Resting-state connectivity in neurodegenerative disorders: Is there potential for an imaging biomarker?

Christian Hohenfeld, Cornelius J. Werner, Kathrin Reetz, NeuroImage: Clinical, Available online 16 March 2018, ISSN 2213-1582, doi:10.1016/j.nicl.2018.03.013.

Biomarkers in whichever modality are tremendously important in diagnosing of disease, tracking disease progression and clinical trials. This applies in particular for disorders with a long disease course including pre-symptomatic stages, in which only subtle signs of clinical progression can be observed. Magnetic resonance imaging (MRI) biomarkers hold particular promise due to their relative ease of use, cost-effectiveness and non-invasivity. Studies measuring resting-state functional MR connectivity have become increasingly common during recent years and are well established in neuroscience and related fields. Its increasing application does of course also include clinical settings and therein neurodegenerative diseases. In the present review, we critically summarise the state of the literature on resting-state functional connectivity as measured with functional MRI in neurodegenerative disorders. In addition to an overview of the results, we briefly outline the methods applied to the concept of resting-state functional connectivity.

While there are many different neurodegenerative disorders cumulatively affecting a substantial number of patients, for most of the studies on resting-state fMRI is lacking. Plentiful amounts of papers are available for Alzheimer's disease (AD) and Parkinson's disease (PD), but only few works being available for the less common neurodegenerative diseases. This allows some conclusions on the potential of resting-state fMRI acting as a biomarker for the aforementioned two diseases, but only tentative statements for the others.

For rare neurodegenerative diseases, no clear conclusions can be drawn due to the few published results. Nevertheless, summarising available data points towards characteristic connectivity alterations in Huntington's disease, frontotemporal dementia, dementia with Lewy bodies, multiple systems atrophy Friedreich ataxia and the spinocerebellar ataxias.

 Resting-state connectivity in neurodegenerative disorders: Is there potential for an imaging biomarker?