The disease begins to occur around age 40 and has incidence with patient age. Incidence seems to be more prominent in men, and tends to progress to incapacity and death over one or two decades. Clinical diagnosis of PD is currently solely dependent on the presentation of the symptoms by the patient which reflect a deficiency of striatal dopamine caused by the destruction of the cells in the substantia nigra. The first sign of PA is usually bradykinesia.
Movements are usually quite slow.
Routine activities may require deliberate planning and thought for execution. Difficulty initiating movements or akinesia, may also be present. Rigidity in the flexors is also present. This is due to an exaggerated response to normal proprioceptive return from the somatic musculature. This may cause difficulties in handwriting as a symptom.