Guillain-Barré syndrome (GBS) is caused by an abnormal immune response in which the body’s immune system mistakenly attacks the peripheral nerves, the network of nerves outside the brain and spinal cord. This immune attack leads to inflammation and damage to the nerves, resulting in muscle weakness, numbness, and sometimes paralysis. The exact cause of why this immune system malfunction occurs is not fully understood, but it is often triggered by an infection or other immune system stimulus.
One of the most common triggers for Guillain-Barré syndrome is an infection with the bacterium *Campylobacter jejuni*, which causes gastrointestinal illness. This infection is the leading known cause that precedes GBS in many cases. Other infections that can trigger GBS include viruses such as cytomegalovirus, Epstein-Barr virus, HIV, and sometimes bacterial infections like Mycoplasma pneumoniae. These infections provoke the immune system to respond aggressively, and due to a phenomenon called molecular mimicry, the immune system confuses components of the peripheral nerves with parts of the infectious agents, leading to an unintended attack on the nerves.
Molecular mimicry is a key concept in understanding the cause of GBS. It means that the immune system creates antibodies or immune cells that target the infectious agent but also mistakenly recognize similar molecules on the nerve cells. This cross-reactivity causes the immune system to damage the myelin sheath—the protective covering of nerves—or sometimes the nerves themselves. The damage disrupts the normal transmission of nerve signals, causing the symptoms of weakness, tingling, and numbness.
Besides infections, other less common triggers have been identified. For example, some cases of GBS have been reported after surgeries, including bariatric surgery, where immune dysregulation and nutritional deficiencies may contribute to the syndrome. Vaccinations and other immune system challenges have also been occasionally linked to GBS, though these are rare and the benefits of vaccines generally outweigh the risks.
The immune attack in GBS primarily affects the peripheral nervous system, which controls muscle movement and sensation. The syndrome often begins with weakness and tingling in the feet and legs, which can spread upward to the arms and face. In severe cases, it can lead to paralysis and affect breathing muscles, requiring urgent medical care.
In summary, Guillain-Barré syndrome is caused by an autoimmune reaction triggered mainly by infections, where the immune system mistakenly attacks the peripheral nerves due to molecular mimicry. This immune-mediated nerve damage leads to the characteristic symptoms of GBS. Understanding these causes helps guide treatment approaches that focus on modulating the immune response and supporting nerve recovery.
