Final answer:
Methohexital is expected to have a normal response in a patient with myotonic dystrophy because it is a barbiturate anesthetic that does not act directly at the neuromuscular junction, unlike succinylcholine or rocuronium which can have altered effects due to the condition.
Step-by-step explanation:
The drug expected to have a normal response in a patient with myotonic dystrophy would likely be Methohexital. Myotonic dystrophy is a condition that affects muscle function, and certain drugs, particularly those that affect neuromuscular transmission, can have altered effects. In this condition, using drugs such as succinylcholine could potentially result in prolonged muscle relaxation or paralysis as it is a muscle relaxant that acts by depolarizing the neuromuscular junction. Rocuronium is also a neuromuscular blocking agent and could pose similar risks. Morphine and etomidate may have more predictable effects on these patients but are not indicated for their action at the neuromuscular junction. Therefore, Methohexital, a barbiturate anesthetic, would be more expected to have a normal response in such patients as it does not act directly at the neuromuscular junction.