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Idiopathic cervical dystonia is the most common form of focal dystonia in adults.1,2 It is characterised by involuntary, sustained contractions of the cervical muscles and produces abnormal head movements or postures. Although deep brain stimulation (DBS) of the globus pallidus internus (GPi) is now accepted in the treatment of a wide spectrum of dystonias including cervical dystonia (for a review, see Krauss3), the mechanisms underlying its beneficial effects on dystonia remain unclear. We report a patient in whom continuous long term (22 month) bilateral pallidal stimulation eventually produced stimulation independent relief of cervical dystonia.
This 54 year old right handed man had a one year history of involuntary head rotation toward the left. He had no previous exposure to neuroleptics and no family history of dystonia. On admission in June 2000, he manifested severe cervical dystonia with neck pain characterised by left and posterior head turn and tilt (fig 1A). The right sternocleidomastoid muscle was contracted and hypertrophied. His cervical dystonia decreased in the supine position or when performing a sensory trick which consisted of putting his right hand on his chin or neck. On the Toronto western spasmodic torticollis rating scale (TWSTRS), his total severity score (TSS) was 25 (maximum = 35), and his total disability score (TDS) was 21 (maximum = 30).
Brain magnetic resonance imaging showed no obvious abnormalities. Sequential pharmacological trials including diazepam (4×2 mg/day), trihexyphenidyl (4×2 mg/day), tiapride (3×25 mg/day), and sulpiride (3×50 mg/day) produced unsatisfactory results. Botulinum toxin (BTX) treatment is now established as a treatment of choice in patients with cervical dystonia, while bilateral pallidal stimulation is still an investigational treatment. However, at the time of these trials, the use of BTX injections was not approved in Japan for the treatment of cervical dystonia. The patient was referred for surgery after informed consent had been obtained from both him and his family.
Quadripolar DBS electrodes (model 3387, Medtronic Inc, Minnesota, USA) were implanted as previously described.4,5 The target points were determined to be 2 mm anterior and 20 mm lateral to the midpoint of the anterior to posterior commissure line, and 1 mm dorsal to the third ventricle floor. The most ventral contacts were placed exactly on the target points (fig 1B, C). As six day stimulation tests confirmed the beneficial effects of DBS, a receiver for the external transmitter was implanted (Mattrix transmitter, model 3272, Medtronic). The cervical dystonia and neck pain were markedly alleviated within minutes of initiating DBS.4 Extensive trials showed that optimal results were produced at a frequency of 60 Hz, pulse width 500 μs, and amplitude 6.0 V.4,5 As the external stimulator that we first employed permitted bipolar but not monopolar stimulation, contact 0 was used as the cathode and contact 1 as the anode. Upon stimulation, the cervical dystonia was markedly alleviated (fig 1D), with TWSTRS TSS and TDS of 6 and 5, respectively. By contrast, when stimulation was discontinued, the dystonic symptoms reappeared immediately and resumed at the preoperative level (fig 1E).
With stimulation, the patient was able to return to his job and resume his normal life. However, he began to complain that using the external transmitter was inconvenient. Moreover, he was afraid of the immediate return of his cervical dystonia when he discontinued stimulation—for example, when replacing the battery or taking a bath. Therefore, in June 2001 the external transmitter receiver was replaced with internal pulse generators (IPGs) (Itrel III, Medtronic Inc). Extensive trials showed that optimal results were produced at 60 Hz, 450 μs, and 2.6 V. Monopolar stimulation was applied using contacts 0 and 1 as the cathode and the pulse generator as the anode. At this optimal setting, his TWSTRS TSS and TDS were 5 and 5, respectively. Continuous bilateral pallidal stimulation allowed him to continue a normal life. With two active electrodes stimulating (at 60 Hz, 450 μs, and 2.6 V) for 24 hours a day, the battery life of the Itrel III is about 24 months. Thus, in April 2003 (22 months after placement of the DBS electrodes), revision of the IPGs was carried out before depletion of the batteries. This was the first time of discontinuation of the DBS since the implantation of the IPGs. Expecting that his cervical dystonia would reappear as usual when stimulation using the external transmitter was discontinued, we planned to switch on the generators immediately after surgery. However, without stimulation, the cervical dystonia did not worsen and at the time of writing (fig 1F) his TWSTRS TSS and TDS continue to be 6 and 5, respectively. Compared with the values obtained before the implantation of the DBS electrodes, there was approximately 76% improvement in the cervical dystonia. Pharmacotherapy had been continued unchanged from before the surgery: diazepam (4×2 mg/day), trihexyphenidyl (4×2 mg/day), tiapride (3×25 mg/day), and sulpiride (3×50 mg/day).
Interestingly, long term (about 22 months) continuous bilateral GPi DBS with IPGs produced stimulation independent relief of this patient’s cervical dystonia, although short term (less than 24 hours because of limited battery life) and discontinuous DBS with the external transmitter had not yielded such beneficial effects. We cannot exclude the possibility that spontaneous remission of the cervical dystonia occurred1 during the use of IPGs. However, our experience with this patient suggests that chronic GPi DBS may result in normalisation of the altered basal ganglia related motor circuits that are implicated in the occurrence of dystonia,6–8 and that over time the normalised state may persist independently of DBS. Alternatively, chronic GPi-DBS may lead to the reorganisation of the functional anatomy of the motor circuits at unknown levels, thus resulting in suppression of dystonia. Long term remission of idiopathic cervical dystonia after BTX treatment has also been reported.9 It is presently unknown whether peripheral BTX injection and GPi-DBS share a common mechanism in producing remission of cervical dystonia. From a practical standpoint, in patients undergoing GPi-DBS for cervical dystonia treatment, it may be necessary to apply DBS as continuously as possible and to avoid any unnecessary discontinuation of the IPGs. In addition, when battery depletion makes it necessary to revise the IPGs, it may be advisable to determine whether further stimulation is actually needed in these patients.
Competing interests: none declared