Abnormal H-reflexes in periodic limb movement disorder; impact on understanding the pathophysiology of the disorder

• Published in: Clinical neurophysiology 2005, Vol.116 (1), p.204-210
• Main Authors: Rijsman, R.M., Stam, C.J., Weerd, A.W. de
• Format: Article
• Language: English
• Subjects: Adult; Aged; Biological and medical sciences; Electric Stimulation - methods; Electrodiagnosis. Electric activity recording; Electromyography - methods; Evoked Potentials, Motor - physiology; Evoked Potentials, Motor - radiation effects; Female; Fundamental and applied biological sciences. Psychology; H-Reflex - physiology; Humans; Investigative techniques, diagnostic techniques (general aspects); Male; Medical sciences; Middle Aged; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Muscle, Skeletal - physiopathology; Nervous system; Nocturnal Myoclonus Syndrome - physiopathology; Pathophysiology; PLMD; Reaction Time - physiology; Reaction Time - radiation effects; Reflex, Abnormal - physiology; RLS; Soleus H-reflex; Time Factors; Vertebrates: nervous system and sense organs
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2004.07.022

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. 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. 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. 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. The results of this study give further insight in the pathophysiology of PLMD and RLS by stressing the importance of diminished central inhibition.