Differential Diagnosis for Ocular Diplopia, Ptosis, Generalized Weakness, and Fluctuating Symptoms

• Single Most Likely Diagnosis

  • Myasthenia Gravis: The patient's symptoms of ocular diplopia, ptosis, generalized weakness, and fluctuating symptoms, along with a positive family history and specific electrophysiological findings (reduced CMAP worsened with Edrophonium test and decremental response on RNS at 2 Hz), are highly suggestive of Myasthenia Gravis. The Edrophonium test, in particular, is a diagnostic tool often used to confirm Myasthenia Gravis due to its ability to temporarily improve muscle strength in affected individuals.

• Other Likely Diagnoses

  • Lambert-Eaton Myasthenic Syndrome (B): Although less likely given the specific response to the Edrophonium test and the pattern of symptom fluctuation, Lambert-Eaton Myasthenic Syndrome could be considered due to its presentation of weakness and fatigue. However, it typically shows an incremental response to rapid nerve stimulation, which contrasts with the decremental response seen in this patient.
  • Congenital Myasthenic Syndromes (CMS): Given the positive family history, CMS could be a consideration. However, the specific pattern of inheritance and the age of onset would need to be further evaluated to distinguish it from acquired Myasthenia Gravis.

• Do Not Miss Diagnoses

  • Botulism: Although rare, botulism can present with similar symptoms, including diplopia, ptosis, and generalized weakness. It is crucial to consider this diagnosis due to its potential for severe outcomes if not promptly treated.
  • Tick-Borne Illnesses (e.g., Tick Paralysis): In endemic areas, tick paralysis can cause ascending paralysis and should be considered, especially if there's a history of tick exposure.

• Rare Diagnoses

  • Slow Channel CMS (A): A subtype of Congenital Myasthenic Syndrome, slow channel CMS is characterized by a prolonged opening of the acetylcholine receptor channel. It is rare and typically presents in early childhood, making it less likely in this scenario without more specific details on age of onset and progression.
  • End Plate Acetylcholinesterase (AChE) Deficiency (C): Another rare form of CMS, AChE deficiency leads to prolonged neuromuscular transmission due to the lack of acetylcholinesterase at the neuromuscular junction. It is a congenital condition and would be an unlikely diagnosis without a clear congenital or early childhood onset pattern.