GBS, or Guillain-Barré syndrome (pronounced ghee-YAN bah-RAY), is a rare autoimmune disorder in which your immune system attacks the nerves outside your brain and spinal cord. It affects roughly 1 in 100,000 people per year and typically starts with tingling in the feet and legs before progressing to muscle weakness that moves upward through the body. Most people recover fully, but GBS can become a medical emergency when it affects breathing muscles or heart function.
How GBS Damages Your Nerves
Your peripheral nerves carry signals between your brain and the rest of your body. Each nerve has a central core (the axon) that transmits electrical signals, wrapped in an insulating layer called myelin that helps those signals travel quickly over long distances. In GBS, your immune system produces antibodies that mistakenly target this nerve tissue instead of the infection it was originally fighting.
In the most common form, the immune system strips away the myelin insulation, slowing or blocking nerve signals. In less common forms, the attack goes deeper and damages the axon itself. Either way, the result is the same: signals from your brain struggle to reach your muscles and skin, causing weakness, numbness, and sometimes pain.
The underlying problem is a case of mistaken identity. Certain proteins on the surface of bacteria or viruses look similar enough to proteins on your nerve cells that the immune system can’t tell them apart. After fighting off an infection, the antibodies continue their attack, this time against healthy nerves.
What Triggers It
Most GBS cases follow an infection that occurred one to six weeks earlier. Campylobacter, a common cause of food poisoning, is the single most frequent trigger in the United States. At least 1 in 20 GBS patients had a recent Campylobacter infection, and some studies put that number as high as 8 in 20. Still, the overall risk is low: only about 1 in every 1,000 people who get a Campylobacter infection will develop GBS.
Other known triggers include cytomegalovirus, Epstein-Barr virus (the virus behind mono), Zika virus, and influenza. In rare cases, vaccination has been linked to a small increased risk. CDC monitoring has found that when flu vaccines are associated with GBS, the increase is consistently in the range of 1 to 2 additional cases per million doses. Among COVID-19 vaccines, evidence suggested an increased risk with the J&J/Janssen vaccine but not with the Pfizer or Moderna vaccines.
Symptoms and How They Progress
GBS almost always begins the same way: a pins-and-needles sensation in the fingers and toes, followed by muscle weakness that starts in the legs and spreads upward. The weakness affects both sides of the body at the same time, which helps distinguish it from conditions like stroke. Symptoms worsen over a period of 12 hours to 4 weeks, with the greatest weakness typically arriving within the first two weeks. After that, most people hit a plateau where symptoms stop getting worse before gradually improving.
The speed of progression varies widely. Some people develop significant weakness within a day or two. Others experience a slower build over several weeks. Beyond weakness and tingling, people often report deep aching pain in the legs and back, difficulty with coordination, and trouble with everyday tasks like gripping objects or climbing stairs.
Autonomic Complications
GBS doesn’t just affect movement and sensation. About 38% of patients develop problems with their autonomic nervous system, the part that controls functions you don’t consciously think about. These complications include sudden swings in blood pressure (both dangerously high and low), abnormal heart rhythms, digestive paralysis, urinary retention, and unexplained fevers. Patients who develop these autonomic problems tend to have more severe disease overall, with a mortality rate of 6% compared to 2% for the full group of GBS patients.
Autonomic dysfunction is more common in people with widespread weakness affecting all four limbs, difficulty swallowing, or weakness in the neck muscles. These patients are also more likely to need a ventilator to breathe, which is one of the most serious complications of GBS.
How GBS Is Diagnosed
There’s no single test that confirms GBS. Doctors piece together the diagnosis from your symptoms, a physical exam, and two key tests. The first is a lumbar puncture (spinal tap), which collects a small sample of the fluid surrounding your spinal cord. In GBS, this fluid typically shows elevated protein levels (above 0.45 g/L) with a normal or near-normal white blood cell count, fewer than 50 cells per microliter. This combination, called albuminocytologic dissociation, appears in about 64% of confirmed GBS cases.
The second test is a nerve conduction study, which measures how fast electrical signals travel through your nerves. This test can also help identify which type of GBS you have, whether the damage is primarily to the myelin insulation or to the nerve fibers themselves. About 99% of GBS patients show abnormalities on nerve conduction testing, though only 59% neatly fit the criteria for a specific subtype.
Types of GBS
GBS has three major subtypes, classified by what the immune system attacks and which nerves are involved. The most common in Western countries is AIDP (acute inflammatory demyelinating polyradiculoneuropathy), where the myelin sheath is the primary target. This form tends to show higher protein levels in spinal fluid and distinctive patterns on nerve conduction studies.
The two axonal forms, AMAN and AMSAN, are more common in East Asia and Central and South America. AMAN affects only motor nerves, so sensation stays intact while muscles weaken. AMSAN damages both motor and sensory nerve fibers, causing weakness along with significant numbness. The axonal forms can progress faster and sometimes take longer to recover from, since regrowing damaged nerve fibers is a slower process than repairing myelin.
Recovery and Long-Term Outlook
The majority of people with GBS recover well. Studies suggest that within one year, 62% to 92% of patients achieve complete or near-complete recovery, regaining the ability to walk, work, and carry out daily activities. Recovery typically begins weeks to months after the plateau phase, though the pace varies considerably from person to person.
Not everyone returns to their previous baseline. Roughly 20% to 35% of hospitalized patients experience some degree of long-term disability, ranging from persistent weakness in the feet or hands to fatigue that lingers for months or years. Fatigue is one of the most commonly reported lasting effects, even among people whose strength returns to normal. Mortality across all GBS cases ranges from 1% to 18%, with the highest risk in older adults and those who need mechanical ventilation.
GBS is a one-time event for most people. Recurrence happens in a small minority, estimated at around 2% to 5%. The recovery timeline is measured in months, not days. Some people improve steadily over 6 to 12 months, while others continue making gradual gains for up to two years after the initial episode.