Differential diagnosis of weakness in ICU

Weakness in ICU is another common case during the clinical exam. I have found this in one of my books and I thought that it might be useful in helping me to organise my thought in synthesising the diagnosis during that time. Critically ill patient frequently have ICU myopathies and polyneuropathy. Weakness is common with SIRS and organ transplantation. Steroids, muscle relaxants and prolonged ventilation increase risk. MRI or CT scan, EMG and muscle biopsy may guide diagnosis.

1. Critical illness: - Clinical illness neuropathy, Myopathy of Intensive Care
2. Autoimmune: -Guillain-Barre syndrome, Myasthenia gravis, Dermatomyositis, Polymyositis
3. Nutritional: -Increased catabolism and wasting, undernutrition
4. Electrolyte disorders: -Phosphate, -Mg, K, Na
5. Endocrine disorders:-Hyper and hypo-thyroidism
6. Infection: -Botulism, poliomyelitis, tetanus, diphtheria, HIV, West Nile, Creutzfekdt-Jacob
7. Toxins: -Organophosphates, lead, tick paralysis, beliadonna
8. Drugs: -Muscle relaxants, steroids, magnesium, aminoglycosides, dapsone
9. CNS injury: -Stroke, spinal cord injury
10. Congenital: -Muscular dystrophy, periodic paralysis, motor neuron disease, spinal muscular atrophy, Tay-Sachs, Lower motor neurone syndromes, myotonia, acute intermittent porphyria
11. Metabolic: -alkalaemia
12. Paraneoplastic: Eaton Lambert syndrome, proximal myopathy

Causes of generallised muscle weakness, hyporeflexia and no sensory signs:

• Guillain Barre Syndrome
• Myasthenia Gravis
• Botulism
• Toxic Neuropathy : thallium, arsenic, hexane
• Acute intermittent porphyria
• Tick paralysis
• Lyme disease
• Poliomyelitis

Q: How would you differentiate a myopathy from a neuropathy clinically?

A: Distinguishing features:

1. Neuropathy

• site of weakness: distal
• sensory: may have concomintant sensory and signs
• reflexes: reflexes lost early
• fasciculations: may be present
• contractures: not a feature
• myocardial dysfunction: not a typical feature

2. Myopathy

• site of weakness: usually proximal
• sensory: usually pure motor
• reflexes: preserved until late
• fasciculations: not typical
• myocardial dysfunction: may have accompanying cardiac dysfunction witn the dystrophies

A young lady presents with a short history of progressive difficulty in walking, and now has shortness of breath. She was brought to DEM with RR 32 b/min, oxygen saturation of 90% on room air. Neurological examination reveals normal higher mental function, reduce power in all four limbs, left sided ptosis, absent DTRs, bilateral plantar responses and no sensory loss.

Q: How would you asses her clinically at this stage?

A: ability to protect, bulbar weakness, pooling of salive and ability to cough

B: evidence of shallow breathing, bilateral chest expansion, focal lung signs

C: evidence of autonomic dysfunction

D: neurological examination

Baseline bloods, ABG

get the past history, examination

In this case the most likely diagnosis is GBS

Q: What conditions may precede or trigger GBS?

A:

i. often preceded by URTI or diarrheal illness caused by various pathogens such as -CMV, EBV, HSV, mycoplasma, chlamydia, campylobacter jejuni.

ii. vaccines - rabies, swine flu

iii. pregnancy

iv. surgery

v. cancer (Hodgkin's disease)

Q: What are the indications for ICU admission?

A:

-rapid progression of symptoms

-aspiration

-bulbar dysfunction

-bilateral facial weakness

-neck weakness with inability to raise head against gravity

-significant dysautonomia

-evidence of respiratory failure

Q: what are the various monitoring parameters you would use to make a decision to intubate this lady?

• Inability to protect airway
• significant hypoxia or hypercarbia
• bedside assessment of respiratory muscle weakness, such as increased RR, decreased VT, paradoxic inward movement of abdomen during respiration, use of acessory muscles, ineffective cough
• 20-30-40 rule (Lawn et al.)

-VC <>