What test is primarily used to investigate Guillain-Barre syndrome?

Lumbar puncture (LP) is the primary test used to investigate Guillain-Barre syndrome (GBS) due to its ability to assess the cerebrospinal fluid (CSF). In patients with GBS, the lumbar puncture typically reveals albuminocytologic dissociation, which is characterized by a high level of protein in the CSF with a normal white blood cell count. This finding is crucial in making a diagnosis because it distinguishes GBS from other conditions that may present with similar symptoms.

While other tests like CT scans, MRIs, and blood tests can provide valuable information in the diagnostic process for various neurological conditions, they do not specifically help in confirming GBS. For instance, imaging studies may rule out structural abnormalities, but they do not provide the same direct insight into the inflammation and immune response characteristic of Guillain-Barre syndrome as a lumbar puncture does. Blood tests can detect antibodies or signs of infection but are not definitive for GBS. Therefore, lumbar puncture is considered the gold standard for diagnosing this condition.