A 46-year-old man presents to his GP with progressive muscle weakness, starting in his feet and moving up his legs to mid-thigh, with tingling in both legs and weakness now also in his arms. The weakness is constant and does not vary throughout the day.

He is usually healthy, on no regular medications, with no unintentional weight change or smoking history. However the patient notes he did experience a diarrhoeal illness around a week before the weakness first began.


Upon examination, power is reduced bilaterally in the upper and lower limbs. Deep tendon reflexes of the lower limbs are also reduced bilaterally. Cranial nerve exam is unremarkable.


Which of the following is the most likely diagnosis?

Options:
explanation: Myasthenia gravis is also an autoimmune condition characterised by muscle weakness. However, in myasthenia gravis the muscle weakness is classically fatigable, and facial muscle and extraocular muscle involvement is common. Furthermore, it is not typically proceeded by an infectious illness. Deep tendon reflexes are typically normal or even increased in myasthenia gravis. Guillain-Barré Syndrome is therefore a more likely diagnosis.
name: Spinal cord injury
label: d
answer: no
explanation: LEMS is primarily an autoimmune disorder that affects neuromuscular junctions by inhibiting the release of acetylcholine. It is often associated with an underlying malignancy; most commonly small-cell lung cancer. The absence of red-flag symptoms such as weight loss, and no reference to respiratory symptoms, makes malignancy less likely in this case. Deep tendon reflexes are typically normal or even increased in LEMS. Guillain-Barré Syndrome is therefore a more likely diagnosis.
name: Lambert-Eaton Myasthenic Syndrome (LEMS)
label: c
answer: no
explanation: Viral myositis is inflammation of the muscles caused by a viral infection. It is often associated with significant muscle pain, tenderness and swelling, which the patient did not mention. In contrast, the primary symptom described in this case is acute muscle weakness. Hyporeflexia is also not characteristic of viral myositis. Guillain-Barré Syndrome is therefore a more likely diagnosis.
name: Viral myositis
label: e
answer: no
explanation: This is the correct answer. GBS is an autoimmune disorder characterised by demyelinating polyneuropathy, often occurring after an infection. Campylobacter is a common precipitating infection, as indicated by the diarrhoeal illness in this case. In GBS, muscle weakness typically starts in the lower limbs and may ascend to involve the upper limbs and even the respiratory muscles in severe cases. It is typically symmetrical, and weakness ascends rapidly over days to weeks. Deep tendon reflexes are often decreased or absent (areflexia or hyporeflexia), due to damage of the myelin sheath.
name: Guillain-Barré Syndrome (GBS)
label: a
answer: yes
explanation: Myasthenia gravis is also an autoimmune condition characterised by muscle weakness. However, in myasthenia gravis the muscle weakness is classically fatigable, and facial muscle and extraocular muscle involvement is common. Furthermore, it is not typically proceeded by an infectious illness. Deep tendon reflexes are typically normal or even increased in myasthenia gravis. Guillain-Barré Syndrome is therefore a more likely diagnosis.
name: Myasthenia gravis
label: b
answer: no

Correct answer: a

Guillain-Barré Syndrome (GBS)