Extent of Pain Distribution in Entrapment of the Greater Occipital Nerve Identified Through Skin Lesions of Herpes Zoster Involving the Greater Occipital Nerve
Article information
Abstract
Herpes zoster (HZ) involving the upper cervical nerves (C2-C4), which innervate the posterior head, is rare. There have also been few reports of HZ lesions involving the greater occipital nerve (GON), which refers to the medial branch of the dorsal ramus of the second cervical nerve. Pain due to GON entrapment radiates not only to the temporo-occipital region, but also to the ear, retro-auricular and sub-auricular areas of the neck, the angle of the jaw, and the posterolateral neck. Herein, we present the case of a patient who underwent decompression surgery for referred trigeminal pain due to GON entrapment and who developed HZ one week later. Skin lesions of HZ involving the GON occurred not only in the occipital area but also in the ipsilateral ear, auricle, posterior and anterolateral neck. This case of HZ involved all cutaneous areas innervated by the C2, C3, and C4 spinal nerves. The extent of the skin lesions indicated where the pain from the GON radiated.
INTRODUCTION
Herpes zoster (HZ) which is commonly called shingles from the Latin cingulum, meaning belt is a distinctive syndrome caused by reactivation of varicella-zoster virus (VZV)1). The skin rash of HZ shows distinctive localization and distribution. Typically, HZ is unilateral, does not cross the midline, and is localized to a single dermatome of a single sensory ganglion (adjacent dermatomes are involved in 20% of cases)6). HZ involves the thoracic nerves and the ophthalmic division of the trigeminal nerve19). HZ does not typically involve C2 or C3, but it does occur in rare cases18,21). However, the distribution of C2 and C3 dermatomes is not well known because diseases specifically affecting these roots are rare.
Entrapment of the greater occipital nerve (GON) has been reported to cause occipital neuralgia and chronic occipital headache due to GON entrapment (COHGONE)7,9-11,18,22,23,25,27). Entrapment of the GON occurs at the exit of the trapezius tunnel formed by a tendinous aponeurotic sling of the trapezius muscle attached to the upper nuchal line3,4,15,16,28). The GON originates in the medial branch of the dorsal rami of the second cervical nerve root. It also receives a branch from the dorsal rami of the C3 root3,28). Pain associated with GON entrapment has been reported to be distributed not only to the suboccipital area, but also the vertex, temples, retro-auricular and subauricular regions, jaw angle, and posterolateral neck7,9-11,18,22,23,25,27). Along with suboccipital pain, it can cause referred pain in the facial trigeminal distribution stemming from sensitization and hypersensitivity of the trigeminocervical complex7,9-11,18,22,23,25,27). To clinically infer GON entrapment and referred trigeminal pain due to GON entrapment, it is important to have a comprehensive understanding of the distribution of pain caused by GON entrapment.
The author recently experienced a case in which a patient who underwent GON decompression for occipital pain associated with referred trigeminal pain developed HZ in the operated GON area one week after surgery. The distribution of skin rashes corresponded closely to the area from which pain radiates due to GON entrapment, a topic that has attracted increasing research interest in recent years7,9-11,18,22,23,25,27). Therefore, to improve our understanding of the pain distribution of GON entrapment, the current work reports on the distribution of skin lesions involving the GON.
CASE REPORT
A 65-year-old female patient visited the hospital with chronic pain in her left gum and left temporo-occipital region. Two years prior, chronic pain had developed in her left upper gums two days after abutment and crowning of two dental implants (Fig. 1). The chronic pain in the upper left gums disappeared after the implants were removed a year later. Two months after the chronic pain in the left upper gum disappeared, she developed spontaneous pain in her left lower gums (Fig. 1). She simultaneously developed pain in her left occipital and neck area (Fig. 1). She was examined again by several dentists, but no abnormalities were found in her teeth. She reported a dull ache in her lower gums lasting all day. Dull pain also persisted in both her left occipital area and the left side of her neck (Fig. 1A). The pain in her left neck radiated to her left shoulder. The pain extended to her left cheek and also occurred intermittently inside her left ear. Her left gum and neck pain was found to be persistent and not triggered by neck posture or jaw movements.
Schematic diagram showing the distribution and characteristics of chronic pain. (A) Two years prior to the patient’s presentation at our center, chronic pain first started in the upper left gums. The gray spots over the left face mark the location of this gum pain (left). Then, pain occurred in the lower left gum (left). At the same time as the left lower gum pain started, chronic pain began to occur in the left occipital and neck area and persisted (middle). The gray areas over the left face and neck indicate the distribution of continuous tightening pain that occurred three months prior to the patient’s visit. A month prior to the presentation, dull pain occurred in the right cheek and right retro-auricular occipital area (right). (B) Intraoperative photographs showing entrapment of the right greater occipital nerve (white arrows) at the trapezial tunnel. Greater occipital nerve entrapment can be observed by lifting the trapezial aponeurotic edge (black arrows). The inset shows the direction of the image and the location of the incision.
Her persistent gum pain was diagnosed as atypical facial pain by her dentist, and she was prescribed medications including clonazepam and gabapentin. Meanwhile, she was also diagnosed with trigeminal neuralgia by a neurologist. Her neck and shoulder pain were diagnosed as cervical strain and occipital neuralgia by a neurosurgeon and an orthopedic surgeon, respectively. Her facial, occipital, and neck pain did not improve despite receiving continuous medication for the atypical facial pain along with physical therapy for about a year. A month prior to the presentation noted at the beginning of this section, she experienced dull pain in her right cheek and right retro-auricular occipital area, and this pain persisted as well (Fig. 1). The patient came to the author in an attempt to determine the cause of her chronic facial, occipital pain, and neck pain of unknown origin.
Although there was persistent pain and discomfort in the face and neck on examination, no objective sensory changes in the face were confirmed. Moreover, no neurological abnormalities were found, including the trigeminal nerve, other cranial nerves, or masticatory function. No allodynia or tenderness was found in the occiput, neck, or face. There were no neck or jaw-related movement limitations. Laboratory tests revealed normal findings, including erythrocyte sedimentation rate and uric acid. Magnetic resonance imaging of the cranial nerves that were suspected of having trigeminal neuropathy did not show vascular compression or abnormal contrast enhancement of the trigeminal nerve. A computed tomography scan of the cervical spine was also performed to identify structural lesions of the craniospinal junction and the pathway from the C2 nerve roots to the GON, but revealed no abnormalities either. Other than chronic intermittent neck and shoulder pain, there was no history of other conditions such as hypertension or diabetes.
Having in mind the possibility of referred trigeminal facial pain due to GON entrapment, occipital nerve block (ONB) of left GON was performed using 2 mL of 2% lidocaine, which relieved the intensity of the temporo-occipital, neck, and left gum pain for 20 hr. One day after receiving ONB, the pain in the left face, occipital, and neck continued to persist with the same intensity as before. The same transient improvement was found in the second block of the left GON, which was implemented two weeks after the first ONB. Considering the chronicity and refractoriness of the pain along with the possibility of referred facial pain due to entrapment of GON, decompression of bilateral GON was recommended after obtaining written informed consent.
Decompression of the GON was performed bilaterally under microscopic vision. Surgical findings confirmed that bilateral GONs were entrapped beneath the tendon aponeurotic edge of the trapezius muscle (Fig. 1B). The patient was discharged 2 days after surgery without any special neurological abnormalities. At the outpatient follow-up 2 weeks after surgery, the surgical wound was found to be clean, and mild numbness and paresthesia were observed in both occipital areas. It was confirmed that the patient's occipital and neck pain had disappeared. The patient felt no pain in her right gum, but the pain in the left gum still persistent. A week later, the patient unexpectedly presented at the outpatient clinic with vesicular rash on the right occipital, anterolateral neck, and shoulder (Fig. 2). The patient reported that three days prior, she had begun experiencing new tingling pain intermittently in the right side of her occipital, and two days prior, she had suddenly developed a rash in her occipital and neck. The patient was diagnosed with shingles through a dermatological examination and prescribed antiviral medication. Because the patient continued to take gabapentin and Ultracet® after surgery, the acute pain caused by shingles was not severe. After 3 months, the patient's bilateral occipital and neck pain improved to the point that they no longer existed. The patient reported a 50% improvement in her left lower gum pain and was taking 200 mg of gabapentin per day. Neuralgia and complications related to HZ were not observed.
Clinical photographs showing the location of skin lesions caused by herpes zoster involving the right greater occipital nerve. (A) Skin lesions located on the right ear, occipital, and posterolateral neck and shoulder. The skin rash covers the entire suboccipital region and posterolateral neck. It includes the entire posterior aspect of the right auricle and the sub-auricular area. (B) The skin rash spread throughout the submandibular area and anterior neck area, including the angle of the mandible. It also extended to the ventral side of the right auricle and the right cheek and subclavicular area.
DISCUSSION
1. HZ and Skin Lesion
VZV is a ubiquitous human alpha-herpes virus that causes varicella (chicken pox) and HZ (shingles)2). Varicella, which results from primary VZV infection, is a common childhood illness associated with fever and a generalized pruritis vesicular rash2). As is characteristic of the alpha-herpes viruses, VZV establishes latency in the cells of the dorsal root ganglia after primary infection2). VZV persists in the sensory ganglia of the cranial nerves and the spinal dorsal root ganglia after varicella has resolved. It may become reactivated after many decades of latency. It was not fully understood what exactly perturbs the latent VZV genome, but reactivation causes HZ in adults1,2). This resurfacing of VZV requires the movement of virions from the neurons, along axons, to the skin, where the virus must then evade innate and adaptive host immune responses, spread from cell to cell, and form lesions that eventually penetrate the epidermis1,2). HZ is a localized, painful, vesicular rash that involves one or adjacent dermatomes and is caused by VZV reactivation2).
The reactivation of VZV from latency causes a localized, pruritic, vesicular rash that typically appears unilaterally in the distribution of one or more adjacent sensory nerves2). In most cases, shingles are unilateral in location and do not cross the midline19). The most common sites for shingles are the thoracic nerves and the ophthalmic division (V1) of the trigeminal nerve2). Shingles is generally known to involve a single dermatome of a single sensory ganglion; however, adjacent dermatomes may be involved in 20% of cases19). Considering that HZ commonly involves only the ophthalmic (V1) division of the trigeminal nerve, it is thought that singles may involve only one sensory nerve branching from a single ganglion.
2. Entrapment of GON and Clinical Manifestations
The distribution of skin lesions of HZ in the current case corresponds to the distribution of pain associated with GON entrapment. Pain stemming from the disease involving the GON is known to be distributed from the suboccipital area to the occipital vertex. However, the pain of chronic GON entrapment radiates more widely than was previously known24,25). Pain stemming from GON entrapment radiates not only to the occipital area but also to the vertex and temporal; retro-auricular and sub-auricular areas; the angle of the jaw; and the lateral and posterior neck24,25). If one fails to consider this radiating pattern of pain of GON entrapment over the posterior head and neck, the pain of GON entrapment can be misdiagnosed as other diseases that cause headache and neck pain24,25).
To this point, diseases involving the GON have been thought to cause symptoms of occipital neuralgia. Occipital neuralgia is a rare cause of cranial headache24,25). It is characterized by paroxysmal shooting or stabbing pain involving the posterior part of scalp with distributions of the GON and lesser occipital nerve (LON)28). Excluding structural causes of occipital neuralgia, occipital neuralgia has been considered to be idiopathic in etiology28). However, several anatomical studies and recent clinical reports have suggested that GON entrapment is the main cause of occipital neuralgia4,15,16,24,25). However, occipital neuralgia is not a sole manifestation of chronic GON entrapment13,24,25). Along with the stabbing pain of occipital neuralgia, GON entrapment commonly manifests as aching and throbbing pain in the temporo-occipital areas and as radiating pain to retro-auricular and posterolateral neck24,25). Chronic continuous aching, tightening, and pressure-like pain in the occipital region does not meet the criteria of occipital neuralgia based on the current classification of headache by the International Headache Society8). Moreover, one study found that many patients with chronic occipital/suboccipital headaches caused by GON entrapment do not show recurrent paroxysms of stabbing pain, which makes such cases difficult to correctly diagnose24). Therefore, chronic occipital/suboccipital pain induced by chronic entrapment of the GON, which is alleviated by its decompression, was referred to as a syndrome of COHGONE24). In fact, COHGONE patients have been treated for several years based on multiple diagnoses associated with chronic occipital headache, including simple headache, migraine, tension headache, chronic migraine, cervicogenic headache, cervical disc herniation, trapezial myofascial pain syndrome, and even psychiatric problems10,12,24,25).
3. Distribution of Pain in GON Entrapment
An important clue that should lead one to suspect occipital and neck pain due to GON entrapment is the distribution of pain. Symptoms of GON entrapment do not radiate only to the occipital vertex, as is observed in occipital neuralgia. The most common misconception is that pain from GON entrapment will only be localized to the dermatome area of the C2 nerve root because GON arises from the C2 nerve root (Fig. 3A)10,12). However, unless structural lesions of the C1-C2 cervical spine only irritate the C2 dorsal root, it is rare to find a disease that causes pain in the distribution of the C2 root.
Currently known dermatomes of the high cervical nerves (C2-C4) and the extent of skin lesions in the current case involving the greater occipital nerve. (A) Foerster’s tactile dermatome map. Redrawn while referencing Foerster’s clinical photographs5). The overlap among the C2, C3, and C4 dermatomes should be noted. (B) The most consistent tactile dermatomal areas based on the best available evidence presented by Lee et al.13). Redrawn with reference to Fig. 4 by Lee et al.13). (C) Extent of skin lesions (gray areas) of herpes zoster in the present case involving the greater occipital nerve. (D) Range of radiating pain due to greater occipital nerve entrapment. Redrawn with reference to Fig. 3 by Son24). [Modified from “Decompression of the Greater Occipital Nerve for Occipital Neuralgia and Chronic Occipital Headache Caused by Entrapment of the Greater Occipital Nerve”, by Son BC, 2022, J Neurol Surg A Cent Eur Neurosurg, 83, pp. 461-70. Copyright 2022 by the Thieme. Modified with permission].
It should also be taken into account that the current dermatome maps are inaccurate and that there is currently a lack of consensus about the location and size of individual dermatomes13). In particular, the dermatomal maps in standard anatomical and medical reference texts show significant variability13). Indeed, almost all areas of skin are innervated by two or more spinal roots. Moreover, there are intrathecal intersegmental anastomoses between dorsal rootlets, thus allowing sensory neurons with a ganglion cell at one dorsal root ganglion to enter the spinal cord at a different level14). In research focusing on dermatomes of the C2 and C3 roots, Poletti studied the tactile and pain dermatome in the pinprick response after a local anesthetic block of the C2 and C3 roots17). Poletti’s C2 and C3 pain dermatomes both fall within the overlapping C2 and C3 tactile dermatomal areas suggested by Foerster (Fig. 3A)5). Based on a review of existing dermatome maps, Lee et al.13) suggested that dermatomes are much larger than they are shown in current anatomy texts (Fig. 3B). As confirmed in this case, the skin lesions caused by HZ that invaded the GON in this case included both the dermatomes of the C2 and C3 nerve roots (Fig. 2). This lesion also appears to involve the C4 dermatome in the shoulder (Fig. 3C).
4. Extensive Communications of the GON in the Occipital and Cervical Areas
The skin of the cervical area is innervated by branches of cervical spinal nerves, via both dorsal and ventral rami3). The dorsal rami supplies skin over the back of the neck and scalp, while the ventral rami supplies skin covering the lateral and anterior portions of the neck, as well as the angle of the mandible3). The dorsal rami of the first, sixth, seventh, and eighth cervical nerves have no cutaneous distribution in the neck.
The medial branch of the dorsal ramus of the second cervical nerve, referred to as the GON, receives a communicating branch from the third occipital nerve before turning dorsally to pierce the semispinalis capitis muscle. The third occipital nerve is the superficial medial branch of the dorsal ramus of the third cervical nerve3). Just above the second cervical spinal process, the third occipital nerve becomes cutaneous over a small area immediately below the superior nuchal line. Its communicating branches joint the cutaneous branches of the greater and LONs. The LON is mainly derived from the ventral rami of the second cervical nerve, although the third occipital nerve sometimes contributes to this as well3,20). The GON communicates with other nerves that distribute the occipital and anterolateral neck3). Along with its common communications with the lesser and third occipital nerves, communications with the superficial auriculotemporal nerve, which is a terminal branch of the mandibular division (V3) of the trigeminal nerve3) and great auricular nerve of the cervical plexus, have also been reported3). Thus, the GON, which is the main peripheral input to the C2 root, has extensive communications with the peripheral nerves derived from both the dorsal and ventral rami of the second and third cervical nerves. Meanwhile, the medial branches of the dorsal rami of the third, fourth, and fifth cervical nerves pierce the trapezius muscle to supply the skin over the back of the neck sequentially3).
The ventral rami of the second, third, and fourth cervical nerves supply the cutaneous branches in the lateral and anterior portions of the neck (i.e., the LON, greater auricular nerve, transverse cutaneous nerve, and suprascapular nerve) via the cervical plexus3). The LON is mainly derived from the ventral rami of the second cervical nerve3,28). Ascending along the posterior margin of the sternocleidomastoideus muscle, it pierces the deep fascia and passes up onto the scalp behind the auricle to supply the skin and ultimately connect with the great auricular nerve, greater occipital, and the auricular branch of the facial nerve3). Its auricular branch supplies the skin on the upper third of the medial aspect of the auricle and connects with the posterior branch of the great auricular nerve. Communication between the LON and the auriculotemporal branch of the mandibular nerve (V3) was also found26). The LON is occasionally derived from the GON3). If GON entrapment occurs in cases where the auricular branch of the LON originates from the GON, then pain from the GON entrapment may radiate directly to the ear, which is believed to be the territory of the LON22). Pain stemming from entrapment of the GON may also radiate to the territories of the greater auricular nerve, the auricular branch of the facial nerve, and the auriculotemporal nerves through diverse communication with the LON. For these anatomical reasons, GON entrapment can sometimes cause ear pain and may radiate to the distribution of C2 and C3 dermatomes (Fig. 3D).
The C1-C3 high cervical nociceptive afferents, which are peripherally represented with the GON, are closely related to the cervical plexus innervating the anterolateral neck. The cervical plexus originates from the second, third, and fourth cervical nerves and includes the transverse cervical cutaneous nerve and the supraclavicular nerve3). The ascending branches of the transverse cutaneous nerve ascend to the submandibular region and are distributed to the skin of the upper anterior areas of the neck. The descending branches pierce the platysma muscle and are distributed anterolaterally to the skin of the neck, as low as the sternum3). In the current case (Fig. 1), it was confirmed that skin lesions of HZ involving the GON occurred extensively in the anterolateral neck, including the angle of the mandible. The suprascapular nerve arises from a common trunk that is formed from rami from the third and fourth cervical nerves and which emerges at the posterior border of sternocleidomastoid3). Descending under the platysma and the deep cervical fascia, the trunk divides into medial, intermediate, and lateral (posterior) branches, which diverge to pierce the deep fascia slightly above the clavicle3). These branches of the supraclavicular nerves supply the skin as far as the midline and as low as the second rib; the skin over pectoralis major and deltoid muscles, and the skin of the upper and posterior parts of the shoulder3). The skin lesion in the current case also occurred in the territory of the suprascapular nerve in the upper anterior chest, including the shoulder and clavicle (Fig. 1).
COCLUSION
The current paper reports a case in which a skin lesion of acute HZ occurred after decompression surgery for referred trigeminal pain due to entrapment of the GON. HZ affecting the high cervical roots is very rare. Moreover, there is no exact correspondence between these dermatomes due to the significant overlap between them. The skin lesions of HZ in the present case involving the GON included all dermatomes of the C2-C4 cervical nerves. The GON, which originates from the dorsal ramus of the second cervical nerve, has close anastomotic communication with its ventral ramus as well as the second, third, and fourth cervical nerves. The extent of this skin lesion demonstrates that pain from GON entrapment may extend not only to the occiput, but also to the ear, posterior, and anterolateral neck.