56. Myotonic Dystrophy Flashcards
A 35-year-old male patient with mild myotonic dystrophy presents for
wisdom teeth extraction.
What is the underlying metabolic problem with this disorder?
It is an intrinsic muscle disorder.
There is delayed muscle relaxation due to abnormal closure of
sodium/chloride channels following depolarisation.
This causes repetitive discharge and contraction
What are the clinical features associated with myotonic dystrophy?
General
Frontal balding
‘Lateral’ smile
Muscle wasting – especially sternocleidomastoids, shoulders and quadriceps
Gonadal atrophy → infertility
Ptosis
Cataracts
Low serum IgG
Neurological
Bulbar problems
Slurred speech
Dysphagia
Can lead to aspiration, a frequent cause of death
Decreased tone and reflexes with muscle wasting
Foot drop
Decreased IQ in 40%
Cardiac
Conduction defects (primary heart block, bundle-branch block and widened QRS) –
may need pacing
Increased QTc and increased PR interval
Cardiomyopathy → cardiac failure
Mitral valve prolapse
Respiratory
Respiratory muscle fatigue → poor cough → LRTI
Restrictive lung defect
Centrally mediated decreased ventilatory response to CO2
Obstructive sleep apnoea
Chronic hypoxaemia → Cor pulmonale
Gastrointestinal
Endocrine
Constipation
Delayed gastric emptying
Diabetes
Hypothyroidism
What are the problems when anaesthetizing these patients?
- Undue sensitivity to anaesthetic drugs (opioids, barbiturates and volatiles)
- Precipitation of myotonia
- Cardiovascular and respiratory problems
- Control of blood sugar
- Drug interactions
- Presentation may be late on
NB. No proven link with malignant hyperthermia.)
Precipitation of myotonia
Anaesthetic and surgical interventions
Diathermy
Cold (monitor temperature)
Pregnancy (atonic uterus and PPH also reported)
Shivering (avoid high volatile concs.)
Suxamethonium
Non-depolarising muscle relaxants
Anticholinesterase drugs
K+ containing solutions
Exercise
What anaesthetic techniques can be used?
Pre-operatively these patients should have:
An ECG (24-hour if appropriate)
Full blood count, urea, electrolytes (NB. K+) and a blood sugar
Pulmonary function tests
Arterial blood gases
Chest X-ray
Intraoperative
Invasive monitoring
would be appropriate (arterial line/CVP/PAFC) if there
is a history of arrhythmias or cardiomyopathy.
Temperature
must be monitored and maintained. Warming mattresses and
warmed i.v. fluids should be used.
Induction and maintenance.
Propofol has been shown to be safe. Extreme
caution with dosing.
Intubation is necessary to protect against aspiration.
High concentrations of volatiles should be avoided
as they can cause
shivering and hence myotonia.
Regional techniques
Muscle relaxant
Post op
Regional techniques will avoid the use of general anaesthetic drugs that
can precipitate myotonia. Nerve blockade will not, however, prevent the
myotonic reflex. Local anaesthetic infiltration into the muscle can prevent
this reflex.
If a muscle relaxant must be used, then the agent of choice would be
atracurium. Neuromuscular block monitoring is essential.
Post-operatively, HDU or ICU care should be considered. Early feeding
should be avoided due to the possibility of aspiration.
