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Updated Jan 2009 by Charles Gomersall

Acute flaccid paralysis


Upper motor neuron lesion (early stages)


  • stroke
  • encephalitis

Acute myelopathy

Lower motor neuron lesion

Anterior horn cell

  • polio

Peripheral neuropathy

Disorder of neuromuscular transmission

Muscle disorders

  • hypokalaemia
  • hypophosphataemia
  • inflammatory myopathy
  • acute rhabdomyolysis
  • trichinosis
  • periodic paralysis

Clues to the cause of weakness

Suggestive clinical features Diagnosis
Fluctuating weakness, fatigability, ptosis Myasthenia gravis
Preceding infection, vaccination, diarrhoea, sensory symptoms Guillain Barre
Skin rash Dermatomyositis, vasculitis
Episodic abdominal pain, psychiatric illness Porphyria
History of mosquito bites, asymmetric flaccid weakness, encephalopathy West Nile virus infection
Family history, retinitis pigmentosa, fits, mental retardation, deafness Mitochondrial myopathy
Critical illness, particularly sepsis Critical illness polyneuropathy & myopathy

Drugs which induce weakness

Clinical syndrome Possible culprit drugs
Myasthenia like syndrome Antibiotics: aminoglycosides, quinolones, imipenem, erythromycin, polymyxins
  Neuromuscular blockers
  Antiarrhythmics: quinidine, procainamide
  Calcium channel blockers: verapamil, diltiazem
  Beta blockers
  Magnesium (including magnesium containing laxatives and antacids)
  Interferon alpha
Myopathy Statins, D-penicillamine, zidovudine, lamivudine, stavudine
Rhabdomyolysis Fibrates

Further reading

Maramattom BV, Wijdicks EFM. Acute neuromuscular weakness in the intensive care unit. Crit Care Med, 2006; 34(11): 2835-2841

İCharles Gomersall, January, 2018 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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