Images: Polysomnographic artifact in a patient with Tourette syndrome

Abstract

Patients with Tourette syndrome frequently have sleep disturbances that may require polysomnographic testing. The use of deep brain stimulators is increasing with expanding indications including children with medically intractable Tourette syndrome. It is important to understand the effect the stimulator can have on polysomnographic monitoring. Herein we present an interesting case of an adolescent with medically intractable Tourette syndrome with a deep brain stimulator implant who underwent a polysomnogram demonstrating rhythmic, monomorphic artifact.

Citation:

Bindra T, Ingram DG. Images: Polysomnographic artifact in a patient with Tourette syndrome. J Clin Sleep Med. 2023;19(12):2149–2151.

INTRODUCTION

Deep brain stimulation (DBS) is an established treatment for patients with movement disorders, epilepsy, and psychiatric conditions. Sleep disturbances are common in patients with Tourette syndrome, which often require additional evaluation with polysomnography. We present an interesting case of the effect of DBS on polysomnographic testing in a patient with medically intractable Tourette syndrome.

REPORT OF CASE

We report on a 20-year-old male with autism spectrum disorder level 1, major depressive disorder, obsessive compulsive disorder, attention deficit hyperactivity disorder, and medically intractable Tourette syndrome with bilateral centromedian nucleus of the thalamus DBS placement. The DBS settings were as follows: amplitude: 1.3–1.45 V, pulse width: 220 us, frequency: 35 Hz, on time: 5 minutes, off time: 1 minute.

The patient had hypersomnolence, which persisted despite use of methylphenidate and cessation of sedating medications when the DBS was placed. His medication list included methylphenidate, duloxetine, lorazepam, topiramate, and montelukast. Prior brain magnetic resonance imaging was unremarkable. He presented for a sleep medicine evaluation due to loud snoring, night sweats, and excessive daytime sleepiness. An overnight polysomnogram was requested in order to evaluate for sleep-related breathing disorders.

The polysomnogram revealed mild obstructive sleep apnea with an apnea-hypopnea index of 8.8 events/h using American Academy of Sleep Medicine scoring criteria 1A. Sleep efficiency, sleep latencies, and arousal indices were within normal limits. There was no significant hypoxemia, hypercapnia, or elevation in limb movements. Artifact was noted in the electroencephalogram, electrooculogram, and chin electromyogram leads without video correlate of body movements or other reproducible artifact. Representative images are shown in Figure 1, Figure 2, and Figure 3. This artifact was present for the entirety of polysomnographic testing. The patient had no prior sleep testing or electroencephalogram testing since DBS placement for comparison. Attempts to correct the artifact including lead placement, referencing, removal of local electronics, and 60 Hz filter, among others, did not resolve the artifact. Turning off the DBS was not attempted during this study.

Figure 1. Polysomnogram with 30-second epoch illustrating artifact in the electrooculogram, electroencephalogram, and chin electromyogram leads.

The artifact obscures evaluation of these tracings.

Figure 2. 10-second epoch demonstrating 20 Hz artifact that is rhythmic and monophasic in the electrooculogram, electroencephalogram, and chin electromyogram leads.

The artifact obscures evaluation of these tracings.

Figure 3. 10-minute epoch illustrating intermittent firing of the DBS with on time of 5 minutes and off time of 1 minute.

The artifact obscures evaluation of the electrooculogram, electroencephalogram, and chin electromyogram lead tracings.

DISCUSSION

Tourette syndrome is a chronic neurologic disorder characterized by persistent motor and vocal tics. Multiple comorbidities have been associated with Tourette syndrome including psychiatric and sleep disturbances. Sleep disorders include sleep onset and sleep maintenance insomnia, parasomnias, and hypersomnolence. Polysomnogram findings include decreased total sleep time, lower sleep efficiency, and elevated arousal index.¹ The associated psychiatric disorders such as obsessive-compulsive disorder, anxiety disorder, and attention deficit hyperactivity disorder, as well as the medications used to treat them, can worsen the sleep disruption that is already inherent in Tourette syndrome. These conditions, however, are not associated with clinically significant electroencephalogram findings.^2,3 Psychotropic medication effects on electroencephalogram vary but include accentuation of beta activity, background slowing with decreased amplitude and/or frequency of the alpha rhythm, and intermixed theta and/or delta activity. They can also decrease seizure activity or reduce seizure threshold resulting in increased spike and wave discharges. They are not responsible for the artifact noted in this case.⁴

DBS can be used in medically intractable Tourette syndrome. A DBS involves placement of unilateral or bilateral electrodes in the deep brain structure corresponding to the disorder under treatment. The leads connect to a pulse generator implanted in the chest wall. The generator delivers high-frequency electrical stimulation to the target brain location, which results in neuromodulation and inhibition of the abnormal activity. This patient’s DBS settings were an amplitude of 1.3–1.45 V, pulse width of 220 us, frequency of 35 Hz, on time 5 minutes, and off time 1 minute, resulting in interference of 20 Hz frequency confirming the etiology of this patient’s polysomnogram artifact. This artifact obscured the electroencephalogram, electrooculogram, and chin electromyogram, which precluded accurate evaluation of the polysomnogram. It is unclear why the resulting interference frequency may differ from the DBS set frequency; however, this was a similar finding in other case reports suggesting the diagnosis is based on the presence of a periodic monomorphic artifact with pauses at the same on/off timing as the DBS setting.⁵

With the growing indications for DBS implantation, the frequency of patients presenting for polysomnography will become more common. It is imperative to be aware of the artifact generated by this device. The appearance of the artifact is periodic and monomorphic for the duration of the stimulation.⁶ Intermittent artifact has also been reported with other neurostimulators such as vagal nerve stimulators and responsive nerve stimulation correlating with the frequency or frequency harmonics of the stimulating frequency and with a duration corresponding to the stimulation period (30 seconds in vagal nerve stimulators and 100 ms in responsive nerve stimulation).⁷

There are no clearly established methods to eliminate DBS artifact. That said, several proposed advanced techniques may aid in filtering this artifact, including matched filtering, manual detection and rejection using notched filters, low pass filtering, and Hampel filtering with aliased spikes identification.^8–10 The device can be deactivated during the testing time, but doing so may risk amplification of the pre-existing condition being treated. Unmasking of the pre-existing condition could then result in additional movement artifact and lack of sleep time captured for adequate polysomnographic interpretation. One alternative option is to consider utilization of home sleep apnea testing, but this only allows for evaluation for sleep apnea and can miss other important physiologic disruptors of sleep.⁵

DISCLOSURE STATEMENT

All authors have seen and approved the manuscript. The authors report no conflicts of interest.

ABBREVIATION

DBS

deep brain stimulation