Diagnostic Tests

Key Facts

  • There are no lab or imaging tests to diagnose PD.
  • Most tests are needed to eliminate another possible diagnosis.
  • The evaluation by a specialist neurologist is still the gold standard.

Clinical Best Practices

  • Diagnose PD using the UK PDS Brain Bank Diagnostic Criteria.
  • Diagnosis may take time and may not be definitive after first visit.
  • Refer to a movement disorder specialist in complex cases.

Even though PD is a clinical diagnosis, there are some special situations where you would want to consider tests. 

Some of the diagnostic tests used in PD include the following:

Smell Test

  • Smell testing with commercially available smell identification tests (University of Pennsylvania Smell Identification Test [UPSITi]), Brief Smell Identification Test (BSITi), or Sniffin’ Sticks could confirm olfactory deficits that might help in the diagnostic certainty for PD;
  • The tests are relatively inexpensive and when PD patients present for the first time, their olfactory deficits are already pronounced compared to controls.

MRI

  • If the patient doesn’t have tremor or much asymmetry or has other red flags (supranuclear gaze palsy, no response to dopaminergic therapy, lower-half parkinsonism or history of strokes, Babinski sign present, urinary incontinence or unexplained sexual dysfunction, history of cancer or an immunocompromised state, early falls) then an MRI of the brain without contrast would certainly be appropriate and recommended.

DaTSCANi

  • DaTSCAN is a commercially available test and that identifies patients with presynaptic parkinsonism.
  • This scan uses an intravenously administered radiolabeled ligand that binds the dopamine transporter (DAT) on the synaptic terminals of nigrostriatal neurons.
  • This test cannot differentiate between PD and other forms of pre-synaptic parkinsonism such MSA, PSP, CBD, or LBD. 
  • Consider using SPECT (DaTSCAN) when you want to differentiate essential tremor and PD, especially in early stages.

Acute Levodopa Test

  • Levodopa is administered to evaluate the improvement of symptoms.
  • This test should not be used for diagnosis of PD.
  • Other parkinsonian disorders may also respond to this test including multiple system atrophy and progressive supranuclear palsy.

Apomorphine Test

  • Apomorphine is a dopamine receptor agonist.
  • The response to an injection of apomorphine is used to evaluate parkinsonian conditions.
  • It should not be used to diagnose PD.

Other Tests

You may want to consider other tests when making the diagnosis:

  • Complete blood cell count and sedimentation rate (Note: if you are considering using clozapine or if your patient is taking clozapine, a white blood cell count would be appropriate due to the risk of agranulocytosis)
  • Chemistry
  • Urine analysis
  • BUN & creatinine
  • Thyroid analysis
  • Liver function
  • Serum ceruloplasmin
  • Copper levels
  • Polysomnography, if a patient has insomnia and/or excessive diurnal somnolence (also if a patient is fighting or talking in his sleep)

Notwithstanding all the previously mentioned tests, the diagnosis of PD remains clinical. Perhaps one of the best predictors of a diagnosis of PD is a relatively slow, gradual progression and a sustained response to levodopa or other dopaminergic therapies.

References: 

Deeb J, Shah M, Muhammed N, et al.  A basic smell test is as sensitive as a dopamine transporter scan:  comparison of olfaction, taste and DaTSCAN in the diagnosis of Parkinson’s disease.  QJM 2010; 103;841-952.

Meara J, Bhowmick BK, Hobson P.  Accuracy of diagnosis in patients with presumed Parkinson’s disease.  Age Aging 1999; 28:99-102.