Differential Diagnosis

• Single most likely diagnosis
  • Botulism: The patient's symptoms of bilateral eyelid weakness, diplopia, dysarthric speech, weak gag reflex, and descending weakness (starting with the cranial nerves and progressing to the upper extremities) are classic for botulism. The recent history of intravenous fentanyl use increases the risk for wound botulism, which is associated with intravenous drug use.
• Other Likely diagnoses
  • Tick paralysis: This condition can cause ascending weakness, but it can also present with cranial nerve involvement and can mimic botulism. However, the lack of a reported tick bite and the pattern of weakness make it less likely.
  • Miller-Fisher syndrome: A variant of Guillain-Barré syndrome, it typically presents with ataxia, areflexia, and ophthalmoplegia. While it could be considered, the patient's reflexes are 2+ throughout, which does not strongly support this diagnosis.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Hypermagnesemia: Although less likely given the clinical presentation, hypermagnesemia can cause significant weakness, respiratory depression, and cardiac arrest. It's crucial to consider and rule out, especially in the context of potential substance use.
  • Hypocalcemia: Severe hypocalcemia can lead to muscle weakness, but it typically presents with tetany, cramps, and Chvostek's or Trousseau's signs, which are not mentioned in the case.
• Rare diagnoses
  • Other rare conditions such as myasthenia gravis or Lambert-Eaton myasthenic syndrome could be considered but are less likely given the acute onset and specific pattern of weakness. These conditions typically have a more chronic course and distinct clinical features not fully aligning with the patient's presentation.