Occipital Nerve Stimulation

Introduction

Primary headache disorders are classified mainly as migraine, tension-type headaches, and the trigeminal autonomic cephalgias, which include cluster headaches. “Primary” refers to a lack of clear underlying causative pathology, trauma, or systemic disease. Secondary headaches are usually associated with an underlying abnormality such as, but not limited to, infection, trauma, tumor, or nerve root compression. It is important to correctly diagnose the headache etiology in order to intelligently approach treatment options.

Occipital neuralgia (ON) is a known cause of headaches and is characterized by sharp, electrical, paroxysmal pain involving the occipital nerves––the greater occipital nerve (GON), the lesser occipital nerve (LON), and the third occipital nerve (TON).

The International Headache Society (IHS) defined ON as a paroxysmal, shooting, or stabbing pain lasting from a few seconds to minutes and mainly starting in the occipital region before radiating within the distribution of the occipital nerves.

The pain is frequently associated with tenderness over the responsible nerve and is often relieved by local anesthetic injection. ON is also known as C2 neuralgia or Arnold neuralgia. Although ON is mainly unilateral, bilateral pathology is not uncommon. The most common trigger is compression of the GON or LON, with the GON involved in over 90% of cases and LON involvement accounting for just 10% of all cases. The incidence of ON is 0.1% to 4.7% of patients with cephalgia.

Peripheral nerve stimulation (PNS) in the occipital region has emerged as a promising treatment modality for patients with medically refractory chronic primary headache disorders emanating from the areas innervated by the occipital nerves (GON, LON, and TON). The gate-control theory of pain, as postulated by Melzack and Wall more than 50 years ago, forms the basis for the mechanism by which the perception of pain is inhibited during chronic nerve stimulation. Current reports suggest that 60% to 80% of patients with chronic cluster headaches who have failed medication management will experience relief in response to occipital stimulation.

Patients implanted with an occipital nerve stimulation (ONS) system may benefit from long-term relief from painful attacks of ON, without any significant side effects.

Clinical Presentation

Beuto et al. described ON in 1821 as a sharp, lightning-bolt pain radiating from the occiput to the vertex.

The medical terms ON and cervicogenic headache (CGH) describe a syndrome of neck and head pain primarily referring to the occiput, as well as the temporal area, forehead, and retroorbital areas, that may arise some distance away, in the upper cervical spine. In contradistinction, the term migraine has several uses. The IHS defines a migraine as a unilateral, throbbing headache associated with photophobia, phonophobia, and nausea; patients, on the other hand, use the same word to describe a “sick” or severe headache. Neither use of the term migraine defines the etiology of the headache. Neck pain is also a common symptom of a migraine attack. In a study of 50 migraine patients by Blau et al., 64% reported neck pain or stiffness associated with migraine attack, with 31% experiencing neck symptoms during the prodrome, 93% during the headache, and 31% during recovery phase.

Greater ON characteristically presents as paroxysmal shooting, stabbing pain from the suboccipital region to the vertex. Because the GON is made up of contributions from C1, C2, and C3, there can be a wide range of clinical presentations. As a subset of CGH, ON can cause pain and paresthesias to the posterior scalp, the periorbital, temporal, and mandibular regions, and the external ear and mastoid regions, as well as pain in the neck and shoulders.

The first three cervical spinal nerve segments (C1-C3) that make up the occipital nerves share a relay station in the brainstem that continues into the upper cervical spinal cord with the trigeminal cell bodies (the cervico-trigeminal complex). The pain of ON and CGHs can therefore be referred to structures innervated by the branches of the trigeminal nerve, namely the forehead, temples, and eyes ( Fig. 8.1 ).

Some patients with unilateral ON, perhaps because of the proximity of the occipital artery, can present with throbbing, unilateral headaches associated with photophobia, phonophobia, and nausea.

There may be a history of occipital pain, often radiating to the face, specifically described as “behind my eye” and “like an ice pick.” Occipital headaches may start as “tension headaches” in the upper cervical region but then center at the base of the skull. ON has a close relationship with cluster headaches, and the use of occipital injections to treat cluster headaches has been described by several authors.

Anatomy

There are three major occipital nerves (GON, LON, and TON) ( Fig. 8.2 ). These three pairs of nerves arise from the C2 and C3 spinal nerves. They are responsible for the innervation of the posterior scalp, part of the vertex, and the posterior auricular region.

Greater occipital nerve

The largest of the three occipital nerves, the GONs, arise from the posterior rami of C2 that run inferiorly between the arch of C1 (atlas) and the lamina of C2 (axis). The GON traverses between the inferior capitis oblique and semispinalis capitis muscle from underneath the suboccipital triangle. The GON rarely travels within the inferior oblique muscle.

There are three parts to the GON, as well as two bends ( Fig. 8.3 ). These are the regions of possible entrapment. The first part runs between the origin of the nerve and the inferior oblique muscle (P1 in Fig. 8.3 ), underneath where the nerve makes its first bend (A1 in Fig. 8.3 ) from a lateral to a medial direction. The second part of the nerve runs cranially between the semispinalis capitis muscle on the one side and the inferior oblique muscle, rectus capitis posterior muscle, and rectus capitis anterior muscle on the other side (P2 in Fig. 8.3 ). When perforating the semispinalis capitis muscle toward the surface, the nerve makes its second bend in a lateral direction (A2 in Fig. 8.3 ). The third part of the nerve runs further laterally, where it perforates the aponeurosis of the trapezius muscle and begins its subcutaneous course (P3 in Fig. 8.3 ). The nerve usually divides into branches after perforating the aponeurosis and joins with the occipital artery ( Fig. 8.4 ). A cutaneous branch of the suboccipital nerve (the C1 dorsal ramus) will occasionally join the GON as it accompanies the occipital artery.