Final answer:
The first symptom seen in the majority of patients with Parkinson's disease is a tremor, commonly starting in one limb and noticeable primarily at rest. This motor symptom is a consequence of the loss of dopamine-producing neurons in the midbrain.
Step-by-step explanation:
Parkinson's disease is a degenerative brain disorder that is caused by the progressive death of dopamine-producing neurons, particularly in the substantia nigra, a region of the midbrain. This condition leads to muscular symptoms such as tremor, rigidity, slowness of movement (bradykinesia), and postural instability. Among these, the first symptom seen in the majority of patients with Parkinson's disease is typically a tremor, often starting in one limb.
Commonly, this tremor is most noticeable when the limb is at rest and decreases with voluntary movement or during sleep. The resting tremor is a key early indicator of Parkinson's disease and can later be accompanied by other motor symptoms like muscle rigidity and difficulty walking, which may progress to a characteristic shuffling walk as seen in advanced stages. Beyond motor symptoms, patients may also experience cognitive symptoms including memory loss, depression, and eventually, dementia.