The mysterious whole-body weakness is a favourite topic of the CICM examiners. In fact, for some reason the college perpetually want the candidates to compare various "weakening" disease states to Guillain-Barre Syndrome. This has now come up so many times that the number of SAQs now merits an unordered list:
Therefore, from a cynical exam-oriented standpoint, it would be worth knowing a lot about GBS because in such questions one stands a reasonable chance of scoring at least half the marks. The other condition does not matter quite so much; although having said this, transverse myelitis has appeared in Question 10 from the second paper of 2019 GBS itself is discussed in greater detail elsewhere. It also receives a thorough LITFL treatment. In this chapter, only comparisons of GBS with other conditions will be listed. For those wishing to have a more thorough and official resource, Garg et al (2017) offer an excellent description of the lower motor neuron syndromes.
This list of plausible differentials was generated with the aid of this excellent article by Garg et al (2017). No effert was expended to make this list comprehensive or definitive.
In brief:
The college answer is presented as a table.
A much better table is presented in the 2006 article by Upinder Dhand (Table 3, pp. 1034).
If one were to cut and paste this table into one's SAQ answer, the college examiners would have been very pleased. So impressive is it, that I have taken the liberty of reproducing it here with minimal modification, without any permission but with the best of intentions.
Differences between GBS and CIP
GBS CIP History and Examination
Recent GI or resp illness. Progressive bilateral symmetric paralysis. Subtypes can be more localized e.g. MF opthalmoplegia and ataxia. Sensory involvement is common. Areflexic. Autonomic involvement may be present
Always occurs in association with a critical illness in particular severe sepsis. May have an association encephalopathy in early stages. It is a symmetrical weakness. May have muscle tenderness, hyporeflexic, diminished distal sensation Not associated with autonomic involvement
Investigations
Albuminocytologic dissociation in CSF. Identification of infection with campylobacter, mycoplasma, EBV,Varicella, CMV. Elevated csf IGG levels and possible serum antiganglioside antibodies
Elevated CK which may be transient.
Nerve conduction studies and EMG
When the demyelinating form is present, you get a reduction in conduction velocity as well as reduction in CMAP. In axonal forms however it is only the distribution of the findings that helps determine the diagnosis.
Critical illness polyneuropathy |
Guillain-Barre |
Critical Illness Myopathy |
|
Clinical setting |
Sepsis Septic encephalopathy |
Antecedent viral illness Surgery Campylobacter jejuni HIV |
Neuromuscular blocking drugs Corticosteroids Asthma Organ transplant |
Motor weakness |
Generalised and distal |
Generalised and ascending |
Generalised and proximal |
Reflexes |
Diminished |
Absent |
Preserved but weak |
Cranial nerve palsy |
Rare |
Common |
Absent |
Dysautonomia |
Normal autonomic function |
Frequent dysautonomia |
Normal autonomic function |
Sensory deficit |
Distal |
Normal sensation, or slightly altered |
Normal sensation |
CK level |
Normal |
Normal |
Elevated |
Nerve conduction |
Reduced CMAP and SNAP amplitude (compound muscle action potentials and sensory nerve action potentials) |
Marked slowing, conduction block |
Reduced CMAP amplitude |
Needle EMG |
Abnormal spontaneous activity Reduced recruitment Large polyphasic motor unit potentials (MUPs) |
Abnormal spontaneous activity Reduced recruitment Normal MUPs (early in disease) |
Minimal spontaneous activity Early recruitment Small polyphasic MUPs; |
Direct muscle stimulation |
Normal |
Normal |
Absent or reduced |
Muscle biopsy |
Neuropathic changes |
Neuropathic changes |
Myopathic changes Thick myosin filament loss Muscle fiber necrosis |
It would be possible but pointless to replicate the table above with myasthenia gravis plugged into the CIPN slot. Instead, a more directed approach will be taken, where clinical features, investigations and treatment are discussed in a tabulated form, best suited to answer Question 20 from the first paper of 2016.
Thus:
Features | Guillain-Barre | Myasthenia Gravis |
Clinical setting |
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Motor weakness |
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Sensory loss |
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Reflexes |
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Cranial nerve involvement |
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Dysautonomia |
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Guillain Barre Syndrome |
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Myasthenia Gravis |
|
Guillain Barre Syndrome |
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Myasthenia Gravis |
|
This was the topic of Question 3 from the second paper of 2018. Judging by the pass rate of ~60%, many did not have much of an idea about the latter disease. In case future exam candidates wish to explore the topic further, they will find it well-reviewed in the paywalled UpToDate article by Krishnan et al (2016). Another inaccessible but excellent article is the 2004 paper by Harzheim et al, trapped in the dungeons of Elsevier. The freegan may avail oneself of the LITFL summary page and this excellent review paper by West (2013) which Chris Nickson links.
The college question wanted the two compared in terms of "relevant history, the clinical features, and the relevant investigation findings". The official college answer to this SAQ was actually quite extensive, and likely represents an earnest effort from the examiners. It would be difficult to improve on such an answer. One can merely rearrange the categories and add some irrelevant tidbits here and there. The product appears below.
Guillian-Barré | Acute Transverse Myelitis |
Pathophysiology | |
Acute inflammatory demyelinating peripheral neuropathy, associated with infection such as:
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Autoimmune inflammation of the spinal cord; may be idiopathic or associated with other illnesses:
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Typical features of history | |
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Power | |
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Tone | |
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Reflexes | |
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Cranial nerves | |
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Autonomic features | |
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Sensory findings | |
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CSF features | |
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Bloods | |
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Nerve conduction studies | |
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Electromyography | |
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MRI | |
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Management | |
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The nerve conduction findings of GBS have been asked about specifically in Question 2 from the first paper of 2019. The following were derived from a guideline by Asbury & Cornblath (1990):
Chapter 57 (pp. 617) Neuromuscular diseases in intensive care by George Skowronski and Manoj K Saxena
van den Berg, Bianca, et al. "Guillain-Barre syndrome: pathogenesis, diagnosis, treatment and prognosis." Nature Reviews Neurology 10.8 (2014): 469-482.
Yuki, Nobuhiro, and Hans-Peter Hartung. "Guillain–Barré syndrome." New England Journal of Medicine 366.24 (2012): 2294-2304.
Raphael, J. C., et al. "Plasma exchange for Guillain-Barré syndrome." Cochrane Database Syst Rev 2.2 (2002).
Venkata Umakant, K., B. Seshulakshmi, and B. Srinivasa Rao. "Miller Fisher Syndrome–An Atypical Clinical Presentation." Intern Med 3.119 (2013): 2.
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Odaka, M., N. Yuki, and K. Hirata. "Anti-GQ1b IgG antibody syndrome: clinical and immunological range." Journal of Neurology, Neurosurgery & Psychiatry70.1 (2001): 50-55.
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Cabrera Serrano, M., and A. A. Rabinstein. "Usefulness of pulmonary function tests and blood gases in acute neuromuscular respiratory failure." European Journal of Neurology 19.3 (2012): 452-456.
Farrero, Eva, et al. "Guidelines for the Management of Respiratory Complications in Patients With Neuromuscular Disease." Archivos de Bronconeumología (English Edition) 49.7 (2013): 306-313.
Hughes, Richard AC, et al. "Supportive care for patients with Guillain-Barré syndrome." Archives of neurology 62.8 (2005): 1194-1198.
Massam, M., and R. S. Jones. "Ventilatory failure in the Guillain-Barré syndrome." Thorax 35.7 (1980): 557-558.
González-Suárez, Inés, et al. "Guillain-Barré Syndrome: Natural history and prognostic factors: a retrospective review of 106 cases." BMC neurology 13.1 (2013): 95.
Dhand, Upinder K. "Clinical approach to the weak patient in the intensive care unit." Respiratory care 51.9 (2006): 1024-1041.
Sanders, Donald B., and Janice M. Massey. "Clinical features of myasthenia gravis." Handbook of clinical neurology 91 (2008): 229-252.
Bird, Shawn J. "Clinical manifestations of myasthenia gravis." Up-to-date 16.1 (2008): 1-8.
Gronseth, Gary S., and Richard J. Barohn. "Practice parameter: Thymectomy for autoimmune myasthenia gravis (an evidence-based review) Report of the Quality Standards Subcommittee of the American Academy of Neurology." Neurology 55.1 (2000): 7-15.
Gajdos, Philippe, Sylvie Chevret, and Klaus V. Toyka. "Plasma exchange for generalised myasthenia gravis." The Cochrane Library (2002).
Gajdos, Philippe, et al. "Treatment of myasthenia gravis exacerbation with intravenous immunoglobulin: a randomized double-blind clinical trial." Archives of neurology 62.11 (2005): 1689-1693.
Jacob, Anu, and Brian G. Weinshenker. "An approach to the diagnosis of acute transverse myelitis." Seminars in neurology. Vol. 28. No. 01. © Thieme Medical Publishers, 2008.
Garg, Nidhi, et al. "Differentiating lower motor neuron syndromes." J Neurol Neurosurg Psychiatry 88.6 (2017): 474-483.
West, Timothy W. "Transverse myelitis—a review of the presentation, diagnosis, and initial management." Discovery medicine 16.88 (2013): 167-177.
Harzheim, Michael, et al. "Discriminatory features of acute transverse myelitis: a retrospective analysis of 45 patients." Journal of the neurological sciences 217.2 (2004): 217-223.
Asbury, Arthur K., and David R. Cornblath. "Assessment of current diagnostic criteria for Guillain‐Barré syndrome." Annals of Neurology: Official Journal of the American Neurological Association and the Child Neurology Society 27.S1 (1990): S21-S24.