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In the ICU, a patient who suddenly cannot move is a clinical emergency. While stroke and intracranial hemorrhage are often the first thoughts, many other neurological causes must be considered—especially in critically ill patients.
This blog walks you step by step through how to localise weakness, differentiate causes, and apply this knowledge to high-yield ICU MCQs.
Step 1: Localising the Cause of Weakness in the ICU
Generalised weakness in ICU patients can be classified based on the level of neurological involvement.
1. Brainstem Pathology – Locked-In Syndrome
When the brainstem is involved, patients may present with:
- Sudden onset quadriplegia
- Preserved vertical eye movements
- Ability to open eyelids
- Complete inability to move limbs
This classic presentation is called Locked-In Syndrome.
👉 Diagnosis: Neuroimaging (MRI brainstem)
2. Motor Neuron Diseases (UMN + LMN Involvement)
Diseases like ALS or other motor neuron disorders show:
- Increased reflexes
- Upper motor neuron signs
- High muscle tone
- Fasciculations
- Positive Babinski sign
- Asymmetrical weakness
These features help differentiate motor neuron disease from peripheral causes.
3. Spinal Cord Causes – Acute Transverse Myelitis
Spinal cord pathology often presents as paraplegia or quadriplegia.
Key features of Acute Transverse Myelitis:
- Motor and sensory loss below a defined spinal level
- Clearly demarcated sensory level
- Possible bladder and bowel involvement
- Rapid progression
👉 Diagnosis: Contrast MRI spine
Other spinal causes include:
- Tumors
- Epidural abscess
- Spinal cord infarction
4. Peripheral Nerve Disorders
Guillain-Barré Syndrome (GBS)
The most common peripheral nerve cause in ICU.
Typical features:
- Ascending symmetrical weakness
- Areflexia
- Recent infection or vaccination
- No UMN signs
👉 Diagnosis:
- Lumbar puncture
- Nerve conduction studies
ICU-Acquired Weakness / Critical Illness Neuromyopathy
Seen in patients with:
- Prolonged ICU stay
- Multi-organ dysfunction
- Sepsis
Clinical clues:
- Symmetrical weakness
- Normal cranial nerves
- Absent reflexes
- Difficulty weaning from ventilator
- Possible diaphragmatic involvement
👉 Investigations:
- Nerve conduction studies
- CPK (may be mildly elevated in myopathy)
Other Peripheral Causes
- Vitamin B12 deficiency
- Glove and stocking sensory loss
- Megaloblastic anemia (↑ MCV, MCH)
- Heavy metal poisoning
5. Neuromuscular Junction Disorders
Myasthenia Gravis
Key features:
- Ptosis and diplopia
- Cranial muscles involved early
- Fatigability (worsens with activity)
- Weakness worse in the evening
👉 Diagnosis:
- ACh receptor antibodies
- EMG
- Edrophonium test
Lambert-Eaton Syndrome
How it differs from Myasthenia:
- Often associated with malignancy
- Weakness improves with exercise (important exam point)
Botulism & Organophosphate Poisoning
- Cranial nerve weakness
- History of toxin ingestion
6. Muscle Disorders (Myopathies)
Common ICU-related causes:
- Critical illness myopathy
- Steroid-induced myopathy
- Electrolyte imbalance
- Malnutrition
- Hypercatabolic states
Clinical pattern:
- Predominantly proximal muscle weakness
- Reflexes are usually preserved initially
Neuropathy vs Myopathy – Quick Differentiation
| Feature | Neuropathy | Myopathy |
| Weakness | Distal | Proximal |
| Sensory symptoms | Present | Absent |
| Reflexes | Lost early | Preserved |
| Fasciculations | May be present | Absent |
UMN vs LMN Lesions – Exam Rule
- Lesión above anterior horn cell → UMN
- Lesion at or below the anterior horn cell → LMN
UMN:
More tone, more reflexes, positive Babinski
LMN:
Less tone, less reflexes, muscle atrophy, fasciculations
High-Yield ICU MCQs Explained
MCQ 1: Transverse Myelitis vs GBS
Most specific feature of transverse myelitis:
✅ Well-defined sensory level on trunk
MCQ 2: Shock in High Thoracic Myelitis
Patient with T4 lesion, hypotension, bradycardia, warm extremities:
✅ Neurogenic shock
MCQ 3: No Improvement After Steroids in Myelitis
Next best step after IV methylprednisolone failure:
✅ Plasmapheresis
Guillain-Barré Syndrome – ICU Essentials
When to Intubate in GBS?
Use the 20–30–40 rule:
- FVC < 20 ml/kg
- MIP < 30 cm H₂O
- MEP < 40 cm H₂O
Additional red flags:
- Bulbar weakness
- Pooling of secretions
- Facial diplegia
- Rising CO₂ despite tachypnea
GBS Overview
- Autoimmune demyelinating neuropathy
- Often post-infection
- Ascending paralysis
- Peak at 2–4 weeks
CSF:
- High protein
- Normal cell count
(Cyto-albuminologic dissociation)
Types of GBS (Exam Favorite)
- AIDP / AMSAN – Motor + sensory
- AMAN – Pure motor
- Miller-Fisher Syndrome – Ophthalmoplegia, ataxia, areflexia
- PCB variant – Pharyngeal, cervical, brachial weakness
- Autonomic GBS – Severe dysautonomia
GBS Treatment
- IVIG or Plasma Exchange (equally effective)
- ❌ No role of steroids
- Supportive ICU care is crucial
Prognostic Scores in GBS
- EGOS – Predicts walking ability at 6 months
- EGRIS – Predicts risk of respiratory failure
Final Takeaway
In ICU patients with weakness, localisation is everything.
From brainstem to muscle, a structured approach helps you diagnose faster, manage better, and answer MCQs confidently.
This session is not just exam-oriented—it mirrors real ICU decision-making, where early diagnosis can change outcomes.
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