The college love generalised weakness. It is frequently lurking in the background of hot cases and it has appeared in many previous SAQs:
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:
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."
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.
Level of pathology | Aetiology | Unique features | Diagnostic approach |
Brainstem | Locked-in syndrome |
Sudden onset Vertical gaze and eyelid opening should be preserved |
MRI CT |
Motor neuron | Motor neuron disease (eg, amyotrophic lateral sclerosis) |
Increased reflexes Assymmetry of signs Increased tone Upper motor neuron signs Characteristic fasciculations |
EMG - there will be "jitter" Diagnosis of exclusion |
Spinal cord | Transverse myelitis |
Motor and sensory loss below the affected level |
MRI |
Compression by tumour |
Gradual onset, may be lateralising |
MRI LP (for cytology) |
|
Compression by abscess |
Subacute onset, may be lateralising |
MRI LP |
|
Spinal cord infarction |
Focal neurology Sudden onset |
MRI |
|
Peripheral nerve | Critical Illness Neuromyopathy |
Normal cranial nerves Symmetrical features; Reflexes absent Diaphragm involved |
CK slightly elevated Clinical diagnosis |
Guillain–Barré syndrome |
Ascending patterns History of recent febrile illness or immunization Reflexes absent No upper motor neuron signs |
LP (increased CSF protein) Nerve conduction studies (conduction will be delayed) |
|
Vitamin B12 deficiency |
Glove and stocking distribution of sensory loss |
Serum B12 levels |
|
Heavy metal poisoning | |||
Neuromuscular junction | Myasthenia gravis |
First comes diplopia; eyes and cranial nerves are hit first There is characteristic fatiguability: weakness increases with sustained exercise. Fade and post tetanic facilitation is present on nerve stimulator testing It will respond to anticholinesterases. |
Acetylcholine receptor antibodies EMG Edrophonium challenge |
Lambert–Eaton syndrome |
Associated malignancy proximal muscle weakness diplopia is uncommon Opposite of fatiguability: weakness resolves with sustained exercise |
EMG |
|
Botulism |
Starts with the cranial nerves |
Botulinum toxin detection |
|
Organopshosphate poisoning |
Cholinergic syndrome |
Mixed cholinesterase studies |
|
Muscle | Steroid myopathy |
Proximal weakness Symmetrical features; Reflexes reduced |
Clinical diagnosis Resolves with withdrawal of steroids |
Electrolyte disturbance |
Generalised weakness |
Electrolyte levels |
|
Atophy due to hypercatabolic state and malnutrition |
Normal reflexes |
Markers of malnutrition |
|
Critical Illness Neuromyopathy |
Normal cranial nerves Symmetrical features; Reflexes absent Diaphragm involved |
CK slightly elevated Clinical diagnosis |
Level of consciousness
Gross bilateral power
Cranial nerve examination
Tendon reflexes
A panel of standard investigations which will exclude many of the above would include the following tests and imaging studies:
Chapter 51 (pp. 568) Acute cerebrovascular complications by Bernard Riley and Thearina de Beer
Chapter 57 (pp. 617) Neuromuscular diseases in intensive care by George Skowronski and Manoj K Saxena
Yuki, Nobuhiro, and Hans-Peter Hartung. "Guillain–Barré syndrome." New England Journal of Medicine 366.24 (2012): 2294-2304.
Jani, Charu. "Critical Illness Neuropathy." Medicine (2011): 237.
Young, G. Bryan, and Robert R. Hammond. "A stronger approach to weakness in the intensive care unit." Critical care 8.6 (2004): 416.
Mareska, Michael, and Laurie Gutmann. "Lambert-Eaton myasthenic syndrome." Seminars in neurology. Vol. 24. No. 2. [New York]: Thieme-Stratton Inc.,[c1981-, 2004.
Reeves and Swenson have an excellent online textbook chapter (12) entitled "Evaluation of the Patient with Weakness"
Centers for Disease Control and Prevention (CDC). "Tetanus surveillance---United States, 2001-2008." MMWR. Morbidity and mortality weekly report 60.12 (2011): 365.
Schiavo, Giampietro G., et al. "Tetanus and botulinum-B neurotoxins block neurotransmitter release by proteolytic cleavage of synaptobrevin." Nature359.6398 (1992): 832-835.
O'Malley, Cynthia D., et al. "Tetanus associated with body piercing." Clinical infectious diseases 27.5 (1998): 1343-1344.
Cook, T. M., R. T. Protheroe, and J. M. Handel. "Tetanus: a review of the literature." British Journal of Anaesthesia 87.3 (2001): 477-487.
Lockman, Juliana, and Ted M. Burns. "Stiff-person syndrome." Practical neurology 7.2 (2007): 106-108.
McLeod, Bruce C. "Therapeutic apheresis: use of human serum albumin, fresh frozen plasma and cryosupernatant plasma in therapeutic plasma exchange."Best Practice & Research Clinical Haematology 19.1 (2006): 157-167.
Raphael, J. C., et al. "Plasma exchange for Guillain-Barré syndrome." Cochrane Database Syst Rev 2.2 (2002).
Reimann, P. M., and P. D. Mason. "Plasmapheresis: technique and complications." Intensive care medicine 16.1 (1990): 3-10.
Coutinho, Agnes E., and Karen E. Chapman. "The anti-inflammatory and immunosuppressive effects of glucocorticoids, recent developments and mechanistic insights." Molecular and cellular endocrinology 335.1 (2011): 2-13.
Sharshar, Tarek, et al. "Neurological examination of critically ill patients: a pragmatic approach. Report of an ESICM expert panel." Intensive care medicine 40.4 (2014): 484-495.
Dhand, Upinder K. "Clinical approach to the weak patient in the intensive care unit." Respiratory care 51.9 (2006): 1024-1041.