Overview of Neuromuscular Disease

Describes a heterogenous group of skeletal muscle defects
Are classified by:
- Cause:
  - Congenital
  - Acquired
- Anatomical site
  - Pre-junctional
  - Junctional
  - Post-junctional

Types of Neuromuscular Disease

Cause	Congenital	Acquired
Pre-junctional	Peripheral Neuropathies: Charcot-Marie-Tooth Fredrichs ataxia	Motor Neuron Disease ALS, Lou Gehrig’s Disease) \| MS GBS Diabetic neuropathy
Junctional		MG Eaton-Lambert Syndrome
Post-junctional	Dystrophicas: Duchenne Becker’s Myotonias: Myotonic Dystrophy Myotonia congenita Hyper-, hypokalaemic periodic paralysis Metabolic disorders	Inflammatory myopathies CIM/CIN

Pre-junctional

Peripheral Neuropathies:

Charcot-Marie-Tooth
Fredrichs ataxia

Motor Neuron Disease ALS, Lou Gehrig’s Disease) |
MS
GBS
Diabetic neuropathy

Junctional

MG
Eaton-Lambert Syndrome

Post-junctional

Dystrophicas:

Duchenne
Becker’s

Myotonias:

Myotonic Dystrophy
Myotonia congenita
Hyper-, hypokalaemic periodic paralysis
Metabolic disorders

Inflammatory myopathies
CIM/CIN

Anaesthetic Considerations

A
- Aspiration risk
  Due to gastric dysmotility.
- Strict extubation criteria
  May require perioperative ICU admission.
B
- Respiratory function
  High incidence of peri-operative respiratory complications due to:
  - Respiratory and pharyngeal muscle impediment
  - Progressive spinal deformities
  - Potential difficult airway
  - Strongly consider perioperative BiPAP
  - Continuous SpO₂ monitoring until consciousness resumed
- CXR
- PFTs
C
- Cardiac function
  - Cardiac reserve may be difficult to quantify as exercise tolerance limited by the disorder
- ECG
- TTE
D
- Avoidance of volatile
  - Primarily due to ↑ risk of rhabdomyolysis, rather than ↑ MH risk (though this may still be present)
  - TIVA with a clean anaesthetic machine is recommended
- Regional anaesthesia
  - Advantageous if significant cardiac or respiratory disease; and so is recommended whenever appropriate
  - Autonomic dysfunction may be exacerbated with regional techniques
  - Consider avoiding if rapidly progressing neurological deficit
- Minimise opioid use
  Multimodal analgesia, including regional techniques preferred.
E
- Avoidance of neuromuscular blockers
  - Depolarising agents contraindicated (except in myasthenia gravis) due to:
    - Massive potassium efflux
      Upregulation of extra-junctional receptors, and presence of foetal γ isoforms of the ACh receptor.
    - Fasiculations may cause trismus and prevent intubation and ventilation.
    - Rhabdomyolysis
  - Non-depolarising agents:
    - Usually show excessive sensitivity
      Use at 10-20% of recommended dose.
    - Monitor block
    - Use agents with a rapid degradation
      e.g. Atracurium.
    - Avoid reversal
      Acetylcholinesterases may lead to hyperkalaemia.
- Thermoregulation
  Usually impaired. Vulnerability to both hypo- and hyperthermia.
  - Ensure normothermia pre-induction and actively warm
  - Hypothermia may:
    - Exacerbate myotonia
    - ↑ sensitivity to non-depolarising agents
    - Aggravate rhabdomyolysis

Complications

Include:

Death
Usually due to respiratory failure.
Respiratory failure
- Exhaustion
- Atelectasis
- Aspiration
  Bulbar weakness.
- OSA
- Spinal deformities
  Restrictive lung disease.
Cardiac
- Cardiomyopathies
- Arrhythmia
Myotonic contractures

Myotonic Contractures

Muscle spasm due to excessive Na⁺ influx or Cl^- efflux across a membrane. Contractures are usually:

Due to drugs or environmental conditions
- Suxamethonium
- Anti-cholinesterases
- Opioids
- Temperature
- Acidosis
- Shivering
Not responsive to:
- Neuromuscular blockade
- Regional/neuraxial anaesthesia
Treated with:
- Correction of cause
- Sodium channel blocking agents
  - Lignocaine
  - Antiarrhythmics

References

Marsh S, Ross N, Pittard A. Neuromuscular disorders and anaesthesia. Part 1: generic anaesthetic management. Contin Educ Anaesth Crit Care Pain. 2011;11(4):115-118.
Bersten, A. D., & Handy, J. M. (2018). Oh’s Intensive Care Manual. Elsevier Gezondheidszorg.