Microstimulators Hold Promise for Some Medically Refractory Headaches

Occipital nerve stimulation (ONS) for medically refractory headache pain has been available since the late 1990s. Offered at all three Mayo Clinic sites, it is most commonly used to treat migraine and cluster headaches that do not respond to conventional medications. Mayo Clinic in Arizona has been involved in several studies of ONS, including work on a microstimulator that is not yet commercially available.

In traditional ONS, a thin wire containing electrodes is implanted under the skin in the back of the head. The wire extends to an implantable, battery-driven impulse generator (IPG). Using a remote, handheld programmer, the patient controls the rate and intensity of the pulses. The pulses create paresthesias, often experienced as a light tingling or buzzing, in the area of the occipital nerve and the distal branches of the second and third cervical nerves.

Although the mechanism is not entirely understood, peripheral nerve stimulation may influence deep brain centers that are responsible for pain modulation, and may gate or block pain signals from ascending from the trigeminal-cervical complex in the lower brainstem and upper cervical spinal cord.

Advantages of Microstimulators

In traditional ONS, the IPG is implanted below the clavicle, in the flank, or in the lower abdomen. In this configuration, he wires can extend more than a meter from the leads to the IPG, a situation that can create mechanical stress, wire migration, and breakage.

Terrence L. Trentman, M.D., former head of the Mayo's Pain Clinic in Arizona, reports that "lead migration has been one of the biggest frustrations that we've experienced with the occipital stimulator. Microstimulators obviate that risk because both the electrodes and the IPG are contained within the stimulating device, which is about the size of a paperclip."

Occipital nerve stimulation system

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Richard S. Zimmerman, M.D., a neurosurgeon at Mayo Clinic in Arizona, notes another advantage, "The microstimulator is less invasive and the surgery carries fewer risks. Traditional stimulators have long wires and require 3 incisions. Microstimulators require only 1 incision and no wires."

Patient Response to ONS at Mayo Clinic Arizona

Dr. Trentman points out that ONS "is reserved for patients for whom all other treatments have failed — people who not only have chronic daily headache, but also have had continuous, severe headaches for years and have tried everything from multiple types of medication to psychological, behavioral, and alternative approaches to pain management."

Recently, Drs. Trentman and Zimmerman, along with David W. Dodick, M.D., neurologist at Mayo Clinic in Arizona and others, conducted the first test of microstimulators. In a small series of tests involving patients with medically refractory chronic cluster headache, 75 percent reported a positive response 3 months after implant. The researchers have also found microstimulation to be effective in patients with hemicrania continua.

ONS complications can include infection and an increase in pain. Traditional ONS is first conducted on a trial basis to screen for increased pain. Dr. Dodick notes that because ONS takes time to work, patients may not experience improvement in the 5- to 7-day trial period. As long as they have no adverse effects and are amenable, they will receive the device after the trial period.