Complex craniofacial pain can be a challenging condition to manage both medically and surgically, but there is a resurgence of interest in the role of neurostimulation therapy. Surgical options for complex craniofacial pain syndromes include peripheral nerve/field stimulation, ganglion stimulation, spinal cord stimulation, dorsal nerve root entry zone lesioning, motor cortex stimulation, and deep brain stimulation. Peripheral nerve/field stimulation is rapidly being explored and is preferred by both patients and surgeons. Technological advances and improved understanding of the interactions of pain pathways with its affective component will widen the scope of neurostimulation therapy for craniofacial pain syndromes.
Key points
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Surgical treatment of complex craniofacial pain syndromes has been shown to achieve significant pain relief (>50%) in medically refractory pain syndromes.
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Appropriate patient selection, risks, and benefits associated with each of these therapies, presence of comorbidities, sensory deficits accompanying the area of pain, and insight into the programming parameters are the key points that need to be considered before selecting these surgical options for complex craniofacial pain syndromes.
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Given the reversibility and minimal invasiveness of peripheral nerve/field stimulation, this modality is being explored at a rapid pace and is preferred by both patients and surgeons.
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Motor cortex stimulation and deep brain stimulation can be considered for patients who fail other less invasive neurostimulation therapy for complex craniofacial pain syndromes.
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There is paucity of reliable data in the literature on the efficacy of these therapies for complex craniofacial pain syndromes and prospective randomized controlled studies are warranted to establish their therapeutic value.
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Peripheral nerve/field stimulation therapy, ganglion stimulation, motor cortex stimulation, and deep brain stimulation therapy are still investigational and off-label therapies for complex craniofacial syndromes.
Introduction
Craniofacial pain is a common condition that affects approximately 10% to 25% of the adult population worldwide with a significant impact on their quality of life. The International Headache Society (2004) classified craniofacial pain into 14 different categories, which provides a useful template in establishing a uniform clinical diagnosis. Women are more frequently affected with craniofacial pain, in the ratio of 2:1. The common causes of face pain include trigeminal neuralgia (tic douloureux or Fothergill disease), trigeminal neuropathic pain, and persistent idiopathic facial pain (PIFP, or atypical face pain). A population-based study reported the lifetime prevalence of trigeminal neuralgia and PIFP to be 0.3% and 0.03% respectively. Of these, trigeminal neuropathic pain and PIFP are complex pain syndromes that are often difficult to manage with medications alone.
According to the International Association for the study of pain, neuropathic pain is defined as “pain initiated or caused by a primary lesion or dysfunction in the nervous system.” Neuropathic pain can be further classified as peripheral or central (depending on the site of the disorder) and acute or chronic (lasting >3 months). Trigeminal neuropathic facial pain (TNP) is defined as a constant burning, cramping, pricking, deep aching, or electric shock–like facial pain along the distribution of trigeminal nerve branches. TNP is often associated with sensory dysfunctions such as paresthesia or dysesthesia, which can manifest as cold, pricking, tingling, or itching sensations along the distribution of pain. The most severe form of facial pain, with complete numbness in the distribution of pain, is referred to as anesthesia dolorosa. TNP can result from surgery, traumatic injury, and herpetic infection (shingles) of the areas innervated by the branches of trigeminal nerve, including the sinuses, teeth, face, or skull. TNP develops in a delayed fashion typically many days to months following the initial insult. In addition, iatrogenic injury to the trigeminal nerve by nerve ablation, rhizotomy, or ganglion ablation to treat trigeminal neuralgia can initiate trigeminal deafferentation or neuropathic pain.
PIFP (atypical face pain) is defined as “Persistent facial pain that does not have the characteristics of the cranial neuralgias and cannot be attributed to other disorders” (International Headache society, 2004). This entity was first described by neurosurgeons Frazier and Russell, in 1924. This condition is often described as severe persistent unilateral facial pain that is deep or poorly localized and usually burning or crushing in nature. Furthermore, there is a normal work-up without an associated sensory loss or other neurologic deficits. There may be a history of surgical or traumatic injury to the face, teeth, or gums before the onset; however, there is no demonstrable local cause that can endorse the persistence of this facial pain. PIFP is usually not confined within the anatomic distribution of the branches of trigeminal nerve and is often a diagnosis of exclusion. This condition affects approximately 1 in 100,000 adults, with no clear gender predilection, although the clinical presentation is more common in women.
Introduction
Craniofacial pain is a common condition that affects approximately 10% to 25% of the adult population worldwide with a significant impact on their quality of life. The International Headache Society (2004) classified craniofacial pain into 14 different categories, which provides a useful template in establishing a uniform clinical diagnosis. Women are more frequently affected with craniofacial pain, in the ratio of 2:1. The common causes of face pain include trigeminal neuralgia (tic douloureux or Fothergill disease), trigeminal neuropathic pain, and persistent idiopathic facial pain (PIFP, or atypical face pain). A population-based study reported the lifetime prevalence of trigeminal neuralgia and PIFP to be 0.3% and 0.03% respectively. Of these, trigeminal neuropathic pain and PIFP are complex pain syndromes that are often difficult to manage with medications alone.
According to the International Association for the study of pain, neuropathic pain is defined as “pain initiated or caused by a primary lesion or dysfunction in the nervous system.” Neuropathic pain can be further classified as peripheral or central (depending on the site of the disorder) and acute or chronic (lasting >3 months). Trigeminal neuropathic facial pain (TNP) is defined as a constant burning, cramping, pricking, deep aching, or electric shock–like facial pain along the distribution of trigeminal nerve branches. TNP is often associated with sensory dysfunctions such as paresthesia or dysesthesia, which can manifest as cold, pricking, tingling, or itching sensations along the distribution of pain. The most severe form of facial pain, with complete numbness in the distribution of pain, is referred to as anesthesia dolorosa. TNP can result from surgery, traumatic injury, and herpetic infection (shingles) of the areas innervated by the branches of trigeminal nerve, including the sinuses, teeth, face, or skull. TNP develops in a delayed fashion typically many days to months following the initial insult. In addition, iatrogenic injury to the trigeminal nerve by nerve ablation, rhizotomy, or ganglion ablation to treat trigeminal neuralgia can initiate trigeminal deafferentation or neuropathic pain.
PIFP (atypical face pain) is defined as “Persistent facial pain that does not have the characteristics of the cranial neuralgias and cannot be attributed to other disorders” (International Headache society, 2004). This entity was first described by neurosurgeons Frazier and Russell, in 1924. This condition is often described as severe persistent unilateral facial pain that is deep or poorly localized and usually burning or crushing in nature. Furthermore, there is a normal work-up without an associated sensory loss or other neurologic deficits. There may be a history of surgical or traumatic injury to the face, teeth, or gums before the onset; however, there is no demonstrable local cause that can endorse the persistence of this facial pain. PIFP is usually not confined within the anatomic distribution of the branches of trigeminal nerve and is often a diagnosis of exclusion. This condition affects approximately 1 in 100,000 adults, with no clear gender predilection, although the clinical presentation is more common in women.
Pathophysiology of complex face pain
Multiple mechanisms have been postulated in the pathophysiology of neuropathic face pain, which accounts for a wide variety of clinical presentations in patients with similar diseases. Therefore, patients with different pain generators and clinical presentations differ in their responses to treatment and overall outcome. As such, patients with posttraumatic TNP may have a different mechanism of pain onset compared with those with a spontaneous origin of TNP. Surgical or traumatic injury to the trigeminal nerve results in impaired functioning of both small unmyelinated and large myelinated nerve fibers with subsequent demyelination of the trigeminal nerve. The phenomenon of abnormal temporal summation of pain signals and reduced temperature thresholds with hot/cold hyperalgesias in patients with TNP can be attributed to hyperexcitability of central neurons and hypersensitization of peripheral C fibers/free nerve endings respectively. This process initiates as a result of interaction between chemicals (histamine, substance P, calcitonin gene–related peptide, glutamate, prostaglandins, bradykinins) released following tissue injury and peripheral nociceptors/free nerve endings, which subsequently can result in alteration in central pain pathways (central hypersensitization) over a period of time. Gender differences have been implicated in the interaction of chemical mediators with peripheral nociceptors and peripheral pain pathways, which may account for the higher incidence of chronic pain conditions in women. The pathophysiology of postherpetic trigeminal neuropathic pain (PHN) involves dysfunction of both peripheral and central pain pathways in varying proportions in different patients. This phenomenon can be attributed to the differences in clinical findings between patients with facial and truncal PHN and those with acute and chronic PHN.
The pathophysiology of PIFP is also not completely understood. PIFP was initially thought to be a component of a somatoform disorder because most patients had associated psychiatric disorders. However, various neuropathic mechanisms have recently been implicated in the pathogenesis of this disorder. The specific pathophysiologic mechanisms underlying the onset of neuropathic pain have not yet been elucidated, but with ongoing research it might be possible to identify precise mechanisms and thus target therapy accordingly.
Pain pathways and nodes of intervention
The pathways related to pain transmission are complex and include both sensory and affective components. The somatic sensations from the skin of the face, forehead, scalp up to the vertex, and mucous membranes of the nasal cavity and paranasal sinuses are carried by branches of the trigeminal nerve. The sensory cell bodies of these first-order neurons lie in the trigeminal or gasserian ganglion in the posterior aspect of the floor of the middle cranial fossa. The sensory fibers of the ganglion are carried in the spinal trigeminal tract to synapse on the second-order neurons within the main sensory nucleus, mesencephalic nucleus, or spinal trigeminal nucleus in the pons. The spinal nucleus of the trigeminal primarily receives afferents related to tactile, nociceptive, and thermal sensations. The subnucleus interpolaris and subnucleus caudalis of the spinal trigeminal nuclei are associated with touch/dental pain and nociception/thermal sensations respectively. The first-order neurons synapse diffusely on second-order neurons across different segments from medulla to cervical cord level. These second-order neurons then cross the midline and ascend in the trigeminothalamic tract to synapse diffusely on the third-order neurons within the ventral posterior lateral (VPL)/ventral posterior medial and ventral posterior inferior nuclei of the thalamus. These third-order neurons then project to the primary and secondary somatosensory cortices for the perception and characterization of the nociceptive stimulus. The thalamic relay station perceives pain as a dull aching sensation and the precise nature of nociceptive stimulus is defined at the cortical level. This pathway constitutes the lateral pain pathways. The medial pain pathways involve the projection of trigeminothalamic tract to the medial thalamic nuclei, limbic system, anterior cingulate cortex, and reticular formation to modulate the affective or emotional aspect of nociceptive stimuli.
Various nodes of surgical intervention in patients with complex face pain include (1) peripheral neuromodulation (peripheral nerve stimulation [PNS] or ganglion stimulation), (2) spinal cord stimulation, (3) deep brain stimulation, and (4) motor cortex stimulation. The selection of a particular treatment modality needs to be individualized based on (1) risk/benefit ratio, (2) presence of sensory loss, and (3) associated comorbidities.
Surgical management of complex face pain
Because of the inadequate understanding of the basic pathophysiology underlying complex face pain, the management of this condition is often difficult and unsatisfactory. Complex face pain is often refractory to conventional medical management. Tolerance, dependence, and side effects of medications used to treat this condition provide an impetus to steer toward surgical options. Various surgical modalities are discussed later.
Peripheral Neuromodulation
Peripheral trigeminal nerve/field stimulation (PNS/peripheral field/nerve stimulation)
This treatment modality for neuropathic pain was first introduced by Wall and Sweet in 1967. Of 8 patients with intense cutaneous pain, 4 experienced pain relief for more than half an hour following stimulation of infraorbital, mandibular, and other nerves. However, it was not until the reintroduction of this modality by Weiner and Reed in 1999 that this therapy gained wider clinical acceptance. In their study of 13 patients with occipital neuralgia, 12 patients experienced greater than 50% pain relief at a mean follow-up of 1.5 to 6 years. Since then, there has been a growing interest and literature in the use of this modality for complex craniofacial pain and other regional pain syndromes.
Clinical assessment, indications, and prerequisite for peripheral field/nerve stimulation PNS
The results of peripheral field/nerve stimulation (PFNS)/PNS therapy depend on appropriate patient selection. It is crucial to differentiate patients with TNP/PIFP and those with classic trigeminal neuralgia. The prerequisites for this therapy are the following:
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Patients with severe, chronic, refractory neuropathic pain (posttraumatic, postherpetic, occipital neuralgia, occipital headaches, or cervicogenic pain) that is affecting the patient’s quality of life. In addition, nonsurgical options such as pharmacotherapy, physical therapy, transcutaneous nerve stimulation, trigger point injections, nerve blocks, Botox, or acupuncture should be exhausted before consideration of this therapy.
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There should be some preservation of sensation in the distribution of pain, because functioning vibrotactile receptors are mandatory for this therapy to be successful. In addition, placing an electrode directly below a patch of allodynia for field stimulation can sometimes aggravate the pain. In these situations bracketing the pain can be useful.
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The pain should be either in the distribution of a single nerve or should be able to be covered by the length of available electrode(s) for PNS and PFNS, respectively, to be successful.
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Patients should be devoid of underlying psychiatric disorders (depression, anxiety, personality disorders, somatization, drug dependence) or for gains secondary to their chronic pain disorder, which can be identified by neuropsychological assessment.
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Similar to spinal cord stimulator placement, a successful PNS/PFNS stimulation trial is mandatory before permanent placement of PNS/PFNS. An externalized trial involves percutaneous placement of the electrodes in the distribution of pain with the externalized leads connected to an external pulse generator for a period of 5 to 12 days. Patients are asked to perform activities to maximize their pain and are taught to self-adjust the programming parameters so as to maximize the pain relief. The duration of the trial is variable between implanters and can be based on response and need for reprogramming. Improvement of greater than 50% of pain relief on a visual analog scale (VAS) is generally considered a successful trial.
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Nerve blocks and transcutaneous electrical nerve stimulation (TENS) therapy does not accurately predict the likelihood of success of PNS/PFNS therapy and should never be considered as a surrogate trial for PNS/PFNS. Nevertheless, success with nerve blocks/TENS therapy might guide the placement of electrodes.
Contraindications of PFNS/PNS
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Patients on anticoagulation therapy or bleeding disorders
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Ongoing psychiatric issues or major cognitive impairment
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Inadequate family support
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Patients on immunosuppression therapy or active infection
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Ongoing medicolegal issues or litigation related to chronic pain
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Patients requiring serial magnetic resonance imaging (MRI) that cannot be substituted with other imaging modalities.
Surgical technique
Following written informed consent, the patient is brought to the operating room and placed in a supine position with the head turned to the side opposite to their pain. Trial placement of electrodes is performed under monitored anesthesia with liberal use of local anesthetic. This technique allows the implanter to verify appropriate coverage with the implanted electrodes. In addition, lidocaine is the local anesthetic of choice because systemic side effects are less severe in the event of an arterial injection. Permanent placement is performed under general anesthesia using routine sterile techniques. The electrodes are typically placed in a lateral to medial direction in the epifascial plane under fluoroscopic guidance using standard anatomic landmarks. Occipital neuralgias are an exception, because electrodes can be placed in medial to lateral direction. Four or 8 contact cylindrical leads (Quad, Octad, Quad Plus, or Quad Compact; Medtronic, Inc, Minneapolis, MN) are placed either close to the nerve or in the region of pain, which is demarcated before surgery. We preferentially use an ON-Q tunneler (I-Flow, Lake Forest, CA) for the placement of cylindrical leads by virtue of its flexibility and atraumatic tip. In PNS, a paddle electrode can be used as an overlay or in a sandwich technique by placing paddle leads on each side of a peripheral nerve after adequate surgical exposure. In addition, ultrasonography guidance can be used to aid the placement of the electrode into the correct plane or to identify the nerve. The electrodes are placed at the level of C2 or directed toward the ipsilateral mastoid to cross the course of occipital nerves for occipital pain. For trigeminal neuropathic pain, the incision is made behind the hairline in a supra-auricular or temporal region and electrodes are implanted along the affected divisions of the trigeminal nerve. The supraorbital electrode should be placed well above the eyebrow and infraorbital electrode below the orbit to the base of the nose. For cluster headache, occipital stimulation alone or a combination of supraorbital and infraorbital stimulation can be useful. In addition, a combination of occipital, supraorbital, or infraorbital stimulation can be used for headaches depending on the area and distribution of pain. The electrodes are secured to the skin after creating a strain-relief loop using a nonabsorbable suture such as silk or Dacron during the trial. Following a successful trial, the trial electrodes are removed and new permanent electrodes are placed, mirroring the exact location of the trial. During permanent implantation, the strain-relief loops of electrodes are similarly secured to the fascia after creating a subcutaneous pocket using nonabsorbable sutures and leads are tunneled beneath the skin of the neck to the generator pocket that is created in the infraclavicular region ( Figs. 1 and 2 ).
Programming parameters
We prefer to use a low rate (20–50 Hz), low pulse width (60–250 milliseconds, occasionally 450 milliseconds), and low amplitude (1.5–2 V) for initial PFNS programming. A simple bipolar configuration limits the number of cathodes and is effective in reducing the energy used and thus prolonging the battery life. A guarded cathode has not been shown to be useful in PFNS therapy.
Review of literature
Most of the published literature on PNS/PFNS has reported significant improvement (>50% on VAS) in localized chronic pain intensity. The supraorbital nerve is the most common nerve stimulated (24 cases) followed by the infraorbital nerve (14 cases), occipital nerve (5 cases), and mandibular nerve (2 cases). More than 70% of patients experienced greater than 50% relief in chronic pain intensity in these studies, with follow-up ranging between 3 months and 4 years. Wound breakdown and hardware-related issues were the primary complications seen in these case series ( Table 1 ).
| Author, Year | Patients (N) | Causes | Area of PFNS Implantation | Results | Follow-up |
|---|---|---|---|---|---|
| Dunteman, 2002 | 2 | Postherpetic (2) | Supraorbital (2) | Effectively treated | 2 y |
| Johnson & Burchiel, 2004 | 10 | Postherpetic (4) Posttraumatic (5) Atypical face pain (1) | Supraorbital (8) Infraorbital (2) | 50% pain relief in 70% of patients Medication use declined in 70% of patients Two failures (50%) in postherpetic group | 26.6 ± 4.7 mo |
| Slavin et al, 2006 | 30 | Craniofacial pain | Occipital (21) Supraorbital (7) Infraorbital (6) In 19 patients more than 1 nerve was stimulated | 73% of patients had >50% pain relief | 35 mo |
| Asensio-Samper et al, 2008 | 1 | Posttraumatic | Supraorbital | VAS 9–10 out of 10 to 2 out of 10 following PFNS | 4 y |
| Reverberi et al, 2009 | 1 | Trigeminal neuropathic pain | Supraorbital and infraorbital | >50% reduction in pain intensity | 5 mo |
| Surjya Prasad Upadhyay et al, 2010 | 1 | Postherpetic | Supraorbital | >50% reduction in pain intensity with improvement in quality of life | 8 wk |
| Yakovlev & Resch, 2010 | 1 | Atypical face pain | Mandibular nerve | >50% reduction in pain intensity | 12 mo |
| Lenchig et al, 2012 | 1 | Posttraumatic | Supraorbital and infraorbital | >50% reduction in pain intensity with improvement in quality of life | 3 mo |
| Stidd et al, 2012 | 3 | Posttraumatic (2) Postherpetic (1) | Supraorbital and infraorbital (2) Supraorbital (1) | >50% reduction in pain intensity | 6–27 mo |
| Feletti et al, 2013 | 6 | Posttraumatic (2) Postsurgical (1) Postherpetic (1) PIFP (2) | Supraorbital (1) Infraorbital (2) Occipital nerve (1) Supraorbital nerve + infraorbital nerve + occipital nerve (1) Occipital nerve + infraorbital nerve + mandibular nerve (1) | VAS from 10 out of 10 to 2.7 out of 10 | 17 mo |
| Our experience (unpublished data) | 80 | Craniofacial pain | Supraorbital + infraorbital + mandibular + occipital nerve | 80% of patients had >50% improvement | 60 mo |
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