Final answer:
The highest priority nursing diagnosis for a client with Parkinson's disease should be impaired swallowing, due to the significant risk for aspiration and potential subsequent pneumonia.
Step-by-step explanation:
When prioritizing nursing diagnoses for a client with Parkinson's disease, the nurse should consider both the primary symptoms of the condition and immediate risks to the client's health. Among the given options, impaired swallowing (c) should be the highest priority because it poses a significant risk for aspiration, which can lead to pneumonia, a serious and potentially life-threatening condition. Parkinson's disease is characterized by symptoms such as slowed movements, balance and posture problems, and muscle rigidity. While all the options are relevant concerns for a patient with Parkinson's disease, addressing the risk of aspiration due to impaired swallowing is critical for maintaining airway integrity and preventing further complications.