Phantom Pain

This chapter discusses phantom pain, defined as an unpleasant or painful sensation in the distribution of the lost or deafferentiated body part. It is more commonly reported in the limbs but also has been reported in other body parts such as the tongue, teeth, nose, breast, part of the gastrointestinal tract, and the penis. The incidence varies from 42.2% to 78.8%. Perception of non-painful sensations from the amputated body part is known as phantom sensation. The severity and frequency of attacks slowly decrease with time during the first 6 months, after which they remain constant. Patients with significant preoperative pain, stump pain, and infection are at increased risk of developing phantom pain. The mechanism of origin is not known; it is thought to be due to peripheral nerve damage, which contributes to neural sensitization at peripheral, spinal, and supraspinal levels. Both chemical mediators and psychological factors are involved. Phantom pain improves with time and responds to conservative medical management, mirror therapy, and psychological counseling. A small percentage of cases are resistant to treatment and may require invasive neuromodulatory treatment options such as spinal cord stimulation and peripheral nerve stimulation.

Multiple Sclerosis

Multiple sclerosis (MS) is a chronic autoimmune demyelinating disease of the central nervous system (CNS). The diagnosis is based on evidence of at lease two different lesions in the CNS, at least two different episodes in the disease course, and chronic inflammation of the CNS as determined by analysis of the cerebrospinal fluid. Central neuropathic pain is the most common form of pain in patients with MS, with an estimated prevalence of about 50%. Along with the classical neuropathic pain features, such as spontaneous pain (dysesthesia and burning) and evoked pain (allodynia and hyperalgesia), patients with MS may also suffer from intermittent neuropathic pain, such as trigeminal neuralgia, Lhermitte sign, and glossopharyngeal neuralgia. In addition to disease-modifying therapies of MS, multiple treatments are available to manage neuropathic pain secondary to MS, including medical, interventional, and surgical treatments with varying levels of evidence.

Brain Infarction (Thalamus and Brainstem)

Central post-stroke pain (CPSP) is a central neuropathic pain condition resulting from lesions of a prior cerebrovascular accident (CVA) mainly affecting the spinothalamocortical tract. About 5%–10% of patients with CVAs develop CPSP. The pain is thought to be secondary to a complex interaction of central disinhibition, central sensitization, and an imbalance of stimuli, although the exact mechanism remains unknown. The pain is located within and associated with sensory dysfunction in a region affected by a prior CVA lesion. The pain is often described as burning, stabbing, and sharp. Allodynia, hyperalgesia, and evoked dysesthesia appear to be major clinical findings for this condition. There are no specific diagnostic criteria for CPSP, and treatment is often difficult. Medications such as tricyclic antidepressants and anticonvulsants are often used. Motor cortex stimulation and deep brain stimulation are active areas of research and offer hope that additional treatment modalities may be identified.

Persistent Idiopathic Facial Pain

Persistent idiopathic facial pain (PIFP) is an enigmatic condition which has caused a great deal of suffering yet has been difficult to define and remains a challenging disorder to treat. In addition, the presentation of PIFP has considerable overlap with many other causes of facial pain making the malady a diagnostic challenge. The condition is often resistant to treatment and patients often have comorbid syndromes or psychological factors. This chapter reviews the history and development of the current diagnostic criteria of PIFP according to the latest edition of the International Classification of Headache Disorders (ICHD). Using a case-based approach, the pathophysiology, epidemiology, differential diagnosis, and treatment options of PIFP are explored.

Trigeminal Neuralgia

Trigeminal neuralgia is a rare neuropathic pain condition but can be very disabling. The hallmark is brief episodes of intense, radiating pain within the territory of trigeminal nerve distribution. It is typically unilateral, often accompanied by facial spasms and can be triggered by facial movements in a majority of patients. Microvascular compression of trigeminal ganglion is the etiology for most patients with classical trigeminal neuralgia. Some patients can have continuous facial pain in addition to paroxysms of pain. Trigeminal neuralgia is a clinical diagnosis, but MRI is done to rule out secondary causes or to detect microvascular compression. Pharmacological therapy with first-line agents—carbamazepine or oxcarbazepine—is the preferred treatment. Patients with failed pharmacological therapy are considered for surgical decompression, ablation procedures, or Gamma Knife surgery.

Thoracic Radicular Pain

Thoracic radiculopathy presents an uncommon spinal disorder that can often be overlooked because numerous structures surround the thoracic spine. Radiculopathy typically originates from mechanical nerve root compression due to degenerative spine changes such as disc herniation, spondylosis, or osteoporosis and its associated vertebral compression fractures. The presentation of radicular pain in the thoracic region is more common in the upper thoracic and, with lateral disk herniations, often associated with some amount of axial pain. Clinical symptoms are leg weakness, numbness and tingling across the chest or abdomen or shoulders, spasticity, and bowel or bladder dysfunction. The vast majority of patients with thoracic pain return to their previous functional level without surgical intervention. Strengthening, postural optimization, and general exercise and mobility comprise the cornerstone of all treatment and prevention of thoracic radicular pain. Medication may include a variety of choices, ranging from NSAIDs to anticonvulsants. Medications to address specific health issues leading to thoracic radiculopathy (diabetes mellitus and osteoporosis) may be of additional benefit. Thoracic epidural injections or paravertebral blocks with corticosteroids and local anesthetics may be a treatment consideration. Surgical intervention is reserved for patients in whom conservative management has failed and who have persistent pain symptoms. Myelopathy is an indication for surgical intervention. Spinal cord stimulation may be effective to address chronic radiculopathy in selected patients.

Cervical Radiculopathy

This chapter discusses cervical radiculopathy, a common, painful condition from cervical root compression, irritation, or both. A thorough history and physical exam can often help in diagnosing the affected nerve root, without the need for reflexive imaging. A series of provocative tests can aid in the differential diagnosis. Most cases will be resolved with conservative management within several weeks of symptoms onset. Evidence-based conservative management includes physical therapy and oral NSAIDs. If symptoms indicate myelopathic changes or are refractory to 6 to 8 weeks of conservative management, advanced imaging such as MRI should be considered. Patients with imaging evidence of a compressive etiology and refractory to conservative therapy should have a surgical consultation. Either an MRI or CT should be obtained before surgical decompression. Both interventional and surgical treatments have had positive outcomes in the short term, but long-term outcomes appear comparable to those with conservative therapies. It is recommended that conservative treatment strategies be used for 6–8 weeks before pursuing procedural or surgical intervention.

Syringomyelia

This chapter discusses syringomyelia, which is dilation of the spinal canal. It can be either congenital or post-traumatic. It is associated with central pain characteristics of predominantly neuropathic pain. Headaches may be present in patients with syringomyelia associated with type 1 Arnold-Chiari malformation. The size of the syrinx does not correlate to the severity of pain. Damage to the deeper layers of the dorsal horn causes an imbalance between the inhibitory and excitatory stimuli with upregulation of substance P. Electromyography shows a mixture of shortened and prolonged action potentials in syringomyelia. Somatosensory-evoked potential may be useful in the electrodiagnosis of syringomyelia. MRI plays a key role in the diagnosis of syringomyelia. Medical treatment is multifaceted and may be unsuccessful in treating the neuropathic pain. Surgery is the definitive treatment, although symptoms of pain may persist after resection. Spinal cord stimulation may offer relief to some patients and can be considered, as long as the dimensions of the vertebral canal are not significantly compromised.

Spinal Cord Injury

Pain from spinal cord injury (SCI) is one of the pain syndromes that is recalcitrant to treatment. It is often a result of injury associated with mechanical trauma and vascular compromise of the spinal cord parenchyma. SCI pain is associated with substantial impact on the patient’s life, interfering with activities of daily living, effective rehabilitation, and quality of life. The underlying mechanism for the development of SCI pain includes neuronal hyperexcitability, reduced inhibition, neuronal reorganization, and plasticity. The diverse factors associated with SCI pain warrant the need for an interdisciplinary approach tailored to the individual patient. The goals of treatment should encompass four domains: pain management, spinal rehabilitation, psychological treatment, and social and environmental modification.

Herpes Zoster and Postherpetic Neuralgia

Herpes zoster is caused by reactivation of the latent varicella zoster virus (VZV) that causes chicken pox. VZV remains dormant in the dorsal root and cranial ganglia and can reactivate later in a person’s life and cause herpes zoster, which appears predominantly in older adults, but may also occur in those that are immunocompromised. Postherpetic neuralgia (PHN) is defined as pain in the affected dermatome that is still present 1 month after development of the vesicles. Adults older than 50 should receive the herpes zoster vaccine as part of routine medical care. Shingrix is a new vaccine recently approved and recommended by the FDA, which is a non-live, subunit vaccine. In contrast to Zostavax, Shingrix is 97% effective against shingles and 91% effective against PHN for people 50 and older. The diagnosis of herpes zoster can be made on the basis of characteristic skin lesions and pain and itching in the involved dermatome. During the acute phase, an antiviral given within 72 hours of onset helps reduce pain and complications and shorten the course of the disease. The diagnosis of PHN is based on a history of herpes zoster, typical dermatomal distribution of the pain, and hyperalgesia and/or allodynia on physical examination. First-line pharmacotherapy includes gabapentin or pregabalin, tricyclic antidepressants, and SNRIs. Combination therapies are often necessary. Interventional options such as epidural injections, paravertebral blocks, selective nerve root blocks, sympathetic nerve blocks, intercostal nerve blocks, trigeminal nerve blocks, spinal cord or dorsal root ganglion stimulation, and intrathecal therapy may be considered in refractory cases.