Source: ninds.nih.gov

Parkinson's disease (PD) belongs to a group of conditions called motor system disorders, which are the result of the loss of dopamine-producing brain cells.  The four primary symptoms of PD are tremor, or trembling in hands, arms, legs, jaw, and face; rigidity, or stiffness of the limbs and trunk; bradykinesia, or slowness of movement; and postural instability, or impaired balance and coordination. 

As these symptoms become more pronounced, patients may have difficulty walking, talking, or completing other simple tasks.  PD usually affects people over the age of 50.  Early symptoms of PD are subtle and occur gradually.  In some people the disease progresses more quickly than in others.  As the disease progresses, the shaking, or tremor, which affects the majority of PD patients may begin to interfere with daily activities.  Other symptoms may include depression and other emotional changes; difficulty in swallowing, chewing, and speaking; urinary problems or constipation; skin problems; and sleep disruptions.  There are currently no blood or laboratory tests that have been proven to help in diagnosing sporadic PD.  Therefore the diagnosis is based on medical history and a neurological examination.  The disease can be difficult to diagnose accurately.   Doctors may sometimes request brain scans or laboratory tests in order to rule out other diseases.