Pathophysiologic and anesthetic considerations for patients with myotonia congenita or periodic paralyses

Anaesthetic management of a parturient with hypokalaemic periodic paralysis for caesarean section: A case report and review of the literature

A 32-year-old multigravida woman, with known familial hypokalaemic periodic paralysis, underwent spinal anaesthesia for an elective lower segment caesarean section. There are several case reports in the literature discussing the optimal anaesthetic technique. In the past there has not been an emphasis on aggressive and early potassium replacement. A target level to commence replacement of potassium at 4.0 mmol/L or less is proposed. Careful preoperative preparation, frequent perioperative monitoring and early potassium replacement resulted in no perioperative episodes of weakness in this case, in contrast with other case reports where potassium was either not monitored or not replaced early enough, resulting in postoperative attacks. Another factor to consider in hypokalaemic periodic paralysis is the avoidance of triggers, including certain medications. Misoprostol was used in this instance to avoid potential electrolyte derangements from other uterotonics.

Diagnostics in skeletal muscle channelopathies

INTRODUCTION

Skeletal muscle channelopathies (SMCs) are a heterogenous group of disorders, caused by mutations in skeletal ion channels leading to abnormal muscle excitability, resulting in either delayed muscle relaxation (myotonia) which characterizes non-dystrophic myotonias (NDMs), or membrane transient inactivation, causing episodic weakness, typical of periodic paralyses (PPs).

AREAS COVERED

SMCs include myotonia congenita, paramyotonia congenita, and sodium-channel myotonia among NDMs, and hyper-normokalemic, hypokalemic, or late-onset periodic paralyses among PPs. When suspecting an SMC, a structured diagnostic approach is required. Detailed personal and family history and clinical examination are essential, while neurophysiological tests should confirm myotonia and rule out alternative diagnosis. Moreover, specific electrodiagnostic studies are important to further define the phenotype of de novo cases and drive molecular analyses together with clinical data. Definite diagnosis is achieved through genetic testing, either with Sanger sequencing or multigene next-generation sequencing panel. In still unsolved patients, more advanced techniques, as exome-variant sequencing or whole-genome sequencing, may be considered in expert centers.

EXPERT OPINION

The diagnostic approach to SMC is still mainly based on clinical data; moreover, definite diagnosis is sometimes complicated by the difficulty to establish a proper genotype-phenotype correlation. Lastly, further studies are needed to allow the genetic characterization of unsolved patients.

[Trigger-free anesthesia : Indications and safe application]

The safe anesthesiological care of patients with neuromuscular diseases poses a particular challenge for anesthetists. Only a small group of muscle diseases and syndromes are associated with an increased risk of malignant hyperthermia and therefore require trigger-free anesthetic procedures avoiding volatile anesthetics and succinylcholine. These diseases are frequently associated with mutations in the RYR1, CACNA1S or STAC-3 genes. In other neuromuscular diseases, anesthetic-induced rhabdomyolysis can occur. Therefore, volatile anesthetics should be avoided in these patients in addition to the contraindication for succinylcholine. In other neuromuscular diseases the risk of a propofol infusion syndrome or myotonic crises can be elevated or the duration of the effect of non-depolarizing muscle relaxants can be changed in an incalculable way. In every case an individual anesthetic aproach including the avoidance of potential pharmacological or non-pharmacological triggers is essential for the safety of the patients.

Real Evidence and Misconceptions about Malignant Hyperthermia in Children: A Narrative Review

Malignant hyperthermia is a rare but life-threatening pharmacogenetic disorder triggered by exposure to specific anesthetic agents. Although this occurrence could affect virtually any patient during the perioperative time, the pediatric population is particularly vulnerable, and it has a five-fold higher incidence in children compared to adults. In the last few decades, synergistic efforts among leading anesthesiology, pediatrics, and neurology associations have produced new evidence concerning the diagnostic pathway, avoiding unnecessary testing and limiting false diagnoses. However, a personalized approach and an effective prevention policy focused on clearly recognizing the high-risk population, defining perioperative trigger-free hospitalization, and rapid activation of supportive therapy should be improved. Based on epidemiological data, many national scientific societies have produced consistent guidelines, but many misconceptions are common among physicians and healthcare workers. This review shall consider all these aspects and summarize the most recent updates.

European Neuromuscular Centre consensus statement on anaesthesia in patients with neuromuscular disorders

BACKGROUND AND PURPOSE

Patients with neuromuscular conditions are at increased risk of suffering perioperative complications related to anaesthesia. There is currently little specific anaesthetic guidance concerning these patients. Here, we present the European Neuromuscular Centre (ENMC) consensus statement on anaesthesia in patients with neuromuscular disorders as formulated during the 259th ENMC Workshop on Anaesthesia in Neuromuscular Disorders.

METHODS

International experts in the field of (paediatric) anaesthesia, neurology, and genetics were invited to participate in the ENMC workshop. A literature search was conducted in PubMed and Embase, the main findings of which were disseminated to the participants and presented during the workshop. Depending on specific expertise, participants presented the existing evidence and their expert opinion concerning anaesthetic management in six specific groups of myopathies and neuromuscular junction disorders. The consensus statement was prepared according to the AGREE II (Appraisal of Guidelines for Research & Evaluation) reporting checklist. The level of evidence has been adapted according to the SIGN (Scottish Intercollegiate Guidelines Network) grading system. The final consensus statement was subjected to a modified Delphi process.

RESULTS

A set of general recommendations valid for the anaesthetic management of patients with neuromuscular disorders in general have been formulated. Specific recommendations were formulated for (i) neuromuscular junction disorders, (ii) muscle channelopathies (nondystrophic myotonia and periodic paralysis), (iii) myotonic dystrophy (types 1 and 2), (iv) muscular dystrophies, (v) congenital myopathies and congenital dystrophies, and (vi) mitochondrial and metabolic myopathies.

CONCLUSIONS

This ENMC consensus statement summarizes the most important considerations for planning and performing anaesthesia in patients with neuromuscular disorders.

Childbirth with epidural analgesia in a pregnant woman with hypokalemic periodic paralysis

Familial hypokalaemic periodic paralysis (FHPP) is an uncommon genetic disease characterized by muscle weakness associated with hypokalaemia. Episodes are precipitated by drugs, stress, metabolic diseases, hypothermia or infection. We report the case of a 38-year-old pregnant women with FHPP who underwent epidural analgesia for labour. Pregnant women with FHPP require multidisciplinary management involving an anaesthesiologist, a gynaecologist and a paediatrician. It is important to maintain normothermia, prevent hyperventilation, monitor electrolytes, avoid glucose infusions and medications that cause hypokalaemia, and administer potassium supplements when required. Locoregional techniques should be preferred over general anaesthesia. Early epidural analgesia reduces the risk of pain that could trigger an episode of FHPP. In the case of general anaesthesia, drugs that can cause malignant hyperthermia should be avoided, and short-acting non-depolarizing neuromuscular blockers with blockade-depth monitoring should be used.

Childbirth with epidural analgesia in a pregnant woman with hypokalemic periodic paralysis

Familial hypokalaemic periodic paralysis (FHPP) is an uncommon genetic disease characterized by muscle weakness associated with hypokalaemia. Episodes are precipitated by drugs, stress, metabolic diseases, hypothermia or infection. We report the case of a 38-year-old pregnant women with FHPP who underwent epidural analgesia for labour. Pregnant women with FHPP require multidisciplinary management involving an anaesthesiologist, a gynaecologist and a paediatrician. It is important to maintain normothermia, prevent hyperventilation, monitor electrolytes, avoid glucose infusions and medications that cause hypokalaemia, and administer potassium supplements when required. Locoregional techniques should be preferred over general anaesthesia. Early epidural analgesia reduces the risk of pain that could trigger an episode of FHPP. In the case of general anaesthesia, drugs that can cause malignant hyperthermia should be avoided, and short-acting non-depolarizing neuromuscular blockers with blockade-depth monitoring should be used.

A case of paramyotonia congenita in pregnancy

Paramyotonia congenita is a rare autosomal dominant non-dystrophic myopathy caused by mutations in the SNC4A gene, which encodes for the voltage-gated sodium channel in skeletal muscle. Symptom onset is typically during early childhood and is characterised by myotonia followed by flaccid paralysis or weakness, usually exacerbated by repeated muscle contractions or cold temperatures. Pregnancy has been reported to increase symptoms of myotonia; however, there is limited information in the literature regarding the possible effects of paramyotonia congenita on pregnancy and labour. We present a successful case of a 20-year-old primigravida with confirmed paramyotonia congenita and review the literature regarding paramyotonia congenita during pregnancy.

Guidelines on clinical presentation and management of nondystrophic myotonias

The nondystrophic myotonias are rare muscle hyperexcitability disorders caused by gain-of-function mutations in the SCN4A gene or loss-of-function mutations in the CLCN1 gene. Clinically, they are characterized by myotonia, defined as delayed muscle relaxation after voluntary contraction, which leads to symptoms of muscle stiffness, pain, fatigue, and weakness. Diagnosis is based on history and examination findings, the presence of electrical myotonia on electromyography, and genetic confirmation. In the absence of genetic confirmation, the diagnosis is supported by detailed electrophysiological testing, exclusion of other related disorders, and analysis of a variant of uncertain significance if present. Symptomatic treatment with a sodium channel blocker, such as mexiletine, is usually the first step in management, as well as educating patients about potential anesthetic complications.

Treatment Updates for Neuromuscular Channelopathies

PURPOSE OF REVIEW

This article aims to review the current and upcoming treatment options of primary muscle channelopathies including the non-dystrophic myotonias and periodic paralyses.

RECENT FINDINGS

The efficacy of mexiletine in the treatment of myotonia is now supported by two randomised placebo-controlled trials, one of which utilised a novel aggregated n-of-1 design. This has resulted in licencing of the drug via orphan drug status. There is also good evidence that mexiletine is well tolerated and safe in this patient group without the need for intensive monitoring. A range of alternative antimyotonic treatment options include lamotrigine, carbamazepine and ranolazine exist with variable evidence base. In vitro studies have shown insight into reasons for treatment failure of some medications with certain genotypes opening the era of mutation-specific therapy such as use of flecainide. In the periodic paralyses, the ability of MRI to distinguish between reversible oedema and irreversible fatty replacement makes it an increasingly useful tool to guide and assess pharmacological treatment. Unfortunately, the striking efficacy of bumetanide in hypokalaemic periodic paralysis animal models was not replicated in a recent pilot study in humans.

SUMMARY

The treatment of skeletal muscle channelopathies combines dietary and lifestyle advice together with pharmacological interventions. The rarity of these conditions remains a barrier for clinical studies but the example of the aggregated n-of-1 trial of mexiletine shows that innovative trial design can overcome these hurdles. Further research is required to test efficacy of drugs shown to have promising characteristics in preclinical experiments such as safinamide, riluzule and magnesium for myotonia or bumetanide for hypokalaemic periodic paralysis.

Electromechanical delay components during relaxation after voluntary contraction: reliability and effects of fatigue

INTRODUCTION

Fatigue effects on total relaxation delay (R-DelayTOT ) components and measurement reliability were investigated.

METHODS

Electromyogram (EMG), force (F), and mechanomyogram (MMG) were recorded during maximum voluntary contraction from the biceps brachii muscle before and after fatigue. The delays between EMG cessation and onset of F decay (R-EMD), between F decay and onset of MMG largest displacement (MMG p-p) (R-Δt F-MMG), from the beginning to the end of MMG p-p (R-Δt MMGp-p ), and from the end of MMG p-p to F cessation (R-Δt MMG-Fend ) were calculated.

RESULTS

R-DelayTOT lasted 366 ± 10 ms. R-EMD, R-Δt F-MMG, R-Δt MMGp-p , and R-Δt MMG-Fend accounted for 6%, 8%, 59%, and 27% of R-DelayTOT , respectively. After fatigue, R-DelayTOT , R-EMD, R-Δt F-MMG, and R-Δt MMGp-p increased by 38%, 22%, 40%, 40%, and 38%, respectively (P<0.05). Reliability was very high (0.853-0.960).

CONCLUSIONS

R-Δt MMGp-p was the main contributor to R-DelayTOT . Fatigue affected all R-DelayTOT contributors, with a smaller effect on R-EMD.

Fatigue effects on the electromechanical delay components during the relaxation phase after isometric contraction

AIM

By a combined electromyographic (EMG), mechanomyographic (MMG) and force (F) analysis, the electromechanical delay during muscle relaxation (R-DelayTOT ) was partitioned into electrochemical and mechanical components. The study aimed to evaluate the effects of fatigue on R-DelayTOT components and to assess their intersession and interday reliability Intraclass correlation coefficient (ICC).

METHODS

During tetanic stimulations, EMG, MMG and F were recorded from the human gastrocnemius medialis muscle before and after fatigue. The latency between EMG and MMG ripple cessations (R-Δt EMG-MMGR , electrochemical R-DelayTOT component); between MMG ripple cessation and F decay onset (R-Δt MMGR -F, first R-DelayTOT mechanical component); and between F decay onset and maximum MMG negative peak (R-Δt F-MMGp-p , second R-DelayTOT mechanical component) was calculated.

RESULTS

Before fatigue, R-Δt F-MMGp-p was the major contributor (61.9 ± 1.7 ms, 75%) to R-DelayTOT (82.7 ± 1.0 ms), while R-Δt EMG-MMGR and R-Δt MMGR -F accounted for 16% (13.3 ± 1.2 ms) and 9% (7.5 ± 1.0 ms) respectively. After fatigue, R-DelayTOT , R-Δt EMG-MMGR and R-Δt MMGR -F increased by 11, 41 and 67%, respectively (P < 0.05), whereas R-Δt F-MMGp-p did not change. Consequently, the relative contribution of R-Δt EMG-MMGR , R-Δt MMGR -F and R-Δt F-MMGp-p , to R-DelayTOT changed to 20 ± 2, 12 ± 1 and 68 ± 2% respectively. Measurement reliability was always from high to very high (ICC 0.705-0.959).

CONCLUSION

Fatigue altered the processes between neuromuscular activation cessation and force decay onset, but not the second mechanical component (cross-bridges detachment rate and series elastic components release). This combined approach provided reliable measurement of the different R-DelayTOT components and it may represent a valid tool to get more insights on muscle electromechanical behaviour.