11.6 Myotonic Dystrophy

Question 1

A 35-year-old man presents for a laparoscopic cholecystectomy. He was diagnosed with myotonic
dystrophy 10 years ago.
a) What is myotonic dystrophy and
how is it inherited? (2 marks)

Answer 1

> > Disorder of chloride conductance
affecting skeletal,
smooth and cardiac
muscle resulting in myotonia
(delayed relaxation of muscle contraction).

> > Associated multisystem features.

> > Autosomal dominance.
May demonstrate anticipation,
i.e. worsening of disease with
successive generations.

Question 2

b) What are the problems of myotonic dystrophy relevant to anaesthesia? (10 marks)**

Answer 2

Airway:
» Delayed gastric emptying and
pharyngeal muscle wasting
increases risk of aspiration.

_________________________
Respiratory:
» Restrictive lung defect due
to progressive spinal deformity.

> > Central and obstructive sleep apnoea.

> > Risk of aspiration and pneumonia.

> > Exaggerated respiratory depressant
effect of opioids and
intravenous anaesthetic agents.

______________________
Cardiovascular:
» Conduction defects (risk of sudden death).

> > Cardiomyopathy.

> > Hypotensive and myocardial depressant
effects of anaesthetic agents may be exaggerated.

______________________________

Neurological:
» Can result in reduced intelligence,
may lead to problems with capacity
and consent.

> > Early cataracts affect vision.

> > Myotonia results from shivering
(avoid hypothermia) or suxamethonium

________________________

Endocrine:
» Increased risk of type 2 diabetes mellitus.

> > Increased risk of hypothyroidism.

Pharmacological:
» Suxamethonium causes myotonia,
which may make intubation difficult.

> > Non-depolarising neuromuscular blocking
agents may have prolonged action
in the presence of muscle wasting
and reversal may cause myotonia.

Ideally use short-acting agents,
e.g. atracurium,
cis-atracurium.

Gastrointestinal:
» Delayed gastric emptying, risk of reflux.

Cutaneomusculoskeletal:
» Muscle wasting. Care with padding.
Care to avoid precipitating myotonia.

Question 3

c) Outline the important aspects of preoperative assessment and intraoperative management that are
specific to myotonic dystrophy. (8 marks)

Answer 3

1. Airway

Assess the safety of airway:
history of poor swallow,
recurrent aspiration pneumonia.

Consider the need for a modified
rapid sequence induction

________________________

Respiratory

Assess for evidence of obstructive
sleep apnoea, restrictive lung
defect, active pneumonia.
Consideration of need for formal
lung function testing.

Positive pressure ventilation

___________________________

Cardiovascular
Assess with history and examination
for the possibility of heart failure
associated with cardiomyopathy,
arrhythmias.
Preoperative ECG required,
preoperative echocardiogram
if indicated.

ECG monitoring: monitor for
arrhythmia.
Blood pressure monitoring: maintain
vigilance for hypotension. Consider
intra-arterial blood pressure monitoring.

__________________________

Neurological Assess capacity for consent.

_____________________________

Endocrine
Diabetic management depends on
usual diabetic regimen and on the
duration of starvation.

VRIII if indicated, or just regular CBG
checks

______________________________

Pharmacology
Avoid sedative premedication to
which the patient may have an
exaggerated response.

Use short-acting neuromuscular
blocking agents;
do not use suxamethonium.

______________________________

Gastrointestinal
H2 receptor antagonist or proton
pump inhibitor premedication in
view of increased risk of reflux

______________________________

Metabolic
Check electrolytes and correct if
necessary to reduce intraoperative
risk of arrhythmia.

Ensure the patient is warmed to
normothermia with forced air
warmer and warmed fluids.