Becker's disease is an autosomal recessive type of myotonia congenita, non-dystrophic myotonia, first described in the 1970s by Peter Emil Becker.1 The worldwide prevalence of myotonia congenita is about 1:100,000 while in some countries (eg. Norway) the incidence may be 10 times higher.2,3 It is linked to mutations in CLCN1 (the same as the autosomal dominant in Thomsen's disease), the gene encoding the skeletal muscle chloride channel. The mutation in Becker's disease, leads to reduced flow of chloride ions during repolarisation leading to sustained muscle contraction.4 The reduced chloride conductance of the mutated chloride channels in Becker's myotonia causes hyper-excitability of the muscle fibre membrane leading to bursts of aberrant action potentials. The clinical picture is characterised by slowed relaxation following forceful voluntary contractions (myotonic stiffness). Myotonia tends to improve with exercise, the so-called ‘warm-up’ phenomenon. It usually presents during the second decade of life with slow progression in later decades. Symptoms are more severe than in Thomsen's disease, and usually involve the lower limbs first. Muscle hypertrophy is a common symptom. Sometimes it is accompanied by gradually progressive weakness, and by peculiar transient episodes of proximal weakness, involving the hands and arm muscles, in particular, which is connected to specific types of mutations.5
Anaesthesiologists should be aware of the risk of using suxamethonium in patients with chloride channel myotonia in whom administration of suxamethonium can cause sustained total body rigidity and subsequent difficulty in airway management.6,7 Patients with myotonic dystrophy also have myotonic response to neostigmine and increased sensitivity to non-depolarising neuromuscular blocking agents.8–10 In such cases rocuronium for neuromuscular blockade with active reversal using sugammadex is preferable.
We report the case of a 27-year-old woman who was diagnosed with Becker type myotonia congenita at the age of 22. She gave written consent for the report to be published. The parturient had a homozygote recessive mutation in the skeletal muscle chloride channel gene CLCN1 (c.1437_1450del, p.480HfsX24) on both alleles because of consanguinity in the family (father and mother were cousins). Her neurological problem began in early childhood (at 4 years of age). She had problems with relaxation which had become rather pronounced with typical warm-up (repeated movements). She had apparent muscular hypertrophy. Her lower limbs were most affected but upper limbs and face were also involved. There were no paretic symptoms and all her difficulties were because of myotonia. Her vital capacity was normal. As is common in patients with this disease, she had adapted to her restrictions. Medication (carbamazepine, baclofen) was only of marginal effect and the patient decided not to take them. The parturient was a primipara, primigravida without any complications during pregnancy. At the time of delivery, her weight was 90 kg. In the medical history, there was transthoracic correction and stabilisation of the thoracic vertebra to the extent of the 5th to 11th vertebra because of scoliosis at the age of 18 and hypothyroidism with pharmacological hormonal substitution.
In 2015, she underwent a scheduled caesarean section at the gestational age of 39 weeks and 4 days for muscular weakness and as a result, an inability to control labour naturally. Owing to the risk of difficult access to the spinal space and parturient refusal of neuroaxial anaesthesia, we decided on general anaesthesia.
During the 3 min pre-oxygenation and 15° tilt table to the left, we prepared a TOF Watch SX device (Organon, Oss, Nederland) for neuromuscular blockade monitoring and an infusion pump Space (BBraun, Germany) with availability of target controlled infusion (TCI) mode. We began to administer propofol IV using TCI [Schnider model, Ce (effective concentration) = 5 μg ml−1] via the cubital vein. When the patient lost consciousness, we proceeded with the calibration of the TOF Watch SX monitor and administered an intubating dose of rocuronium in a dose 1 mg kg−1. Using the single twich mode we attempted orotracheal intubation while applying the Sellick manoeuvre when the single twich decreased to 10%. The intubation conditions were excellent (modified Viby-Mogensen score) with no resistance to laryngoscopy and partial abduction of the vocal cords. The Cormack–Lehane score was 2. There was no cardiovascular or movement response to intubation. After the initial dose of propofol, we terminated the infusion of propofol but resumed it during the birth. A newborn male infant was delivered 5 min and 8 s after the beginning of a TCI of propofol. At the same time, we set the Ce of propofol to 5 μg ml−1, administered sufentanil 15 mcg IV, 5 IU of oxytocine bolus IV, 10 IU of oxytocine in infusion and cephazoline 2 g IV. The newborn was assessed by an experienced neonatologist, given an Apgar score in the 1st, 5th and 10th minute (9–10–10), acid–base balance values from the umbilical artery gave no cause for concern (pH 7.28, pCO2 7.8, pO2 3.6, BE – 1.4). We stopped the propofol infusion after the completion of peritoneal suturing. Before the end of surgery, we administered piritramide 15 mg s.c., sufentanil 5 mcg IV and paracetamol 1 g IV. There were no surgical complications. Blood loss during the procedure was 500 ml. When the Ce of propofol decreased to 1 μg kg−1, deep neuromuscular blockade was indicated by TOF 0, PTC 0. For this reason, we administered sugammadex 4 mg kg−1 IV. After 2 min and 15 s, we measured the TOF ratio at 98%. The patient was conscious and ready to be extubated. After extubation, the parturient was breathing adequately, communicative, and the postoperative pain visual analogue scale (VAS) score was 3. The total volume of propofol administered during TCI was 53 ml (530 mg). It took 40 min from induction of anaesthesia to extubation. The patient was transferred to the recovery room, where she remained with no respiratory problems, no signs of residual neuromuscular blockade or worsening of pain. After 2 h, she was transferred back to the gynaecological ward to the monitored in the postoperative room. We performed the post-anaesthesiological check-up of the patient at 24 h and 3 days after the caesarean section for subjective complaints. The only complaint after the surgery was pain in the wound (VAS 2). On the fourth day after surgery, the patient was discharged.
To the best of our knowledge, this is the first report of the anaesthetic management of a parturient with Becker's myotonia congenita who had undergone a caesarean section under general anaesthesia. We decided to perform the anaesthesia with respect to Becker's myotonia congenita pathophysiology and to prevent possible complications of the anaesthetic management of this high-risk patient. There are some concerns about the risk of malignant hyperthermia in patients with myotonia congenita, and therefore, tendencies to administer only malignant hyperthermia non-triggering anaesthetic agents. However, Parness et al.5,11 drew attention to the fact that myotonic patients with malignant hyperthermia crisis can have mutations at two distinct genetic loci, one for myotonia and one for malignant hyperthermia susceptibility. For this reason, we decided on the anaesthesia using non-triggering anaesthetics (propofol, rocuronium and sufentanil), although the association with malignant hyperthermia is regarded as highly unlikely according to a recent review.12 For propofol administration, we used the target-controlled infusion (TCI, Schnider model) because of good control of the plasma/ effective concentration. As an anaesthetic agent in a patient with chloride channel myotonia, propofol appears to be the ideal drug, given its antimyotonic effect as a result of modulations of voltage-gated sodium channels within the sarcolemma membrane of the skeletal muscle. The propofol should be administered via the large forearm vein as this reduces the incidence of pain and thus also prevents a possible myotonic reaction.12 For neuromuscular blockade, we used rocuronium with the availability of the selective relaxant-binding agent, sugammadex at the end of the surgery at any level of neuromuscular blockade. This approach to caesarean section in a myotonic patient has been published by Stourac et al.13 in a case report of successful use of the combination of rocuronium and sugammadex in a parturient with myotonic dystrophy who had undergone a caesarean section a few years previously without sugammadex and who had prolonged neuromuscular blockade with the need for mechanical ventilation.
There are published studies confirming the safety of neostigmine in malignant hyperthermia-susceptible patients.14 On the other hand, anticholinesterase drugs may precipitate myotonia because of increased sensitivity to the stimulatory effects of acetylcholine.15 Given the physiology of Becker's myotonia congenita and eventuality of active reversal of a non-depolarising block using sugammadex, we opted for sugammadex over neostigmine. In addition, early reversal using neostigmine, even in a healthy population, can lead to a longer period of ‘blind paralysis’.16 With respect to the ‘Summary of Product’ for sugammadex (Bridion), we chose a dose 4 mg kg−1 in which the median time to recovery of the T4/T1 ratio to 90% is described as around 3 min. The ‘Summary of Product’ allows re-administration of sugammadex in the situation of recurrence of neuromuscular blockade postoperatively after an initial dose of 4 mg kg−1 sugammadex. A repeat dose of 4 mg kg−1 sugammadex is recommended with monitoring of depth of residual neuromuscular blockade.17 The risk of reintubation because of muscle weakness or myotonic reaction was obviated using sugammadex and monitoring in the recovery room for the first 2 h postoperatively.
In this report, our patient with myotonia congenita Becker showed normal recovery of the TOF ratio to more than 90% after the administration of sugammadex (4 mg kg−1) from deep blockade (TOF 0) in 2 min. She had normal sensitivity to rocuronium at induction (decrease to single twich 10% in 32 s) and showed normal response to sugammadex.18,19
In conclusion, this case shows the possibility of using rocuronium as part of a rapid sequence induction of general anaesthesia for caesarean section in a parturient with Becker's myotonia congenita with effective use of sugammadex as an active reversal agent providing well tolerated and rapid reversal of neuromuscular blockade.
Acknowledgements relating to this article
Assistance with the case report: many thanks to Ivo Krikava for help with anaesthesia management and to Lukas Hruban with obstetrical management.
Financial support and sponsorship: this case report was supported by the Czech Ministry of Health Internal Grant Agency (NT 13906-4/2012).
Conflicts of interest: none.
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