V. Bocek

Preserved cutaneous silent period in cervical root avulsion

Objective: Brachial plexus injuries are usually severe and involve the entire brachial plexus, sometimes occurring with root avulsions. Imaging and electrodiagnostic studies are an essential part of the lesion evaluation; however, the results sometimes show a discrepancy. The cutaneous silent period (SP) is a spinal inhibitory reflex mediated by small-diameter A-delta nociceptive fibers. The aim of the study was to determine if cutaneous SP testing may serve as a useful aid in evaluation of brachial plexus injury and/or in the diagnosis of root avulsion. Methods: In 19 patients with traumatic brachial plexus injury (15 males, age 18–62 years) we performed a clinical examination, CT myelography and neurophysiological testing. A needle EMG was obtained from muscles supplied by C5-T1 myotomes. Cutaneous SP was recorded after painful stimuli were delivered to the thumb (C6 dermatome), middle (C7) and little (C8) fingers while subjects maintained voluntary contraction of intrinsic hand muscles. Results: Electrodiagnostic and imaging studies confirmed root avulsion (partial or total) maximally involving C5, C6 roots in 12 patients, whereas only in 4 of them the cutaneous SP was partially absent. In the remaining subjects, the cutaneous SP was preserved. Conclusion: In brachial plexopathy even with plurisegmental root avulsion, the cutaneous SP was mostly preserved. This method cannot be recommended as a reliable test for diagnosis of single root avulsion; however, it can provide a quick physiological confirmation of functional afferent A-delta fibers through damaged roots and/or trunks. The clinicians may add this test to the diagnosis of spinal cord dysfunction.

Pallidal stimulation in dystonia affects cortical but not spinal inhibitory mechanisms.

BACKGROUND Deep brain stimulation (DBS) of the globus pallidus interna is an effective tool for the treatment of dystonia with possible distant effects reaching beyond the basal ganglia network. AIM We analyzed the cortical silent period (CoSP) to test inhibitory circuits at the cortical level, and the cutaneous silent period (CuSP) and the H-reflex to test inhibitory circuits at the spinal level. METHODS The upper limb muscles of 16 patients (9F, aged 54±(SD)16years) with generalized (N=9) and cervical (N=7) dystonia treated with DBS bilaterally were examined by the CoSP, CuSP and H-reflex in two states with random order: (i) in DBS ON and (ii) in DBS OFF condition two hours later, and compared with healthy controls. RESULTS While the CuSP and H-Reflex did not differ between groups and remained unaffected by DBS, the CoSP was influenced significantly in dystonia. The CoSP onset latency was shortened (p<0.05 corrected) and the CoSP duration prolonged (p<0.01 corrected) in ON versus OFF condition. This effect was especially larger in generalized or phasic type of dystonia. Compared to healthy controls, the CoSP latency and duration became shorter in patients during the OFF condition only. CONCLUSION The pallidal DBS did not affect the spinal inhibitory circuitry in dystonia. However, the abnormally low cortical inhibition was normalized after DBS possibly offering more efficient suppression of aberrant dystonic movements.

ID 113 – Neurophysiology and biopsy of paraspinal muscles in idiopathic scoliosis

Objective The pathogenesis of idiopathic scoliosis (IS) remains poorly understood. Local changes in deep paraspinal muscles and/or dysfunction of spinal inhibitory circuits are not fully elucidated. We compared the morphological and functional changes of paraspinal muscles on both sides of the scoliosis curve. Methods Before corrective surgery we performed EMG and muscle biopsy of paraspinal muscles at convexity and concavity of scoliotic curve in 10 subjects with IS (8 women, 11–29years). Cutaneous silent period (CSP) induced by noxious digit II stimulation in thenar muscles was recorded in IS patients and in healthy volunteers. Results Right curve convexity had 8 subjects. All of them presented changes in muscle fiber distribution with numerical predominance of type I on the curve convexity. Seven subjects have increased MUP amplitude on this side (range 10–62%). CSP did not significantly differ between concavity and convexity but shortening of CSP duration was observed in more pronounced scoliotic curve. Conclusion Our findings demonstrate a significant asymmetry in fiber type distribution corresponding with an altered function in paraspinal muscles with predominance on convexity of scoliotic curve. Spinal inhibitory reflex is preserved; however, it could be modulated in more progressive IS. Supported by Grants PRVOUK P34, IGA-NT 13693.

ID 140 – Left-side asymmetry in cortical and spinal inhibitory circuits in stiff-person syndrome: A case report

Objective Stiff-person syndrome (SPS) is an autoimmune disease characterized by progressive rigidity and generalized muscle stiffness caused by loss of GABA-ergic inhibition. Diffuse impairment of the GABA-system can be observed by neurophysiological methods. We investigated intracortical and spinal inhibition and correlate these findings with clinical status. Methods Fifty-one years old male with a two years history of stiffness and muscle spasms was investigated in our department. Subsequently, we performed EMG, paired TMS and cortical (CoSP) and spinal (CSP) silent periods. Results The patient had 50 times higher serum level of anti-GAD. He suffered from severe lumbar hyperlodosis, hypertrophy of axial muscles, and slightly asymmetrical generalized stiffness more pronounced on the left extremities. EMG discovered continuous involuntary muscle activity. Intracortical short-time inhibition (ICSI) after TMS stimulation was abnormal while stimulated both hemisphere and was more pronounced from the left APB muscle. CoSP and CSP were both abnormally shortened with more shortening when recorded from the left side. Conclusion Our findings confirmed loss of GABA-ergic inhibition in SPS. Involvement of both GABA-A and GABA-B inhibitory circuit systems are present with makeable left-side asymmetry corresponding to clinical status.