The patient with Parkinson disease typically presents with a masklike facial expression. Why does he or she have a masklike facial expression? How are the eyes, mouth, and laryngopharynx affected by this disease?

The masklike facies with wide-open, fixed, staring eyes are causes by the rigidity of the facial muscles. This rigidity also affects chewing and swallowing. As described above the muscular movement, such as facial movement, chewing, smiling becomes difficult or doesn’t occur at all due to the imbalance of excitatory and inhibitory neuronal activity[Ign17]. As the disease progresses, due to the dopamine loss in the brain, it interferes with the sympathetic nervous system.