Which of the following is not a common symptom of Myasthenia gravis (MG): ptosis, dysphagia, proximal limb weakness, or loss of sensation with weakened or absent reflexes?

Myasthenia Gravis: Clinical Features and Distinguishing Characteristics

The incorrect statement about Myasthenia gravis is option D: "Loss of sensation with weakened or absent reflexes" as sensory function remains intact in MG, and reflexes are typically normal.

Clinical Presentation of Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune disorder affecting the neuromuscular junction, characterized by fluctuating muscle weakness that worsens with activity and improves with rest. The key clinical features include:

Ocular Symptoms

• Ptosis occurs in up to 40% of patients initially and eventually in 80% with disease progression 1
• Diplopia and other extraocular movement abnormalities are common
• Ocular symptoms may be isolated (MGFA class 1) or part of generalized disease 1

Bulbar Symptoms

• Dysphagia is a common manifestation 1
• Dysarthria and facial muscle weakness may occur
• Bulbar symptoms can progress to respiratory compromise in severe cases

Motor Symptoms

• Proximal limb weakness with upper limbs more affected than lower limbs 1, 2
• Weakness is typically symmetrical but can be asymmetrical
• Fatigable weakness is characteristic - strength deteriorates with repeated use
• Normal deep tendon reflexes (unlike Guillain-Barré syndrome) 1, 3

Sensory Function

• Sensory function remains intact throughout the disease course 4
• No sensory loss occurs in MG, which is a pure motor disorder 5
• Pain may be present but is not associated with sensory deficits

Distinguishing MG from Other Neuromuscular Disorders

MG vs. Guillain-Barré Syndrome (GBS)

• GBS presents with progressive weakness often with sensory symptoms and decreased/absent reflexes 1, 3
• GBS typically has an ascending pattern of weakness (legs to arms) 1
• GBS involves sensory loss and weakened/absent reflexes 1, 3
• MG has normal sensation and typically normal reflexes 4

Key Diagnostic Features of MG

• Fatigable weakness that improves with rest 5
• Positive response to acetylcholinesterase inhibitors (e.g., edrophonium test) 5
• Presence of autoantibodies (AChR in 80-85%, MuSK in 5-8%, LRP4 in <1%) 2
• Characteristic findings on electrophysiological testing (decremental response on repetitive nerve stimulation) 2

Pathophysiology

MG is caused by autoantibodies targeting components of the neuromuscular junction:

• Most commonly against acetylcholine receptors (AChR) 6
• Can also target muscle-specific kinase (MuSK) or low-density lipoprotein receptor-related protein 4 (LRP4) 6
• These antibodies reduce available acetylcholine receptors and disrupt neuromuscular transmission 5
• Unlike neuropathies, the sensory pathways remain intact 4

Management Considerations

• Acetylcholinesterase inhibitors (pyridostigmine) for symptomatic treatment 1
• Immunosuppressive therapy with corticosteroids and steroid-sparing agents 2
• Thymectomy in appropriate patients 4
• IVIG or plasmapheresis for myasthenic crisis 7
• Avoidance of medications that can exacerbate MG (β-blockers, fluoroquinolones, aminoglycosides, macrolides) 1

Clinical Pearls

• Respiratory function should be closely monitored as respiratory failure can occur in myasthenic crisis 7
• Infections are common triggers for exacerbations 7
• During crisis, acetylcholinesterase inhibitors should be temporarily discontinued 7
• Normal sensation with fatigable weakness strongly suggests MG rather than a neuropathy 4