Dopamine-Responsive Dystonia Workup

Updated: Mar 25, 2019
  • Author: Nirjal K Nikhar, MD, FRCP; Chief Editor: Amy Kao, MD  more...
  • Print
Workup

Approach Considerations

Lab studies used in the diagnosis and evaluation of dopamine-responsive dystonia (DRD) include the following:

  • Complete blood count (CBC) with peripheral smear examination - To rule out acanthocytosis

  • Serum studies for blood urea nitrogen (BUN), creatinine, liver function, copper, and ceruloplasmin

  • Cerebrospinal fluid (CSF) studies

  • Ceruloplasm

CSF examination is not performed routinely, but some subjects may show significant reductions in CSF levels of neopterin and biopterin. [34]

Measuring CSF pterins [17] may be useful in distinguishing the 3 disorders that are responsive to levodopa: GTPCH-deficient DRD (decreased biopterin and neopterin), TH-deficient DRD (normal biopterin and neopterin), and early-onset parkinsonism (reduced biopterin and normal neopterin).

Polysomnography

Polysomnography in DRD shows a decreased number of twitch movements during REM sleep (approximately 20% of normal). The ratio does not decrease with age, and it does not follow the decremental age variation and incremental nocturnal variation of healthy subjects. [35]

Phenylalanine loading test

Abnormality in phenylalanine metabolism has been useful in diagnosing DRD for most (50% of patients), but not all, patients. [36, 37, 38] The basis for this test is that BH4 is required as a cofactor in the breakdown of phenylalanine to tyrosine. In DRD, BH4 deficiency results in accumulation of phenylalanine.

Molecular biology

This can confirm the diagnosis in some cases. [39]

Histology

In one autopsy case, the only neuropathologic finding was a decrease in melanin-pigmented neurons in the pars compacta of the substantia nigra. TH immunoreactivity in the substantia nigra was normal, no inclusion bodies or gliosis was noted, and no evidence of a degenerative process in the striatum was observed. [40]

Next:

Imaging Studies

MRI

Brain magnetic resonance imaging (MRI) may show abnormalities in the basal ganglia, suggesting Wilson disease or Hallervorden-Spatz disease.

PET scanning

PET scan uptake of [18 F]dopamine may be reduced in early onset Parkinson disease, but it is normal in DRD. [41, 42, 43]

A multitracer PET study has shown that the availability of the striatal dopamine D2 receptors is increased in DRD, whereas dopamine D1 receptors and dopamine transporter ligand binding are unchanged. The pattern of changes in the striatal dopaminergic system in DRD is different from that reported in juvenile Parkinson disease. The increased D2 receptor availability may be due to reduced competition by endogenous dopamine and/or compensatory response to dopamine deficiency. [44]

SPECT scanning

Single-photon emission computed tomography (SPECT) scanning with iodine-123 (123 I) 2beta-carbomethoxy-3beta-(4-iodophenyl)tropane (b-CIT) can differentiate DRD (normal) from early onset Parkinson disease (reduced). [45]

Previous