A 28-year-old farmer is brought to the emergency department 2 hours after accidental exposure to an organophosphate pesticide. On examination, he has profuse salivation, bronchospasm, miosis, and bradycardia. His colleague, exposed to the same pesticide but presenting 6 hours later, shows similar muscarinic signs but additionally has muscle fasciculations and flaccid paralysis. Which feature best distinguishes the later presentation from the earlier one?