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.