Guillain–Barré Syndrome (GBS)
Guillain–Barré syndrome is an acute immune-mediated disorder of the peripheral nervous system that causes rapidly progressive weakness and sensory disturbance. It most commonly follows a recent infection and is characterised by ascending paralysis and reduced or absent reflexes. Unlike central nervous system conditions, Guillain–Barré syndrome affects peripheral nerves, leaving cognition and consciousness intact. Guillain–Barré syndrome is a neurological emergency due to its potential for rapid progression, respiratory compromise, and autonomic instability. Understanding the pathophysiology is essential for recognising early deterioration and anticipating life-threatening complications.
What You Need to Know
Guillain–Barré syndrome is an acute immune-mediated disorder of the peripheral nervous system in which the body’s immune response mistakenly targets components of peripheral nerves, most commonly the myelin sheath. Myelin acts as an insulating layer that allows rapid saltatory conduction, meaning electrical impulses jump efficiently between nodes along the nerve. When myelin is damaged, action potential transmission slows or fails, disrupting communication between the spinal cord and peripheral muscles.
This disruption leads to rapidly developing weakness and sensory disturbance. Because the pathology affects peripheral nerves rather than the brain or spinal cord itself, weakness is flaccid rather than spastic and typically symmetrical. Symptoms often begin in the lower limbs and progress proximally in an ascending pattern, reflecting the widespread involvement of peripheral nerve roots and longer nerves.
At an overview level, Guillain–Barré syndrome is characterised by:
Immune-mediated injury to peripheral nerve myelin or axons
Impaired nerve conduction causing weakness and sensory disturbance
Rapid symptom progression over days to weeks rather than gradual decline
Motor impairment usually predominates, producing difficulty walking, climbing stairs, or lifting the arms as weakness ascends. Sensory symptoms such as paraesthesia or numbness may be present but are often less prominent. The acute and rapidly progressive nature of Guillain–Barré syndrome distinguishes it from chronic neuromuscular disorders and reflects sudden immune injury rather than long-term neurodegeneration.
Beyond the Basics
Immune-mediated demyelination
Peripheral nerve myelin is essential for rapid and efficient electrical conduction. Myelin acts as an insulating layer that allows impulses to travel by saltatory conduction, where the electrical signal jumps between nodes along the nerve. In Guillain–Barré syndrome, antibodies and activated immune cells mistakenly target myelin components, leading to segmental demyelination, meaning sections of myelin are stripped away along the nerve fibre.
Loss of myelin slows conduction velocity and can produce conduction block, where action potentials fail to propagate past the damaged segment. This explains the abrupt onset of weakness and loss of deep tendon reflexes, as motor signals are unable to reach muscles effectively despite intact motor neurons.
Axonal involvement and disease severity
Not all forms of Guillain–Barré syndrome are limited to myelin injury. In some variants, the immune response targets the axon itself, which is the long projection of the neuron that carries electrical signals. Axonal damage disrupts signal transmission more profoundly and is associated with greater weakness and slower recovery.
Recovery differs because remyelination, the process of restoring myelin, can occur relatively quickly once inflammation settles. Axonal regeneration, by contrast, requires regrowth of nerve fibres over long distances, which is slow and often incomplete. This difference accounts for the wide range of severity, recovery time, and long-term outcome seen across Guillain–Barré syndrome presentations.
Autonomic nervous system dysfunction
Peripheral nerves include autonomic fibres that regulate involuntary functions such as heart rate, blood pressure, gastrointestinal motility, and sweating. Immune-mediated injury to these fibres disrupts autonomic control, producing instability rather than predictable dysfunction.
Autonomic involvement may cause fluctuations in heart rate and blood pressure, cardiac arrhythmias, impaired temperature regulation, or gastrointestinal dysmotility. These changes can occur independently of limb weakness severity and may evolve rapidly. Because autonomic instability can be sudden and life-threatening, it represents a major source of morbidity in Guillain–Barré syndrome even when motor impairment appears relatively mild.
Clinical Connections
Ascending weakness in Guillain–Barré syndrome develops as motor nerve conduction progressively fails. Early symptoms often include difficulty walking, climbing stairs, or rising from a seated position, followed by proximal spread to the thighs, trunk, and upper limbs. Loss of deep tendon reflexes is a characteristic clinical feature and helps differentiate peripheral nerve involvement from central causes of weakness, where reflexes are typically preserved or increased. Sensory function is often relatively spared, meaning individuals remain fully aware of their worsening mobility, which can be highly distressing.
Several clinical features signal progression and increasing risk:
Worsening symmetrical weakness moving proximally over hours to days
Reduced or absent reflexes indicating peripheral nerve conduction failure
Preserved cognition despite severe physical impairment
As weakness ascends, involvement of respiratory muscles becomes a critical concern. Impaired function of the diaphragm and intercostal muscles can lead to reduced vital capacity and respiratory failure, sometimes developing rapidly and without prominent warning symptoms. Autonomic involvement adds further complexity, with fluctuations in heart rate and blood pressure increasing the risk of sudden cardiovascular instability, even in individuals who appear otherwise stable.
The peripheral nature of the pathology means higher cortical function remains intact throughout the illness. Awareness, comprehension, and insight are preserved, even when severe paralysis is present. Clear communication, frequent reassessment, and anticipation of escalating respiratory or cardiovascular support are therefore central to safe care, particularly during the early and most dynamic phase of the condition.
Concept Check
Why does Guillain–Barré syndrome cause flaccid rather than spastic weakness?
How does demyelination impair peripheral nerve conduction?
Why does weakness typically ascend from the lower limbs in Guillain–Barré syndrome?
How can autonomic nervous system involvement affect clinical stability?
Why is respiratory monitoring a priority in patients with Guillain–Barré syndrome?