Blockades for Sympathetically Maintained Pain (SMP)
The sympathetic nervous system has been implicated in numerous pain syndromes while interruption of the sympathetic flow has been proven to relieve certain pain syndromes. Such pain syndromes are referred to as Sympathetically Maintained Pain Syndromes (SMP). To optimize the outcome following sympathetic blockade, accurate diagnosis of sympathetically maintained pain (SMP) should be made.1,2
Sympathetically maintained pain presents clinically with neuropathic pain picture i.e. burning, Stabbing, shooting in nature with allodynia. Classically these SMP, like other neuropathic pain syndromes, respond to Tricyclic Antidepressants (TCA) and anticonvulsant drugs (AC). Laboratory tests can also confirm some degree of neuropathic pain component which can probably be sympathetically maintained pain (triple phase bone scan).1
There is no gold standard criteria to determine if the neuropathic pain syndrome is SMP or not; some have suggested that two or more of the following four test to be positive. The four tests include:
- good pain relief following sympathetic blockade which is directly related to the duration of the local anesthetic agent used, preferably a local anesthetic agent should be used versus a placebo;
- response to intravenous phentolamine infusion which produces system sympathetic blockade;
- aggravation of the pain following infusion of norepinephrine;
- the relief of the pain with infusion of clonidine or application of clonidine patch.
The classical targets for sympathetic blockade are the sphenopalatine ganglia (for vascular headache, and cranial neuralgias), stellate (cervicothoracic) sympathetic ganglia (for SMP and vascular disorders, in the upper extremities), celiac/splanchnic plexus (abdominal SMP and visceral malignant and non-malignant pain), lumbar sympathetic ganglia (lower extremity SMP and related pain syndromes), superior hypogastric (for pelvic pain and pelvic visceral malignancies), and ganglia impar (peri-anal and rectal pain). See Table 1 for a summary of the blockades discussed in subsequent sections.1-9
In addition to the pharmacological and non pharmacological therapies, local anesthetic and neurolytic blocks to the sympathetic axis are effective for controlling pain. During the performance of sympathetic blockade, it is recommended that an IV access be maintained should complication occur as well as monitors —including temperature — for the extremities to indicate successful sympathetic blockade to that extremity.1-3
Sphenopalatine Ganglia Block (SPG)Indications: 1. Vascular Headache. 2. Facial Neuralgia. 3. Spheno-palatine neuralgia.
Potential Complications: Mechanical — traumatic injury to the maxillary nerve, vascular trauma / hematoma, epistaxis and pain at the site of the injection. Pharmacological — intravascular injection, damage to the maxillary nerve by the neurolytic agent and seizure from the local anesthetic agent
Cervicothoracic / Stellate Ganglion BlockIndications: 1. Head and neck painful conditions if SMP (herpes Zoster pain and post-herpetic neuralgia). 2. CRPS type I (RSD) and II (Causalgia) and other sympathetically maintained pain syndromes to the upper extremities and to the anterior chest wall. 3. Vascular insufficiency /vascular disorders including Raynaud’s disease, and other vascular conditions to the upper extremities, head and neck, including some vascular type of headaches (migraine, cluster headaches).
Contraindications: Contralateral phenic nerve palsy, blood dyscrasia/coagulopathy, local sepsis and patient refusal.
Potential Complications: Mechanical — pain from the injection, hematoma, pneumothorax, pneumomediastinum, injury to the esophagus, brachial plexus and vasovagal attacks. Pharmacological — Horner’s syndrome, spinal analgesia, brachial plexus and phrenic nerve block leading to difficulty in breathing, recurrent laryngeal nerve block leading to hoarseness of voice, and seizure because of intravascular injection.
Celiac/ Splanchnic Nerve Plexus BlockIndications:1. Acute/chronic pancreatitis and hepatobiliary disorder including biliary sphincteric disorder (biliary dyskinisia). 2. Abdominal visceral pain syndrome including abdominal malignances. 3. Abdominal angina. 4. To differentiate visceral pain from somatic pain syndrome of the abdominal cavity (somatic pain will nor respond to celiac plexus block).
Potential Complications: Mechanical — injury to the blood, kidney and ureter lung and pleura (pneumothorax, hemopneumothorax, pleurisy), paraplegia because of intravascular/intrathecal injection or because of trauma to the blood supply to the spinal cord (artery of Adamkeiwicz). Pharmacological — hypotention, and diarrhea because of sympathetic blockade, intravascular injection (seizure), alcohol neurolytic block can cause alcohol withdrawal in people with disulfiram therapy for alcohol abuse. Phenol should be avoided in patients who have vascular prosthesis, as it can attack the prosthesis. IV access should be maintained and pre-load of fluid is also advisable to reduce the severity of hypotention.
Lumbar Sympathetic BlockIndications: 1. CRPS type I and II (SMP). 2. Vascular insufficiency /disorder to the lower extremity. 3. Neuropathic pain i.e. post-herpetic neuralgia. to the lower extremities. 4. Visceral pain (renal colic)
Potential Complications: Mechanical — Infection,trauma to the lumbar nerve and disc, intravascular, intrathecal and epidural injection. Kidney trauma (hematuria). Pharmacological — Intravascular or intrathecal injection of local anesthetic agent or neurolytic agent, hypotension, paraplegia and, in case of neurolytic block, genitofemoral neuralgia.
Superior Hypogastric Plexus BlockIndications: Treatment of pelvic pain including malignancy, endometriosis or pelvic inflammatory diseases/adhesions.