Chapter Overview
Chapter Synopsis: Occipital neurostimulation (ONS) provides a minimally invasive, reversible, and effective treatment for a number of intractable headache disorders. The technique is thought to work by inhibiting central nociceptive impulses by stimulation of the peripheral extensions of the trigeminocervical complex, the nerve branches of C2 and C3. A multicenter study showed that the technique shows promise for treatment of chronic headaches. Successful electrode implantation for occipital neurostimulation requires significant consideration of nerve anatomy and technical details of the various available devices. Ideally implantation should avoid unpleasant dysthesias, which can result from superficial placement, and occipital muscle stimulation that causes spasm when electrodes are implanted too deep. As in all forms of neurostimulation, lead migration represents a potential technical failure that can require surgical replacement; incidence is particularly high with ONS.
Important Points:
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Stimulation of the occipital nerve, which originates from the C2 nerve root, is a valuable tool in treating cervicogenic headache, occipital neuritis, chronic migraine, and chronic cluster headache.
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Current prospective randomized studies are pending to access the evidence-based impact of this therapy on migraine.
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In some cases ONS may be combined with stimulation of other cranial nerves to avoid the need for more invasive intracranial procedures.
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The risk of ONS is relatively low compared to spinal cord stimulation or intracranial procedures.
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The most common problems are migration, erosion, and infection. This chapter gives the reader some highlights to reduce complications.
Indications
ONS has been used successfully in the treatment of occipital neuralgia and many primary headache disorders such as migraine, transformed migraine, cluster headache, and hemicrania continua. Few reports also demonstrated its efficacy in secondary headache disorders, including cervicogenic headache, C2-mediated headaches, posttraumatic, and postsurgical headaches.
Mechanism of Action
The most accepted mechanism of action is that stimulation of the distal branches of C2 and C3, being the peripheral anatomical and functional extension of the trigeminocervical complex, may inhibit central nociceptive impulses. Positron emission tomography (PET) scan studies showed increased regional cerebral blood flow in areas involved in central neuromodulation in chronic migraine patients with occipital nerve electrical stimulation. Additional functional imaging may further define the exact mechanism of action as these studies become more widely available in multicenter studies.
Efficacy and Safety
Recently the preliminary results of a multicenter prospective randomized single-blind controlled feasibility study that was conducted to examine the safety and efficacy of ONS for treatment of intractable chronic migraine were reported. Patients who responded favorably to occipital nerve block (ONB) were randomized 2 : 1 : 1 to adjustable stimulation (AS), preset stimulation (PS), or medical management (MM). Those who did not respond to ONB formed an ancillary group (AG).
Three-month objectives included reduction in headache days/month, decrease in overall pain intensity (0 to 10 scale), and responder rate (>50% drop in headache days/month or >3-point drop in overall pain intensity from baseline). One hundred ten subjects were enrolled from nine centers; 75 were assigned to a treatment group (AS = 33, PS = 17, MM = 17, AG = 8). Sixty-six subjects completed diary data during a 3-month follow-up (AS = 28, PS = 16, MM = 17, AG = 5). At 3 months, percent reduction in headache days/month was 27% (AS), 8.8% (PS) (p = 0.132), 4.4% (MM) (p = 0.058), and 39.9% (AG) (p = 0.566). P values were for comparison to the AS group.
Reduction in overall pain intensity was 1.5 (AS), 0.5 (PS) (p = 0.076), 0.6 (MM) (p = 0.092), and 1.9 (AG) (p = 0.503). Responder rate was 39% (AS), 6% (PS) (p = 0.032), 0% (MM) (p = 0.003), and 40% (AG) (p = 1.000). The authors concluded that ONS may be a promising treatment for intractable chronic migraine and ONB may not be predictive of response to ONS.
Anatomy
The GON arises from the C2 dorsal ramus and curves around the inferior border of the inferior oblique muscle (IOM) to ascend on its superficial surface between the IOM and the semispinalis capitis at the C1 level. Then it penetrates the semispinalis capitis and invariably the splenius muscle to end subcutaneously near the nuchal line by penetrating the trapezius muscle or its apponeurosis. There is considerable anatomical variation in the course of the GON. Bovim and colleagues found that the GON pierces the trapezius in nearly half the subjects; however, others have described a much lower likelihood of penetration of the trapezius muscle. The GON was invested in the aponeurosis of the trapezius at its insertion.
The GON usually penetrates the semispinalis capitis muscle fibers at a distance between 2 and 5 cm caudad to the occipital protuberance. More cranially it may also penetrate the trapezius muscle fibers or aponeurosis, becoming superficial between 5 and 18 mm below the intermastoid line.
Technique for Occipital Neurostimulation
The procedure can be performed with local anesthetic and conscious sedation, monitored anesthesia care, or general anesthesia (especially in the prone position for better airway control).
The technique was originally reported by Weiner and Reed in 1999. Earlier reports involve placement of the leads subcutaneously at the C1 level. The stimulator lead can be directed medially from a lateral entry point medial and inferior to the mastoid process or laterally from a midline entry point.
The authors prefer a lateral point entry in unilateral cases since the patient can be placed in the lateral decubitus position. However, the midline point entry is more appropriate in bilateral cases when the patient is positioned prone.
Level and Depth of Lead Placement
The level and depth of lead placement are crucial for a successful ONS trial. Placing the leads too superficially risks failure of nerve stimulation and lead erosion through the skin or patients experiencing unpleasant burning sensations. On the other hand, leads placed too deep risk stimulating posterior neck muscles and causing unpleasant muscle spasms.
Positioning the stimulator lead subcutaneously at the C1 level places it at a significant distance from the nerve, with the posterior neck muscles (mainly trapezius and semispinalis capitis) intervening. Thus, to stimulate the GON itself, the intervening muscles are likely to be recruited as well ( Fig. 19-1 ).
Lead placement adjacent to the nuchal line would be less prone to muscle stimulation because the GON is superficial at this level.
Lead Type
Original reports of the procedure described using quadripolar leads, although recent technical and practice trends favor the use of octipolar leads. There are no comparative studies of quadripolar vs. octipolar lead use in ONS. However, the added electrode contacts in the octipolar leads allow for exponentially more stimulation configuration arrays. Because the lesser occipital nerve runs laterally to the GON at the level of the nuchal line, longer octipolar leads also capture lesser occipital nerve branches, which leads to better coverage ( Fig. 19-2 ). Paddle-type leads deliver electric current in one direction only, whereas cylindrical percutaneous leads deliver current circumferentially. Some clinicians prefer the paddle-type leads in redo cases secondary to percutaneous lead migrations because the paddle leads can be easily sutured into the surrounding fascia. The downside of the paddle is that the larger profile may lead to discomfort or erosion. The implanting doctor must weigh the benefits and the risks ( Fig. 19-3 ).
