Prelude to Surgical Treatment

The fundamental requirement for successful pain management, whether the treatment is surgical or nonsurgical, is an understanding of the nature of the pain being treated. Different types of pain respond differently to treatment; thus, the etiology and characteristics of a patient’s pain must be understood in order to develop a rational treatment plan. In general, pain can be classified as acute or chronic and as nociceptive or neuropathic. Classification of a pain complaint into these simple categories facilitates formulation of a proper treatment scheme.

Acute pain is a signal of actual or impending tissue injury and is generated by activation of nociceptors in tissue that has sustained an injury or insult. Acute pain resolves as injured tissue heals. Chronic pain, conversely, outlasts the typical period required for healing of an acute injury. Some definitions of chronic pain are based on the duration of pain (e.g., pain that lasts longer than 3 or 6 months). This is not an accurate distinction, however, because different types of acute injury require different lengths of healing time, and the transition of acute pain to chronic pain can vary according to the nature of the injury.¹

Although sometimes difficult to make, the distinction between acute and chronic pain is important. Treatment of acute pain should be aimed at achieving analgesia while promoting tissue healing. This treatment might include rest or immobilization, analgesics, and passive physical therapy.² In contrast, chronic pain does not serve a useful physiologic purpose (unless tissue injury is ongoing). In some cases, chronic pain no longer reflects disease but instead is considered a disease itself.³ Physical deconditioning is also a common accompaniment of many chronic pain disorders, such as failed back surgery syndrome (FBSS). Thus, many patients with chronic pain require physical reactivation and rehabilitation rather than the rest and relaxation recommended in the treatment of acute pain. This means that chronic pain often requires a treatment program opposite that used to treat acute pain and that the distinction between acute and chronic pain is critical because treating chronic pain as acute pain only promotes further disuse and deconditioning.² The differentiation of acute and chronic pain is also important because psychological and social factors that can complicate a pain complaint might be more common in patients with chronic as opposed to acute pain. In fact, in some cases, psychosocial factors can be the predominant cause of a complaint of chronic pain.

The distinction between nociceptive and neuropathic pain is also important because the two types of pain usually respond differently to specific treatments. Nociceptive pain is generated when injury or disease (e.g., a broken arm, cancer pain with local tissue invasion) activates the nociceptors that stimulate central nervous system nociceptive pathways. Nociceptive pain, which patients describe as “throbbing,” “aching,” or “dull,”⁴ is thus a normal, protective response of the nociceptive systems. In contrast, neuropathic pain is the result of a pathologic process (injury or disease) affecting the peripheral or central nervous system. Such neuronal injury leads to abnormal neuronal excitability, spontaneous discharges, and ephaptic transmission, which might, in turn, lead to generation of pain with or without peripheral, let alone nociceptive, input. Thus, in contrast to nociceptive pain, neuropathic pain reflects abnormal neuronal activity. Neuropathic pain, which patients describe as “burning,” “shooting,” “tingling,” or “shock-like,”⁴ can be continuous or paroxysmal (lancinating). Although nociceptive pain usually responds to opioids (e.g., the pain of a broken arm can be treated with morphine), neuropathic pain tends to resist opioid treatment (at least at typical doses) and frequently requires treatment with nonopioid medications.

Pain is sometimes classified according to its association with cancer or lack thereof. This classification can be useful because cancer pain might respond differently than noncancer pain to specific interventions. Although nociceptive pain predominates in patients with cancer, neuropathic pain can also occur (e.g., with tumor invasion of the nervous system). The shortened life expectancy of some cancer patients also becomes a treatment consideration because tolerance to medication becomes a minimal concern, and surgical procedures performed for cancer pain do not have to yield many years of relief.

Surgical treatment of intractable pain is not usually the first treatment option. In most cases, treatment of intractable pain should follow a rational process with the simplest, safest methods used first and interventional treatments reserved for later use.⁴ A simple way of picturing this approach is a pain treatment ladder, similar to the one proposed by the World Health Organization.⁵ On the lowest rungs are the simplest, safest measures. Each higher rung reflects a more invasive treatment, which, just like climbing to higher rungs on a ladder, entails greater risk should complications arise. Medical therapy, beginning typically with nonopioids (e.g., nonsteroidal anti-inflammatory medications) in conjunction with adjuvant therapies when appropriate, should generally precede surgical intervention. If adequate pain control is not obtained with nonopioids, mild opioids might be required, to be replaced by strong opioids if necessary. In most cases, pain relief is most readily achieved using scheduled rather than “as needed” analgesic dosing.^6,7 Neuropathic pain frequently requires treatment with nonopioid medication, although opioids can be helpful for some patients. For continuous neuropathic pain (e.g., constant burning, dysesthetic pain), useful adjuvant medications include antidepressants (e.g., tricyclic antidepressants such as amitriptyline), clonidine, local anesthetics (e.g., mexiletine), and capsaicin cream.⁷ Paroxysmal, lancinating, or evoked neuropathic pain might improve with anticonvulsants (e.g., carbamazepine, phenytoin, gabapentin) or baclofen.⁷ Nonpharmacologic adjuvant therapy, including psychological support, relaxation therapies, coping strategies, passive physical therapy (e.g., massage, heat/cold), transcutaneous electrical nerve stimulation, and orthoses)^6,7 can be useful in the treatment of nociceptive or neuropathic pain.

Simple interventional therapies (e.g., nerve blocks, peripheral nerve ablations) might be useful supplements to medical management. Augmentative therapies (e.g., SCS and neuraxial analgesic infusion) are typically the next step, followed by ablative therapies if augmentative approaches are unsuccessful or inappropriate. An element of flexibility should be maintained in the approach to patients with pain, however, and treatment should be tailored to meet individual needs. For example, dorsal root entry zone (DREZ) lesioning can relieve pain associated with spinal nerve root avulsion and, in some cases, is preferable to more conservative neuroaugmentative techniques. Also, a patient with intractable pain related to late-stage cancer might be treated more appropriately by cordotomy than by implantation of an intrathecal drug infusion system.

Patient Selection for Surgical Pain Therapies

In most cases, surgical intervention is reserved for patients in whom conservative therapies result in inadequate pain relief or are associated with unacceptable side effects or risks; no absolute contradictions to surgery exist; and treatment of the underlying cause of pain is not possible, practical, or appropriate.^4,8 For example, radicular leg pain from lumbar spinal stenosis can be treated with decompressive lumbar laminectomy; however, if a patient also has severe coronary artery disease that increases operative risk or has persistent pain after prior spinal surgery that reduces the potential benefit of surgery, SCS might be the safest and most appropriate treatment.^8,9

The pain should have a definable organic cause. It is especially important to identify the cause of chronic pain of nonmalignant origin in order to reduce the likelihood of significant underlying or primary psychological dysfunction. Psychological dysfunction can be common in patients with chronic pain disorders and might preclude a good outcome to surgical treatment. Thus, a formal psychological evaluation might be appropriate for many (or most) patients being considered for surgical treatment of intractable pain. Contraindications to surgical intervention include overt psychological dysfunction, such as active psychosis, suicidal or homicidal behavior, major uncontrolled depression or anxiety, serious alcohol or drug abuse, or serious cognitive deficits. Other psychological problems, which may be viewed as “risk factors,” include somatization disorder, personality disorders (e.g., borderline or antisocial), history of serious abuse, major issues of secondary gain, nonorganic signs on physical examination, unusual pain ratings (e.g., 12 on a 10-point scale), inadequate social support, unrealistic outcome expectations, and, in the case of implantable augmentative devices, an inability to understand the device or its use. Patients with psychological risk factors are not necessarily precluded from surgical treatment, but the treatment program should address the psychological issues to facilitate a good outcome.¹⁰

Neurosurgical Therapies for Intractable Pain

Neurosurgeons can use anatomic, augmentative (or neuromodulation), and ablative therapies (Table 164-1).¹¹ The treatment offered should be tailored to meet the needs of each individual patient and the skills of the treating physician. Specific interventions vary in their appropriateness as a treatment for pain in specific body regions (Tables 164-2 through 164-5). Patient-related factors that must be taken into consideration when selecting a therapy include the etiology, distribution, and characteristics (nociceptive or neuropathic) of the pain; life expectancy; and psychological, social, and economic issues relevant to the pain complaint. The relative advantages and disadvantages of anatomic, augmentative, and ablative therapies should be weighed in view of these factors, and a choice among these three general approaches should be made before choosing a specific intervention. Selecting the right treatment for the right patient at the right time increases the likelihood of a successful outcome.

TABLE 164-1 Neurosurgical Pain Therapies

DREZ, dorsal root entry zone.

Modified from North RB. Neurosurgical procedures for chronic pain: general neurosurgical practice. Clin Neurosurg. 1992;40:182-196.

TABLE 164-2 Neurosurgical Procedures for Treatment of Head and Neck Pain

TABLE 164-3 Neurosurgical Procedures for Treatment of Upper Trunk, Shoulder, and Arm Pain

TABLE 164-4 Neurosurgical Procedures for Treatment of Lower Trunk and Leg Pain

TABLE 164-5 Neurosurgical Procedures for Treatment of Diffuse Pain

Augmentative therapies fall into two categories: stimulation (SCS, PNS, deep brain stimulation [DBS], and motor cortex stimulation [MCS]) and neuraxial (intrathecal and intraventricular) drug infusion. These neuromodulation therapies have largely replaced ablative techniques as procedures of choice for pain management and are generally preferred as initial surgical treatments because of their relative safety and reversibility and the availability of a specific prognostic trial.

Ablative therapies, however, have a role in the treatment of certain pain syndromes^12,13 and can target almost every level of the peripheral and central nervous systems. Thus, ablative therapies can be directed at preventing transmission of nociceptive information into the central nervous system at the level of peripheral nerves (neurectomy, neurotomy), roots (ganglionectomy, rhizotomy), and the spinal cord dorsal horn (DREZ, including nucleus caudalis DREZ). Ascending nociceptive pathways can be disrupted at the level of the spinal cord or brainstem (cordotomy, myelotomy, tractotomy) or within the brain (thalamotomy, cingulotomy).

Augmentative and ablative therapies are reviewed briefly here to provide a broad perspective about the applications of neurosurgical pain therapies. A detailed discussion of indications, techniques, and outcomes of many of these techniques is available in other chapters.