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Transcranial Magnetic Stimulation

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

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Transcranial Magnetic Stimulation

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  1. Transcranial Magnetic Stimulation Rachel McAteer BME 281

  2. 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

  3. 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.

  4. 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.

  5. 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)

  6. Two Main Categories: • Diagnostic cases • Therapeutic cases

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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>

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