39. ICU Neuropathy

Question 1

What are the causes of muscle weakness in critically ill patients?

Answer 1

1. Pre-existing medical conditions
   Guillain–Barre´ syndrome
   Myasthenia gravis
   CNS lesions, e.g. trauma, polio, MND
2. Drug related
   Muscle relaxants
   Aminoglycosides (may interfere with neuromuscular transmission)
   Magnesium (in pre-eclampsia)
   Steroids (typically proximal weakness/wasting)
   Poisoning, e.g. botulinum toxin, organophosphates
3. Metabolic
   Hypokalaemia
   Hypophosphataemia
4. Myopathy (acquired)
   Immobilization, disuse atrophy
   Malnutrition
   Necrotising myopathy
   Critical illness myopathy (CIM)
5. Critical illness neuropathy

Question 2

Tell me a bit more about critical illness neuropathy.

Answer 2

1. This is an acquired neuropathy
   commonly found in association with
   severe sepsis and multiple organ failure,
   increasing in frequency with prolonged
   ICU stay and sepsis.
2. The problem affects more than half of adult patients
   admitted to general ICUs for more than 1 week
   and more than 70% of those with sepsis and multiorgan failure.
3. It has been recognized as a clinical entity since 1983 when described by
   Bolton et al.
4. The cause remains unknown and there is no specific treatment.
5. Clinically, there is a flaccid weakness
   with absent/reduced tendon reflexes
   and muscle wasting.

Question 3

How can CIW present

Answer 3

Neuromuscular weakness typically presents when attempting to wean the
patient from the ventilator. Earlier diagnostic clues may be a relative lack of movement after regaining consciousness and/or the loss of deep tendon reflexes.

Other diagnoses should be considered, although most cases will be due to
critical illness polyneuromyopathy.
Spinal cord disease should be excluded,
West Nile virus infection, acute
disseminated encephalomyelitis, etc.

A neuromuscular transmission defect
(e.g. NMBs, unrecognized myasthenia gravis).

Porphyria and recurrent chronic inflammatory demyelinating
polyneuropathy.

Question 4

Differentiating the most common causes of ICU-acquired generalized weakness

Answer 4

Differentiating the most common causes of ICU-acquired generalized
weakness (myopathy, neuropathy, or a combination of the two),

is useful because they have differing prognoses.

Electromyography is helpful in differentiating CIP from CIM.

An elevated serum creatine kinase may help to identify CIM.

Muscle biopsy can address the relative contribution of
myopathy to the picture because the neuropathy can be adequately
assessed electrophysiologically (nerve conduction studies).

CSF protein levels are normal (cf. Guillain–Barre´ ).

Question 5

CIM

Answer 5

The prognosis for recovery from a CIM is more favourable, most patients
recovering fully within 1–3 months.

Patients with widespread muscle necrosis may recover incompletely

Question 6

CIP

Answer 6

Patients with CIP recover slowly because the axons regenerate at 1 mm/day.
This takes many months and recovery is often incomplete Evidence of
polyneuropathy is apparent after 5 years in over 90% of CIP patients.