Primary erythromelalgia is a peripheral neuropathy of unknown etiology that presents with episodic pain, edema, erythema, and heat.1 Erythromelalgia usually presents in a symmetrical distribution and is more common in the lower than the upper extremities.1 Primary erythromelalgia is an autosomal dominant disorder that presents with both neuropathological and microvascular involvement.1 Nociceptors are primarily affected.1 The main defect is in a sodium-gated voltage channel; hyperexcitability of C fibers (unmyelinated, small diameter, slow conduction) in the dorsal root ganglion results in the severe, burning pain.1 Whether peripheral nerve blocks (PNBs) exacerbate nerve damage or can be used as a treatment option remains unknown.
PNBs reduce the amount of narcotic consumption, allow a smoother transition to oral analgesics, and increase blood supply to grafts. However, PNBs do not come without complications, including a failed or partial block, bleeding, infection, and potential nerve damage. Limited data on PNBs in patients with neuronal injuries exist. The double-crush phenomenon implies that axoplasmic flow impairment or neuronal mechanical compression in ≥2 areas along an axon can result in more severe deficit than otherwise anticipated based on the severity of the individual lesions.2 This phenomenon has been described for carpal tunnel syndrome, Charcot–Marie–Tooth, and other conditions. The evidence for or against performing PNBs in these conditions is limited,3 but anesthesiologists remain wary of performing a PNB in a patient with an underlying peripheral neuropathy.
This case report is the first to describe a safe and effective PNB in a patient with primary erythromelalgia. We obtained informed, written consent for publication of this patient’s medical information for the benefit of educating health care professionals.
A 79-year-old woman was scheduled for a left reverse total shoulder arthroplasty for severe osteoarthritis. Her medical history was significant for atrial fibrillation, mitral valve prolapse, stable coronary artery disease, and primary erythromelalgia. The patient was diagnosed with erythromelalgia 4 years ago, when she presented with pain, erythema, and edema of the lower extremities. Her lower extremity nerve conduction study (NCS) was normal; subsequently, she suffered a flare of her lower and upper extremities and was placed on a 10-day course of oral prednisone. The flare consisted of increased pain, edema, and skin changes and had been resolved for just under 1 year when she came for her preassessment consultation. She remained asymptomatic.
After discussion of the benefits (eg, better postoperative analgesia, decreased narcotic consumption, and less nausea and vomiting) and risks (eg, bleeding, infection, pneumothorax possibly requiring a chest tube, nerve damage, respiratory distress/hypoxia from phrenic nerve involvement, local anesthetic systemic toxicity, and a failed/partial block), the patient provided consent to receive an interscalene nerve block (ISNB) and superficial cervical plexus block. The patient was prepared and draped in the usual fashion. Under sterile technique and real-time ultrasound guidance, an ISNB was performed using a 50-mm, 22-gauge blunt block needle. Twelve milliliters of 0.5% ropivacaine with 2 mg of preservative-free dexamethasone was administered in the interscalene groove at the level of the C5 and C6 roots, yet external to the epineurium. There were no immediate complications. The patient developed decreased sensation to cold and pinprick and weakness in the expected distribution of C5 and C6 dermatomes. She subsequently underwent a general endotracheal anesthetic for her surgery with 150 μg intravenous (IV) fentanyl, 40 mg IV lidocaine, 100 mg IV propofol, 40 mg IV rocuronium, and 0.6 mg IV hydromorphone intraoperatively and 0.4 mg IV hydromorphone in the postanesthetic care unit. The patient also received 8 mg IV dexamethasone and 2 g IV cefazolin. A size 7.5 endotracheal tube was secured. Motor function returned later that evening. The patient reported that the nerve block lasted approximately 40 hours before return of sensation, requiring oral analgesics. Both the motor and sensory deficit had completely resolved by the second postoperative day, and no residual deficits were reported during a telephone follow-up interview on postoperative day 5. She was satisfied with her care and the perioperative analgesic regimen.
To our knowledge, this is the first report of a safe and effective ISNB in a patient with primary erythromelalgia. The population-based overall age-adjusted and sex-adjusted incidence for erythromelalgia is 1.3 in 100,000 people per year,4 with primary and secondary erythromelalgia accounting for 1.1 and 0.2 in 100,000 people per year, respectively.4 The condition is more common in women (2 per 100,000 women) than in men (0.6 per 100,000 men).4 Secondary erythromelalgia may be related to essential thrombocytosis, polycythemia rubra vera, mushrooms (ie, Clitocybe acromelalga, Clitocybe amoenolens), obstructive sleep apnea, myeloid leukemia, connective tissue disorders, multiple sclerosis, and other factors.1 The pathophysiology for primary erythromelalgia remains unknown. The most common mechanisms postulated for its pathophysiology are secondary to vascular impairment with precapillary sphincter constriction, arteriovenous shunting, and reactive hyperemia.1
Primary erythromelalgia characterization has not been well delineated. The histological changes described are nonspecific, do not show any thrombi, and demonstrate a decrease in small nerve fiber density.5 Negative NCS does not completely rule out the diagnosis. NCS may be negative in 70%–90% of subjects, depending on the nerve being stimulated.6 Therefore, negative NCS in this patient does not fully rule out damage to the small nerve fibers. Her NCS was performed of her lower extremities and not her upper extremities, with a recent lower and upper extremity flare requiring oral prednisone.
Nerve injury from PNBs occurs with an approximate incidence of 0.03% but can be more frequent in patients with predisposing factors.3 The risk of nerve damage is potentially higher in proximal nerves than more distal nerves because of a higher neural tissue-to-connective tissue ratio.3 The mechanisms of peripheral nerve injury include mechanical, neurotoxic, and ischemic.3 Mechanical needle trauma to nerve fascicles is possible, but numerous animal and anatomical studies have shown that this is likely not the most common mechanism of injury from regional anesthesia because intraneural needle placement without local anesthetic administration rarely results in injury.7,8 The bulk of the evidence suggests that nerve injury from regional anesthesia is more commonly related to the neurotoxic effect of local anesthetics when injected past the epineurium.7,8 Perineural microhematoma can also lead to nerve ischemia by direct compression, especially of the vasa nervorum.9 An ISNB consists of an injection at the level of the proximal roots of the brachial plexus, a short distance after they have left the neural foramen. Nerve roots are conceivably more susceptible to nerve injury because they are monofascicular nerves with a delicate epineurium and contain a high nerve tissue-to-connective tissue ratio.
The “double-crush” theory proposed by Upton and McComas2 in 1973 maintains that patients with preexisting neurological disease are at increased susceptibility to neuronal compromise after a low-grade secondary insult. The American Society of Regional Anesthesia guidelines suggest that there is not enough evidence to guide management in patients with hereditary and acquired neuropathies, but a full discussion including risks and benefits should be entertained with the patient (class III evidence).3 Careful consideration should be given to modify the anesthetic technique, such as using ultrasound, decreasing the concentration of the local anesthetic, excluding vasoconstrictor adjuncts (eg, epinephrine), and decreasing the total dose of local anesthetic.
A systematic review and meta-analysis demonstrated that perineural dexamethasone prolongs PNB duration.10 Further research demonstrates that PNB duration is increased with perineural injection of dexamethasone rather than IV administration.11,12 Also, the duration of a PNB is prolonged with the addition of dexamethasone if epinephrine is added to the solution (without epinephrine, IV versus perineural dexamethasone showed no difference in block duration).13 Moreover, perineural dexamethasone did not increase the risk of neurological complications.14 Further evidence demonstrates increased PNB analgesia with IV dexamethasone alone, when looking at local anesthetic alone compared to local anesthetic + peripheral dexamethasone compared to local anesthetic + IV dexamethasone.15 In our patient, the PNB duration was approximately 40 hours, which is longer than expected. One speculation of the increased duration of action may be secondary to the diseased nerve and the interaction with the local anesthetic. Another plausible explanation may be the coadministration of perineural dexamethasone with IV dexamethasone. To our knowledge, there is no evidence looking at PNB duration with systemic and perineural dexamethasone.
If performing a PNB in a patient with primary erythromelalgia, a complete discussion of benefits, risks, and alternatives should ensue. The ultrasound-guided PNB should be performed with meticulous technique by the most experienced anesthesiologist. Depending on the surgical site, the PNB should be performed more distal if possible, rather than proximal, to minimize the potential toxicity and possibility of nerve damage. A mixture of epinephrine within the local anesthetic to decrease the local anesthetic absorption may benefit these patients from a PNB duration, but vasoconstricting agents potentially may increase the risk of nerve damage. Furthermore, perineural dexamethasone will prolong the duration of the block. Perhaps it would be reasonable to administer IV dexamethasone in a patient with primary erythromelalgia only to accept the slightly decreased PNB analgesic prolongation. Reserving a PNB as a postoperative rescue block may be considered. A limitation from this report is the lack of longer follow-up, involving a physical examination. We recommend a physical examination, and, should deficits be found, the appropriate neurological consultation and investigations should be ordered. Guidance from American Society of Regional Anesthesia guidelines in patients with primary erythromelalgia will not be helpful, and the pros and cons of PNB should be assessed on a case-to-case basis.
We present a patient with primary erythromelalgia who underwent a reverse total shoulder arthroplasty under a combined ISNB, superficial cervical plexus block, and general endotracheal anesthesia with no residual neurological deficits.
Name: Gianni R. Lorello, BSc, MD, MSc, CI, FRCPC.
Contribution: The author helped care for the patient, conceive and design the study, and draft and revise the manuscript.
Name: Anahi Perlas, MD, FRCPC.
Contribution: The author helped revise the manuscript.
This manuscript was handled by: BobbieJean Sweitzer, MD, FACP.
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