Acute Non-Traumatic Weakness

Reviewed and revised 13 April 2016

OVERVIEW

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

FACTORS TO CONSIDER IN THE DECISION TO INTUBATE

General

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

Subjective

• 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

Objective

• 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

IMMEDIATELY LIFE-THREATENING CAUSES

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

DIFFERENTIAL DIAGNOSIS

Overview

• 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

Hemiparesis

• 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

ASSESSMENT

Clinical assessment

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

Investigations

• 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

NEUROLOGICAL LOCALISATION BASED ON PHYSICAL EXAMINATION

• 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

MANAGEMENT

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

LITFL

• CCC — Spinal cord infarction

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.