What muscle groups are involved in Guillain-Barré Syndrome (GBS)?

Muscle Groups Involved in Guillain-Barré Syndrome (GBS)

In Guillain-Barré Syndrome (GBS), muscle weakness typically begins in the lower limbs and ascends to involve the upper limbs and cranial muscles, with lower extremity weakness being predominantly proximal and upper extremity weakness predominantly distal. 1, 2

Pattern of Muscle Involvement

• Classic GBS presents with rapidly progressive bilateral weakness that starts in the lower limbs (80% of cases) and ascends to the arms and cranial muscles, accompanied by decreased or absent reflexes 1, 3
• Lower extremity weakness is predominantly proximal in 68% of patients 2
• Upper extremity weakness is predominantly distal in 73% of patients 2
• Four-limb weakness is the most common presentation at the time of diagnosis (96% of cases) 2
• Trunk muscles are involved in approximately 34% of patients, which is unusual compared to other polyneuropathies 2

Cranial and Respiratory Muscle Involvement

• Cranial nerve involvement occurs in 72% of patients with GBS, often affecting muscles of facial expression, eye movement, swallowing, and speech 2
• Respiratory muscle weakness requiring mechanical ventilation develops in approximately 20-25% of patients, representing a life-threatening complication 1, 4
• Bulbar muscles can be affected, particularly in variants like pharyngeal-cervical-brachial weakness, leading to difficulty swallowing and speaking 1

Clinical Variants and Their Muscle Involvement Patterns

• Classic sensorimotor GBS: Affects both sensory and motor functions with widespread muscle involvement 1
• Pure motor variant: Weakness without sensory signs, affecting 5-70% of cases depending on geographical region 1
• Paraparetic variant: Weakness restricted to the legs (5-10% of cases) 1
• Pharyngeal-cervical-brachial variant: Selective weakness of pharyngeal, cervical and brachial muscles without lower limb involvement (less than 5% of cases) 1
• Miller Fisher syndrome: Characterized by ophthalmoplegia (eye muscle weakness), ataxia and areflexia (5-25% of cases) 1

Progression of Muscle Weakness

• The ascending pattern is most common (78% of cases), but contiguous parts of the body are not always successively involved 2
• Most patients reach maximum disability within 2 weeks of symptom onset 1, 3
• Muscle weakness can progress rapidly, with some patients developing complete paralysis within days 1
• After the progressive phase, patients reach a plateau phase lasting from days to weeks or months before recovery begins 1

Pathophysiological Basis of Muscle Involvement

• GBS is primarily a peripheral nerve disorder affecting the peripheral nervous system through immune-mediated mechanisms 1, 5
• In acute inflammatory demyelinating polyneuropathy (AIDP), the most common form in Europe and North America, immune reactions target Schwann cells or myelin 5
• In acute motor axonal neuropathy (AMAN), more common in East Asia, the immune response targets gangliosides on motor axolemma 5
• Early muscle pathology in GBS can include necrosis, phagocytosis, and ultrastructural changes such as filamentous bodies and mitochondrial aggregates 6

Clinical Implications for Assessment

• Careful examination of the pattern of muscle weakness is essential for diagnosis, especially in early stages of the disease 2
• Monitoring respiratory function is critical in all patients, as respiratory failure can occur without symptoms of dyspnea 1
• The pattern of muscle weakness (ascending, predominantly proximal in lower limbs, predominantly distal in upper limbs) helps distinguish GBS from other causes of acute flaccid paralysis 2, 7