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Emergency caesarean section in a patient with myotonic dystrophy: a case of failed postoperative extubation in a patient with mild disease.

Myotonic dystrophy or dystrophia myotonica (DM) is an autosomal dominant genetic disorder most notably characterised by a prolonged relaxation, wasting and weakness in certain skeletal muscle groups. The pathology of DM however, extends to other organ systems and as such, can be associated with significant perioperative complications in up to 52% of cases1. Complications are predominantly perioperative pulmonary complications (PPC) following general anaesthesia but can also include generalised muscle weakness and cardiovascular complications (1,2). This report describes a case of a DM patient with mild disease who experienced PPC and explores the current literature on the subject in the context of anaesthesia.


A 21-year-old primipara with DM at 35 weeks gestation was referred by a regional hospital to a tertiary antenatal clinic as a 'high-risk' pregnancy.

Though the patient had been diagnosed with DM at the age of 13 years, the referral stated that she had "no symptoms" from her disorder. The patient appeared to have a low intelligence quotient and appeared apathetic with minimal insight into her disease or its implications on her pregnancy.

The main finding on formal assessment was myotonia in both hands and feet, which was precipitated by cooling. Significant to anaesthesia, there were no signs of respiratory muscle involvement, and she had no history of perioperative complications with the two general anaesthetics since her diagnosis of DM (diathermy of warts and removal of an ovarian cyst at 18 years of age).

Echocardiography reported normal myocardial function, and the electrocardiogram showed no conduction abnormalities. Q waves in leads II, III and aVF met the voltage criteria for left ventricular hypertrophy, however, the consulting cardiologist believed these to be "a normal variant associated with axes".

The anaesthetic department was also alerted to the patient and an assessment was conducted with the following recommendations on the anaesthetic chart:

* "Suxamethonium contraindicated, non-depolarising muscle relaxants with care".

* "Keep warm".

* "OK for spinal or epidural if she wishes".

Genetic counselling was also provided and the patient was informed of the one in two chance of her offspring inheriting the disorder.

At 38 weeks gestation the patient presented in the early hours of the morning, following ruptured membranes at home, in spontaneous labour. A 'pathological' cardiotocography trace and foetal scalp lactate of 5.9 were promptly detected, and an emergency caesarean section was booked. A decision for general anaesthesia was made to meet the urgency of the delivery, and the patient arrived at the operating theatre at approximately 0300 hours.

A modified rapid sequence induction was then conducted following a 30 ml dose of oral sodium citrate 8.8%. Agents used included sodium thiopentone 3 mg/kg, a single dose of rocuronium 0.5 mg/kg with cricoid pressure and anaesthesia was maintained with at least 1 minimum alveolar concentration of desflurane. Intubation and ventilation were uneventful, with no evidence of aspiration or abnormal muscle tone. Normothermia was maintained with intravenous fluid warming and a convection blanket.

Following the delivery of a healthy live female infant, intravenous boluses of cephazolin 2 g and syntocinon 5 IU were given, and an infusion of syntocinon 10 IU/hour was commenced. The patient was allowed to resume spontaneous ventilation and achieved normal tidal volumes with the assistance of pressure support ventilation. With these parameters within normal range, her neuromuscular blockade was not pharmacologically reversed to avoid an anticholinesterase-induced myotonia.

At one hour after her induction, the patient emerged enough to squeeze her hands and elevate her head off the pillow on command. Having satisfied these clinical indicators she was extubated in the operating theatre. However she was unable to maintain her ventilation unassisted, and within one minute of extubation, she rapidly desaturated. Manual continuous positive airway pressure with 100% oxygen was applied, and her saturation recovered to only 90%.

Auscultation of the chest demonstrated reduced breath sounds with bilateral crackles in the upper zones, and a diagnosis of atelectasis and retained secretions was made.

The patient was re-intubated after an inhalational induction of 6% sevoflurane without any further muscle relaxation, and she was ventilated for a further hour with pressure support ventilation. At two hours and fifteen minutes after her initial induction, she emerged again, and was able to elevate her head off the pillow. When she regained enough strength to sustain a head lift of greater than five seconds, she was extubated a second time and received 15 l of oxygen/minute via a non-rebreathing mask. On this Fi[O.sub.2] she maintained a saturation of 95%.

Postoperatively, she was transferred to the intensive care unit as an unplanned admission for monitoring. Over the following two hours, she was weaned down to a Fi[O.sub.2] of 50% and she maintained an oxygen saturation of over 95%. A mobile anteroposterior chest X-ray revealed no abnormalities, and she was finally discharged to the maternity unit with morphine patient-controlled analgesia at six hours postoperatively. The rest of her admission was uneventful.


Myotonic dystrophy is a genetic defect on chromosome number 19. It is caused by the amplification of the cytosine-thymine-guanine trinucleotide repeat, which codes for a member of the myotonin protein kinase family. The function of this enzyme is unclear (3). It shows an autosomal dominant inheritance with amplification with subsequent generations. It is the commonest of the muscular dystrophies with an incidence of 1 in 8000 (4).

There are two main clinical grading scales used in DM. The five level scale (muscular impairment rating scale) (Table 1) as developed by Mathieu et al (5) assesses muscular disability and the 4 level scale as used by Gillam6 is based on functional status (Table 2).

Our patient was Grade 2 on the muscular impairment rating scale and Grade 1 on Gillam's functional grading (i.e. a patient with mild disability due to DM).

DM can be difficult to diagnose. Several case reports describe patients who in retrospect had shown symptoms of DM for many years and had been only diagnosed following a PPC (1,7-9). One case report describes the diagnosis of a patient with DM, three weeks into his postoperative ICU admission for PPC (9). In other reports some patients have only been diagnosed with DM following the birth of children with congenital myotonic dystrophy (7,8).

A high clinical suspicion for DM should be maintained in patients with the following history, signs and symptoms shown in Table 3.

A multi-organ disorder

Outside of this pathology in skeletal muscles, this defective enzyme in DM impacts upon other body systems, making the entire clinical picture far more complex than simply myotonia.


DM is conspicuously a disorder of the skeletal muscles. However, smooth muscle defects also occur and patients with DM have been shown to have a higher incidence of abnormal intestinal motility (9). Vascular smooth muscle effects can lead to decreased global and regional coronary perfusion even when left ventricular size and function are normal (3).

The earliest and most common signs arise from ptosis and facial muscle weakness, characterised by an expressionless face (10). This is then followed by the wasting and weakness of the sternocleidomastoids, distal limb muscles and the muscles of respiration. Pharyngeal muscle weakness places the patient with DM at increase risk of perioperative aspiration (4).

In the respiratory musculature, progressive deterioration in respiratory function is common with reductions in functional residual capacity, the maximal peak inspiratory pressure (9,11) and the development of restrictive lung disease pattern on spirometry (7). Diaphragmatic weakness and associated intercostal myotonia can lead to failure in ventilation. The typical clinical scenario is chronic alveolar hypoventilation leading to carbon dioxide retention (12).

Moreover, patients with DM have altered response to both hypoxia and hypercapnia. The reduced hypoxic response is especially marked, while the response to hypercapnia is more variable and can occur even with patients with Grade 1 disease (13).


The primary cardiac abnormalities on electrocardiogram are conduction defects, particularly atrioventricular block. Sudden deaths have been reported as these defects can progress to either ventricular arrhythmias or complete heart block (5). Cardiomyopathy has been identified at autopsy in more than 50% of DM patients (1).


Hypo-fertility is common amongst DM patients as a result of hypogonadism, and when pregnancy does occur it often leads to an exacerbation of DM (7). Other complications are also increased in parturients with DM, including spontaneous abortions, polyhydramnios, prematurity, prolonged labour and uterine hypotonia following a caesarean delivery (7). Neonates of affected mothers who are born with congenital myotonic dystrophy have generalised hypotonia, often resulting in respiratory failure and sometimes death (8).


Peripheral insulin resistance causes glucose intolerance and can develop into diabetes mellitus (14). DM patients have an increased incidence of hypothyroidism (14). There is an association with low intelligence quotient and apathy (1).

Pharmacodynamics of DM during anaesthesia

Intravenous induction drugs

There have been several reports (1,9,15) of increased respiratory depression with thiopentone. Later studies (1,16,17) failed to confirm these results. In a series of 219 (the largest case series reported), Mathieu found that early ventilatory failure occurred in only 1.3% of patients given thiopentone, which was no higher than the control group (2). Prolonged respiratory depression did occur in some patient with mild disease and may be associated with an abnormal central respiratory control and an idiosyncratic peripheral muscle effect1.

Propofol has been associated with both local and systemic myotonia (5,18). There have been case reports of prolonged respiratory depression (15,19), though these have also been countered by numerous reports of uneventful anaesthetics when propofol has been either the agent of induction and/or maintenance (total intravenous anaesthesia) (10,15,20).

The above reports indicate that the use of both these induction agents is not without problems11. The most important factor in using these drugs is anticipation of possible adverse reactions9 particularly prolonged respiratory depression requiring ventilation.

Inhalational induction drugs

These may produce shivering which can precipitate myotonia in the early postoperative period. Although most frequently associated with halothane, shivering may occur after enflurane or isoflurane (16). Higher concentrations of volatile anaesthetic agent may abolish myotonic contractions (14) but increase the incidence of postoperative shivering. Volatile anaesthetic agents may present a risk to already compromised cardiovascular and respiratory systems (20).

Of the modern inhalational agents, halothane (1,2), isoflurane (21) and sevoflurane (22-24) have all been used in many cases without complications. Published reports on the use of desflurane in DM patients are still limited (10).

Muscle relaxants


In the modern pharmacopoeia of muscle relaxants, depolarising agents have largely been advised against for patients with a muscle disorder. In the case of DM however, the rationale for such caution is far from conclusive. While there have been reports of myotonia with suxamethonium, other authors have not been able to induce myotonia with suxamethonium. Mathieu found no instance of myotonia in 113 cases (2). In Imison's series, none of the three patients who received suxamethonium had myotonia (4). Myotonia in the masseter and the chest wall muscles can be induced by suxamethonium, leading to difficulty with intubation and ventilation (1). While the incidence of myotonia with suxamethonium is low, the availability of safer alternatives strengthens the recommendation to avoid suxamethonium (1,6,14).

Non-depolarising muscle relaxants

Since the pathology of DM exists in the cellular structure of the muscle and not at the neuromuscular junction, non-depolarising muscle relaxants are unable to prevent myotonic contractions. Most authors recommend the use of short acting non-depolarising relaxants, e.g. vecuronium and atracurium, with the use of peripheral nerve stimulators (10). There has been a report of the prolonged action of vecuronium despite a reduced [ED.sub.50] (3).

In the only case report where rocuronium was used on a DM patient, the patient developed C[O.sub.2] narcosis several hours postoperatively and required a period of non-invasive ventilation (25). The authors concluded that due to the risk of postoperative respiratory failure in patients with DM, non-invasive ventilation could be considered. Rocuronium was used in one case in Imison's4 series without any reversal or postoperative complications, however no other details were published.


Opioids have been implicated in prolonged respiratory depression in DM patients (1). Almost all authors recommend minimising the patient's exposure to opioids.

Acetylcholine esterase inhibitors

There has been a single report of neostigmine inducing myotonia in a patient with DM (1). Several authors have failed to confirm this and neostigmine has been used numerous times without inducing myotonia (10,25). There have also been several cases of inadequate reversal following the use of neostigmine, even with multiple doses of up to 7.5 mg. It has been postulated that neostigmine may be acting on normal unblocked muscle producing acetylcholine-induced depolarisation blockade (1). In the face of the low incidence of neostigmine-induced myotonia, the benefits of routine use of neostigmine to reverse the effects of non-depolarising agents would appear to outweigh the risk of complications from residual blockade.


While there have been case reports of successful use of sugammadex in Duchenne muscular dystrophy (26) and myasthenia gravis (27), the role of sugammadex in patients with neuromuscular disease has yet to be fully established. The pharmacology of sugammadex would suggest that it may prove ideal for the reversal of neuromuscular blockade in patients with DM. Further research in this area is needed.

Other perioperative triggers

Myotonia may be precipitated by hypothermia, shivering and mechanical or electrical stimulation, e.g. electrocautery. The use of peripheral nerve stimulators has the potential to produce myotonia11, however they have been used without causing myotonia (10,20) and are recommended by several authors.

Careful attendance to maintaining body temperature is crucial. The use of fluid warming, convection heating, minimising exposure and control of room temperature are all essential techniques to minimise the risks of PPC.


Based on the grading systems above there is an increase in the rate of PPC in patients with severe DM (1,2). Other factors which Mathieu (2) identified were upper abdominal surgery and an age greater than 37 years. Patients with proximal muscle weakness (Grade 4 and 5) are at up to 14 times increased risk of PPC compared with patients with less severe muscular disability (2).

Equally important, as in this case report, PPCs have clearly been documented in grade I to II patients (2,9,25) with no apparent debilitation from DM. These cases highlight the difficulty of predicting which patients are at risk of PPC, and the need for awareness of possible undiagnosed DM for patients with clinical indicators of DM as listed in Table 3 (8,9).

No general anaesthetic technique has been shown to be superior in patients with DM. In this particular case report, it remains unclear whether the main factor contributing to PPC can be or indeed should be attributed to any particular mechanism, be it residual neuromuscular blockade or an altered respiratory drive. Nevertheless, the literature suggests that a simple prudent measure such as limiting the use of opioids and the vigilant use of PNS and neostigmine can minimise the risk of PPC from respiratory depression. Concurrently, the avoidance of suxamethonium and maintaining normothermia will minimise the potential of precipitating a myotonic response during the perioperative period.

An understanding of the relative risks of PPC in the various grades of DM leads this author to agree with the recommendation that high level postoperative monitoring (9,11,25,28,29) and postoperative ventilation should always be available when planning for surgery in any patient with DM.


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(2.) Mathieu J, Allard P, Gobeil G, Girard M, De Braekeleer M, Begin P. Anesthetic and surgical complications in 219 cases of myotonic dystrophy. Neurology 1997; 49:1646-1650.

(3.) Boyle R. Antenatal and preoperative genetic and clinical assessment in myotonic dystrophy. Anaesth Intensive Care 1999; 27:301-306.

(4.) Imison AR. Anaesthesia and myotonia - an Australian experience. Anaesth Intensive Care 2001; 29:34-37.

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(6.) Gillam PM, Heaf PJ, Kaufman L, Lucas GB. Respiration in dystrophia myotonica. Thorax 1964; 19:112-120.

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(8.) Chung HT, Tam AY, Wong V, Li DF, Ma J, Huang CY et al. Dystrophia myotonica and pregnancy - an instructive case. Postgrad Med J 1987; 63:555-557.

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(25.) Ioscovich A, Barth D, Briskin A. Biphasic intermittent positive airway pressure (BIPAP) ventilation support in the postoperative period for patients with myotonic dystrophy. The Internet Journal of Anesthesiology 2006; 10. From http://www. volume_10_number_2_2/article/biphasic_intermittent_positive _airway_pressure_bipap_ventilation_support_in_the_post- operative_period_for_patients_with_myotonic_dystrophy.html Accessed September 2008.

(26.) Coakley JH, Calverley PMA. Anaesthesia and myotonic dystrophy. Lancet 1989; 2:1053-1054.

(27.) Branthwaite MA. Myotonic dystrophy and respiratory function. Anaesthesia 1990; 45:250-251.

P. M. OWEN *, C. CHU ([dagger]) Department of Anaesthesia, Gosford Hospital, Gosford, New South Wales, Australia

* F.A.N.Z.C.A., M.B., B.S., M.B.A., B.E. (Elec.) Hons., Staff Anaesthetist.

([dagger]) F.A.N.Z.C.A., M.B., B.S., Consultant Anaesthetist.

Address for correspondence: Dr P. Owen, Department of Anaesthesia, Gosford Hospital, Gosford, NSW 2250.

Accepted for publication on November 11, 2010.
Muscular Impairment Rating Scale (5)

Grade Description

1 No muscular impairment

2 Minimal signs
 Myotonia, jaw and temporal wasting, facial weakness,
 neck flexor weakness, ptosis, nasal speech, no distal
 weakness except isolated digit flexor weakness

3 Distal weakness
 No proximal weakness except isolated elbow extensor

4 Mild to moderate proximal weakness

5 Severe (MRC scale [less than or equal to] 3/5) proximal

MRC=modified Medical Research Council scale.

Myotonic dystrophy grading of disease based on functional status (6)

Grade Description

1 Mild

2 Moderately severe, but patient still able to undertake
 light work or domestic duties

3 Patient severely incapacitated, unable to walk far and
 considered semi-invalid

4 Patient bedridden

Clinical indicators which correlate with a suspicion of muscular

History Signs

History of myotonia including Ptosis
 family history Decreased facial expression
History of cataracts Distal muscle wasting (predominantly
Obstetric complications of small muscles of hands and feet)
 Spontaneous abortions
 Neonatal hypotonia,
 respiratory failure

History Symptoms

History of myotonia including Muscle weakness--especially facial,
 family history neck and extremities
History of cataracts Dysphagia
Obstetric complications Reduced exercise tolerance
 Spontaneous abortions
 Neonatal hypotonia,
 respiratory failure
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Author:Owen, P.M.; Chu, C.
Publication:Anaesthesia and Intensive Care
Article Type:Report
Geographic Code:8AUST
Date:Mar 1, 2011
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