormal motor programs or subroutines.
Hamano
T
T
Department of Neurology, Kyoto University School of Medicine, Japan.
Kaji
R
R
Katayama
M
M
Kubori
T
T
Ikeda
A
A
Shibasaki
H
H
Kimura
J
J
D000328:Adult; D003265:Contingent Negative Variation / Q000502:physiology*; D004569:Electroencephalography; D004576:Electromyography; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D005385:Fingers / Q000503:physiopathology; D006236:Handwriting; D006801:Humans; D008297:Male; D008875:Middle Aged; D009120:Muscle Cramp / Q000503:physiopathology*