Critical Illness Neuromyopathy (CINM) / ICU-acquired weakness

1. Critical illness polyneuropathy (CIP) - axonal motor and sensory neuropathy
2. Critical illness myopathy (CIM) - primary skeletal-muscle dysfunction
3. A mixed form is common.

Etiology and risk factors

• Sepsis and systemic inflammatory response
• Multiorgan failure
• Prolonged mechanical ventilation and ICU stay
• Immobilization
• Hyperglycemia
• Renal failure
• Use of corticosteroids, especially with neuromuscular blocking agents
• Severe COVID-19, burns, trauma, and prolonged critical illness

Pathogenesis

• Systemic inflammation and microcirculatory dysfunction
• Axonal degeneration in peripheral nerves in CIP
• Muscle membrane inexcitability, mitochondrial dysfunction, protein breakdown, and myosin-filament loss in CIM
• Immobilization causes rapid muscle wasting and weakness.

Clinical features

• Usually develops after severe critical illness or prolonged ICU admission
• Symmetrical, flaccid weakness of all four limbs
• Predominantly distal weakness in CIP; proximal and diffuse weakness are prominent in CIM
• Depressed or absent tendon reflexes
• Difficulty weaning from ventilator due to diaphragm and respiratory-muscle weakness
• Sensory loss may occur in CIP but is absent in pure CIM
• Facial and ocular muscles are generally spared
• No altered consciousness attributable to the neuromyopathy itself

Diagnosis

1. Clinical assessment
   • Awake/cooperative patient: Medical Research Council (MRC) sum score <48/60 suggests ICU-acquired weakness.
   • Exclude sedation, residual neuromuscular blockade, electrolyte abnormalities, CNS lesion, and Guillain-Barré syndrome.
2. Nerve conduction studies and EMG
   • CIP: reduced compound muscle action potential and sensory nerve action potential amplitudes, with axonal motor-sensory polyneuropathy.
   • CIM: reduced muscle action potentials with relatively preserved sensory nerve responses; myopathic EMG changes.
   • Direct muscle stimulation can help distinguish CIM from CIP.
3. Laboratory tests
   • Creatine kinase may be normal or mildly elevated in CIM.
   • Check electrolytes, thyroid function, glucose, and drug exposure.
4. Muscle biopsy
   • Rarely needed; may show selective loss of thick myosin filaments in CIM.

Management

• Prompt treatment and source control of sepsis
• Optimize oxygenation, perfusion, nutrition, and organ support
• Avoid prolonged/deep sedation where possible
• Minimize corticosteroids and neuromuscular blockers unless clearly indicated
• Avoid severe hyperglycemia while maintaining safe glucose control
• Early mobilization, passive and active physiotherapy, respiratory physiotherapy
• Gradual ventilator weaning and nutritional rehabilitation
• Multidisciplinary rehabilitation after ICU discharge

Prognosis

• CIM generally has a better and faster recovery than CIP.
• Recovery may take weeks to months; severe CIP can persist for months or years.
• It increases duration of ventilation, ICU and hospital stay, disability, and reduced quality of life.