Causes and Diagnoses

Causes and Diagnoses of Parkinson's Disease

We know that Parkinson's disease is caused by the death of nerve cells in the brain that produce the chemical dopamine, but we don't know the exact reason the nerve cells deteriorate. Some possible reasons are:

  • Exposure to toxins
  • Genetic predisposition
  • Advanced age

The symptoms of Parkinson's disease appear when at least 60 percent of the dopamine-producing neurons are damaged.


Parkinson's disease can be difficult to diagnose. At present, diagnosis is a two-step process:

Step 1: Identify the presence of Parkinsonism – this requires an evaluation by a neurologist with experience in Parkinson’s disease

Parkinsonism is a clinical syndrome defined by the presence of the following symptoms:

  • Slowness of movement (bradykinesia)
  • Rigidity or stiffness of the limbs
  • Postural Instability (stooped, slumped posture) or loss of balance
  • Resting tremor (especially a pattern called pill rolling)

The presence of two of these four primary features of the syndrome is required to make the diagnosis of Parkinsonism.

Step 2: Identify the cause of Parkinsonism

Parkinson's disease is responsible for 75 percent of all cases of Parkinsonism. Other causes include:

  • Medications: Long-term use of certain drugs can induce symptoms similar to Parkinson's disease.
  • Structural or vascular lesions: Tumor, stroke and hydrocephalus
  • Other degenerative disorders: Progressive Supranuclear Palsy (PSP), Multiple System Atrophy (MSA), Corticobasal Degeneration, Dementia with Lewy Bodies

Atypical Parkinsonisms

Progressive Supranuclear Palsy (PSP)

PSP is a rare neurodegenerative disease that was first described by Richardson in the 1960's. It is characterized by the presence of parkinsonian symptoms in combination with limited ocular movements, specifically inability to look down voluntarily. PSP unlike PD begins on both sides at the same time. PSP patients rarely have tremor. The major disability is difficulty with balance. However, patients can have speech and swallowing dysfunction and memory problems as well. PSP can be misdiagnosed as PD, especially early in the disease. The cause of PSP remains unknown. Generally symptoms progress more rapidly than in PD, and patients do not respond to PD medications. The main interventions are supportive care and family education.

Multiple System Atrophy (MSA)

MSA is a global term used, since 1969, to describe a group of neurodegenerative conditions that are characterized by the presence of parkinsonism in conjunction with symptoms of other bodily functions. Hence the term “multiple system” atrophy. MSA presents with autonomic or motor deficits. Resting tremor may occur in MSA, but is not a predominant feature. MSA symptoms vary in onset and severity from one person to another. MSA takes several different forms.

Forms of MSA

  • MSA-P: MSA-P causes parkinsonian symptoms such as slowed movements and rigidity that generally do not respond to levodopa therapy. Patients also have pronounced autonomic instability manifested in symptoms such as urinary dysfunction and blood pressure instability.
  • MSA-C: Patients with MSA-C have difficulties with balance, coordination, and speech. They may also have parkinsonian symptoms and autonomic disturbances.

"Pure" manifestations of these MSA syndromes are rare. There is no single diagnostic test that assures 100 percent certainty in making the diagnosis. Sometimes patients present with clinical findings similar to PD. It is only with the progression of the disease that patients will develop the atypical features of MSA. Generally, patients with MSA do not have a robust response to PD medications, though some patients do benefit from such medications, especially early in the disease process. MSA progresses faster than PD, and similar or slightly slower to that of PSP. There is no known familial predisposition to MSA.

The Movement Disorders Clinic offers comprehensive care and management of all forms of parkinsonism including atypical syndromes such as PSP and MSA.

Meet the Team

The Northwestern Medicine Parkinson’s Disease and Movement Disorders Center specializes in the diagnosis and treatment of all movement disorders.