Key Concepts
Introduction
Parkinson disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) of the midbrain, resulting in dopamine deficiency in the basal ganglia and the characteristic motor symptoms: resting tremor, rigidity, bradykinesia, and postural instability (TRAP mnemonic). Understanding the cellular pathophysiology is essential for nurses because it explains the rationale for dopamine replacement therapy, anticipation of disease progression, and management of motor and non-motor complications. The substantia nigra pars compacta normally contains approximately 400,000-600,000 dopaminergic neurons that project to the striatum (caudate nucleus and putamen) via the nigrostriatal pathway. These neurons synthesize dopamine from tyrosine (tyrosine → L-DOPA via tyrosine hydroxylase → dopamine via DOPA decarboxylase) and release it into the striatum, where it modulates basal ganglia motor circuits. Clinical symptoms of PD appear when approximately 60-80% of dopaminergic neurons are lost, indicating substantial presymptomatic neurodegeneration. Lewy bodies are the pathological hallmark of PD: intracytoplasmic eosinophilic inclusions composed primarily of misfolded alpha-synuclein protein surrounded by ubiquitin and neurofilament proteins. Alpha-synuclein is normally a presynaptic protein involved in vesicle trafficking and...