Parkinson’s disease can indeed cause trembling that affects only one side of the body, especially in its early stages. This characteristic is one of the hallmark features of the disease and helps distinguish it from other movement disorders. The tremor typically begins on one side, often in a hand or fingers, and is most noticeable when the affected limb is at rest. This is known as a resting tremor, and it often has a distinctive “pill-rolling” quality, where the thumb and index finger appear to roll something small between them.
The reason Parkinson’s tremors often start unilaterally (on one side) relates to how the disease affects the brain. Parkinson’s disease primarily involves the degeneration of dopamine-producing neurons in a region called the substantia nigra, which is part of the basal ganglia. The basal ganglia are critical for controlling movement, and they influence the opposite side of the body. Because the damage in Parkinson’s is often initially uneven or asymmetric, symptoms like tremor, rigidity, and slowness of movement (bradykinesia) tend to appear more prominently on one side first.
This asymmetry is a key diagnostic clue. For example, a person might notice a slight shaking or trembling in their right hand while the left side remains unaffected. Over time, as the disease progresses, symptoms usually begin to appear on the other side as well, but the initial unilateral presentation is very common.
The tremor in Parkinson’s is different from other types of tremors because it is most prominent at rest and tends to lessen or disappear when the person uses the affected limb voluntarily. This resting tremor typically occurs at a frequency of about 4 to 6 hertz, which means the shaking happens 4 to 6 times per second. It is often described as rhythmic and regular, and it can be accompanied by other motor symptoms such as muscle rigidity, slowness of movement, and changes in posture.
Besides tremor, other motor symptoms of Parkinson’s disease also tend to start asymmetrically. Rigidity, which feels like stiffness or resistance when moving a limb, and bradykinesia, which is the slowing down of movement, often affect one side more than the other initially. This can lead to noticeable differences in arm swing while walking or differences in facial expression on one side of the face.
The unilateral nature of early Parkinson’s symptoms is important for clinicians because it helps differentiate Parkinson’s disease from other neurological conditions that might cause tremors or movement problems but usually affect both sides of the body more symmetrically from the start.
As the disease advances, the symptoms typically become more bilateral, meaning both sides of the body are affected, but the side that was initially involved often remains more severely impacted. This progression reflects the continuing loss of dopamine neurons and the spread of pathological changes within the brain.
In summary, Parkinson’s disease commonly causes trembling on only one side of the body at the beginning. This resting tremor is a classic sign and usually appears in the hand or fingers. The asymmetry of symptoms is due to uneven damage in the brain’s motor control centers and is a key feature that helps in diagnosing Parkinson’s disease. Over time, symptoms usually spread to involve both sides, but the initial one-sided tremor remains a distinctive and important clinical hallmark.