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L-dopa test

German: L-Dopa-Test
Synonym: L-dopa challenge

1 Definition

The L-dopa test is a neuropharmacologic test that is used for the diagnosis of dopamine dependent neurological diseases (Parkinson’s disease, restless legs syndrom).

2 Indication

  • Early diagnosis of the Parkinson’s syndrome (test for nigrostriatal dysfunction)
  • Unclear or atypical Parkinson’s syndrome
  • Restless legs syndrome

3 Procedure

The L-dopa-test is done by administering a 100-200mg dose of L-dopa and a peripheral decarboxylase inhibitor (i.e. benserazide), dissolved in water, to the patient. The effect of L-dopa should begin 25-60 minutes after the administration and should persist for 4-6 hours. In case of no initial effect the L-dopa dosage can be increased up to 1000mg. L-dopa most of the time leads to nausea and vomiting which makes it reasonable to start a prophylactic treatment with a prokinetic agent (Domperidone – 3x10mg daily) a couple of days beforehand. In addition, a 30mg dose of Domperidone should be administered 1 hour prior to the examination.

4 Evaluation

In case of Parkinson’s disease, the L-dopa-test will lead to significant improvement of symptoms (UPDRS – increase >30% starting value). A positive test supports, but does not prove the diagnosis of a Parkinson’s syndrome. With a restless leg syndrome the symptoms most often subside entirely after the L-dopa test. The severity of the symptoms can be scaled by their responsiveness to L-dopa. The test has a sensitivity of 80% and a specificity of 100% for RLS.

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