There are four main, or primary, symptoms of PD. To diagnose PD, at least two of these symptoms must be present.
Tremor is the most characteristic symptom of PD and may be the first symptom in up to 70% of patients. It appears as a “beating” or oscillating movement, usually of the hands and occasionally of the feet or chin. The movement is regular (4–6 beats per second) and is rhythmic, with each movement resembling the other.
The tremor usually appears when the muscles of the hands or feet are relaxed or at rest, hence the name resting tremor. The tremor usually, but not always, decreases or disappears when the muscles of the hands or feet contract during movement. The resting tremor of PD usually begins on one side of the body and later spreads either to the leg or to the other arm. The thumb is usually involved early and prominently.
The tremor looks like you are rolling a cigar, coin, or pill between your thumb and index finger—hence the name “pill-rolling” tremor. In 20% of people with PD, the tremor is also present or only present during movement. Tremors are usually named for their most prominent component and are categorized as sustention or postural tremors (present when sustaining a posture of your arms or body produces the tremor), action or kinetic tremors (present when you move your hands), or intention tremors (appearing or exaggerated as you reach for a specific object). Postural, action and intention tremors are usually prominent in another disorder, essential tremor.
Rigidity in PD is described as stiffness or tightness of the muscles. Normally muscles contract and tighten when they move and relax or soften when at rest. In rigidity, the muscles of your arm or leg stay contracted and stretching them becomes difficult. Because of rigidity, your arm may not swing when you walk. The mask-like or expressionless face that characterizes PD also results, in part, from rigidity of your facial muscles. Some people with PD have “cogwheel rigidity” in which an arm or a leg “catches” during movement, resembling the way a cog catches in a wheel. The small, illegible, compressed handwriting (called micrographia) and the decreased eye blink of people with PD are also related, in part, to rigidity.
Bradykinesia means slow (brady) movement (kinesia). In addition to slow movement, bradykinesia includes an incompleteness of movement, a difficulty in initiating movement, and an arrest of ongoing movement. The incompleteness of movement is as important as the slowness of movement. Bradykinesia is the most prominent, and usually the most disabling, symptom of PD. With bradykinesia, you may have difficulty walking, as well as difficulty speaking, swallowing and turning.
Postural instability is a lack of balance or unsteadiness while standing or changing positions. The postural instability of standing or balancing yourself on one foot (called static balance) involves different mechanisms than the postural instability of changing positions, such as when you’re turning or pivoting, which is called dynamic balance. Some of the things that you did automatically, such as “righting” or correcting yourself after being bumped or pushed, become difficult and you may fall. The postural reflexes that initiate the corrective movements are located deep in the brain and are affected in PD.