Transcranial duplex in the differential diagnosis of parkinsonian syndromes A systematic review

Transcranial duplex scanning (TCD) of the substantia nigra (SN) is increasingly used to diagnose Idiopathic Parkinson's Disease (IPD). Up until now 70 diagnostic studies have been published, not only on investigation of the SN, but also of the lenticular nucleus (LN) and the Raphe nuclei (RN). We systematically reviewed all diagnostic TCD studies in parkinsonian patients up to June 2008. We found 35 eligible studies. Of the 1534 IPD patients investigated in the 35 studies 200 (13 %) had an inconclusive SN-TCD. An increased echo-intensity of the SN was seen in 1167 (87 %) of the 1334 IPD patients, 276 (12 %) of the 2340 healthy controls and in 41 (30 %) of the 138 patients with an atypical parkinsonian syndrome (APS). On the contrary, a pathological LNTCD was found more often in APS patients (79 %) than in IPD patients (23 %) and healthy controls (6 %). A decreased echo-intensity of the RN was found more often in depressed (46 %) than in non-depressed IPD patients (16 %). SN-TCD accurately differentiates between patients with IPD and healthy controls, but not between patients with IPD and APS. LN-TCD is only moderate accurate to delineate IPD from APS, but combinations of SN- and LN-TCD may be more promising. RN-TCD has only marginal diagnostic accuracy in diagnosing depression in IPD and non-IPD patients. Before TCD can be implicated, more research is needed to standardize the TCD technique, to investigate the TCD in non-research settings and to determine the additional value of TCD compared with currently used clinical techniques like SPECT imaging.