Investigations
1st investigations to order
nerve conduction studies
Test
Interpretation of electrophysiology can be difficult, especially in early stages. However, clear electrophysiological evidence of demyelinating polyneuropathy is useful for outcome prediction.[112][140]
Retrospective data indicate that a single neurophysiological examination may be diagnostically useful, provided that accurate neurophysiological criteria are employed.[114][115] Serial electrophysiology studies may be unhelpful.[115] However, a second examination (although not always practical) is recommended in patients showing no clear demyelinating features, low amplitude distal compound muscle action potentials, or conduction block without temporal dispersion.[116] Given the dynamic nature of the disease, a second study may be of benefit in determining the subtype of GBS.[116]
Result
prolonged distal and F-wave latencies and reduced conduction velocities; H reflex prolonged or absent
lumbar puncture
Test
Classic finding is elevated cerebrospinal fluid (CSF) protein with normal cell count (albuminocytological dissociation).[11] However, CSF protein may be normal during the first 2 weeks of the illness, and the extent of albuminocytological dissociation may vary in different populations and with different GBS variants.[5][89][11][117]
Extremely high protein levels (10 g/L [1000 mg/dL]) are associated with development of high intracranial pressure and papilloedema.
Cell counts are typically <5 cells/mm³. However, up to 15% of patients with GBS may have mild pleocytosis of 5 to 50 cells/mm³.[89]
How to perform a diagnostic lumbar puncture in adults. Includes a discussion of patient positioning, choice of needle, and measurement of opening and closing pressure.
Result
elevated CSF protein, normal/slightly high lymphocytes (<50 cells/mm³)
LFTs
Test
Hepatic aminotransferases may be elevated during the first few days, and often rapidly normalise by 1 to 2 weeks.[132] Elevation of hepatic enzymes is associated with more severe disease.[133] The cause is unclear. Epstein-Barr virus and cytomegalovirus infection have been suggested, but serological markers are often negative.[132]
Result
elevated aspartate aminotransferase and alanine aminotransferase as high as 500 U/L; bilirubin may be transiently elevated but rarely high enough to cause jaundice
spirometry
Test
Should be carried out at 6-hour intervals initially at the bedside. Intensive care unit monitoring and elective intubation should be considered if any of the following is present: vital capacity <20 mL/kg (odds ratio 15.0); maximal inspiratory pressure worse than -30 cmH₂O; maximal expiratory pressure <40 cmH₂O; or reduction of 30% or more of vital capacity, maximal inspiratory pressure, or maximal expiratory pressure.[125]
How to insert a tracheal tube in an adult using a laryngoscope.
How to use bag-valve-mask apparatus to deliver ventilatory support to adults. Video demonstrates the two-person technique.
Result
may show reduced vital capacity, maximal inspiratory pressure, or maximal expiratory pressure
Investigations to consider
anti-ganglioside antibody
Test
The presence of subtype-specific anti-ganglioside antibodies may be useful when the diagnosis remains unclear despite clinical examination, cerebrospinal fluid analysis, and electrodiagnostic tests.[108][110][111] However, a negative result does not rule out GBS.[11]
If clinical features suggest a less common variant, particularly Miller-Fisher syndrome (MFS) or the pharyngeal-cervical-brachial variant, testing for the anti-GQ1b and anti-GT1a, respectively, may have some diagnostic utility. Anti-GQ1b antibody is found in up to 90% of patients with MFS.[131]
Result
MFS: GQ1b, GT1a GQ1b; MFS/GBS overlap syndrome: GQ1b, GM1, GM1a, GD1a, GalNac-GD1a; pharyngeal-cervical-brachial variant, GT1a; acute motor-sensory axonal neuropathy: GM1, GM1b, GD1a; acute motor axonal neuropathy: GM1, GM1a, GD1a, GalNac-GD1a; acute inflammatory demyelinating polyradiculoneuropathy: antibodies unknown
serology
Test
An increase in titres for infectious agents including cytomegalovirus (CMV), Epstein-Barr virus (EBV), Mycoplasma, H influenzae, and C jejuni may help in establishing aetiology for epidemiological purposes but is of limited clinical use. Some data suggest that positive serological markers for C jejuni are associated with worse prognostic outcome.[30][130]
Result
presence of Campylobacter jejuni, CMV, EBV, Mycoplasma pneumoniae, or Haemophilus influenzae
stool culture
Test
Testing for C jejuni may be considered if there is an antecedent history of diarrhoea or if the patient has been in regions where acute motor axonal neuropathy is prevalent.
Result
presence of Campylobacter jejuni or poliovirus (pure motor syndrome)
HIV antibodies
Test
Indicated if the patient is at high risk of HIV or if cerebrospinal fluid lymphocytic pleocytosis is detected (>10 cells/mm³).
Result
positive in HIV infection
spinal MRI
Test
Sensitive but non-specific.
Enhancement of the cauda equina nerve roots with gadolinium on lumbosacral MRI was found to be 83% sensitive for acute GBS and was present in 95% of typical cases.[144]
May be useful when diagnosis is unclear and electrophysiological abnormalities are equivocal. Can exclude disease processes involving the spinal cord (i.e., epidural abscess, transverse myelitis, spinal stenosis, spinal cord stroke, or tumour).
Result
may show enhancement of cauda equina nerve roots with gadolinium
Borrelia burgdorferi serology
Test
Should be performed early to aid exclusion of other causes.
Result
positive in Lyme disease
cerebrospinal fluid (CSF) meningococcal polymerase chain reaction
Test
Should be performed early to aid exclusion of other causes.
Result
positive in meningococcal meningitis
CSF cytology
Test
Should be performed early to aid exclusion of other causes.
Result
positive in carcinomatous meningitis
CSF angiotensin-converting enzyme
Test
Should be performed early to aid exclusion of other causes.
Result
positive in sarcoidosis
chest x-ray
Test
Should be performed early to aid exclusion of other causes.
Result
bilateral hilar lymphadenopathy in sarcoidosis
CSF VDRL
Test
Should be performed early to aid exclusion of other causes.
Result
positive in neurosyphilis
CSF West Nile polymerase chain reaction
Test
Should be performed early to aid exclusion of other causes.
Result
positive in West Nile virus infection
Emerging tests
ultrasound imaging of peripheral nerves
Test
An emerging technique that may help to diagnose inflammatory neuropathies, including GBS.[145] Serial nerve ultrasound studies could be useful for demonstrating nerve recovery in GBS.[146] Currently this is only available in a research setting.
Result
morphological alterations of the nerves may be visible, e.g., enlargement of cross-sectional area
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