Clinical syndrome

‘Sympathetically maintained pain’ is defined as ‘pain that is maintained by sympathetic efferent innervation or by circulating catecholamines (especially norepinephrine).’¹ This presents an assumed pain mechanism, not a clinical syndrome, and therefore it can be present in different pain syndromes. The most common places where it occurs are the extremities and the face. Disturbances in the mechanism of the sympathetic system of the face and the upper extremity can give the following symptoms: swelling, hyperhidrosis, disturbances in the temperature regulation of the skin, and changes in skin coloring. There are several diseases and syndromes that can show disturbances in the sympathetic innervation. One example is the complex regional pain syndrome type 1 (CRPS-1) that is characterized by continuing pain after an initiating noxious event or after an immobilization, allodynia, or hyperalgesia with which the pain is disproportionate to any inciting event.² There is a growing controversy on the value of sympathetic blocks in CRPS-1 and 2. A recent review raises questions on the efficacy of local anesthetic sympathetic blockade as a treatment of CRPS. In this review it was concluded that less than one-third of patients involved in trials obtained full pain relief.³ Further studies are needed to clarify this indication.

Furthermore, there is typically evidence of edema, alteration in skin blood flow or abnormal pseudomotor activity in the part of the body the pain is experienced. In all instances, other potential diagnoses that can mimic the symptoms of CRPS must be excluded.

Indications and contraindications

Indications for the performance of a stellate ganglion block with local anesthetic are similar to those for recommending radiofrequency (RF) lesioning. These include:

Contraindications to perform a stellate ganglion blockade include: anticoagulant therapy or coagulation disorders (since the needle is inserted near important vascular structures such as the carotid artery, and an inadvertent vascular puncture is possible); local infection in the overlying soft tissue or systemic infection; recent cardiac infarction; marked impairment of the cardiac stimulus conduction, since a stellate ganglion block blocks the cardiac acceleration nerves (the sympathetic fibers of T1 to T4) creating a risk of intractable bradycardia; and contralateral pneumothorax or pneumonectomy, since a known complication of the stellate ganglion block is pneumothorax.

A relative contraindication is glaucoma since repeated stellate ganglion blocks can provoke glaucoma.

Side effects and complications

Side effects of a stellate ganglion block are temporary ipsilateral Horner’s syndrome (miosis, ptosis, and enophtalmia), conjunctival injection, nasal congestion, and facial anhidrosis. Furthermore, temperature differences between the blocked arm and the contralateral arm (raised skin temperature in the ipsilateral arm) and visible engorgement of the veins on the ipsilateral hand and forearm can occur. Each of these alterations provides proof that the sympathetic system is blocked. In this fashion, an accurate assessment about the response to a diagnostic block can be made.

One of the most serious complications can occur if there is an unintentional injection involving the vertebral and/or the carotid artery,⁷ as seizures that are difficult to treat will result. Accidental injection intrathecally will lead to respiratory failure and the requirement of mechanical ventilation.^8–11 In anticipation of these potential complications, it is advised that an intravenous line be in place prior to the blockade. A less serious but quite disconcerting side effect results from inadvertent diffusion of local anesthetics into nearby nerve structures. In particular, blockade of the recurrent laryngeal nerve typically results in hoarseness, the sensation of a mass in the throat, and sometimes a subjective shortness of breath. Of course, this complication can be dangerous when the blockade has been performed bilaterally in patients with preprocedural respiratory impairment.¹² In other instances, a partial blockade of the brachial plexus with temporary paralysis of arm musculature can result.¹³ If the phrenic nerve is blocked, a temporary unilateral paralysis of the diaphragm transpires with resultant respiratory impairment.¹⁴

Another complication that can lead to respiratory impairment occurs when the apex of the lung is pierced and a pneumothorax ensues. This is more likely to occur if an anterior technique at the C7 level is used as compared to other approaches.

Outcomes

There are only a handful of published studies regarding the efficacy of a stellate ganglion block. In 1983, Bonelli et al. performed a randomized, controlled trial in patients with reflex sympathetic dystrophy (RSD) of the upper extremity in which they compared the efficacy of stellate ganglion block using 15 ml bupivacaine 0.5%, up to a total of eight blocks, with treatment by a regional intravenous sympathetic block using 20 mg guanethidine every 4 days up to a total of four blocks.¹⁵ They concluded that there was a significant improvement in the visual analogue scale (VAS), skin temperature, and skin plethysmography as compared to baseline. There were no significant baseline differences between the two groups. Malmqvist et al. published a randomized controlled trial in 1992 which assessed the efficacy of stellate ganglion blocks using different concentrations and volumes of local anesthetic and different sites of injection.¹⁶ They called the sympathetic block ‘complete’ if the following five criteria were met: the presence of a change in skin temperature, skin blood flow, resistance response and skin resistance level, and the symptoms of Horner’s syndrome. They concluded that it is difficult to perform a block that meets all the five criteria since only six of the 54 blocks met all five criteria. They claimed that injection toward C7 (instead of injection toward C6) and a high concentration were more likely to achieve a successful block. The volume seemed of less importance.

There has been only one study performed addressing RF lesioning of the stellate ganglion for the treatment of pain in the upper extremity caused by RSD.¹⁷ It was a poorly designed retrospective study.

In 1998, Price et al. published a study with a small number of participants in which they compared the efficacy of a sympathetic ganglion block using 1% lidocaine/bupivacaine and a block with normal saline in patients with CRPS-1 using a double-blinded, cross-over paradigm.¹⁸ Four of the seven patients received a stellate ganglion block, and three received a lumbar sympathetic block. In both the local anesthetic group and the saline group there was a large reduction in pain relief accompanied by the reversal of mechanical allodynia 30 minutes after the block in six in of the seven patients. There was no significant difference in the initial peak reduction between the groups. The mean duration of pain relief was significantly longer in the local anesthetic group. The authors concluded that both magnitude and duration of pain relief should be closely monitored to provide optimal efficacy in procedures that use local anesthetics to treat CRPS.

Forouzanfar et al. published a retrospective study in 2000 in which they reviewed 86 stellate ganglion RF ablation procedures used in different chronic pain syndromes.¹⁹ They concluded that this technique is most likely to benefit patients suffering from CRPS-2, ischemic pain, cervicobrachialgia, or post-thoracotomy pain. They emphasized that the clinical efficacy of this technique still remains to be proven in a randomized, controlled trial.