Diagnostic Value Transcranial Duplex Scanning and Single Photon Emission Tomography in Patients Suspected of Having Idiopathic Parkinson Disease or Atypical Parkinson Syndromes

PD is a progressive neurodegenerative illness that affects about 50.000 people in the Netherlands. Diagnosis is based on clinical criteria. However, purely on clinical grounds, especially in the early stage, it is not possible to differentiate PD from other parkinsonian syndromes like multiple system atrophy, Progressive Supranuclear Palsy, vascular parkinsonism, drug induced parkinsonism and essential tremor. Accurate differentiation is important because treatment and prognosis varies between the different syndromes.

At present SPECT scans are used mostly. However the SPECT is only used in the minority of the patients suspected of PD mainly because the costs and the discussion about their sensitivity and specificity to diagnose PD. We are currently finishing a meta-analysis on the diagnostic value of the SPECT in patients with parkinsonian diseases.

Recently an alternative method to visualise the alterations in the cerebral dopaminergic pathways of PD patients has been proposed: TCD of the substantia nigra in the brainstem. This technique has high inter-observer reliability. Becker discovered in 1994 that patients with PD had bilateral hyperechogenicity of the substantia nigra. Neuropathological studies confirm the increased echogenicity is because of iron deposition. However the reason of the increased level of iron is unknown.

Several publications confirm the observation that up to 90% of PD patients have increased echogenicity of the substantia nigra. In healthy subjects and in patients with essential tremor this hyperintensity of the substantia nigra is only found in 10%. However 60% of the healthy subjects with increased echogenicity also have decreased nigra-striatal function on (18)-F-dopa-PET. So TCD might possibly be an early (presymptomatic) marker for PD.

If substantia nigra scanning is combined with scanning of the nucleus lentiformis, the differentiation between PD and APS is increased. Another advantage is that with the same technique the raphe nuclei can be made visible. Several studies confirm the echogenicity of raphe nuclei is decreased in PD patients with a depression.