Transcranial Magnetic Stimulation Rachel McAteer BME 281

What is TMS? Non-invasive method of neurostimulation/neuromodulation Causes: Depolarization – makes a cell’s membrane potential more positive Hyperpolarization – makes a cell’s membrane potential more negative Induces controlled and controllable manipulations in behavior

How it works: Uses a rapidly changing magnetic field to induce weak electric currents, through pulses. Induced by electromagnetic induction Generally reach no more than 5cm into the brain *Coil is held above the head; pulses penetrate skin and skull.

Plastic-enclosed wire coils deliver pulses A. Figure-8 coil B. Double-cone coil Round coil * Four-leaf coils are also used (not pictured) B. C. A.

Kinds of TMS Single-Pulse TMS – Delivers one stimulus at a time Paired-Pulse TMS – Pairs of stimuli separated by a variable interval Repetitive TMS (rTMS) – Delivered in trains (can be of low or high frequency)

Two Main Categories: Diagnostic cases Therapeutic cases

Diagnostic Used clinically to: Measure activity of certain brain circuits Survey the damage done to particular muscles following stroke, multiple sclerosis, motor neuron disease, and other injuries or disorders Locate tumors and other lesions to generate preoperative motor maps

Therapeutic rTMS Used for both rehabilitation and symptom alleviating purposes Possible therapy for tic disorders, autism, migraines, tinnitus, and in the treatment of certain psychiatric disorders including PTSD, schizophrenia, and, popularly, Major Depressive Disorder

Risks/side effects Common side effects: local pain, headache, and mild discomfort Could potentially displace ferromagnetic objects (e.g titanium skull plates) Can induce voltages in nearby electronic devices/wires Temporary increases in auditory thresholds Induction of seizures Syncope

Discussion Diagnostic: Diagnostically, the only FDA approval is the Navigated Brain Stimulation System for pre-surgical planning in patients undergoing brain surgery. Proven equally successful as traditional imaging methods in producing preoperative motor maps. When compared to direct cortical stimulation (DCS), it was found that TMS was able to recognize every motor site mapped by DCS

Therapeutic: FDA has currently only approved rTMS as a treatment for Major Depressive Disorder (MDD) (under Class II restrictions – special controls). Generally inconsistent results: Ebmeier and colleagues - conducted a 5-day study with 15 patients that called for them to be treated twice per day. At the end of the study, the participants saw a reduction of 44% on Hamilton depression scales. Another trial testing 100 patients, however, saw most to be treatment-resistant. Current trials include using TMS with: autism, MDD, improving speech aphasia

References Hallet, Mark; Pascual-Leone, Alvaro ; Rossi, Simone;    Rossini, Paolo M. "Safety, ethical considerations, and application guidelines for the use of transcranial magnetic stimulation in clinical practice and research" Clinical Neurophysiology 120. 12  (2009):  2008-2039. Web. US National Library of Medicine National Institutes of Health. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3260536/> <http://www.medscape.org/viewarticle/420840> < http://www.ncbi.nlm.nih.gov/pubmed/22579164> <http://en.wikipedia.org/wiki/Transcranial_magnetic_stimulation#Diagnostic_use> <https://www.unitedhealthcareonline.com/ccmcontent/ProviderII/UHC/en-US/Assets/ProviderStaticFiles/ProviderStaticFilesPdf/Tools%20and%20Resources/Policies%20and%20Protocols/Medical%20Policies/Medical%20Policies/Transcranial_Magnetic_Stimulation.pdf> <http://www.sciencedaily.com/releases/2012/07/120726180305.htm>