Approach to the ICU patient with generalised weakness

The college love generalised weakness. It is frequently lurking in the background of hot cases and it has appeared in many previous SAQs:

• Question 25 from the first paper of 2012
• Question 11 from the second paper of 2009
• Question 20 from the first paper of 2006
• Question 5 from the second paper of 2005
• Question 15 from the second paper of 2003

Additionally, weakness (specifically myasthenia gravis) became the topic of Viva 1 from the second paper of 2015. Copious words are written about this issue in many reputable sources. The objective of this page is not to reproduce the same information you can find in UpToDate or in Oh's Manual. The point is to have a quick reference summary of relevant differences, and a framework for answering CICM SAQs on this topic.

This ties in with several other local summaries:

• Features that distinguish myopathy from neuropathy
• Intensive Care for Guillain-Barre Syndrome
• Critical illness polyneuromyopathy
• Features that distinguish Guillain-Barre syndrome from critical illness polyneuromyopathy

The canonic resource is Oh's Chapter   57  (pp. 617)-   Neuromuscular  diseases  in  intensive  care by George  Skowronski  and  Manoj  K  Saxena. However, if one were to limit one's reading to one resource, one should make it the 2006 article by Upinder Dhand from Respiratory Care, titled "Clinical approach to the weak patient in the intensive care unit."

Differential diagnosis of weakness in the critically ill patient

In order to render easier the process of discussing these conditions, I have arranged them in a table, together with their specific features and diagnostic methods. This table was in turn inspired by Table 3 ("Semiology of main peripheral nervous system syndromes") from a 2014 issue of the ESICM "Pragmatic Guidelines" for the neurological examination of critically ill patients.

Clinical examination:

Level of consciousness

• Perform a GCS. The brainstem-damaged or "locked in" patient will not perform well in this test.
• The patient with critical illness polyneuromyopathy (CIP) will be conscious.

Gross bilateral power

• Symmetry favours CIP
• Sparing of distal motor power tends to exclude focal CNS lesions
• Assymetry of motor findings favours a focal CNS lesion.
  • A "level" of motor features suggests some spinal pathology
  • Lateralising motor features suggest motor cortex pathology
• Fatiguability (Myasthenia gravis vs. "reverse" fatiguability with Lambert-Eaton syndrome)

Cranial nerve examination

• Normal cranial nerves suggest a purely peripheral or spinal problem.

Tendon reflexes

• Tendon reflexes are absent in neuropathies, and merely decreased in myopathies. They should be essentially normal in de-conditioning or with residual sedative effect.

Investigations

A panel of standard investigations which will exclude many of the above would include the following tests and imaging studies:

• Electrolyte levels
• CK level
• B12 level
• Acetylcholine receptor antibodies (for myasthenia gravis)
• CXR looking for malignancy (as support for a diagnosis of Eaton-Lambert syndrome)
• Inflammatory markers
• Lumbar puncture
• Nerve conduction studies
• Electromyography
• MRI of the brainstem and spine
• Muscle biopsy if no satisfactory explanation is found.