Occipital Nerve Stimulation

Occipital nerve stimulation (ONS) is a form of neuromodulation therapy aimed at treating headache and craniofacial pain. This therapy involves an implantable device composed of an electrode and pulse generator. The lead is placed into the subcutaneous tissues innervated by the greater and lesser occipital nerves, and the pulse generator is implanted into a subcutaneous pocket in the chest, abdomen, or back.

Prior to implantation, a trial is performed in which leads are placed under the skin and are connected to an external battery. The trial is performed under sedation, and the patient is discharged the same day. Afterward, the patient tries the therapy for 4–7 days and keeps a detailed pain diary.

A permanent device is implanted only if the patient reports significant improvements in pain and quality of life. The permanent implantation is placed under sedation or anesthesia, and the patient is discharged the same day.

The device is programmed by a clinical specialist appointed by the manufacturer.

This type of therapy has been evolving as a treatment for intractable occipital headache syndromes since the first implant in 1993, and the data to support its use are robust. Multiple authors have reported that successful neuromodulation for occipital headache syndromes can be accomplished with subcutaneous regional electrode placement. Available literature on the use of peripheral neurostimulation for headache includes occipital nerve stimulation, supraorbital nerve stimulation, and infraorbital nerve stimulation. Recently, other neurostimulatory techniques such as cervical epidural neurostimulation have been explored for cluster headaches, as well. ^[1]  

Neurostimulation is FDA-approved for the treatment of certain intractable pain syndromes, although it is not approved for headache, chronic migraine, and craniofacial pain and thus occipital nerve stimulation continues to represent an off-label use.

Mechanism of action

The theory of neuromodulation refers to therapeutic alteration of activity, electrically or chemically, in the central, peripheral, or autonomic nervous systems via the process of inhibition, stimulation, modification, or other forms of regulation. Occipital nerve stimulation is a form of neuromodulation that is reversible and adjustable and that can be tailored to an individual’s specific needs.

The mechanisms of action ^[2] for the paresthesia patterns and pain relief obtained from an occipital nerve stimulation are incompletely understood but appear to involve the following:

• Subcutaneous electrical conduction

• Dermatomal stimulation

• Myotomal stimulation

• Sympathetic stimulation

• Local blood flow alteration

• Peripheral nerve stimulation

• Peripheral and central neurochemical mechanisms

• Trigeminovascular system and Trigeminocervical tract

One prevalent theory is the involvement of the trigeminocervical system, which is the anatomic overlap of the trigeminal and occipital afferent systems at the level of C2 in the spinal cord. Trigeminal afferent pathways, and thus primary headache disorders, can be modulated at the C2 level by occipitally mediated afferents. In addition, electromodulation works to reduce blood flow to the pain-stimulating areas and to reduce abnormal excitation of the peripheral pain fibers, thus preventing central sensitization of trigeminal sensory nerve pathways, potentially reducing on-cell activity, and modulating the descending system at the level of the dorsal horn.

The gate control theory described by Melzack and Wall in 1965 (see image below) has been postulated to be one mechanism of action by which occipital nerve stimulation works for the treatment of local neuropathic pain. ^[3] According to this theory, stimulation activates large myelinated afferents, which “close the pain gate” in the substantia gelatinosa by enhancing the inhibitory actions of local circuit neurons in the dorsal horn on central transmission cells. Since pain states are maintained by continuous firing of unmyelinated and small myelinated afferents, a proportionately greater increase in the activation of large myelinated afferents closes the gate and stops pain transmission via presynaptic inhibition.

Indications for occipital nerve stimulation include the following:

• Chronic, intractable primary headache disorder ^[4]

• Chronic, intractable secondary headache disorders

• Neuropathic pain involving the occipital or suboccipital region

Migraine affects 12% of the US population, and women account for 70% of affected individuals. It is estimated that up to 5% of persons who have migraines experience daily or near daily headaches (transformed migraine, chronic daily headaches). Furthermore, 1%–2% are so poorly responsive to medication paradigms that this failure can lead to various consequences, including narcotic dependence, severe restrictions in daily activities, failed personal and career objectives, and an overwhelming sense of hopelessness and despair.

Of patients with migraines, 3%–13% progress to chronic migraine, which is defined as headache pain more than 3–5 days per month. In many cases, the migraines are intractable to medical therapy. Patients in whom medical therapy has failed and who have headache pain that is refractory to preventive medication may benefit from occipital nerve stimulation trials.

Surgical modalities for treating the occipital nerve are reserved as a last resort after failure of medical management. The surgical modalities include decompressive, ablative, and stimulating procedure such as occipital nerve stimulation. Furthermore, occipital nerve stimulation is a nonablative procedure.

The benefits of occipital nerve stimulation have been described in a number of conditions, including the following:

• Occipital neuralgia (intractable) ^[5]

• Occipital headaches

• Migraine (intractable) ^{[6, 7]}

• Cervicogenic headache

• Postherpetic neuralgia

• Tension headache

• Cluster headaches

• Posttraumatic pain

• Posttraumatic headache

• Chronic daily headaches (transformed migraine)

• Chronic headache attributed to whip lash

• New daily persistent headache

• Hemicranias continua

• Headache secondary to idiopathic intracranial hypertension

If the patient’s quality of life does not improve during the trial period (see Pre-Procedure Planning), the device is not implanted. 

If there is concern that the patient’s headaches are due to either medication overuse or opioid use, this may disqualify them from implantation, despite quality-of-life improvement during the trial period. ^[8]

 

 

Complications of occipital nerve stimulation placement are avoidable by taking certain necessary steps, as follows:

• Anchoring leads to fascia at retromastoid incision

• Swabbing all candidates to rule out methicillin-resistant Staphylococcus aureus (MRSA) colonization.

• Preoperative (prior to implantation) antibiotic treatment to eliminate MRSA colonization

• Trimming patient's occipital region hair with clippers

• Sterile surgical technique to help reduce the incidence of infection

Procedure Planning

Prior to implantation, a trial is performed in which leads are placed under the skin and are connected to an external battery. The trial is performed under sedation, and the patient is discharged the same day. Afterward, the patient tries the therapy for 4–7 days and keeps a detailed pain diary.

A permanent device is implanted only if the patient reports significant improvements in pain and quality of life. 

Positive response to transcutaneous electric nerve stimulation is also a good predictor for repsonse to ONS for treatment of occipital headache. ^[9]

Complication prevention

Complications of occipital nerve stimulation placement are avoidable by taking certain necessary steps, as follows:

• Choosing the right candidate for surgery; this is an elective surgery, and patients should be medically optimized (eg, good control of diabetes)

• Good sterile intraoperative surgical technique

• Swabbing all candidates to rule out MRSA colonization

• Anchoring leads to fascia at retromastoid incision

• Preoperative antibiotic treatment to eliminate MRSA colonization prior to implantation.

Several studies with long-term follow-up (>10 years) demonstrate that, in more than 150 patients with implants, approximately 75% of patients rated either good or excellent long-term pain relief, with a 15% fair rating and a 10% poor rating. ^[2]  

A 2011 study by Mogilner and Mammis found that 82% patients who underwent implantation reported continued significant benefit from stimulator use. ^[10]

The ONSTIM trial published data in 2011 showing that at 3 months 39% of patients reported at least 50% reduction in headache days per month or a 3-point reduction in pain intensity with adjustable stimulation, compared with 0% in the medically managed group. ^[11]

In 2012, Silberstein et al. published results from their multicenter, double-blind, randomized controlled trial evaluating occipital nerve stimulation for migraine. They reported that significantly more patients achieved 30% pain reduction, a reduction in headache days per month, and reductions in migraine-related disability when compared to sham stimulation. ^[12]

In their 2017 single center, double-blind, randomized controlled trial Mekhail et al. reported a signifciant reduction in headache days, pain intensity, and migraine-related disability in patients utilizing occipital nerve stimulation for chronic migraine. ^[13]

Complications

Placement of an occipital nerve stimulator is a relatively safe procedure with a low complication rate. The specific complications include the following: ^{[14, 15, 16]}

• Lead migration or fracture

• Surgical site infection

• Wound erosion

• Revision surgery for other reasons (primarily elective cosmetic adjustments to the leads) 

• Hardware malfunction 

• Battery failures

• Inadequacy of stimulation-related coverage

• Seromas

• Hematomas

• Pain and numbness at lead sites

Few major complications have been reported, and the minor complications are easily treatable and usually do not affect the efficacy of the therapy. The most common device related complications include migration, erosion, and infection. ^[17]

Compared with other forms of peripheral nerve stimulation, ONS generally has higher rates of complication, especially related to lead migration and infection. The long wire course from lead placement to the pulse generator, thin subcutaneous tissue in the scalp, and flexion, extension, and rotation of the head can lead to dislodgement of the leads. ^[18]