Greater occipital nerve block
   Greater occipital nerve block is indicated for occipital neuralgia, commonly seen in patients after whiplash injury, falls on the back of the head and other close head injuries. Patients are often misdiagnosed as tension headache or migraine. The patients may have continuous headaches in the occipital, parietal and sometimes in the frontal region. The headaches may be increase several times a week and may be accompanied with nausea and vomiting. This condition is easily confused with migraine attacks. Physical examination may reveal positive tenderness over the greater occipital nerve. Palpitation of the greater occipital nerve often makes the headache worse.
   The occipital nerve block is the easiest interventional procedure for neurologists to perform. For the procedure, one can palpate the posterior occipital protuberance, move 1.5-2 cm laterally and feel for occipital artery pulsation and groove, then inject 2-3 ml of 0.5% bupivacaine with 20 mg of triamcinolone down to the bone and fan out. According to my own data, for patients with occipital neuralgia after whiplash injuries, a greater occipital nerve block may provide immediate headache relief in 90% of patients that lasts for an average of 28 days.

Sphenopalatine ganglion block for headache and facial pain
   The sphenopalatine ganglion is a small triangular structure located in the pterygopalatine fossa, posterior to the middle turbinate and inferior to the maxillary nerve. It is covered by a thin layer, about 1 to 5 mm, of connective tissue and mucous membrane. Anesthetization of the sphenopalatine ganglion is accomplished via the transnasal approach. The patient is placed supine on the treatment table with the nose pointed at the ceiling. A cotton applicator soaked with 2% to 4% lidocaine is inserted into the nose on the side of headache. To avoid mechanical discomfort, the cotton applicator should not be inserted deeply into the upper posterior wall of the nasopharynx. A slow drip of 2-4 ml of lidocaine over a 2 to 4 min period into the nose through the cotton applicator often achieves the goal of a sphenopalatine ganglion block with the local anesthetic flowing down to the back of nasopharynx by gravity. Sphenopalatine ganglion blocks have been reported to be effective in the relief of a wide variety of pain conditions of the head including acute migraine attacks, cluster headache, atypical facial pain, and head and facial RSD. The procedure is easy to perform in the clinic and may be helpful for neurologists without special training in interventional pain management to treat an acute headache attack.

Gasserian ganglion lesions for trigeminal neuralgia
   The first choice for treatment of trigeminal neuralgia is carbamazepine. It can be used with other medication such as baclofen. Gasserian ganglion lesions are indicated when patients fail other medication treatments. These procedures include radiofrequency thermocoagulation, balloon compression, and glycerolysis. Radiofrequency thermocoagulation is the most commonly used procedure. This procedure is often performed by neurosurgeons, interventional pain specialists or interventional radiologists. The treatment requires inserting a radiofrequency needle through the face and foramen ovale into the base of the skull under the guidance of fluoroscopy or CT. After the needle reaches the Gasserian ganglion, radiofrequency energy is applied to induce thermocoagulation; 87% to 91% of patients experience immediate pain relief. In a five-year follow up, 50% patients still had good pain relief. Common side effects of this technique include corneal anesthesia, masticator weakness and anesthesia dolorosa. Recently, stereotactic radiosurgery for trigeminal neuralgia has been used more widely due to its non-invasive nature; 59% to 70% of patients have complete pain relief in a one- to two-year follow up. However, this procedure may be more costly than other procedures mentioned above.

Stellate ganglion block
   The stellate ganglion is a sympathetic ganglion innervating the ipsilateral upper extremity, the neck and the head. The structure is usually located in front of the junction between C7 vertebral body and the transverse process. Stellate ganglion block is primarily indicated for complex regional pain syndrome of the head, neck and upper extremities. Uncontrolled clinical reports indicate this procedure provides effective pain relief or may even reverse the course of early stage complex regional pain syndrome type I. Other indications include vascular insufficiency of the arm and acute herpes zoster infection.
   Technically, this block is achieved by inserting a needle through the neck to the front of the junction between the C7 vertebral body and the transverse process. Traditional hand palpation technique without guidance of fluoroscopy bears significant risks of injecting local anesthetics into critical structures in the neck, such as the carotid and vertebral arteries or intrathecal space. Incorrectly located injections of local anesthetics may lead to loss of consciousness, seizures, paralysis, cardiac arrest and death. Recent use of fluoroscopic guidance for stellate ganglion block dramatically decreases the possibility of serious side effects and increases the rate of success.

Lumbar sympathetic block
   The lumbar sympathetic nerves mainly originate from the L1 and L2 segments of the lumbar spine and are located in front of the lumbar spine and supply the sympathetic innervation of the lower extremities. A lumbar sympathetic block is indicated for the diagnosis and treatment of the complex regional pain syndrome of the lower extremities, acute peripheral vascular insufficiency and acute herpes zoster of the lower extremities. The procedure is achieved by inserting a six to seven inch spinal needle into the anterolateral edge of the L2 vertebral body under the guidance of fluoroscopy. Ten to 20 ml of local anesthetics is injected to block the lumbar sympathetic nerve. Some patients with complex regional pain syndrome may experience complete pain relief, which lasts from hours to weeks. However, more studies are needed to confirm the clinical efficacy of this procedure.

Intravenous regional block
   The intravenous regional block (Bier block) is another treatment modality commonly used for CRPS I. This procedure is achieved by the injection of local anesthetic and other medications such as bretylium into the vein of the affected limb. A high-pressure cuff is applied to the proximal part of the limb immediately before the injection and for about 20 to 30 minutes after to prevent loss of the medication into the systemic circulation. A variety of medications have been used in the Bier block, including guanathedine, labetalol, corticosteroids, clonidine and bretylium. However, only bretylium has been proved by a double blind, clinically controlled study to be effective for CRPS I. Bier block is the treatment of choice for early stage CRPS limited to one limb that does not respond to other conservative treatments.

Epidural corticosteroid injection
   Pain specialists have used epidural corticosteroid injection (ESI) for decades to treat back and neck pain. The procedure is further divided into cervical ESI, thoracic ESI and lumbar ESI (LESI) with the purpose of treating the pain originated from different spinal regions. By 1995, there were at least twelve so-called double-blind, placebo-controlled studies investigating the clinical efficacy of LESI for low back pain. Of these studies, only six yielded positive results, while the other studies did not support the use of LESI for low back pain. Actually several of these studies exhibited the critical flaw of treating “low back pain” as a single entity. It is now realized that low back pain is a clinical syndrome that may be caused by a variety of pathologies in the lumbar spine and adjacent organs. It is not reasonable to treat low back pain with epidural corticosteroid injections regardless of the cause. More recent, well-designed, placebo-controlled studies have provided clinical evidence that LESI decreases lumbar radicular pain caused by lumbar disc herniation. The pain-relieving effect of LESI may last up to three months. Corticosteroids appear to speed the rate of recovery and return of function, allowing patients to reduce medication levels and increase activity while waiting for the natural improvement expected in most spinal disorders. Recent studies also support the use of LESI for pain relief in patients with spinal stenosis.
   It is now believed that the pain in patients with disc herniation and associated radiculopathy is not due to mechanical compression, but is due to chemical inflammation. Past the age of 60, more than 90 percent of the normal population has a variety of degenerative spine changes including disc herniation, spinal stenosis and foraminal stenosis. The majority of persons with these changes, however, do not have pain. Human discs contain high levels of phospholipase A2. This enzyme is responsible for the liberation of arachidonic acid from cell membranes, and has a theoretical inflammatory potential. It therefore appears that the primary function of a local corticosteroid injection is to suppress the function of phospholipase A2 and to decrease the inflammation around the nerve roots. It is reasonable to let patients have a trial of LESI before considering a surgical treatment for lumbar disc herniation. The procedure often prevents back surgeries. As long as pain is relieved and the patient is free of neurological deficits, a herniated disc should be left alone without further treatment.

Lumbar facet joint block
   This procedure is indicated for lumbar facet joint pain syndrome. Lumbar facet joint syndrome may be found in up to 35% of patients with low back pain. Clinically, this syndrome may mimic lumbar radiculopathy (sciatica). Patient may complain of low back pain, often on one side, with pain radiating down to the back or front of the thigh. Clinical examination may reveal tenderness on either or both side(s) of lumbar spine over the lumbar facet joints. Back extension and lateral rotation to the painful side may increase the low back pain, because this maneuver increases the pressure on the lumbar facet joints. The straight leg raising test is often negative. Traditionally, pain specialists have performed intra-joint corticosteroid injections. Over the last decade, this procedure has largely been replaced by a diagnostic medial branch (nerve innervating the lumbar facet joints) block with small amount of local anesthetics. If the patient has significant pain relief after the diagnostic medial branch block, radiofrequency destruction of the medial branch will be performed to denervate the lumbar facet joints. A recent study found thirty six patients (80%) with forty five procedures achieved significant pain relief over a mean duration of 36 weeks after this treatment.

Percutaneous disc decompression
   Over 300,000 spine surgeries are performed each year in the United States. A majority of these surgeries are conducted for lumbar disc herniation. Traditionally, neurosurgical and orthopedic techniques for lumbar disc herniation include lumbar laminectomy, discectomy, and lumbar fusion. A significant number of patients end up with so-called “failed back surgery syndrome”. Recurrent disc herniation, epidural abscess, scar tissue formation around nerve roots, facet joint syndrome, and muscle spasm may contribute to the clinical features of this syndrome. To avoid possible complications of open surgery, minimal invasive techniques for disc decompression have been developed. These techniques include Chymopapain, Nucleotome, laser discectomy, Nucleoplasty, and Disc DeKompressor. Chymopapain is a proteolytic enzyme from the Papaya fruit. This enzyme may induce enzymatic decompression of the nucleus pulposus of the herniated disc. Initial clinical reports were highly positive. However, due to its serious side effects, such anaphylactic shock, transverse myelitis and even death, chymopapain has been largely replaced by other techniques.
   Percutaneous Nucleotome was developed by a Japanese orthopedic surgeon, Dr. Hijikata in 1975. This procedure inserts a 7-mm-diameter tube into the annulus and removes the disc material with specially designed forceps. This procedure has a reported success rate of 72%. However, due to the large diameter of the cannula, this technique is no longer commonly used. Ascher and Choy introduced YAG laser discectomy in 1986. This is still being commonly used by spine surgeons, neurosurgeons and some interventional pain specialists. This technique utilizes an 18 G probe, and generates laser energy to evaporate part of the nucleus pulposus. It decreases the intradiscal pressure with a reported success rate for back pain relief of 78% to 80%. Due to heat generated by the laser energy, patients may experience severe pain during the procedure and increased muscle spasm after the procedure.
   Over the last six years, two new percutaneous disc decompression techniques have been reported. Introduced in 2000, DISC Nucleoplasty utilizes a unique plasma technology called Coblation® to remove tissue from the center of the disc. During the procedure, the DISC Nucleoplasty SpineWand is inserted into the center of the disc where a series of channels are created to remove tissue from the nucleus. The clinical efficacy of this technique, however, is yet to be confirmed.
   Disc DeKompressor was introduced in 2003. This procedure uses a 1.5 mm percutaneous lumbar discectomy probe to aspirate the disc material. It is minimally invasive with less risk for nerve root damage. This technique is indicated for patients with contained disc herniation and lumbar radiculopathy. A preliminary study reported a decrease of pain of more than 70% in eight of ten patients. Generally, minimal invasive percutaneous disc decompressions provide alternatives for open surgery with less risk of the failed back surgery syndrome. However, more studies are needed to confirm the long-term efficacy of this procedure.

Deep brain stimulation
   Deep brain stimulation (DBS) was first introduced in the 1950s. This technique has been used to treat intractable low back pain (failed back surgery), post-stroke pain, phantom limb pain and pain due to peripheral neuropathies. DBS may be a useful tool when all other modalities have failed. Stimulation sites include the periventricular/periaqueductal grey matter (PVG/PAG), internal capsule (IC), and sensory thalamus (ST). Owen reported a success rate of 70% for treatment of post-stroke pain in an open label study of 15 patients(57). However, multiple reports presented inconsistent results. FDA regulations prohibited the use of DBS to treat pain in the USA between late 1980s and 1990s, and later the FDA designated DBS treatment of pain as ‘off-label’. Currently, the general consensus remains doubtful regarding the efficacy DBS for chronic pain. In contrast, motor cortex and spinal cord stimulation may provide more effective and reliable pain relief.

Motor cortex stimulation
   Motor cortex stimulation has been used for the treatment of central and neuropathic pain syndromes since 1991. It is best indicated for medically unresponsive central and neuropathic pain including that due to thalamic, putaminal, and lateral medullary infarction, traumatic trigeminal neuropathy (not idiopathic trigeminal neuralgia), postherpetic facial neuralgia, brachial plexopathy, and neuropathic pain after a spinal cord injury, and phantom limb pain. There have only been scattered case reports regarding motor cortex stimulation for complex regional pain syndromes. Cortical stimulation is not indicated for patients with a history of seizures. Personality disorders such as severe depression or psychotic disorders need to be screened out prior to using this procedure.
   The motor cortex stimulation leads are placed on the dura surgically with the target selected on the primary motor cortex based on somatotopic anatomic landmarks. The optimal stimulation level is that which provides the best pain relief yet does not cause a seizure, pain from dural stimulation, or electromyographic activity. With improved mapping techniques for the epidural stimulation sites in 12 patients with medically intractable neuropathic facial pain, Nguyen reported good to excellent pain relief in 75% of the patients.
   The precise mechanism for the motor cortex stimulation in relieving pain remains unknown. Studies have demonstrated that motor cortex stimulation leads to an increase in cerebral blood flow in the ipsilateral thalamus, cingulate gyrus, orbitofrontal cortex, and midbrain. The extent of pain relief correlates best, however, with anterior cingulate gyrus blood flow. Two other hypothesized mechanisms for pain relief after motor cortex stimulation include direct activation of inhibitory interneurons in the spinal cord or indirect inhibition during stimulation.

Spinal cord stimulation
   The spinal cord stimulation (SCS) (dorsal column stimulation) utilizes an electrodes placed in the epidural space, immediately behind the spinal cord, to stimulate the dorsal column of the spinal cord. The exact mechanism of SCS is unclear. However, it is believed that the gate-control theory of pain conduction plays a major role. When the dorsal column of the spinal cord is stimulated, it may attenuate the conduction of the pain signal on the spinothalamic tract through collateral inhibition. Inhibitory neurotransmitters such as gamma-aminobutyric acid (GABA) may also be involved.
   SCS is indicated for failed back surgery syndrome, complex regional syndrome, and unremitting pain due to peripheral vascular disease. Recent studies have indicated that SCS may also improve pain caused by a refractory angina and improve circulation in the coronary arteries. Some authors have reported treatment of severe peripheral neuropathy and post-herpetic neuralgia with SCS. The value of SCS for amputation stump pain, phantom limb pain and spinal cord injury is yet to be established. Patients seeking spinal cord stimulator treatments usually have failed all the other conservative treatments, such as medication, physical therapy, and nerve blocks with anesthetics and/or corticosteroids. The spinal cord stimulator is not indicated for severe depression.
   Patients should have a SCS trial prior to permanent implantation. During the trial, a percutaneous lead is inserted through the skin into the epidural space. Once the tip of the lead reaches the appropriate level, it is connected to an external pulse generator. When the stimulator is turned on, the patient feels tingling and numbness. If the painful area is covered by the stimulation, the pain is decreased by more than 50% and the patient is satisfied with the stimulation, a permanent implantation may be considered. The procedure of permanent implantation of the SCS is performed by pain specialists or neurosurgeons in operating room. It requires a percutaneous insertion of an electrode into the epidural space under the guidance of fluoroscopy. The tip electrode is threaded up to T9 to T11 level in the epidural space immediately behind the dorsal column for the treatment of low back and leg pain. The other end of the electrode is connected through a subcutaneous tunnel to an internal pulse generator buried under the skin in the low back or abdominal wall. The strength of the stimulation can be changed through a remote control. Common complications of spinal cord stimulator implantation include infection, moving of the electrodes, and failure of pain relief, even after a “satisfied” trial. Serious complications, such as spinal cord compression, or epidural abscesses are rare.

Intrathecal drug delivery systems
   For patients with chronic severe pain, especially malignant pain, who are unable to tolerate the side effects of oral or intravenous medications, intrathecal delivery of medication offers a useful alternative. The technique of intrathecal delivery of medication has evolved since 1979. Currently, the SynchroMed programmable pump is the mostly widely used system. The pump is usually implanted subcutaneously in the abdominal wall. The pump contains about 18 ml of medication. It is connected to one end of a small diameter tube that runs to the intrathecal space. The pump continuously delivers small amounts of medication directly into the lumbar cerebrospinal fluid. Pumps are now programable with external magnetic control to adjust the dosage and time of medication.
   Commonly used medications for pain management include morphine, hydromorphone, bupivacaine, and clonidine. Ziconotide is a novel peptide that blocks the entry of calcium into neuronal N-type voltage-sensitive calcium channels, and prevents the conduction of nerve signals. Ziconotide intrathecal infusion has been approved by the United States Food and Drug Administration for the treatment of intractable severe chronic pain. Baclofen is a GABAb agonist. It has been used through an intrathecal delivery system for the treatment of severe spasticity, and may also decrease the pain related to spasticity.