Parkinson Disease l: Introduction

In Parkinson disease, dopamine-producing neurons in the pars compacta of the substantia nigra gradually degenerate and die. This progressive loss of dopamine disrupts signaling in the motor circuit of the basal ganglia, leading to characteristic motor symptoms including resting tremor, muscle rigidity, bradykinesia, and postural instability.

Parkinson disease causes resting tremor, muscle rigidity, bradykinesia (slowness of movement), and postural instability. Patients may experience hand tremors at rest, stiffness during movement, or a shuffling gait. These motor features result from dopamine loss disrupting basal ganglia signaling and progressively worsen over time.

Lewy bodies are abnormal protein structures containing misfolded alpha-synuclein that accumulate within affected neurons in Parkinson disease. They represent a pathological hallmark of the disease and are associated with neuronal degeneration. The accumulation of these structures contributes to the progressive neurodegeneration characteristic of Parkinson disease.

Genetic mutations in LRRK2, PINK1, DJ-1, PRKN, SNCA, and GBA genes have been linked to inherited and early-onset Parkinson disease. For example, LRRK2 mutations impair cellular waste clearance, leading to neuronal damage. These genetic factors contribute to disease development alongside environmental influences.

Environmental exposures including pesticides, industrial chemicals, and heavy metals increase Parkinson disease risk. Prolonged exposure to paraquat has been specifically linked to the disease. These environmental factors likely interact with genetic predisposition to trigger neurodegeneration in susceptible individuals over time.

Risk for Parkinson disease increases significantly with age, especially after 60. Being male and having a family history of the disease also raise risk substantially. These non-modifiable factors make age, sex, and genetic predisposition important considerations in disease development and progression.

Parkinsonism refers to conditions with similar motor symptoms but different causes, including toxin exposure from manganese, carbon monoxide, or MPTP. Certain medications like metoclopramide and reserpine can cause reversible Parkinsonism. Other disorders such as Huntington disease and multiple system atrophy may also present with Parkinsonian features.