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Safety of TMS

Safety_concerns

Guidelines

References

Safety concerns

Contraindications

Studies should always exclude patients with

• intracranial metal implants¹, unless the physical properties of the metal are known, and the benefits outweigh the risks
• cardiac pacemakers and other electronic implants¹, which may be disturbed by the magnetic field
• increased intracranial pressure or significant heart disease² resulting from trauma or large infarctions, due to increased seizure risk
• medication which reduces the seizure threshold², such as TCAs
• Those with high alcohol consumption² - abstinence may increase risk of seizure
• Those with immediate-family history², or with known, untreated epilepsy

Children should also be excluded from studies³, unless there is overwhelming clinical benefit to be gained.

Pregnancy has not been shown to be affected by rTMS⁴, and may even be recommended to treat depression since no antidepressant medication has been shown to be safe for the foetus. However, until this is further explored, pregnant women are currently excluded from studies.

Single-pulse TMS

Single-pulse TMS has no known harmful side effects¹.

Repetitive TMS (rTMS)

rTMS is a much more powerful and potentially dangerous therapy, and so subjects are at risk of more serious side effects:

• Seizure induction - This is the most critical concern with rTMS, particularly at higher frequencies e.g. >5Hz⁵. Patients particularly at risk are those with brain pathology (previous stroke, tumour etc.), history of epilepsy, those taking medication lowering the seizure threshold. Though the risk is low (~1/1000 studies⁶), seizures have been induced in 7 individuals to date. However, these seizures have been shown to be self-limiting, and further seizures are no more likely than before the rTMS⁷.
• Hearing loss - The click associated with coil discharge has caused transient increases in the auditory threshold. This can be avoided if the participant and the operator wear foam earplugs⁵.
• Headache - Local stimulation of the muscles and nerves from the coil, especially with stimulation over the frontal areas, can result in headache, the most common side effect. This can be overcome with the use of mild analgesics⁶.
• Cognitive and motor effects - Varying effects on cognitive, perceptual and motor functions have been observed. These include finger tapping, improved verbal memory, dysphoria and euphoria³.
• Endocrinological effects - No changes in hormones have been observed³.
• Immunological effects - This was seen as an increase in CD8+ T-lymphocytes after left-side stimulation, and a decrease in these cells if the contralateral side was stimulated. These changes seem to be transient, resolving after 24 hours³.
• Kindling - This is the cumulation of effects repetitive stimulation, resulting in a seizure. This is mainly seen in frequencies of around 60Hz, and pulse durations of 1ms, which are both outside the effective range of current magnetic stimulators.
  A related concept is that of long-term potentiation, where repetitive stimulation induces long-lasting synaptic changes. This is why children, who would be more vulnerable to this problem, are advised against rTMS³.
• Effects from magnetics fields - The National Research Council concluded that there are no proven health risks associated with electromagnetic fields. However, this applies to chronic exposure to low-level intensities. rTMS involves brief focal exposure to high-intensity fields, and few investigations have been carried out on this aspect³.

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Guidelines

Suggested guidelines for the use of rTMS were set out at the International Workshop on the Safety of Repetitive Transcranial Magnetic Stimulation in 1996³. These covered legal and ethical implications, and the safe parameters in the use of rTMS, as well the management of the consequences of adverse effects.

• Ethical requirements

1. Informed consent must be obtained from subjects
2. Potential benefits must outweigh risks
3. Avoid uneven distribution of benefits and burdens of rTMS resulting from economic, social or physical conditions

Requirements 2 and 3 vary according to the criteria of the rTMS study: Class 1 involves experimental treatment of disease, and may involve significant side effects. Class 2 aims to improve understanding of the disease/treatment/safety of rTMS, with potential clinical value, and demands maximum subject protection. Class 3 studies normal subjects’ brain function, with potential scientific value, and also demands maximum subject protection.

• Stimulation parameters

Stimulation parameters have been set for rTMS 1Hz, determining maximum safe durations for certain intensities. Class 1 studies, which aim to clinically benefit the patient, can tolerate higher degrees of risk, and therefore may exceed stimulation parameters set for classes 2 and 3 shown below.

Maximum safe duration (s) of single trains of rTMS
(Reproduced from Wassermann, 1998³)
 
 

• Physiological monitoring

An experienced physician should observe the participant throughout the procedure. EEGs and EMGs can be monitored under certain circumstances to ascertain decreases in excitation threshold or intracortical spread.

• Neuropsychological monitoring

Tests can also be carried out in all classes of study, to determine neuropsychological effects, such as a change in reaction time, memory, verbal skills, mood and overall functional state.

• Staff involved in the procedure

The team should involve skilled operators and life-support equipment. A qualified clinical neurophysiologist should monitor the patient during rTMS. A physician or nurse skilled in seizure management should also be present.

• Management of seizures

Medical and psychological support should be provided, such as life-support equipment, the means to request further help, informing the patient of the risks. Anti-epileptic drugs should be used only under guidance of a skilled physician in more serious cases, e.g. seizures lasting over a few minutes, ones resulting in hypoxia, acidosis etc.

• Contraindications

As described above.

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References

1. http://www.biomag.helsinki.fi/tms/Thesis/dt.html#6 (Transcranial Magnetic Stimulation: Modelling and New Techniques)

2. Lorberbaum JP, Wassermann EM. Safety Concerns of TMS. In: George MS, Belmaker RH. TMS in Neuropsychiatry. Washington: American Psychiatry Press; 2000. p141-161

3. Wassermann EM. Risk and safety of repetitive transcranial magnetic stimulation: report and suggested guidelines from the International Workshop on the Safety of Repetitive Transcranial Magnetic Stimulation, June 5-7, 1996. Electroencephalography and clinical Neurophysiology. 1998; 108: 1-16.

4. Nahas Z, Bohning DE, Molloy MA, Oustz JA, Risch SC, George MS. Safety and Feasibility of Repetitive Transcranial Magnetic Stimulation in the treatment of Anxious Depression in Pregnancy: A Case Report. J Clin Psychiatry 1999; 60: 50-52.

5. Ebmeier KP & Lappin JM. Electro-magnetic Stimulation in Psychiatry. Advances in Psychiatric Treatment,2001; 7 (3), in press http://www.rcpsych.ac.uk/pub/pubsfs.htm

6. http://www.elsevier.nl/inca/homepage/sah/ifcn/doc/rtms-inf.htm (International Federation of Clinical Neurophysiology. Information Brochure on rTMS)

7. George MS, Lisanby SH, Sackheim HA. Transcranial Magnetic Stimulation: Applications in Neuropsychiatry. Arch Gen Psychiatry. 1999; 56: 300-11.

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