TMS for Tinnitus: Transcranial Magnetic Stimulation Effective?

by

Transcranial magnetic stimulation (TMS) is showing promise as a non-invasive treatment approach for tinnitus in some patients.

Research indicates it may be able to reduce tinnitus loudness and annoyance by modulating brain activity.

However, significant questions remain regarding optimal protocols.

Key Facts:

  • TMS uses electromagnetic coils placed on the scalp to deliver magnetic pulses that can modulate neural activity.
  • Studies suggest it may reduce tinnitus by dampening hyperactivity in auditory regions of the brain.
  • Trials have targeted areas like the auditory cortex, temporoparietal cortex, and dorsolateral prefrontal cortex.
  • Low frequency stimulation around 1 Hz is most common, but a range of frequencies have been tested.
  • Benefits have been shown on tinnitus questionnaires, but results vary across studies.
  • Larger trials with extended follow-up are needed to verify effects and optimize protocols.

How TMS Works to Modify Neural Activity in Tinnitus

TMS utilizes electromagnetic induction to modulate electrical activity in the brain.

A stimulating coil is placed against the scalp and short magnetic pulses are generated.

This creates electric currents in the underlying neural tissue, which can excite or inhibit activity depending on the parameters used.

For tinnitus treatment, the goal is generally to reduce hyperactivity in brain regions involved in auditory processing, which is often observed in people with tinnitus.

Low frequency TMS around 1 Hz is thought to have an overall inhibitory effect on neural firing that could dampen this hyperactivity.

Frequencies above 5 Hz tend to be excitatory.

TMS can impact both local circuits and broader network connections.

Studies suggest effects may result from long-term depression in synapses, changes in brain oscillations, and secretion of neuromodulators like BDNF.

Results can persist beyond the treatment period, reflecting longer term neuroplastic changes.

Targeting the Auditory Cortex

Many TMS trials have targeted the auditory cortex in the temporal lobe, located underneath the temples.

This region plays a key role in auditory perception and has shown hyperactivity linked to tinnitus.

The goal is to directly dampen this excessive neural firing using inhibitory stimulation.

Some small studies stimulating the auditory cortex have found reduced tinnitus loudness and annoyance on questionnaires and analog scales.

However, larger trials have not always replicated significant therapeutic effects compared to sham TMS.

This suggests auditory cortex stimulation alone may not be sufficient for many patients.

TMS: Expanding Beyond Auditory Areas

Recent research indicates tinnitus may also involve a broader network of regions involved in attention, emotion, and memory.

This includes frontal areas like the dorsolateral prefrontal cortex (DLPFC).

Studies manipulating frontal regions along with auditory areas have shown promise.

One approach is to first activate the DLPFC with high frequency TMS, followed by slow frequency inhibition of auditory regions.

Others are exploring bilateral stimulation of both left and right auditory cortices combined with frontal sites.

Triple site approaches targeting the DLPFC along with left and right auditory cortex may be more effective than single site stimulation.

But not all studies have found a clear benefit over auditory cortex TMS alone.

More research is needed to verify effects of multi-region protocols.

Key Variables in TMS Protocol Design

Many variables can affect TMS outcomes, including the parameters of stimulation.

Optimal protocols are not yet clear.

Some key factors researchers are investigating include:

  • Frequency: Most common is 1 Hz for inhibition but ranges up to 50 Hz have been tested.
  • Number of pulses: Often 1000-2000 per session but up to 4000 or more. More is not always better.
  • Sessions: Typically delivered on consecutive weekdays for up to 2 weeks but longer treatment courses need study.
  • Intensity: Expressed as a percentage of resting motor threshold. Often set at 100-110%.
  • Coil orientation: Should be specified as this impacts induced current direction.
  • Coil type: Standard figure-eight coils but newer coils can stimulate wider regions.
  • Neuronavigation: Allows MRI-guided targeting but may not improve over conventional methods.
See also  TMS is Effective But Underutilized for Major Depression vs. Standard of Care (2024 Study)

Benefits and Limitations Seen in Clinical Trials

A 2021 meta-analysis of 28 randomized controlled trials found TMS led to moderate but statistically significant improvement in tinnitus questionnaires and analog scales.

Effects were greatest for auditory cortex stimulation protocols.

However, a separate meta-analysis of 10 studies using 1 Hz TMS of the auditory cortex found no significant effects on tinnitus severity compared to sham TMS.

Individual trials have also had mixed results, with some but not all reporting therapeutic benefits.

Varying trial outcomes may reflect differences in protocols as well as small sample sizes.

The literature overall indicates potential efficacy, but large multi-site trials with extended follow-up are critically needed to verify effects.

Standardized protocols will also be key for any future clinical applications.

Durability of TMS Treatment Effects in Tinnitus Patients

An important question is whether benefits are sustained long-term after a TMS treatment course.

Studies assessing outcomes weeks to months after TMS have found a range of results.

In one trial, tinnitus improvements were maintained over a 180 day follow-up period.

But others have observed effects partially wearing off within weeks after TMS.

The trajectory of long-term outcomes likely depends on the durability of neuroplastic changes induced.

Again, larger controlled studies with follow-up at 6-12 months post-treatment are needed to properly assess sustained impacts on tinnitus perception.

Neuroimaging to Map TMS Effects

Neuroimaging techniques like EEG, PET and fMRI are providing insights into how TMS alters neural activity in tinnitus patients.

However, imaging findings have varied across studies.

Some have reported changes in spontaneous oscillatory activity after TMS treatment, along with increased functional connections between relevant brain networks.

But others found no changes in intrinsic connectivity.

More work is needed to unravel TMS effects on brain function in tinnitus.

Imaging may also help optimize protocols by targeting stimulation based on the functional and structural profiles of individual patients.

This personalized approach could potentially improve outcomes.

Safety and Tolerability of TMS for tinnitus

TMS is considered safe with minimal side effects when appropriate protocols are followed.

Headaches or local discomfort during stimulation are sometimes reported.

Seizure risk is very low.

Effects on hearing have been a concern, as the auditory cortex is stimulated.

But trials specifically assessing hearing before and after TMS have found no negative impacts.

This is likely because treatment intensities are below the threshold for damage and patients wear earplugs.

Is TMS Cost-Effective for Tinnitus?

The upfront cost of TMS equipment is a barrier for wider availability.

A full setup including the stimulator, coils and neuronavigation system can require an investment of up to $100,000.

Reimbursement for TMS treatment varies across insurance providers.

However, the costs of current tinnitus therapies over a patient’s lifetime are also substantial.

And TMS has the advantage of being non-invasive with minimal side effects.

Hopefully growing evidence for efficacy will improve clinical access to TMS.

TMS, Tinnitus, Future Research Directions…

Moving forward, large randomized controlled trials at multiple sites are critical for confirming the therapeutic potential of TMS in tinnitus.

Extended long-term follow-up will also be important.

Comparisons of different multi-site protocols can help identify optimal parameters.

Customizing treatment using imaging and EEG profiles could make TMS more precise.

And cost-effectiveness studies will aid in policy decisions regarding reimbursement.

TMS shows significant promise as part of the tinnitus treatment arsenal.

But key questions remain before it can become a standard clinical tool.

Ongoing research initiatives will hopefully provide the data needed to demonstrate robust and sustainable benefits from this technology.

References