Parkinson’s disease (PD) 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.

Parkinson’s disease is often defined as a ‘Parkinsonian syndrome’ that is idiopathic (having no known cause), although some atypical cases have a genetic origin.

The progression of Parkinson’s disease and the degree of impairment vary from individual to individual. Many people with Parkinson’s disease live long productive lives, whereas others become disabled much more quickly. Premature death is usually due to complications such as falling-related injuries or pneumonia.

Parkinson’s disease is a heterogeneous and genetically complex disorder of largely unknown etiology. It is the second most common neurodegenerative disease in the general population. Approximately four million people worldwide are estimated to be living with Parkinson’s disease. Incidence of Parkinson’s increases with age, but an estimated four percent of people with PD are diagnosed before the age of 50. Adult-onset Parkinson’s disease is most common, but early-onset Parkinson’s disease (onset between 21-40 years), and juvenile-onset Parkinson’s disease (onset before age 21) also exist.

Modern treatments are effective at managing the early motor symptoms of the disease, mainly through the use of levodopa and dopamine agonists. As the disease progresses and dopaminergic neurons continue to be lost, these drugs eventually become ineffective at treating the symptoms and at the same time produce a complication called dyskinesia, marked by involuntary writhing movements. Diet and some forms of rehabilitation have shown some effectiveness at alleviating symptoms. Surgery and deep brain stimulation have been used to reduce motor symptoms as a last resort in severe cases where drugs are ineffective.

Classification

The term Parkinsonism is used for a motor syndrome whose main symptoms are tremor at rest, stiffness, slowing of movement and postural instability. The main motor symptoms are collectively called “Parkinsonism” or “Parkinsonian syndrome”. Parkinsonian syndromes can be divided into four subtypes according to their origin:

  • Primary or idiopathic
  • Secondary or acquired,
  • Hereditary Parkinsonism
  • Parkinson plus syndromes or multiple system degeneration

Parkinson’s disease is the most common form of Parkinsonism and is usually defined as “primary” Parkinsonism, meaning parkinsonism with no external identifiable cause.

Signs and symptoms

Primary symptoms

Four motor symptoms are considered cardinal in PD: tremor, rigidity, slowness of movement, and postural instability.

The primary symptoms of Parkinson’s disease are all related to voluntary and involuntary motor function and usually start on one side of the body. Symptoms are mild at first and will progress over time. Some individuals are more affected than others. Studies have shown that by the time that primary symptoms appear, individuals with Parkinson’s disease will have lost 60% to 80% or more of the dopamine-producing cells in the brain.

Characteristic motor symptoms include the following:

  • Tremors: Trembling in fingers, hands, arms, feet, legs, jaw, or head. Tremors most often occur while the individual is resting, but not while involved in a task. Tremors may worsen when an individual is excited, tired, or stressed.
  • Rigidity: Stiffness of the limbs and trunk, which may increase during movement. Rigidity may produce muscle aches and pain. Loss of fine hand movements can lead to cramped handwriting (micrographia) and may make eating difficult.
  • Bradykinesia: Slowness of voluntary movement. Over time, it may become difficult to initiate movement and to complete movement. Bradykinesia together with stiffness can also affect the facial muscles and result in an expressionless, “mask-like” appearance.
  • Postural instability: Impaired or lost reflexes can make it difficult to adjust posture to maintain balance. Postural instability may lead to falls.
  • Parkinsonian gait: Individuals with more progressive Parkinson’s disease develop a distinctive shuffling walk with a stooped position and a diminished or absent arm swing. It may become difficult to start walking and to make turns. Individuals may freeze in mid-stride and appear to fall forward while walking.
Secondary symptoms

While the main symptoms of Parkinson’s disease are movement-related, progressive loss of muscle control and continued damage to the brain can lead to secondary symptoms. These vary in severity, and not every individual will experience all of them. Some of the secondary symptoms include:

  • anxiety, insecurity, and stress
  • depression
  • confusion, memory loss, and dementia (more common in elderly individuals)
  • Executive dysfunction, Slowed cognitive speed
  • constipation
  • insomnia, daytime drowsiness
  • mask-like face expression
  • small handwriting
  • slowed, quieter speech, and monotone voice
  • pain, paresthesia, Fatigue
  • Dystonia (abnormal, sustained, painful twisting muscle contractions)
  • difficulty in speech, swallowing and excessive salivation
  • diminished sense of smell (hyposmia or anosmia)
  • excessive sweating
  • Altered sexual function
  • skin problems, oily skin
  • urinary incontinence
  • Psychotic symptoms—hallucinations or delusions
  • low blood pressure upon standing (orthostatic hypotension)
  • blurred or double vision, decreased blink rate, dry eyes