Parkinson's disease (also known as Parkinson disease, Parkinson's, idiopathic Parkinsonism, primary Parkinsonism, PD, or paralysis agitans) is a degenerative disorder of the central nervous system. The motor symptoms of Parkinson's disease result from the death of dopamine-generating cells in the substantia nigra, a region of the midbrain; the cause of this cell death is unknown. Early in the course of the disease, the most obvious symptoms are movement related; these include shaking, rigidity, slowness of movement and difficulty with walking and gait. Later, cognitive and behavioral problems may arise, with dementia commonly occurring in the advanced stages of the disease. Other symptoms include sensory, sleep and emotional problems. PD is more common in the elderly, with most cases occurring after the age of 50.

Symptoms
Disease starts insidiously, may be in the upper limb of one side and then spreading. Loss of associated movements is often the first indication.

• Tremors: Trembling in fingers, hands, arms, feet, legs, jaw, or head.
• Rigidity: Stiffness of the limbs and trunk, which may increase during movement. Rigidity may produce muscle aches and pain.
• Bradykinesia: Slowness of voluntary movement.
• Postural instability: Impaired or lost reflexes can make it difficult to adjust posture and to maintain balance.
• Parkinsonian gait: Individuals with more progressive Parkinson's disease develop a distinctive shuffling walk with a stooped position and a diminished or absent of arm swing
• Parkinsonian mask- Face is expressionless and fixed, eyelids do not blink, voice is monotonous.

Secondary symptoms include: anxiety, insecurity, and stress, confusion, memory loss, and dementia (more common in elderly individuals), constipation, depression, male erectile dysfunction

Causes
Parkinson's disease is caused by a lack of dopamine due to the loss of dopamine-producing cells in the substantia nigra.