A 42-year-old male agricultural worker is brought to the ICU with organophosphate poisoning. At admission (2 hours post-exposure), he has pinpoint pupils, profuse salivation, bronchospasm, and muscle fasciculations. His serum acetylcholinesterase is 15% of normal. A second patient with the same exposure is evaluated 48 hours later with generalized muscle weakness, ptosis, and respiratory depression but normal pupil size and no salivation. His acetylcholinesterase is 70% of normal. Which single finding most reliably distinguishes the second patient's condition (intermediate syndrome) from the first patient's acute cholinergic crisis?