Neurology · Topic 20 of 22

ICU-Acquired Weakness

Neurology · critical illness neuromuscular

ICU-Acquired Weakness

Symmetric limb and respiratory weakness born of critical illness: an MRC sum score under 48, no cure — prevention is the treatment.

Key numbers

MRC sum score below 48MRC sum < 48/60

01 · Defined byMRC sum score below 48

Diagnose clinically with the MRC sum score (6 muscle groups each side, 0–5 each, maximum 60): a score under 48 defines ICU-acquired weakness, and under 36 marks severe weakness.

02 · RiskSepsis, organ failure, immobility, hyperglycemia

Risk rises with illness severity — sepsis, shock, multiorgan failure, renal replacement — and with long mechanical ventilation, immobilization and ICU stay, hyperglycemia, early parenteral nutrition, older age and female sex.

03 · DoPrevent: normal glucose, light sedation, early mobility

No drug treats ICU-acquired weakness, so prevention is the strategy: avoid hyperglycemia, minimize sedation, postpone parenteral nutrition past the first ICU week, and mobilize early once the patient is safe.

What it is

Core idea

Symmetric limb weakness, face spared must knowICU-acquired weakness is generalized, symmetric weakness of limb and respiratory muscles, usually sparing facial and ocular muscles, arising during critical illness with no cause other than the illness and its treatment.

Three forms: polyneuropathy, myopathy, or bothICU-acquired weakness includes critical illness polyneuropathy (peripheral nerve injury), critical illness myopathy (muscle injury) and the combined polyneuromyopathy.

Causes & risk factors

Why it happens

Steroids and paralytics: possible, unproven riskThe link between corticosteroids or neuromuscular blockers and ICU-acquired weakness is inconsistent; blockers infused for more than 48 hours or combined with steroids may promote weakness, so limit both to clear indications.

Myopathy recovers better than neuropathyCritical illness myopathy usually recovers well, often fully, whereas neuropathic involvement leaves 50–75% of patients with persistent weakness or even tetraparesis.

Diagnosis & monitoring

Work-up

MRC testing needs an awake, cooperative patientThe MRC sum score and handgrip dynamometry require an awake, cooperative patient and cannot separate neuromyopathy from deconditioning; electrophysiology helps when the patient cannot participate.

Management

Orders

Delay parenteral nutrition past the first weekIn randomized trials, postponing parenteral nutrition beyond the first ICU week reduced ICU-acquired weakness compared with early parenteral nutrition.

Nerve conduction: SNAPs separate neuropathy from myopathyNerve conduction studies need no patient cooperation: both CIP and CIM reduce CMAP amplitude, but sensory (SNAP) amplitudes fall in CIP and are preserved in CIM, where CMAP duration is prolonged.

Treat with physical rehabilitationThere is no drug treatment; management is supportive, centered on physical rehabilitation, which improves outcomes in critically ill patients.

Red flags & don'ts

Avoid harm

Weakness prolongs ventilation and raises mortality complicationICU-acquired weakness, including diaphragm weakness, prolongs mechanical ventilation and failed weaning, lengthens ICU and hospital stay, and increases one-year mortality and long-term disability.

Critical illness polyneuropathy or myopathy?

Commonly confused

Site of injury	Peripheral nerves
CMAP amplitude	Reduced
Sensory (SNAP) amplitude	Reduced
CMAP duration	Normal
Recovery	Often incomplete

Commonly confused

Tell apart

Exclude GBS, myasthenia and other causes firstICU-acquired weakness is a diagnosis of exclusion: first consider primary neuromuscular disease that led to the ICU stay, such as Guillain-Barré syndrome or myasthenia gravis.

More detail

Reference

Show 5 reference facts

ICU-acquired weakness affects about 30–50% of critically ill patients, more with sepsis, multiorgan failure and prolonged ventilation; respiratory muscle weakness occurs in about 80% of those affected.

Aminoglycosides and longer vasopressor exposure (mostly beta-agonist catecholamines such as norepinephrine) have also been associated with ICU-acquired weakness.

Normoglycemia, not insulin itself, explains the lower neuromyopathy risk in tight-control trials; the optimal ICU glucose target remains debated after the largest trial favored intermediate targets.

Evidence for neuromuscular electrical stimulation and drug therapies to prevent ICU-acquired weakness is inconsistent or low quality.

Even mild weakness at ICU discharge (MRC sum ≤ 55) is linked with lower handgrip strength, walking distance and physical quality of life and higher mortality five years later.

Pearl

No drug treats ICU-acquired weakness — normal glucose, light sedation and early mobility are the prevention.

Sources · Vanhorebeek I, Latronico N, Van den Berghe G. ICU-acquired weakness. Intensive Care Med 2020;46:637–653 · Spoeri M et al. ICU-Acquired Weakness: An Unsolved Clinical Problem — A Narrative Review. J Clin Med 2026;15:3623 · Fan E et al. An official American Thoracic Society clinical practice guideline: the diagnosis of intensive care unit-acquired weakness in adults. Am J Respir Crit Care Med 2014;190:1437–46 · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).