Differential Diagnosis of Myasthenia Gravis

The differential diagnosis for myasthenia gravis (MG) includes a range of conditions that can mimic its symptoms, which primarily involve muscle weakness and fatigue. Here's a categorized list of potential diagnoses:

• Single Most Likely Diagnosis

  • Lambert-Eaton Myasthenic Syndrome (LEMS): This condition is often considered the single most likely diagnosis to be confused with myasthenia gravis due to its similar presentation of muscle weakness. However, LEMS typically involves more proximal muscle weakness and can be associated with autonomic dysfunction and small cell lung cancer.

• Other Likely Diagnoses

  • Congenital Myasthenic Syndromes: These are a group of rare genetic disorders that affect the neuromuscular junction, leading to symptoms similar to MG but typically presenting at birth or in early childhood.
  • Botulism: This condition, caused by the toxin produced by Clostridium botulinum, can lead to muscle weakness, drooping eyelids, and difficulty swallowing, mimicking some symptoms of MG.
  • Hyperthyroidism: Although not directly affecting the neuromuscular junction, hyperthyroidism can cause muscle weakness, among other symptoms, which might be confused with MG in some cases.

• Do Not Miss Diagnoses

  • Guillain-Barré Syndrome: An acute autoimmune disorder that can lead to rapid-onset muscle weakness and paralysis. It's crucial to distinguish this from MG due to its potential for respiratory failure and the need for immediate treatment.
  • Tick Paralysis: Caused by a toxin in the saliva of certain ticks, this condition can lead to ascending paralysis and, if not recognized and treated promptly, can be fatal.

• Rare Diagnoses

  • Mitochondrial Myopathies: A group of disorders affecting the mitochondria, which can lead to muscle weakness among a myriad of other symptoms.
  • Inclusion Body Myositis: The most common acquired myopathy in adults over 50, characterized by progressive muscle weakness and wasting, particularly affecting the distal muscles.
  • Neuromuscular Junction Disorders due to Toxins or Drugs: Certain medications (like aminoglycosides) and toxins can impair neuromuscular transmission, leading to symptoms that might resemble MG.