Guillain-Barre Syndrome Workup

Updated: Jan 14, 2022
  • Author: Michael T Andary, MD, MS; Chief Editor: Milton J Klein, DO, MBA  more...
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Approach Considerations

Guillain-Barré syndrome (GBS) is generally diagnosed on clinical grounds. Basic laboratory studies, such as complete blood counts (CBCs) and metabolic panels, are normal and of limited value in the workup. They are often ordered, however, to exclude other diagnoses and to better assess functional status and prognosis. The ordering of specific tests should be guided by the patient's history and presentation.

Electromyography (EMG) and nerve conduction studies (NCS) can be very helpful in the diagnosis. Abnormalities in NCS that are consistent with demyelination are sensitive and represent specific findings for classic GBS. Delayed distal latencies, slowed nerve conduction velocities, temporal dispersion of waveforms, conduction block, prolonged or absent F waves, and prolonged or absent H-reflexes are all findings that support demyelination. Needle EMG may be normal in acute nerve lesions, and it may take 3-4 weeks for fibrillation to develop. In the acute phase, the only needle EMG abnormality may be abnormal motor recruitment, with decreased recruitment and rapid firing motor units in weak muscles. Unfortunately, electrodiagnostic studies can be completely normal in acute GBS and a normal study does not rule GBS. [108, 109]

Frequent evaluations of pulmonary function parameters should be performed at bedside to monitor respiratory status and the need for ventilatory assistance.

Lumbar puncture for cerebrospinal fluid (CSF) studies is recommended. During the acute phase of GBS, characteristic findings on CSF analysis include albuminocytologic dissociation, which is an elevation in CSF protein (>0.55 g/L) without an elevation in white blood cells. The increase in CSF protein is thought to reflect the widespread inflammation of the nerve roots.

Imaging studies, such as magnetic resonance imaging (MRI) and computed tomography (CT) scanning of the spine, may be more helpful in excluding other diagnoses, such as mechanical causes of myelopathy, than in assisting in the diagnosis of GBS.


Peripheral Neuropathy Workup

A basic peripheral neuropathy workup is recommended in cases in which the diagnosis is uncertain. These studies may include the following:

  • Thyroid panel

  • Rheumatology profiles

  • Vitamin B-12

  • Folic acid

  • Hemoglobin A1C

  • Erythrocyte sedimentation rate (ESR)

  • Rapid protein reagent

  • Immunoelectrophoresis of serum protein

  • Tests for heavy metals


Biochemical Screening

Biochemical screening includes the following studies:

  • Electrolyte levels

  • Liver function tests (LFTs)

  • Creatine phosphokinase (CPK) level

  • ESR

The following should be considered:

  • LFT results are elevated in as many as one third of patients

  • CPK and ESR may be elevated with myopathies or systemic inflammatory conditions

  • A stool culture for C jejuni and a pregnancy test are also indicated

  • The syndrome of inappropriate antidiuretic hormone (SIADH) may occur


Serologic Studies

Serologic studies are of limited value in the diagnosis of GBS. Assays for antibodies to the following infectious agents may be considered:

  • C jejuni

  • Cytomegalovirus (CMV)

  • Epstein-Barr virus (EBV)

  • Herpes simplex virus (HSV)

  • HIV

  • Mycoplasma pneumoniae

An increase in titers for infectious agents, such as CMV, EBV, or Mycoplasma, may help in establishing etiology for epidemiologic purposes. HIV has been reported to precede GBS, and serology should be tested in high-risk patients to establish possible infection with this agent.

Serum autoantibodies

Serum autoantibodies are not measured routinely in the workup of GBS, but results may be helpful in patients with a questionable diagnosis or a variant of GBS. Antibodies to glycolipids are observed in the sera of 60-70% of patients with GBS during the acute phase, with gangliosides being the major target antigens. [110]

Specific antibodies found in association with GBS include the following:

  • Antibodies to GM1: Frequently found in the sera of patients with the acute motor axonal neuropathy (AMAN) or acute demyelinating polyradiculoneuropathy (AIDP) variants of GBS

  • Anti-GM1 antibodies: Elevated titers are closely associated antecedent C jejuni infections

  • Anti-GQ1b antibodies: Found in patients with GBS with ophthalmoplegia, including patients with the Miller-Fisher variant

Other antibodies to different major and minor gangliosides also have been found in GBS patients.


Nerve Conduction Studies

Nerve conduction studies (NCS) can be very helpful in the diagnostic workup and prognostic evaluation of patients with suspected GBS. Abnormalities in NCS that are consistent with demyelination are sensitive and represent specific findings for classic GBS. [108]

Signs of demyelination can include the following:

  • Nerve conduction slowing

  • Prolongation of the distal latencies

  • Prolongation or absence of the F-waves [1, 2]

  • Conduction block or dispersion of responses: Evidence frequently demonstrated at sites of natural nerve compression.

Changes on NCS should be present in at least 2 nerves in regions that are not typical for those associated with compressive mononeuropathies (preferentially in anatomically distinct areas, such as an arm and a leg or a limb and the face).

Although NCS results classically show a picture of demyelinating neuropathy in most patients, axonal neuropathy and inexcitable results are found in certain subgroups. The inexcitable studies may represent either axonopathy or severe demyelination with distal conduction block.

Other characteristics of GBS include the following:

  • Nerve motor action potentials: May be decreased, but this is technically difficult to determine until the abnormality is severe; the extent of decreased action potentials correlates with prognosis

  • Compound muscle action potential (CMAP): Amplitude may be decreased

  • Sensory abnormalities: Exhibited by most patients, but these findings are much less marked than they are in motor nerves; sural sparing is a common finding in patients with clinical sensory deficits

  • Abnormal (delayed, small, or absent) H-reflex: May be noted

The needle examination is of limited value in GBS. Reduced motor unit recruitment and absent denervation help to support the suggestion of a demyelinating mechanism, although the same changes can be observed in early axonal damage with pending wallerian degeneration. In severe cases, denervation changes may be observed later in the disease course.

In the axonal variant of the disease, absent or markedly reduced distal CMAP is observed on NCS. On needle examination, profuse and early denervation potentials (fibrillations) also support the conclusion that there has been axonal injury.

In some cases, neurophysiologic testing is normal in patients with GBS, especially in the first 1-2 weeks of the disease. This is believed to be due to the location of demyelinating lesions in proximal sites not amenable to study. [109]  For example, a retrospective, single-center study by Luigetti et al found that in 37% of patients with GBS who underwent an early nerve conduction study (ie, 4 days or less after disease onset), neurophysiologic results were normal. As a result, the investigators, whose study involved 71 patients with GBS, suggested that extensive neurophysiologic assessment should be performed in patients who are in the early phases of GBS. [111]


Pulmonary Function Tests

Maximal inspiratory pressures and vital capacities are measurements of neuromuscular respiratory function and predict diaphragmatic strength. Maximal expiratory pressures also reflect abdominal muscle strength. Frequent evaluations of these parameters should be performed at bedside to monitor respiratory status and the need for ventilatory assistance.

Forced vital capacity (FVC) is very helpful in guiding disposition and therapy. [86] Patients with an FVC of less than 15-20 mL/kg, maximum inspiratory pressure of less than 30 cm water, or a maximum expiratory pressure of less than 40 cm water generally progress to require prophylactic intubation and mechanical ventilation. Respiratory assistance should also be considered when there is a decrease in oxygen saturation (arterial partial pressure of oxygen [PO2] < 70 mm Hg).

Negative inspiratory force (NIF) is a relatively easy bedside test to measure respiratory muscle function and can easily be performed every half hour to hour in difficult cases. Normal is usually greater than 60 cm water. If the NIF is dropping or nears 20 cm water, respiratory support needs to be available.


Lumbar Puncture

Most, but not all, patients with GBS have an elevated CSF protein level (>400 mg/L), with normal CSF cell counts. Elevated or rising protein levels on serial lumbar punctures and 10 or fewer mononuclear cells/mm3 strongly support the diagnosis.

A normal CSF protein level does not rule out GBS, however, as the level may remain normal in 10% of patients. CSF protein may not rise until 1-2 weeks after the onset of weakness.

Normal CSF cell counts may not be a feature of GBS in HIV-infected patients. CSF pleocytosis is well recognized in HIV-associated GBS.


Magnetic Resonance Imaging

MRI is sensitive, but nonspecific, for diagnosis. However, it can reveal nerve root enhancement and may be an effective diagnostic adjunct. [112, 113]

Spinal nerve root enhancement with gadolinium is a nonspecific feature seen in inflammatory conditions and is caused by disruption of the blood-nerve barrier. Selective anterior nerve root enhancement appears to be strongly suggestive of GBS, [114] with the cauda equina nerve roots being enhanced in 83% of patients.


Other Studies

Muscle biopsy may help to distinguish GBS from a primary myopathy in unclear cases. Many different abnormalities may be seen on electrocardiography, including second- and third-degree atrioventricular (AV) block, T-wave abnormalities, ST depression, QRS widening, and various rhythm disturbances.



Lymphocyte and macrophage infiltration is observed on microscopic examination of peripheral nerves, with macrophage influx believed to be responsible for the multifocal demyelination seen in GBS. A variable degree of wallerian degeneration also can be observed with severe inflammatory changes.

Cellular infiltrates are scattered throughout the cranial nerves, nerve roots, dorsal root ganglions, and peripheral nerves.