Resting state MRI: a new marker of prodromal neurodegeneration?

Abstract

This scientific commentary refers to ‘Basal ganglia dysfunction in idiopathic REM sleep behaviour disorder parallels that in early Parkinson’s disease’, by Rolinski et al. (doi:10.1093/brain/aww124). Like most neurodegenerative diseases, Parkinson’s disease has a long prodromal period; that is, a time when symptoms or signs have emerged, but are not sufficiently advanced to diagnose clinical parkinsonism. This condition can currently be diagnosed by detecting combinations of motor and non-motor signs. Diagnostic criteria for prodromal Parkinson’s disease have recently been published (Berg et al. , 2015). Unlike other diseases, prodromal Parkinson’s disease diagnosis relies mostly upon clinical examination. Established biomarkers of prodromal Parkinson’s disease are relatively limited; only PET/SPECT scanning and substantia nigra (SNpc) ultrasound have some prospective evidence of predictive value (Berg et al. , 2015). This is a major limitation for the field; we need biomarkers to both diagnose prodromal Parkinson’s disease (to identify candidates for neuroprotective therapy) and to assess progression (to give a quantifiable biological outcome for neuroprotective trials). In this issue of Brain , Rolinski and co-workers suggest a potential new biomarker of prodromal Parkinson’s disease: resting state functional MRI (Rolinski et al. , 2016). If MRI could be used as a biomarker, it would offer a number of key advantages: it has a well-established standardized acquisition and infrastructure, and is globally available. However, a typical clinical MRI in Parkinson’s disease is normal. If a test is normal in established disease, it is hard to imagine using it to diagnose a prodromal state. However, as MRI techniques advance, this may change. For example, with increased magnet strength and sequences sensitive to brain iron (susceptibility weighted imaging, neuromelanin sequences), the architecture of the substantia nigra can be delineated with greater precision. Studies have suggested that a loss of the normal hyperintense …