Objective: STN-DBS is an effective,generally well-tolerated therapy in selected patients experiencing motor fluctuations,dyskinesia,resistant tremor despite oral/transdermal treatment. Side-effects can occur due to spread of electrical current to adjacent structures.Here,we report a case of tongue twisting movement as a pyramidal tract stimulation side effect of STN-DBS.

Background: A 53-year old woman, suffered of shoulder pain, stiffness, flexed posturing of right arm,right foot dragging was diagnosed with idiopathic Parkinson’s disease at age 38. At age 43 she experienced motor fluctuations,left leg foot posturing,inward turning, intermittent dyskinesia. Laboratory evaluations, genetic testing for parkinsonism were negative. MRI was unremarkable.DATscan was positive.L-dopa challenge test revelaed an improvement of 45.6%.

Method: She underwent STN-DBS at age 51 under general anaesthesia without microrecordings using the Leksell frame and an MRI-guided,MRI-verified technique. Initial DBS settings were 4- 1.8mA and 10- 1.6mA; 60µs, 130Hz. Eight months postoperatively, patient presented with right foot dystonia affecting gait. As the DBS settings were adjusted to 2-, 2mA; 60µs, 130Hz,right foot dystonia disappeared but a twisting, turning movement of the tongue occurred and worsened as the stimulation increased to 2.5mA and to 2.8mA.

Results: The tongue twisting movement ceased as the stimulation was directed towards segment 3-, a more dorsal contact. Since the tongue twisting movement was stimulation related, quite consistent, and the VTA revealed a slightly lateral positioning of left lead within the STN,this unique movement is considered an uncommon form of stimulation related corticobulbar side-effect of STN-DBS.

Conclusion: Corticospinal and corticobulbar tracts, known as the pyramidal tract lying lateral to STN are responsible for challenging side effects of STN-DBS including muscle contractions, twitches, gait, speech disturbances,pain due to the spread of the current.It can be difficult to distinguish these pyramidal clinical signs from muscle spasms resulting from dystonia related to DBS or speech disturbances,pain which may arise from either pyramidal tract stimulation or stimulation of medial zona incerta, cerebellothalamicus fasciculus. In this case, tongue twisting movement was considered a rare side-effect of STN-DBS due to possible stimulation of the piramdal tract.

References: 1. Holl, E., Petersen, E., Foltynie, T., Martinez-Torres, I., Limousin, P., Hariz, M. and Zrinzo, L. (2010). Improving Targeting in Image-Guided Frame-Based Deep Brain Stimulation. Operative Neurosurgery, 67, pp.ons437-ons447. 2. Foltynie, T., Zrinzo, L., Martinez-Torres, I., Tripoliti, E., Petersen, E., Holl, E., Aviles-Olmos, I., Jahanshahi, M., Hariz, M. and Limousin, P. (2010). MRI-guided STN DBS in Parkinson’s disease without microelectrode recording: efficacy and safety. Journal of Neurology, Neurosurgery & Psychiatry, 82(4), pp.358-363. 3. Akram, H., Sotiropoulos, S., Jbabdi, S., Georgiev, D., Mahlknecht, P., Hyam, J., Foltynie, T., Limousin, P., De Vita, E., Jahanshahi, M., Hariz, M., Ashburner, J., Behrens, T. and Zrinzo, L. (2017). Subthalamic deep brain stimulation sweet spots and hyperdirect cortical connectivity in Parkinson’s disease. NeuroImage, 158, pp.332-345. 4. Aviles-Olmos, I., Kefalopoulou, Z., Tripoliti, E., Candelario, J., Akram, H., Martinez-Torres, I., Jahanshahi, M., Foltynie, T., Hariz, M., Zrinzo, L. and Limousin, P. (2014). Long-term outcome of subthalamic nucleus deep brain stimulation for Parkinson’s disease using an MRI-guided and MRI-verified approach. Journal of Neurology, Neurosurgery & Psychiatry, 85(12), pp.1419-1425. 5. Mahlknecht P, Akram H, Georgiev D, Tripoliti E, Candelario J, Zacharia A, Zrinzo L, Hyam J, Hariz M, Folthynie T, Rothwell JC, Limousin P (2017). Pyramidal tract activation due to subthalamic deep brain stimulation in Parkinson’ s disease. Movement Disorders 32 (8): 1174-1182.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/first-case-of-tongue-twisting-during-screening-of-stn-dbs-for-parkinsons-disease-a-unique-form-of-pyramidal-tract-activation/