Weakness
Red flags
- Ascending weakness + bulbar or respiratory involvement
- FVC <20 mL/kg, or falling >30% from baseline -> ICU (not SpO2 - it falls last)
- Single-breath count <20, orthopnoea, paradoxical abdominal movement
- Sensory level, bilateral leg weakness, urinary retention, saddle anaesthesia -> cord compression
- MRI whole spine within hours; dexamethasone if malignant
- Hyperacute onset (seconds-minutes) -> stroke, haemorrhage, spinal infarct
- Fever + back pain + weakness -> spinal epidural abscess
- Fluctuating weakness worse at end of day + diplopia/dysphagia -> myasthenic crisis
- K+ <2.5 or >6.5 -> periodic paralysis, profound hypokalaemia
- Rhabdomyolysis: CK >5x ULN + myoglobinuria -> AKI, hyperkalaemia
- Painless, rapidly progressive, no sensory signs, brisk reflexes in a wasted limb -> MND
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