Not only does GBS appear in SAQs (Question 10 from the first paper of 2013) but it inevitably finds its way into the hot cases. If there's a GBS at the hospital where the exam is being held, you bet your arse they're going in front of the candidates. Locally, chapters of interest include Approach to the ICU patient with generalised weakness and Features that distinguish Guillain-Barre syndrome from critical illness polyneuromyopathy.
Distally, a LITFL article on GBS offers an extensive and well-referenced revision resource.
Diagnostic criteria for GBS
- Progressive course
- Weakness in both arms and both legs
Features suggestive of GBS
- Progression over days to 4 weeks
- Symmetry of features
- Cranial nerve involvement
- Recovery after 2-4 weeks
- Autonomic dysfunction
- Absence of fever at onset
- High protein in CSF
Features suggestive of poor prognosis in GBS
- Age over 60
- Rapid progression in less than 7 days
- Mechanical ventilation
- A preceding diarrhoeal illness
Overall, the mortality in GBS patients admitted to ICU is around 25% according to Oh's Manual
- Campylobacter jejuni
- Influenza A
- Epstein–Barr virus
- 2-8 weeks of minor illness
- No fever to begin with
- Ascending paraesthesia
- Ascending neuropathy
- Cranial nerves frequently involved (the Miller Fisher variant - classically, ataxia areflexia and ophthalmoplegia)
- Autonomic nervous system is frequently involved
- CSF protein is elevated, and monocytes and lymphocytes are present in the CSF
- Blood IgG may be elevated
- The Miller Fisher variant may have GQ1b antiganglioside antibodies and the axonal forms may have antiganglioside GM1 antibodies
- Nerve conduction studies: reduced conduction velocity and prolonged distal latencies are the cardinal findings
- LITFL lists the following NCS features:
- Reduced conduction velocity
- Multifocal conduction blocks
- Abnormal temporal dispersion of compound muscle action potentials
- Prolonged distal latencies
- Prolonged F-waves
- A contrast MRI may demonstrate enhancement and thickening of anterior nerve roots, but this is not diagnostic. Radiopedia has a thing about it.
- MRI probably has greater value in ruling out other causes of ascending weakness (eg. a stinking huge epidural abscess).
Important staging investigations
These are the investigations which will guide you as to whether you can afford to let the primary team monitor this patient for a while longer, or whether you need to take them to the ICU immediately and prepare for imminent intubation.
Spirometry - FVC
- An FVC less than 20ml/kg (i.e. 1400ml for a normal 70kg male) is quoted by LITFL as a trigger for ICU admission, likely on the basis of a 2005 consensus statement.
- Spanish guidelines recommend a decrease of 50% from FVC predicted by age/height/gender as a trigger for at least noninvasive ventilation (i.e. they are concerned about hypercapnea)
- An FVC less than 15ml/kg is suggested as the trigger for invasive mechanical ventilation
- Interestingly, these people may actually have a higher FVC while supine rather than sitting up, much like the patients with a high spinal injury.
MIPs - Maximum Inspiratory Pressures
- If the MIP is less than 30cmH2O, they need a tube.
- This demonstrates respiratory muscle weakness
MEPs - Maximum Expiratory Pressures
- If the MEP is less than 40cmH2O, they need a tube.
- As well as demonstrating respiratory and abdominal muscle weakness, this finding also suggests that the patient will be unable to generate enough pressure to cough effectively.
Peak Expiratory Flow
- A PEF rate less than 250 L/min seems to be associated with a need for mechanical ventilation
- Like the MEP, it is an indirect suggestion that the ability to cough has become impaired.
- There is a distinct user friendliness advantage with the peak flow measurements. Whereas spirometry and MIP/MEP measurements are hard to organise, the peak flow meter is widely available, and any shaved ape could be trained to use it.
An excellent article exists to fill this section, and I will only touch on a few of the issues they have detailed recommendations for:
Why do we intubate these people?
- They are too weak to support a satisfactory minute volume
- They are too weak to cough
- Their airway protection is lost when bulbar cranial nerves become involved
When do we offer them a tracheostomy?
- Late, is the short answer.
- If the pulmonary function tests fail to improve with treatment and two weeks of intubation has passed without change, a tracheostomy should be offered.
- Patients showing subtle improvement might be able to wait for another week.
- Corticosteroids are counterproductive.
- Plasmapheresis works: 4 exchanges of 1-2 plasma volumes, over 1-2 weeks.
Plasma exchange for Guillain-Barre syndrome aims to clear the aetiological autoantibody from the bloodstream. In essence, we say "we have no idea which antibody is causing the demyelination, so we will get rid of all of them". The evidence seems to support a 5-treatment regimen; it seems that six treatments are no better than four. Because there is no missing proteins to replace, the exchanged plasma can be FFP or albumin - it does not seem to matter to the resolution of disease. However, because FFP has a slightly higher risk of transfusion reactions, so in general albumin is the recommended replacement solution, unless there are specific reasons to replace blood proteins.
- IV immunoglobulin is at least as effective as plasmapheresis. Dose is 2g/kg. The college answer to Question 20 from the first paper of 2016 mentions a Cochrane review, probably referring to Hughes et al (2014) who demonstrated that in severe disease IVIG within the first 2 weeks "hastens recovery as much as plasma exchange".