Most people with Parkinson's disease develop a tremor that is most prominent in the hands and fingers. It tends to occur when the limb is relaxed (a resting tremor), disappearing when performing tasks such as drinking or eating. About 30% of people with Parkinson's disease never develop a tremor.

Stiffness is a common early sign of Parkinson's disease and is most obvious in the arms, shoulder or neck, although it can occur in all muscle groups. People may have difficulty getting out of a chair, turning or rolling over in bed, or walking. Fine finger movements such as doing up a button or tying a shoelace may also be difficult. Pain or a deep aching sensation in the muscles may also be felt.

Bradykinesia means slowness of movement and is a disabling and frustrating symptom of Parkinson's disease. People have difficulty initiating movement and movement may be slow. There may also be a lack of coordination when moving and normal activities can prove difficult. Activities once performed quickly and comfortably, such as washing or dressing, may take several hours if not assisted. Bradykinesia can also make the face seem flat or expressionless.

Loss of balance tends to develop later in this disease. Because of impaired balance and co-ordination (postural instability) a Parkinson's patient can develop a forward or backward lean. They may start to walk with small steps as if hurrying forward to keep balance. Frequent falls are also common.

A range of other symptoms may be experienced including pain, depression, slow slurred speech, decreased blinking and difficulties in walking or writing.

Pathological changes in Parkinson's Disease

• Progressive loss of pigmented dopaminergic neurones in the substantia nigra
• Presence of Lewy Bodies in pigmented neurones in the substantia nigra
• Lewy bodies consist of some misfolded proteins including alpha-synuclein and ubiquitin.
• alpha-synuclein, a protein that is highly expressed in the brain and that tends to aggregate in patients with PD. It is thought that this process either interferes with normal alpha-synuclein function or is itself toxic to cells. 
• Symptoms appear after 60-80% of dopaminergic cells show signs of degeneration, and striatal dopamine levels have decreased by 20-50%

The consequences of these changes in dopamine levels are discussed in the main article

Deep Brain Stimulation

Deep brain stimulation involves implanting leads, which have electrodes at the end, into one of 3 target sites in the brain:

• the thalamus (this procedure is known as thalamic stimulation)
• the globus pallidus (this procedure is pallidal stimulation)
• the subthalamic nucleus (this procedure is subthalamic stimulation)

The leads are usually implanted under local anaesthetic, so the person will be awake, or they may be woken up part-way through the operation in order to ensure the electrodes are correctly positioned.

A small electric current will be sent through the leads to test how the person's symptoms respond to stimulation and ensure that the desired optimal response is obtained. The leads are connected to a device like a pacemaker placed under the skin around the chest or stomach area to allow the patient to switch the stimuli on as required.