Acute Non-Traumatic Weakness

Reviewed and revised 13 April 2016


Acute non-traumatic weakness may occur as a result of a wide variety of underlying etiologies, many of which are life-threatening

  • Key considerations include:
    • assessment of the need for intubation and respiratory support
    • identification of time-critical emergencies
    • determination of the underlying cause, based on clinical assessment and investigations, including a careful physical examination to facilitate neurological localisation and diagnosis



  • Increasing generalized muscle weakness
  • Dysphagia
  • Dysphonia
  • Dyspnea on exertion and at rest


  • Rapid shallow breathing
  • Tachycardia
  • Weak cough
  • Interrupted speech (gasping for air)
  • Use of accessory muscles
  • Abdominal paradoxical breathing
  • Orthopnea
  • Weakness of trapezius and neck muscles: inability to lift head from bed
  • Inability to perform single-breath count: count from 1 to 10 in single exhalation (roughly equal to FVC <1.0 L)
  • Cough after swallowing


  • Decreased level of consciousness (have a lower threshold to control the airway if patient requires transfer or movement to unmonitored areas)
  • Hypoxemia
  • Vital capacity <1 L or 20 mL/kg, or 50 % decrease in VC in a day
  • Maximum inspiratory pressure >-30 cm H2O
  • Maximum expiratory pressure <40 cm H2O
  • Hypercapnia (occurs late)

Base the decision to intubate on a global overview of the above factors – not any single parameter – and take into account the time course and anticipated trajectory of illness

  • reassess the patient frequently
  • intervene before the onset of hypercapnia if possible


These include:

  • stroke syndromes
  • aortic dissection
  • CNS infections
  • spinal cord syndromes
  • seizure disorders
  • envenoming (e.g. snake)
  • acute toxicity e.g. organophosphates, heavy metals
  • electrolyte/ metabolic disorders



  • Myopathic – rhabdomyolysis, ischaemic, congenital, CIW
  • NMJ – myasthenia gravis, botulism
  • Neuropathic – GBS, CIW, polio
  • Spinal Cord – infarct, infection, tumour
  • Brain stem – haemorrhage, infarct, infection, mass lesion
  • Brain – haemorrhage, infarct, infection, tumour
  • Systemic – organ failures, electrolytes, sepsis, toxins


  • Acute stroke: ischemic, hemorrhagic, or subarachnoid hemorrhage
  • Intracranial mass
  • Meningitis/encephalitis
  • Hypoglycemia/hyperglycemia
  • Postictal Todd’s paresis
  • Hemiplegic migraine
  • Brown-Sequard syndrome

Quadriparesis/Paraparesis ± Sensory Level

  • Spinal cord compression
  • Spinal cord infarction
  • Transverse myelitis

Proximal Weakness

  • Acute myopathy
  • Guillain–Barré syndrome (GBS)
  • Diabetic lumbosacral radiculoplexus neuropathy (DLRN)
  • Myasthenia gravis
  • Lambert-Eaton myasthenic syndrome (LEMS)

Distal Weakness

  • Vasculitic neuropathy
  • Toxin induced peripheral neuropathy
  • Nerve compression syndromes

Any severe medical illness may have weakness as a presenting symptom, and psychiatric diagnoses may also mimic neuromuscular disorders


Clinical assessment

  • Relevant history
  • Examination
    • systemic features
    • neurological examination (see neurological localisation, below)


  • Laboratory
    • glucose, electrolytes, Ca, Mg, PO4, UEC, LFTs, and coags
    • TFTs, CK, ESR
    • others according to suspected etiology: e.g. CSF, vasculitis screen
  • Imaging (according to suspected etiology)
    • CTB, CTB +/- contrast +/- angiogram +/- venogram
    • MRI brain +/- angiography
    • CT or MRI spine


LocalisationPattern of weaknessSensory lossReflexesAcute causes
Cerebral cortex, brainstem, or spinal cordDistal > proximal, extensors > flexors, hemiparesis or single limbMay be present depending on whether sensory tracts or cortex are involvedIncreased (may be decreased initially)Acute stroke, SAH, seizure, hypertensive encephalopathy
Spinal cordDistal > proximal, extensors > flexors, paraparesis, quadriparesis, rarely hemiparesisIncreased (may be decreased initially)Epidural abscess, tumor, spinal cord infarct
Anterior horn cellProximal and distal, fasciculations are prominentabsentDecreased if muscle bulk is severely decreased; increased in ALSALS, polio
Peripheral nerveIn the distribution of the nerve, or diffusely present as stocking/glove weaknessPresentDecreasedGuillain-Barre Syndrome
Neuromuscular junctionFirst in eye muscles, neck extensors, pharynx, diaphragm, followed by more generalized weaknessAbsentNormal, decreased if muscle is paralyzedBotulism, tick bite, organophosphates
MuscleProximalAbsentNormal unless muscle severely weakRhabdomyolysis
  • However, in the acute phase, UMN lesions may be difficult to differentiate from a LMN lesion
    • acute UMN lesions may result in flaccid paralysis, normal or reduced tone, and unreliable reflexes
    • in acute LMN lesions there may be insufficient time for atrophy to be evident and fasciculations are rarely seen


Airway and respiratory management

  • Assess for intubation (see factors to consider, above)
    • key life threats are:
      • airway obstruction due to oropharyngeal collapse
      • respiratory failure due to diaphragmatic weakness
      • respiratory failure due to aspiration from inadequate airway protection
  • Non-invasive ventilation
    • Consider as a temporizing measure in a neurologically stable patient with a neuromuscular condition expected to have rapid resolution (e.g., myasthenia gravis exacerbation)
    • Consider use for pre-oxygenation prior to intubation
  • Avoid suxamethonium if there is evidence of underlying progressive neuromuscular disease (e.g., Guillain-Barre Syndrome, chronic muscular weakness, or prolonged immobility) — use rocuronium (1.2 mg/kg IV IBW) for rapid sequence intubation
  • Myasthenia gravis
    • Succinylcholine is relatively ineffective, double the standard dose if used (e.g. 3 mg/kg IV)
    • Alternatively, use  half-dose of non-depolarizing agents (e.g. rocuronium 0.6 mg/kg IV IBW)
  • If autonomic instability is present or anticipated
    • Prepare atropine/glycopyrrolate, fluids, and vasopressors prior to intubation
    • anticipate swings and avoid overshoot (i.e. don’t chase hypotension too aggressively with vasopressors, as there may be a dramatic swing to severe hypertension as a result of autonomic instability)

Specific therapy

  • according to underlying cause

Supportive care and monitoring

References and Links


Journal articles

  • Flower O, Bowles C, Wijdicks E, Weingart SD, Smith WS. Emergency neurological life support: acute non-traumatic weakness. Neurocrit Care. 2012 Sep;17 Suppl 1:S79-95. PMID: 22972018.

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Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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