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Exams and Tests

Diagnosing Parkinson's disease can be difficult. No specific blood tests or diagnostic studies are currently available to make the diagnosis. In fact, a brain tissue sample, though not practical, is the only way to be absolutely sure of the diagnosis. Studies have shown that a misdiagnosis rate of 25-35% is not uncommon. This rate drops to around 8% when a movement disorder specialist helps make the diagnosis.

For now, if you suspect you may be experiencing symptoms of PD, consult with your doctor and ultimately visit a neurologist who specializes in movement disorders.

• Early-stage diagnosis
  
  
  • In the past, at least 2 of the cardinal symptoms (tremor, rigidity, and bradykinesia) needed to be present to make the diagnosis of PD. These criteria alone were found to be incorrect in 25% of cases.
    
    
  • Studies that look back at people with PD after the diagnosis is certain have found that the features that best predict PD are resting tremor, asymmetric presentation (symptoms on 1 side of the body), and a powerful response to a medication called levodopa (Dopar, Larodopa). These criteria may not always provide accurate diagnosis either because of other diseases that are similar to PD.
    
    
  • In order to increase the precision of an early diagnosis, a PD battery has been suggested. This includes a more complete assessment including motor function, olfaction, and mood.
  
  
• Late-stage diagnosis
  
  
  • In the late stages of disease, the symptoms are usually unmistakable and the diagnosis can be confirmed by a simple history and complete physical exam.
    
    
  • Slowness and difficulty with movement should be quite apparent in the late stages.
    
    
  • Most people will have tremor at this stage, although not all, thus creating a diagnostic challenge.
    
    
  • Imaging tests (such as MRI and CT scan) may be performed in the beginning to rule out other possible causes.
  
  
• Possible imaging technique diagnosis
  
  
  • It is hoped that one day a specific imaging technique will be capable of detecting early and late PD and provide a means to follow disease progression and the effectiveness of treatment.
    
    
  • Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are imaging techniques that are both sensitive and specific for the diagnosis and separation of PD from Parkinson's syndromes.
    
    
  • These tests are not cost-effective for obvious cases.
    
    
  • The ultimate utility of these techniques will be in screening populations felt to be a high risk.
    
    
    • A phase of PD happens before you have symptoms (called a preclinical phase). That is, you will not have symptoms until more than about 80% of dopaminergic cells are lost.
      
      
    • At this point in time, with PET, screening can be done in this phase and demonstrate dopaminergic changes before you have symptoms.
      
      
    • It cannot, however, be used to predict which people with these changes will go on to develop PD.