Neuromuscular disorders

Question 1

What is myotonic dystrophy?

Answer 1

• Most common & most serious myotonia affecting adults
• sustained muscle contraction, manifesting in the inability to relax muscle groups
• Autosomal dominant inheritance
• Multisystem disease with progressive involvement of skeletal, cardiac & smooth muscle

Question 2

What are clinical features of mytonic dystrophy?

Answer 2

• Resp dysfunction - restrictive lung defect, OSA
• Cardiac dysfunction - cardiomyopathy, dysrhythmias, mitral valve prolapse
  -GIT: Bulbar dysfunction, delayed gastric emptying
• Endocrine dysfunction - diabetes

Question 3

What are some clinical features on exam for myotonic dystrophy?

Answer 3

o Respiratory & cardiovascular signs
o Triad of frontal baldness, mental retardation & cataracts

Question 4

What are some Ix for myotonic dystrophy?

Answer 4

o Electromyographic findings are diagnostic – prolonged discharges of repetitive muscle action potentials
o ECG + echocardiography for cardiac reserve
o CXR for lung fields
o RFTs + ABG for respiratory reserve
o U&Es & glucose to exclude endocrine dysfunction

Question 5

What are some anaesthetic goals in myotonic dystrophy?

Answer 5

1. Avoid factors that may precipitate myotonia
   o Drugs – suxamethonium, neostigmine
   o Hypothermia, shivering
   o Mechanical or electrical stimulation – eg. surgical manipulation, electrocautery
2. Manage Aspiration risk 2° dysphagia & altered gastric motility
3. Avoid oversedation
   o Increased sensitivity to sedatives & analgesic agents

Question 6

What is muscular dystrophy?

Answer 6

Group of inherited muscle diseases characterised by painless degeneration & atrophy of skeletal muscles

includes Duchenne’s (no dystrophin), Becker’s (partially absent dystrophin) amongst others

Question 7

What are important clinical features of duchenne’s muscular dystrophy?

Answer 7

MSK: waddling gait, frequent falling & difficulty climbing stairs

Cardiac:
Degeneration of cardiac muscle:
o Conduction defects
o Characteristic ECG – tall R waves in V1, deep Q waves in limb leads, short PR interval & sinus tachycardia
o Dilated cardiomyopathy (50% have this by 15 years)
o Mitral regurgitation 2° papillary muscle dysfunction or decreased myocardial contractility

Resp:
o Severe respiratory muscle weakness & weak cough lead to loss of pulmonary reserve & accumulation of secretions
o Kyphoscoliosis contributes to further restrictive lung disease
o Sleep apnoea & development of pulmonary hypertension

GIT:
o Dysphagia, reflux

Question 8

What are some clinical features on exam for duchenne’s muscular dystrophy?

Answer 8

o Progressive, symmetrical muscle weakness & wasting
o Severe proximal muscle weakness
o Normal sensation, intact reflexes
o Kyphoscoliosis
o Cardiorespiratory examination – look for cardiomyopathy, mitral valve prolapse, pneumonia

Question 9

What are some Ix for duchenne’s muscular dystrophy?

Answer 9

o Serum creatinine kinase - Used to track disease progression – elevated early due to increased skeletal muscle membrane permeability & skeletal muscle necrosis, reduced to below normal as muscles atrophy
o ECG, CXR, ABG, RFTs
o Echocardiography

Question 10

What are some anaesthetic issues with duchenne’s muscular dystrophy?

Answer 10

o Aspiration risk 2° hypomotility of GIT & weak laryngeal reflexes
o Suxamethonium – contraindicated as it can an provoke rhabdomyolysis, hyperkalemia
o Non-depolarising muscle relaxants – avoid or use sparingly as a delay in onset/offset is usually seen, potentially leading to a prolonged block
o anaesthesia-related rhabdomyolysis with volatiles
o High risk post op resp complications

Question 11

What is motor neurone disease?

Answer 11

Progressive condition of unknown aetiology characterised by degeneration of motor neurons

Question 12

What are the clinical features on history of motor neurone disease?

Answer 12

o Diet & swallow function, solids/fluid diet
o Frequency of chest infections – indication of aspiration

Question 13

What are the clinical features on exam of motor neurone disease?

Answer 13

o General skeletal muscle atrophy
o Autonomic dysfunction
o Upper motor neuron signs - Spasticity – increased tone with associated clonus
o Lower motor neuron signs - Reduced tone

Question 14

What are the anaesthetic issues of motor neurone disease?

Answer 14

• Aspiration risk
• Hyperkalemic response to suxamethonium
• Use non-depolarising muscle relaxants in reduced doses with continuous monitoring due to increased sensitivity
• Respiratory complications common, with the risk of postoperative ventilation & subsequent weaning difficulties, infection & atelectasis
• Prepare for autonomic dysfunction

Question 15

What is Guillain-Barre Syndrome?

Answer 15

Autoimmune inflammatory polyneuropathy of motor, sensory, autonomic & cranial nerves

Question 16

What are clinical features of Guillain-Barre Syndrome?

Answer 16

o Progressive motor weakness, usually ascending from legs
o Resp muscle weakness
o Autonomic dysfunction

Question 17

What are clinical features on exam of Guillain-Barre Syndrome?

Answer 17

o Neurological exam - generalised muscle weakness, reduced/absent reflexes, normal sensory
o Respiratory function - PEF, FEV1, FVC (more Ix)

Question 18

What are some anaesthetic issues associated with Guillain-Barre Syndrome?

Answer 18

• Avoid suxamethonium – can precipitate hyperkalemic arrest
• Non-depolarising muscle relaxants – sensitivity may vary from extreme sensitivity to resistance depending on
  disease phase
• Autonomic dysfunction
• Avoid peripheral nerve blockade → multi-hit hypothesis of nerve injury
• Anticipate postoperative mechanical ventilation

Question 19

What are the clinical indications for intubation & ventilation in Guillain-Barre Syndrome?

Answer 19

Vital capacity < 15ml/kg or peak expiratory flow < 250L/min

Question 20

What is Multiple Sclerosis?

Answer 20

Most frequently occurring demyelinating neuromuscular disorder

Question 21

What are important questions on history for multiple slcerosis?

Answer 21

o Relapses, remissions
o Triggers – infection, temperature, stress, trauma
o Typical complaints & symptoms during exacerbation
o Ability to cough & clear secretions
o Medication list - can be on steroids as well as chemo agents eg cyclophosphamide

Question 22

What are important features on exam for multiple slcerosis?

Answer 22

Complete neurological exam
-Look for limb ataxia
-Check motor strength + sensation in all limbs
- Check extraocular movements

Signs of autonomic neuropathy

Question 23

What are some anaesthetic implications of MS?

Answer 23

o Postoperative exacerbation possible regardless of anaesthetic technique or drugs used
o LAs may exacerbate symptoms due to increased sensitivity of demyelinated axons to LA toxicity
o Exercise caution when using suxamethonium if patient is debilitated – hyperkalemia
o Potential for prolonged response to non-depolarising muscle relaxant
o Temperature maintenance is important – symptoms can deteriorate with increases in temperature

Question 24

What is myasthenia gravis?

Answer 24

Chronic autoimmune disorder caused by a decrease in functional postsynaptic acetylcholine receptors at NMJ resulting from their destruction/inactivation by circulating antibodies

Question 25

What are the clinical features of myasthenia gravis?

Answer 25

skeletal muscle weakness that improves with rest

most commonly affects ocular muscles, but can affect any skeletal muscle (including respiratory muscles)
-Ptosis & diplopia
-Weakness of pharyngeal & laryngeal muscles results in dysphagia, dysarthria & difficulty handling saliva
- Arm, leg or trunk weakness can occur
- Myocarditis

Question 26

What is the leventhal criteria?

Answer 26

• Duration of myasthenia >6 yrs
• COPD
• Pyridostigmine >750mg in 24 hrs
• FVC <2.9 L

Question 27

What are the anaesthetic issues with myasthenia gravis?

Answer 27

o Aspiration risk
o Avoid exacerbation of muscle weakness i.e continue normal therapy and avoid drugs that worsen it
o Preserve respiratory function
o Abnormal neuromuscular response to both depolarizing (resistant) & non-depolarising (sensitive) muscle relaxants

Question 28

What is a myasthenic crisis?

Answer 28

Severe resp failure due to muscle insufficiency, usually precipitated by infection

Question 29

What is a cholinergic crisis?

Answer 29

Due to IV anticholinesterases increasing the amount of Ach. Presents with excess cholinergic activity i.e bradycardia, hypotension, bronchospasm, secretions, sweating, vomiting and diarrhoea

Question 30

What is parkinson’s disease?

Answer 30

Idiopathic & progressive neurodegenerative disorder characterised clinically by rigidity, resting tremor, postural
instability & bradykinesia (slowness of movement)

Question 31

What are some features on history of parkinson’s disease?

Answer 31

o Timing of onset of symptoms (usually > 65 yrs)
o Progression since diagnosis
o Functional limitation at present
o Complications:
- Dysphagia, aspiration
- GORD, reduced GIT motility
- Postural hypotension
- Depression, dementia

Question 32

What are some features on exam of parkinson’s disease?

Answer 32

Gait & abnormal movements:
Shuffling gait
Bradykinesia

Resting tremor
Abnormal tone at wrists - cogwheel rigidity

Question 33

What are some anaesthetic issues with parkinson’s disease?

Answer 33

o Continue medical therapy up to start of anaesthesia
o autonomic neuropathy
o aspiration risk - dysphagia plus delayed gastric empyting
o Avoid dopamine antagonists eg droperidol