Objective: To distinguish between patients with dystonia according to the clinical outcome of pallidal stimulation (GPi DBS) using intracortical inhibition of the motor cortex assessed by paired transcranial magnetic stimulation (TMS).

Background: GPi DBS is an effective treatment for dystonic syndromes with a relatively high variability of clinical benefit. Patients with dystonia typically have a lower ability to suppress unwanted movements. Therefore we expected a decreased intracortical inhibition of motor cortex in these patients, which can be potentially reversed by GPi DBS.

Methods: We examined 22 patients (mean age 51±(SD)17 years) with dystonia of various distribution and origin treated by GPi DBS in different time intervals from implantation

Descriptive patient’s data

Patient	Age at onset	Body distribution	Etiology	Duration of GPi DBS (years)	BFMDS/TWSTRS before surgery	BFMDS/TWSTRS GPi DBS ON	Responsiveness
1	Late adulthood	Generalized	Idiopathic	4	39	28.5	Partial responder
2	Childhood	Generalized	DYT 1	6	27	2.5	Responder
3	Early adulthood	Generalized	Idiopathic	3	50	22.5	Responder
4	Childhood	Generelized	Postanoxic	1	47.5	46	Non-responder
5	Childhood	Generelized	DYT 1	5	28.5	14	Responder
6	Childhood	Generelized	PKAN	9	77.5	55	Partial responder
7	Childhood	Generelized	PKAN	8	70.5	80	Non-responder
8	Infancy	Generelized	Postanoxic	3	50.5	47.5	Non-responder
9	Late adulthood	Generelized	Idiopathic	4	15	x	Non-responder
10	Late adulthood	Generelized	Idiopathic	3	8	0	Responder
11	Late adulthood	Generelized	Idiopathic	5	20.5	7	Responder
12	Early adulthood	Generelized	Idiopathic	6	29	24.5	Non-responder
13	Late adulthood	Generelized	Idiopathic	2	33	13.5	Responder
14	Late adulthood	Generelized	Idiopathic	3	21	12.5	Partial responder
15	Late adulthood	Generelized	Possible MSA-P	1	16.6	15.5	Non-responder
16	Early adulthood	Cervical	Idiopathic	4	24	17	Partial responder
17	Early adulthood	Cervical	Idiopathic	4	20	16	Non-responder
18	Late adulthood	Cervical	Idiopathic	1	26	22	Non-responder
19	Early adulthood	Cervical	Idiopathic	5	24	5	Responder
20	Late adulthood	Cervical	Idiopathic	3	25	22	Non-responder
21	Childhood	Cervical	Idiopathic	4	29	6	Responder
22	Early adulthood	Cervical	Idiopathic	7	24	14	Partial responder

. Paired TMS with subthreshold conditioning stimuli followed by a supratreshold testing stimuli 2.5 ms later were applied to the motor cortex to elicit short-latency intracortical inhibition (SICI) of motor evoked potentials (MEP) in the abductor pollicis brevis muscle in two conditions: (i) in GPi DBS ON and (ii) in GPi DBS OFF condition two hours later. The clinical effect (CE) was expressed as a change in the dystonic score (Burke-Fahn-Marsden Dystonia rating Scale or Toronto Western Spasmodic Torticollis Scale) between actual GPi DBS ON condition and the preoperative state.

Results: The SICI was less effective in patients than in controls regardless of the ON and OFF conditions (p<0.001). Non-responders (n=9; <25% CE) showed abnormally low SICI, partial responders (n=5; 25%-50% CE) showed higher SICI and the highest SICI was in responders (n=8; >50% CE, p<0.05). The MEP onset latency was shorter in patients in GPi DBS ON than in OFF condition (p<0.001). In addition, the shortest MEP onset latency was observed in non-responders, followed by partial responders and responders (p<0.001).

Conclusions: Our results suggest that the best responders to chronic GPi DBS treatment exhibited a similar level of intracortical inhibition as in healthy controls. On the contrary, non-responders were unable to increase their reduced cortical inhibition and effectively suppressed dystonic symptoms. We speculate that decreased intracortical inhibition with abnormally fast transmission volley in these patients is underpinned by the poor complexity of the motor network. Supported by the grant IGA MZ CR NT12282-5/2011.

« Back to 2016 International Congress

MDS Abstracts - https://www.mdsabstracts.org/abstract/clinical-effects-of-pallidal-stimulation-in-dystonia-are-quantitatively-related-to-intracortical-inhibition/