Use of sugammadex in patients with neuromuscular disorders: a systematic review of case reports

Background Sugammadex is a modified gamma-cyclodextrin that acts by selectively encapsulating free amino-steroidal neuromuscular relaxants. Several case reports have been published on the use of sugammadex in patients with neuromuscular disorders that include neuromuscular junction diseases, myopathies, neuropathies, and motor neurone disorders. The primary aim of this review is to systematically review the evidence on the use of sugammadex in patients with this heterogeneous group of diseases and provide recommendations for clinical practice. Methods A systematic electronic search of Medline, Embase and CINAHL databases was done until June 2019, to identify case reports describing the use of sugammadex in adult surgical patients with neuromuscular disorders. Results Of the 578 records identified through database searches, 43 articles were finally included for the systematic review. Of these, 17 reports were on patients with myopathy, 15 reports on myasthenia gravis, 9 reports on motor neuron diseases and 2 reports on neuropathies. Conclusions Majority of the articles reviewed report successful use of sugammadex to reverse steroidal muscle relaxants, especially rocuronium, in patients with neuromuscular diseases. However, with sugammadex, unpredictability in response and uncertainty regarding optimum dose still remain issues. Quantitative neuromuscular monitoring to ensure complete reversal and adequate postoperative monitoring is strongly recommended in these patients, despite the use of sugammadex.


Background
Neuromuscular disorders are a large heterogeneous group of diseases that are usually progressive and produce symptoms at widely differing age ranges with varying degrees of severity [1]. They can be classified into motor neuron diseases, neuropathies, neuromuscular junction disorders or myopathies depending on which section of neuromuscular system is affected [1] (Table 1). Epidemiological studies report an increase in the prevalence of neuromuscular disorders worldwide [2][3][4]. There have been several publications expressing concerns over the choice of muscle relaxants in patients with neuromuscular disorders presenting for surgery but perhaps, the reversal of the effects of muscle relaxants is a greater concern.
Sugammadex (Bridion®, Organon/Schering-Plough USA) a modified γcyclodextrin, acts by selectively encapsulating free molecules of amino steroidal neuromuscular relaxants such as vecuronium and rocuronium forming 1:1 inclusion complex in the plasma, thereby creating a concentration gradient resulting in the reduction of the relaxant available at the neuromuscular junction [5][6][7]. The complex is pharmacologically inert, is not affected by acid-base status or temperature [8] and produces no hemodynamic changes [6]. Thus, sugammadex has been found to have a good safety profile so far, compared with neostigmine [9].
Due to its rapid onset of action, sugammadex has enabled rocuronium to be used in difficult intubation scenarios, where traditionally suxamethonium has been the relaxant of choice [10]. Sugammadex also permits the anesthesiologist to use high dose of rocuronium both for rapid sequence induction and intubation [11] as well as to ensure optimal surgical conditions, by enabling a complete motor recovery and reduced need for postoperative ventilatory support [12]. Moreover, the time taken by sugammadex to adequately reverse moderate to deep block has been found to be shorter than that for neostigmine [10]. Hence, the use of sugammadex is being increasingly reported in patients with neuromuscular disorders. However, synthesis of the evidence from these isolated case reports may provide a more meaningful guidance to the anesthesiologists with their management of such patients and to generate new research hypotheses.
The purpose of the following review is to evaluate the evidence supporting the use of sugammadex as a reversal agent in patients with neuromuscular disorders, in terms of its efficacy and dose requirements and to summarize various aspects that need to be considered during administration of this drug. A detailed review of neuromuscular diseases and their anesthetic considerations is outside the scope of this article.

Methods
A search was done by the reviewers (U.G and L.S) in Medline, Embase and CINAHL using the key Medical Subject Headings (MeSH) terms, "sugammadex", "neuromuscular diseases", "neuromuscular junction disorders", "myopathy", "neuropathy", "hereditary motor sensory neuropathy", "motor neuron disease", "neuromuscular transmission disorders", "Neuromuscular blocking" for studies including case reports on adult humans, and published in peer-reviewed journals, without any restriction on the year of publication. The last search was on 24 June 2019. Adult surgical patients with all variants of neuromuscular diseases who received sugammadex for reversal were eligible for inclusion. Paediatric case reports were excluded. Conference abstracts without full text availability and the articles that were not in English were excluded. Controlled trials on sugammadex, studies that did not use neuromuscular monitoring or did not report train-of-four ratio (TOF ratio) or count (TOF count) were excluded. Authors were not contacted for additional information. Duplicates were removed. Full texts of the articles from the relevant abstracts were reviewed. The reference list of the articles thus obtained was manually searched for any additional relevant article by L.S.
Two reviewers (U.G and S.K) independently screened the title and abstracts of all the articles from the literature search to select articles for full-text review with the inclusion and exclusion criteria. Any discrepancy was resolved by mutual consensus and discussion with the reviewer (L.S). Data were extracted by U. G and S. K into an excel sheet and included author, year, country, patient details, nature of disease, type of surgery, duration of surgery, anesthetic agents, neuromuscular blocking agent and its dose, neuromuscular monitor used, dose of sugammadex and its response and postoperative course. Details of the selection process are given in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) diagram ( Fig. 1).

Results
The search identified 578 citations, 72 relevant abstracts were screened, from which 29 articles excluded, leaving 43 articles suitable for review (Fig. 1). There were 22 publications from Europe, 15 publications from Asia and five from Australia. The maximum number of reports (n = 17) concerned patients with myopathies, followed by patients with myasthenia gravis (n = 15). One Australian paper [13] reported two cases, of which one concerned a patient with myotonic dystrophy and the other about a patient with spinal muscular atrophy. For the sake of classification, it was considered as two different reports. Two reports were on patients with neuropathies and nine on motor neuron diseases.

Discussion
Respiratory involvement in neuromuscular disorders can range from a reduction in inspiratory and expiratory muscle strength resulting in alveolar hypoventilation, poor clearance of airway secretions to atelectasis and respiratory failure 1 . There may be coexisting mild to moderate bulbar dysfunction increasing risk of aspiration and obstructive and central sleep apnea [14]. Hence, muscle relaxants have been cautiously or even sparingly used in patients with neuromuscular disorders in order to avoid the need for postoperative ventilatory support. However, inadequate relaxation due to restricted use of muscle relaxants can compromise the success of some abdominal and gynecological procedures [15,16]. Use of suxamethonium in patients with neuromuscular disorders may risk them with its undesirable side effects such as myalgia, malignant hyperthermia, decreased heart rate, masseter spasm, anaphylaxis, increased intracranial and intraocular pressure, hyperkalemia and prolongation of neuromuscular block in patients with congenital or acquired variations in plasma cholinesterase activity [17,18]. The response and duration of action of rocuronium can be variable and unpredictable in these patients [19]. Since patients with neuromuscular disorders may also have other associated conditions such as cardiomyopathy [20], systemic and pulmonary hypertension and arrhythmias, the conventional combination of reversal agents (neostigmine and anticholinergic drugs) may cause cardiac rhythm disturbances. Previous case reports have also described prolonged neuromuscular blockade similar to depolarizing block or a tonic response following the use of neostigmine in patients with neuromuscular disorders [21]. Other drawbacks of anticholinesterases such as neostigmine include relatively slow onset along with questionable reliability and predictability of reversal [22].
A recent Cochrane review concluded that sugammadex is faster, more efficient and safer than neostigmine in reversing moderate and deep paralysis [23] 2 . Within our literature search, evidence was collected on the use of sugammadex in four main types of neuromuscular disorders:

Neuromuscular transmission disorders (Table 2)
Myasthenia gravis is a common autoimmune disorder that can manifest as muscle weakness that is either generalized or isolated to ocular/bulbar muscles. It may also be associated with autonomic instability. Dosing of muscle relaxants may pose challenges in patients with myasthenia gravis. They could be resistant to suxamethonium with up to twice-normal ED 50 values, with increased risk of phase II blockade at higher doses [24]. In     contrast, patients with myasthenia gravis are sensitive to non-depolarizing relaxants due to a decreased number of acetylcholine receptors and hence a dose reduction of these drugs has been recommended [25][26][27]. In the studies reviewed, the bolus intubating dose of rocuronium used in the patients with myasthenia gravis ranged from 0.09-1.2 mg/kg. Factors such as the use of pyridostigmine and its dose may also impact on the effects and the duration of non-depolarising agents [28]. Moreover, since the acetylcholine esterase is already inhibited by pyridostigmine, reversing residual block with neostigmine may not be fully effective [24,25,27]. Use of sugammadex can provide fast and reliable recovery irrespective of preoperative continuation or cessation of pyridostigmine [29]. A large retrospective cohort study has shown a significant reduction in myasthenic crisis and hospital costs following surgery when sugammadex was used [30].
In the literature reviewed, the documented dosing of sugammadex was also found to vary between reports ( Table 2). A dose of 2 mg/kg sugammadex has been noted to be sufficient even with a TOF count of 0 at the time of administration [31] whereas a dose of 4 mg/kg has been used by other authors [29,32]. In the largest case series to date on the use of sugammadex in myasthenic patients, administration of sugammadex at 2 or 4 mg/kg depending on a TOF count to ≥2 or 0-1 respectively, resulted in full reversal with a duration of less than 2 min on average [33]. 3 However, as per the other reports in our review, complete reversal of relaxant effect occurred within around 3-4 min following sugammadex administration. Interestingly, four reports [32,[34][35][36] describe persistent residual paralysis in patients with myasthenia gravis even after administration of sugammadex. Kiss et al. [34] described the persistence of neuromuscular blockade in a patient with myasthenia gravis, resulting in the administration of a total dose more than 16 mg/kg, in addition to administration of pyridostigmine via nasogastric tube. This was attributed to both redistribution of muscle relaxant and artifact from neuromuscular monitors. Surgery-induced exacerbation of myasthenia gravis has also been noted to result in residual paralysis despite a sugammadex dose of 4 mg/kg [32,35].
In terms of monitoring the adequacy of reversal, motor recovery can occur later at the corrugator supercilii muscle (CSM) than at the adductor pollicis muscle (APM) in patients with ocular myasthenia gravis as opposed to individuals without the disease [37]. 4 In addition, recovery of TOF ratio may be faster than that of first twitch (T1) height after sugammadex administration as observed by Iwasaki et al. in two patients with myasthenia gravis. 4 While the TOF ratio at the APM returned to 90% within 1.5 min and 6.5 min in their two patients, T1 recovery took up to 12 min and 13 min respectively and required additional doses of sugammadex. 4 Hence the authors recommended monitoring TOF ratio as well as the recovery of T1 height to baseline at both APM and CSM, in patients with myasthenia gravis [37]. However, recovery of TOF ratio was found to lag behind T1 recovery in the case reported by Sugi et al. [35]. 4 Myopathies (Table 3) Muscular dystrophies are a heterogenous group of progressive neuromuscular disorders resulting from genetic mutations that cause dystrophic changes in muscles. The most common varieties are Duchenne, Becker and myotonic dystrophies [38]. Patients suffer varying patterns of skeletal muscle weakness depending on the mutation, cardiac abnormalities including cardiomyopathies with or without conduction defects and are prone to pulmonary infection and failure. Myotonic dystrophy is also characterized by prolonged contraction of muscle with defective relaxation. Renal dysfunction may be a common complication in patients with myotonic dystrophy [39]. Patients with myotonic dystrophy tend to show myotonic responses to suxamethonium [40] and increased sensitivity to non-depolarising muscle relaxants [41]. Reactions to neostigmine can also be unpredictable [21,41]. None of these reactions were observed by Imison et al. in the retrospective study on myotonic dystrophy patients [42].
Ten reports discussed the use of sugammadex patients with myotonic dystrophy and two reports in patients with Becker and Duchenne muscular dystrophy [20,43] ( Table 3). The dose of rocuronium have been very variable with these studies. Reduced doses (< 0.6 mg/kg) of rocuronium have been administered to aid intubation in majority of the cases in our review 3 [13,20,[43][44][45][46][47][48][49]. With these cases, the reversal times to TOF ratio of 0.9 with 2 mg/kg sugammadex ranged from 2 min [20,45,46] to 5 min [13,44,48]. However, two authors have 3 Reduced dose of rocuronium has been used in these patients while the standard recommended dose of sugammadex has been successfully used to reverse muscle relaxants in the majority of the published case reports. 4 Variations from normal recovery patterns of muscle strength following administration of reversal agent have been observed in patients with neuromuscular diseases. In myasthenia gravis especially in ocular myasthenia, both spontaneously and with administration of sugammadex, earlier recovery of TOF ratio versus first twitch height and earlier recovery at corrugator supercilii muscle versus adductor pollicis muscle were observed. Hence, monitoring TOF ratio as well as the recovery of first twitch height to baseline at both the muscles is recommended.   reported delayed neuromuscular recovery time of 10 min [43,49], but no explanations were given. It is possible that slight underdosing of sugammadex could have contributed to the delay with Mangla et al. [49]. Three authors had used 1 mg/kg rocuronium to aid intubation, possibly related to their rapid sequence induction [50][51][52]. With all these cases, standard recommended doses of sugammadex were administered according to the TOF count and TOF ratio of 0.9 was reached within reasonable time (< 3 min). 3 While response times to both rocuronium and sugammadex were not delayed, Stourac et al. observed prolonged duration of paralysis with rocuronium [51]. Polymyositis and dermatomyositis cause symmetrical weakness of proximal muscles due to an inflammatory process of the muscle itself with no impact on neuromuscular junction. However, two case reports on the use of sugammadex in patients with dermatomyositis, describe a delay in complete neuromuscular blockade (up to around 5 min), which the authors attribute to vascular pathology associated with the disease process resulting in slow diffusion of rocuronium to neuromuscular junction [53,54] (Table 3). Prolonged reversal time with sugammadex [54] was observed by Suzuki et al. while the other two reports concluded that reversal time was unaffected in these inflammatory myopathies.
Neuropathies (Table 4) A number of neuromuscular disorders could be grouped under neuropathies. One report on transverse myelitis and one report on multiple sclerosis were selected for this review (Table 4). Multiple sclerosis is a frequently occurring demyelinating neuropathy. The reports on multiple sclerosis patients did not suggest an altered dose of rocuronium or unusual response to sugammadex. However, a resistance to rocuronium was described by Staikou et al. manifesting as delay in onset of action following 1 mg/kg of rocuronium [55]. Transverse myelitis involves myelin destruction due to spinal cord inflammation. Prolonged paralysis was reported in a patient with transverse myelitis following the administration of 1.2 mg/kg rocuronium for rapid sequence induction [56].
Motor neuron diseases (Table 5) Motor neuron diseases are a group of disorders characterized by progressive motor neuron degeneration, the most common of which is amyotrophic lateral sclerosis (ALS). It mainly involves lower motor neurons although in ALS both upper and lower motor neurons are affected [57]. In a patient with ALS reported by Kelsaka et al., clinical signs of inadequate recovery were observed despite a TOF ratio > 0.90. Two minutes after sugammadex 2 mg/kg was administered, the patient recovered clinically and was extubated uneventfully [58] (Table 5). A similar discrepancy between TOF ratio and clinical signs of muscle strength recovery was also reported by Chang et al. [59,60]. 5 These authors henceforth questioned the reliability of TOF ratio to guide extubation in patients with this condition and proposed that this discordance may be related to the site and the severity of disease [59][60][61]. In fact, in patients reversed with sugammadex, a TOF ratio of 0.9 may not guarantee complete reversal without complete recovery of first twitch height (T1) [62]. Interestingly, no such issue was noticed by Yoo et al. in their patients with ALS or progressive muscle atrophy (PMA) in spite of their preexisting bulbar dysfunction. However, they had administered 5 mg/kg sugammadex as the pre-reversal TOF count was zero [63].
Use of sugammadex has also been investigated in patients with other motor neuron diseases (Table 5). Patients with spinobulbar muscular atrophy (Kennedy's disease) are at increased risk of laryngospasm and bulbar dysfunction and therefore aspiration [64]. Administration of sugammadex 2 mg/kg with TOF count of 1 has been reported to have resulted in 100% reversal within 180 s in a patient with Kennedy's disease [65]. Two papers reported the management of patients with spinal muscular atrophy [13,66]. Although an immediate and adequate response to sugammadex was observed in both these patients, an increased sensitivity and prolonged paralysis from rocuronium was reported by Vilela et al. [66].
Based on our literature search, the implications for the use of sugammadex can be found as endnotes.

Other relevant considerations of sugammadex
Use of sugammadex does not guarantee adequate recovery unless confirmed by TOFr of at least 0.9 6 . Since sugammadex does not form complexes with suxamethonium and benzylisoquinolinium muscle relaxants (mivacurium, atracurium and cisatracurium), it cannot be used to reverse these agents [67]. Further, factors such as age [68], cardiac output [69], increased stress due to surgery and pregnancy [35,56] may contribute to delayed return of muscle power following sugammadex administration. 7 . In 5 Discordance between TOF ratios and clinical recovery have been reported in amyotrophic lateral sclerosis, which has been stated to be related to severity of disease and type of muscles involved. 6 Quantitative neuromuscular monitor is essential in the management of these patients with a TOF ratio of > 0.9 at peripheral muscles before extubation, to ensure adequate pharyngeal function and airway protection as well as to prevent complications such as atelectasis and pneumonia. 7 Since delayed or failed recurarisation and long recovery times have been reported with adequately dosed sugammadex reversal even in normal surgical patients, presence of additional factors such as renal dysfunction, temperature fluctuation, acid-base or electrolyte imbalances in these patients or interaction with other medications (i.e. magnesium, baclofen,) necessitate prolonged post-operative observation, especially for respiratory insufficiency in patients with neuromuscular diseases.   fact, even in routine surgical population, in spite of reversing with sugammadex, 2% of the patients were found to have residual paralysis (TOF < 0.9) in the recovery room [70] 7 . Fluctuations in muscle power may occur even after seemingly adequate reversal with sugammadex due to the redistribution of unbound muscle relaxant from the peripheral to the central compartment causing a rebound of blockade [71]. Despite the rapid reversal, there is no firm evidence to prove superiority of sugammadex over neostigmine in the prevention of postoperative pulmonary complications according to a recent review [72].
There have been reports of suspected hypersensitivity reactions to sugammadex [73,74] but more evidence is needed in this regard to confirm its true incidence. In addition, there are concerns about displacement and capturing interactions with sugammadex. In particular, sugammadex may capture the prostagenic compound in oral contraceptive making it less effective [10]. Sugammadex is not also recommended for patients with severe renal impairment or those on dialysis [75] although evidence suggests that the complex with rocuronium can be removed by haemodialysis [76].

Limitations of the review
There are several limitations to this review. As this review summarizes the findings of various case reports, there are inherent drawbacks such as missing information, inability to draw inferences on causality and publication bias [77]. Non-English reports, abstracts without full texts and pediatric case reports are not included in this review. Since the primary goal of this article is to investigate the use of sugammadex patients in neuromuscular disorders and its clinical considerations, details on the disease severity and medications in every reported case were avoided. Since based on case reports, it has not been possible to provide conclusive evidence on the correct dose and timing of administration of sugammadex in patients with neuromuscular disorders.

Conclusion
Anesthetic management of patients with neuromuscular disorders is challenging due to the variability in the type, severity of the disorder and the extent of dysfunction in various muscle groups and their sensitivity to muscle relaxants in each patient.
Multiple case reports have been published describing the successful reversal of rocuronium with sugammadex in patients with neuromuscular disorders, however, there are also reports of adverse reactions and instances of inadequate reversal with administration of sugammadex. Currently, as there is limited knowledge on optimal dosing and timing of administration of sugammadex, a similar unpredictability in response also seem to occur with the use of sugammadex in this cohort of patients. Hence despite the advantages of sugammadex in this high-risk group of patients, it is strongly recommended to use quantitative neuromuscular monitoring to ensure complete recovery from the effects of steroidal muscle relaxants and to exercise extended postoperative supervision in these patients.