1. Discuss the physiologic disease of MS

Multiple sclerosis is a chronic inflammatory demyelinating disease of the central nervous system, which results in demyelination and scarring occurring around the brain and spinal cord [1]. The etiology of MS is complex, and thought to include an array of genetic, immunologic, and environmental mechanisms [2–3]. Although presentation and severity can vary greatly, symptoms predominately start in early adulthood (20 to 40 years) and disproportionately affect women [2]. Initial clinical manifestations may include vision disturbances (diplopia, loss of vision, painful eye movements), sensory deficits (numbness and tingling of the extremities or trunk, facial muscle dysfunction), limb weakness/gait ataxia, and bowel and bladder dysfunction [3–4]. Additionally, autonomic dysfunction can manifest as orthostatic hypotension or cardiac dysrhythmias [5]. Pain is also common and patients may experience burning sensations throughout their extremities and painful muscle spasticity [6]. In addition, patients may demonstrate Lhermitte’s sign, which consists of a painful electric-shock-like sensation down the back and extremities during neck flexion [6]. Approximately 80 to 90% of patients with MS have a relapsing–remitting course, which consists of relapses of disease symptoms alternating with periods of partial to complete recovery [2–4].

Diagnosis usually involves documented clinical symptoms, MRI identification of demyelinating plaques in the brain and spinal cord, and examination of the CSF for presence of oligoclonal bands [1–2].Treatment may consist of immunosuppressants (corticosteroids, methotrexate, cyclophosphamide, cyclosporine), plasma exchange, and immunomodulatory therapy (interferon beta, glatiramer acetate, natalizumab, mitoxantrone, teriflunomide, fingolimod) [2, 4, 6].

2. Explain the primary anesthetic concerns in patients with MS

Primary anesthetic concerns for patients with MS are related to their specific symptomatology and aimed at risk reduction for perioperative MS exacerbations. First, patients should undergo a thorough preoperative evaluation that includes (but is not limited to) a description of the MS presentation, documentation of recent attacks (including symptoms), and a full neurologic exam to document current neurologic deficits [6]. In addition, it is important preoperatively to consider the pharmacologic therapy patients are taking for their MS and related symptoms or side effects [4, 6] (Table 11.1).

It is also important to determine preoperatively if the patient has any current clinical cardiac or respiratory dysfunction related to their MS. Clinical symptoms such as shortness of breath and inability to generate a good cough may lead the provider to conduct further testing prior to elective surgery. In addition, cardiac and autonomic dysfunction, including arrhythmias and orthostatic hypotension, may also indicate a need for further preoperative evaluation. Autonomic dysfunction can lead to marked intraoperative hypotension that may be unresponsive to typical therapy such as intravenous fluid and vasopressors [6].

Stressful situations have the potential to induce an MS exacerbation and thus it is important to limit emotional and physical stress during the perioperative period. This includes providing adequate sedation and anxiolysis for any preoperative procedures. Perioperative temperature monitoring and avoidance of hyperpyrexia is also warranted as fever can trigger MS exacerbation [3, 6]. The use of regional anesthesia vs. general anesthesia for intraoperative care is best determined on an individual basis, with consideration given to type of surgery and patient preference. Overall, there are no clear data suggesting that one type of anesthesia is superior with reference to inducing an MS exacerbation.

3. Review the risks and benefits of peripheral and neuraxial techniques in patients with MS

Evidence regarding the use of neuraxial techniques in patients with pre-existing MS is sparse, contradictory, and often limited to case series and observational reports. Older case studies reported increased local anesthetic uptake in demyelinated areas of the spinal cord, leading to exaggerated physiologic response and implicating this anesthetic technique in increasing MS exacerbations [7–8]. However, a more recent prospective observational study of 254 parturients with MS found that epidural analgesia did not affect the rate of relapse or worsen pre-existing neurologic symptoms [9–10]. In addition, successful spinal anesthesia has been reported in a parturient without increased anesthesia duration or neurologic complications in a 12-month follow-up [11]. Further, recent reviews and editorials have strongly suggested that both spinal and epidural anesthesia/analgesia may be safely administered for patients with MS [1, 6, 12].

Data for peripheral nerve block (PNB) use in patients with MS remain limited and controversial. Although MS is a disease of the central nervous system, peripheral nerve involvement may often be subclinical, making it difficult to determine which patients may be at higher risk for nerve injury [13–15]. In fact, Gartzen et al. performed nerve conduction studies in 54 patients with MS and found that 16 had abnormal nerve conduction velocities [14]. Case reports have also been published describing brachial plexus injury after interscalene nerve block for total shoulder arthroplasty and prolonged lower extremity motor and sensory blockade after paravertebral injections [16–17]. However, determining the exact etiology for injury and the role that MS plays is controversial [12, 18–19]. Conversely, case reports also describe the successful use of PNBs without adverse neurologic effect [20]. Due to the lack of clinical studies and mostly anecdotal case reports, anesthesiologists are left to their own judgment regarding the use of PNBs in patients with MS. However, the use of ultrasound and avoidance of epinephrine in local anesthetic solutions may reduce the chance of additional nerve compromise [1, 5, 21].

4. Compare and contrast this with the risks and benefits of regional anesthesia for other neuropathies

Many types of acquired or genetic neuropathies may be encountered in clinical practice and each presents a unique challenge to the anesthesiologist. While it is beyond the scope of this chapter to review every known neuropathy, we will focus on two specific disease states that may appear in clinical practice: Guillain–Barré syndrome (GBS) and Charcot–Marie–Tooth syndrome (CMT).

Guillain–Barré syndrome is an acquired immunologically mediated demyelinating disorder of unknown etiology. It typically presents with ascending symmetric paresthesias and weakness that begin in the lower extremities and can affect respiratory function [22]. Guillain–Barré syndrome presents several challenges to the anesthesiologist including perioperative autonomic instability, possible drug interactions due to upregulation of postsynaptic acetylcholine receptors, exaggerated response to stimulants, and rapid progression of symptoms that can lead to the need for postoperative mechanical ventilation. The primary advantage of regional anesthesia (RA) is the potential avoidance of intubation requiring intravenous muscle relaxants. Neuraxial techniques are generally considered safe in the setting of GBS, with multiple published reports of both parturients and surgical patients undergoing neuraxial anesthesia with no sequelae [22–26]. Unfortunately, cases of peripheral nerve blocks in patients with GBS have not been reported in the literature. However, there may be advantages to the use of peripheral nerve blocks in patients with GBS. In addition to avoiding intubation and neuromuscular blocking agents, peripheral nerve blocks may also avoid the potential hemodynamic shifts that can occur with both general and neuraxial anesthesia.

Charcot–Marie–Tooth syndrome is the most common hereditary peripheral neuropathy. It can affect both the axon and the myelin of the nerve terminal, depending on the type: demyelinating (type 1) and primary axonal loss (type 2). Charcot–Marie–Tooth syndrome typically manifests with slowly progressive distal weakness, muscle atrophy, and sensory loss. This leads to immobility, deformity, and chronic pain. Many CMT patients require multiple orthopedic surgeries where the use of RA would have advantages; however, administration of RA to patients with CMT remains controversial, mainly due to the concern of local anesthetic neural toxicity. Currently, there are no prospective studies in the literature that examine RA in this patient population. However, multiple published case reports support the safety for both neuraxial and peripheral nerve blocks [27–30]. The use of nerve stimulation is often ineffective in CMT patients, making ultrasound guidance key in the performance of a successful block [28, 30–31].