OVERVIEW
- ICU Acquired Weakness (ICUAW) includes critical illness myopathy (CIM), critical illness polyneuropathy (CIP), or a mixture of both (myopathy is typically predominant)
- very common in the mechanically ventilated (25-60% in those mechanically ventilated for > 7 days)
- increasing body of evidence that ICUAW leads to poor quality of life and persistent weakness lasting long after ICU discharge
PATHOPHYSIOLOGY
Multifactorial pathogenesis may involve:
- axonopathy, not demyelinating
- mitochondrial dysfunction
- microvascular ischaemia
- sodium channelopathy
- catabolism
- immobility
RISK FACTORS
- sepsis
- systemic inflammation
- poor glycaemic control
- steroids
- neuromuscular blocking agents
- immobility
- malnutrition
- female sex
- pre-existing sarcopenia
CLINICAL FEATURES
- onset is typically about 1 week into a critical illness
- Sensation is preserved (deficits can be present with axonopathy; difficult to assess in ICU due edema and coma)
- Symmetrical deficits
- Mostly proximal weakness
- Reflexes are present, though diminished
- CSF findings are normal
- Cranial nerve function and autonomic nervous system function are usually intact
- CK may be raised if myopathy is present
- Nerve conduction studies (if performed) show normal conduction velocities with decreased compound muscle action potentials (CMAPs)
- score of <48 on the MRC sum score (MRC-SS) of muscle strength is diagnostic of ICUAW
INVESTIGATIONS
Investigations are often not necessary, however they may be required depending on the possible differential diagnoses and implications for management and prognosis
Laboratory
- CK (mildly elevated – and transiently so – in critical illness myopathy (not so with critical illness neuropathy)
- UEC
- B12 level
- Acetylcholine receptor antibodies (for myasthenia gravis)
- Inflammatory markers (e.g. CRP)
- Lumbar puncture
Imaging
- CXR (evidence of malignancy causing Eaton-Lambert syndrome)
- MRI of the brainstem and spine
Special tests
- Nerve conduction studies andelectromyography: CIP shows sensorimotor axonopathy with decreased compound muscle action potentials (CMAP) and sensory-nerve action potentials, but preserved conduction velocities (CV). CIM shows reduced amplitude and increased duration of CMAPs. ICUAW often is a mixture of CIP and CIM.
- Muscle biopsy if no satisfactory explanation is found
DIFFERENTIAL DIAGNOSIS
Key differentials of ICU-acquired weakness
- Critical illness polyneuropathy
- presents around a week into a critical illness, typically with limb weakness and atrophy, reduced tendon reflexes, loss of peripheral sensation to touch and pain, preservation of CN function, electrophysiological studies -> motor and sensory neuropathy, biopsies -> axonal degeneration and denervation -> atrophy of muscles
- Residual paralysis
- exclude using peripheral nerve stimulation (minimal response to TOF, PTc)
- Residual sedation
- calculation of dose, duration and ability to clear medications (response to antagonism; naloxone, flumazenil)
- Acute myopathy
- risk factors = neuromuscular blockage and corticosteroids, motor findings with no sensory abnormalities, CK elevated, electrophysiological testing -> myopathy, muscle biopsy -> loss of thick filaments
- Spinal cord lesions
- associated with a sensory level and hyperreflexia
- Brain stem problems
- cranial nerve lesions
- Guillain-Barre syndrome
- ascending motor weakness, loss of reflexes, some peripheral sensory deficits, pain, post-viral, high protein in CSF, responsive to Ig and plasmapheresis
Differential diagnosis of rapidly progressive limb weakness (with or without respiratory failure)
- CNS
- Encephalitis, acute disseminated encephalomyelitis, transverse myelitis, brainstem or myelum compression, leptomeningeal malignancy
- Motor neurons
- Poliomyelitis, West Nile virus anterior myelitis, amyotrophic lateral sclerosis, progressive spinal muscular atrophy
- Plexus
- Neuralgic amyotrophia, diabetes mellitus
- Nerve roots
- Guillain-Barré syndrome, acute onset chronic inflammatory demyelinating neuropathy, Lyme disease, cytomegalovirus-related radiculitis, HIV-related radiculitis, leptomeningeal malignancy
- Peripheral nerves
- Guillain-Barré syndrome, acute onset chronic inflammatory demyelinating neuropathy, iatrogenic, toxic, critical illness myopathy-neuropathy, vasculitis, diphtheria, porphyria, thiamine deficiency, porphyria, Lyme disease, metabolic or electrolyte disorders (hypokalaemia, phosphataemia or magnesaemia, hypoglycaemia)
- Neuromuscular junction
- Myasthenia gravis, botulism, intoxication
- Muscles
- Critical illness myopathy-neuropathy, mitochondrial disease, acute rhabdomyolysis, polymyositis, dermatomyositis
MANAGEMENT
- intensive glycaemic control
- minimise use of corticosteroids and neuromuscular blockade
- physiotherapy – consider including early mobilisation
- electrical muscular stimulation (EMS)
- minimise sedation
- electrolyte replacement
- optimise nutrition
- ventilator weaning
PROGNOSIS
Short term
- increased ventilation
- increased ICU stay
- increased mortality
Long term
- most recover to be able to walk independently
- small amount have mild disability
- 30% have severe quadriparesis, quadriplegia or paraplegia
References and Links
LITFL
- CCC — Mobilisation in ICU
Journal articles
- Deem S. Intensive-care-unit-acquired muscle weakness. Respir Care. 2006;51:(9)1042-52; discussion 1052-3. [pubmed]
- Dhand UK. Clinical approach to the weak patient in the intensive care unit. Respir Care. 2006 Sep;51(9):1024-40; discussion 1040-1. [PubMed] [Free Full Text]
- Fan E, Cheek F, Chlan L, 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:(12)1437-46. [pubmed]
- Hermans G, De Jonghe B, Bruyninckx F, Van den Berghe G. Interventions for preventing critical illness polyneuropathy and critical illness myopathy. Cochrane Database Syst Rev. 2009;(1)CD006832. [pubmed]
- Hermans G, De Jonghe B, Bruyninckx F, Van den Berghe G. Clinical review: Critical illness polyneuropathy and myopathy. Crit Care. 2008;12:(6)238. [pubmed]
- Khan J, Burnham EL, Moss M. Acquired weakness in the ICU: critical illness myopathy and polyneuropathy. Minerva Anestesiol. 2006;72:(6)401-6. [pubmed]
- Kress JP, Hall JB. ICU-acquired weakness and recovery from critical illness. N Engl J Med. 2014;370:(17)1626-35. [pubmed]
- Truong AD, Fan E, Brower RG, Needham DM. Bench-to-bedside review: mobilizing patients in the intensive care unit–from pathophysiology to clinical trials. Crit Care. 2009;13:(4)216. [pubmed] [PMC free article]
Critical Care
Compendium
Leave a Reply