Final answer:
Diphenhydramine is the medication from the provided options that may be effective in reversing dystonia symptoms due to its anticholinergic properties. Botulinum toxin injections are also a significant treatment for involuntary muscle contractions associated with dystonia.
Step-by-step explanation:
The medication that may be effective in reversing the signs and symptoms of dystonia is D) Diphenhydramine. Dystonia is a movement disorder in which a person's muscles contract uncontrollably. Diphenhydramine is an antihistamine known to help relieve movements disorders such as dystonia because it has anticholinergic effects, which can counteract the involuntary muscle contractions.
Other treatments for disorders involving excessive involuntary muscle contractions include botulinum toxin injections, which have shown to significantly reduce symptoms and improve patients' quality of life.
In comparison, Promethazine may have anticholinergic properties but is not a primary treatment for dystonia; Morphine sulfate is an opioid pain medication and does not treat dystonia; and Lidocaine is a local anesthetic but does not address the neuromuscular issues associated with dystonia.