Central motor conduction studies and diagnostic magnetic resonance imaging in children with severe primary and secondary dystonia

Abstract

CMCT Central motor conduction time DBS Deep brain stimulation MEP Motor-evoked potential PVL Periventricular leukomalacia AIM Dystonia in childhood has many causes. Imaging may suggest corticospinal tract dysfunction with or without coexistent basal ganglia damage. There are very few published neurophysiological studies on children with dystonia; one previous study has focused on primary dystonia. We investigated central motor conduction in 62 children (34 males, 28 females; age range 3-19y, mean age 10y 8mo, SD 4y 8mo) with severe dystonia to evaluate corticospinal tract integrity before consideration for deep brain stimulation.METHOD Distal motor and F-wave latencies were measured in the ulnar and ⁄ or posterior tibial nerves. Transcranial magnetic stimulation was applied over the motor cortex and motor-evoked potentials were recorded in the activated abductor digiti minimi and ⁄ or abductor hallucis muscles. Central motor conduction time (CMCT) was calculated using the F-wave method.RESULTS CMCT was normal in 50 out of 62 patients; 12 patients showed prolonged CMCT to upper and ⁄ or lower limbs. Most children with severe primary and secondary dystonia had normal CMCT, indicating corticospinal tract integrity despite abnormal imaging in 42 out of 50 patients. Abnormal CMCT was found in two out of 12 patients with normal imaging.INTERPRETATION This study provides new CMCT data for children with severe primary and secondary dystonia. Over 50% of children with evidence of periventricular white-matter damage from magnetic resonance imaging had normal CMCT, challenging traditional pathophysiological models. This is consistent with recent diffusion tensor imaging in children with periventricular white-matter damage, showing disruption of sensory connections rather than corticospinal tract damage. CMCT helps refine our understanding of imaging changes in complex motor disorders of childhood.Dystonia is defined as 'a neurological syndrome characterized by involuntary, sustained, patterned, and often repetitive muscle contraction of opposite muscles, causing twisting movements or abnormal postures during motor tasks'. 1 The underlying pathophysiology of dystonia is not fully understood. Some primary dystonias in adults are characterized by reduced cortical inhibition and increased cortical plasticity using paired associated stimulation studies. 2 However, there are very few neurophysiological studies in children with dystonia, or in patients of any age with secondary dystonia. Deep brain stimulation (DBS) of the globus pallidus internus is now a well established management tool for both adults and children with dystonia. [3][4][5][6] Best DBS results are obtained in patients with primary generalized dystonias, in whom dramatic results have been observed, with up to 88% improvement in some children with this condition, as assessed by the Burke-Fahn-Marsden dystonia rating scale. 3,6,7 Reported levels of improvement with DBS in secondary dystonia vary widely between individual patients from 0 to 71%, 4,7,8 averaging arou...

Proportion of life lived with dystonia inversely correlates with response to pallidal deep brain stimulation in both primary and secondary childhood dystonia

“…Because the study was a retrospective audit of routine clinical practice, ethics approval was not required and consent was neither required nor obtained. All children had generalized dystonia refractory to medical treatment, in the absence of significant spasticity or corticospinal tract impairment as judged by clinical assessment, neuroimaging studies, and transcranial magnetic brain stimulation measurement of central motor conduction time . Patients were categorized into four aetiological groups: (1) primary dystonia, (2) secondary dystonia caused by static lesions (secondary‐static), (3) secondary dystonia caused by progressive conditions (secondary‐progressive), and (4) NBIA dystonia.…”

Recognizing the Common Origins of Dystonia and the Development of Human Movement: A Manifesto of Unmet Needs in Isolated Childhood Dystonias

“…The FA value may therefore be a useful marker of the connectivity of the brain: higher FA values corresponding to greater structural connectivity and integrity of the white matter fiber tracts within the brain and vice versa . For instance, in a cohort of children selected on clinical, conventional radiological, and neurophysiological assessments (61, 62) preparatory to management of dystonia with DBS or ITB, the mean DBS-group FA value was >0.5, but the FA value was <0.5 in the ITB group (63). Such statistical imaging parameters may in the future, with neurophysiological parameters become a means of appropriately stratifying children with dystonia into prognostic groups suitable for intervention with DBS or ITB.…”

“…Such measures lead to categorical and quantitative data, e.g., the latency of central motor conduction times (61, 62). White matter integrity as measured by the FA value (62, 63) may be used to partition cases most likely to benefit from DBS or ITB (63) and thereby improve the prognosis for a favorable outcome from DBS for dystonia along with somatosensory-evoked potentials (SSEP) (J-P Lin unpublished results).…”

The International Classification of Functioning (ICF) to evaluate deep brain stimulation neuromodulation in childhood dystonia-hyperkinesia informs future clinical & research priorities in a multidisciplinary model of care

“…We present a comprehensive scheme for approaching movement disorders in children, including dystonia and choreoathetosis of necessity originating from many disparate aetiologies. Searching for common themes has helped us as a clinical group, to define core issues relating to refinement of the phenotype with neurophysiological, 62,141 radiological 63,142,143 and functional metabolic 144 assessments respectively. These approaches help us understand the physiological context of dystonia and contribute to patient-selection for DBS and also allow interpretation of outcomes, which further refines the selection iteration process.…”