Abnormal H-reflexes in periodic limb movement disorder; impact on understanding the pathophysiology of the disorder.
OBJECTIVE
To get more insight in the pathophysiological basis of periodic limb movement disorder (PLMD) with or without restless legs syndrome (RLS), we investigated whether these patients have spontaneous changes in H-reflexes or show altered reflex patterns after (external) inhibition or excitation of the relevant spinal segment.


METHODS
The ratio of the peak-to-peak values of the maximal soleus H-reflex and the maximal direct muscle potential (H/M ratio), H-reflex recruitment curves, vibratory inhibition and recovery curves of the soleus H-reflex in double stimulus experiments were measured in 9 PLMD patients and 11 controls.


RESULTS
In comparison to controls the vibratory inhibition, predominantly reflecting pre-synaptic inhibitory action, was depressed in PLMD patients. The soleus H-reflex recovery curves showed increased late facilitation and depressed late inhibition, both reflecting diminished inhibition due to post-synaptic central activity.


CONCLUSIONS
Our data indicate diminished inhibition at spinal level in PLMD patients. This is probably due to altered function of the descending spinal tracts, peripheral influence or changes at the inter-neural circuitry at spinal level itself, or combinations of these 3 possibilities.


CONCLUSIONS
The results of this study give further insight in the pathophysiology of PLMD and RLS by stressing the importance of diminished central inhibition.
Rijsman
R M
RM
Department of Clinical Neurophysiology, Centre for Sleep and Wake Disorders, MCH-Westeinde Hospital, Lijnbaan 32, Post Box 432, 2501 CK The Hague, The Netherlands. l.rijsman@mchaaglanden.nl
Stam
C J
CJ
de Weerd
A W
AW
D000328:Adult; D000368:Aged; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology* / Q000528:radiation effects; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology*; D020189:Nocturnal Myoclonus Syndrome / Q000503:physiopathology*; D011930:Reaction Time / Q000502:physiology / Q000528:radiation effects; D012021:Reflex, Abnormal / Q000502:physiology*; D013997:Time Factors