Differential Diagnosis for a 39-year-old Man with Double Vision and Weakness

Single most likely diagnosis

• Myasthenia Gravis: This autoimmune disorder is characterized by fluctuating muscle weakness that worsens with activity and improves with rest. The patient's symptoms of ptosis (greater on one side), diffuse weakness that worsens after repetitive action, and episodes of choking while eating are classic for myasthenia gravis. The worsening of symptoms later in the day also fits this diagnosis.

Other Likely diagnoses

• Thyroid Ophthalmopathy: Although less likely given the absence of specific thyroid-related symptoms, thyroid ophthalmopathy can cause double vision and ptosis due to inflammation and swelling of the tissues around the eye. However, the diffuse weakness and worsening with repetitive action are not typical.
• Multiple Sclerosis: This condition can cause a wide range of neurological symptoms, including double vision (diplopia), weakness, and problems with coordination and balance. However, the pattern of worsening with activity and the specific combination of symptoms presented might be less typical for MS.

Do Not Miss (ddxs that may not be likely, but would be deadly if missed)

• Botulism: This rare but potentially life-threatening illness can cause double vision, difficulty swallowing (dysphagia), and muscle weakness. The episodes of choking while eating could be indicative of botulism, making it a critical diagnosis not to miss.
• Stroke or Transient Ischemic Attack (TIA): Although the patient's symptoms have been worsening over weeks, it's essential to consider the possibility of a stroke or TIA, especially given the sudden worsening over the last few days. However, the pattern of weakness and the absence of other focal neurological deficits make this less likely.

Rare diagnoses

• Lambert-Eaton Myasthenic Syndrome (LEMS): This rare autoimmune disorder can cause muscle weakness, fatigue, and autonomic dysfunction. While it shares some similarities with myasthenia gravis, LEMS typically involves more proximal muscle weakness and might have different responses to repetitive activity.
• Mitochondrial Myopathies: These are a group of disorders caused by mitochondrial dysfunction that can lead to muscle weakness, among other symptoms. However, they are rare and would typically present with a broader range of systemic symptoms and possibly a family history of similar conditions.