Neuromuscular Disorder

Question 1

In which situation that NMD needs to be considered?

Answer 1

When SOB & T2RF cannot be explained by body habitus, radiographic appearance & obstructive spiro

Question 2

What are the causes of NMD?

Answer 2

Rapid onset:
Envenomation
Guillain-Barre Syndrome (GBS)
Myasthenia Gravis crises
Poisoning
ICU-acquired weakness
Hypokalemia
Organophosphates

Slow onset:
Muscular dystrophy
Amyotrophic Lateral Sclerosis (ALS)
Lambert-Eaton syndrome
Pompe’s disease
Duchenne Muscular Dystrophy
Myasthenia Gravis
Spinal Muscular Dystrophy

Question 3

What’s the Ix?

Answer 3

1) CXR – hemidiaphragm elevation
2) Spirometry – restrictive pattern, reduced VC on supine [normal supine VC excludes muscle weakness]
3) Body box – reduced TLC
4) DLCO – reduced DLCO, supranormal KCO
5) CPET – reduced VO2 max with ventilatory limitation & hypercapnia
6) MIP <50cmH2O, MEP <80cmH2O
7) Transdiaphragmatic pressure
8) Diaphragm EMG
9) Bloods e.g. CK, for MG: anti-MUSK & anti-acetylcholine receptor
10) PSG – desat & raised CO2 in REM

Question 4

What’s the Rx?

Answer 4

1) Avoid being overweight

2) Sleep positioning – semi-recumbent (to improve diaphragm mechanical efficiency)

3) BPAP – indications: - FVC <80% predicted with Sx
- FVC <50% predicted without Sx
- MIP <60cmH2O or MEP<40
- SNIP <70 (male), <60 (female)
- Hypercapnia PaCO2 >45
- SpO2 ≤90% for ≥2h of sleep time
- PSG: AHI ≥ 5, SpO2 ≤ 88% for ≥5mins

4) Airway clearance –
- sialorrhea Mx: anticholinergic
- poor cough effort: manual assisted cough, mechanical insufflation-exsufflation cough assist device, high frequency chest wall oscillation

5) Diaphragm plication

6) Consider IMV via tracheostomy in pts on NIV who have:
- Worsening bulbar function
- Frequent aspiration
- Insufficient cough
- Chest infection
- Declining lung function

7) If not willing for tracheostomy –> palliative care

Question 5

What are the signs and symptoms of resp failure in NMD?
Sx(6) , signs(9) & lab data(5)

Answer 5

Sx:
1) Increasing weakness
2) Dysphagia
3) Dysphonia
4) SOBOE & at rest
5) Fatigue
6) Sleepiness

Sg:
1) Rapid shallow breathing
2) Tachycardia
3) Weak cough
4) Staccato speech
5) Accessory muscle use
6) Abdo paradox
7) Orthopnea
8) Weak trapezium & neck muscles
9) Cough after swallowing

Lab:
1) VC: ≤15ml/kg, or ≤1L, or 50% drop from stable state, or >20% drop from sitting to supine position
2) MIP ≤30cmH2O
3) MEP ≤40cmH2O
4) Nocturnal desat
5) PaCO2 >45

Question 6

Indications for NIV in NMD (7)

Answer 6

1) FVC <80% predicted with Sx
2) FVC <50% predicted without Sx
3) MIP <60cmH2O or MEP<40
4) SNIP <70 (male), <60 (female)
5) Hypercapnia PaCO2 >45
6) SpO2 ≤90% for ≥2h of sleep time
7) PSG: AHI ≥ 5, SpO2 ≤ 88% for ≥5mins