Mild cognitive impairment (MCI) confers a particularly high annual risk of 10-15% of conversion to Alzheimer's disease (AD). Recent findings suggest that regional brain iron concentration measured by quantitative MR relaxation rate R2' may be useful as a biomarker to evaluate the progression of AD.

In this study, we examined the impact of white matter lesion (WML) pathology measured by visual ratings on the validity of iron concentration in converting and stable MCI patients.

Retrospective magnetic resonance imaging data were collected for 65 MCI patients. All patients underwent 1.5 Tesla MRI: WML were visually rated on T2 images using the Fazekas and the Scheltens scales, iron concentrations of subcortical regions of interest (ROI) were measured on T2* maps by calculating the transverse relaxation rate R2'. Further, volumes of gray matter (GM), withe matter (WM) and cerebrospinal fluid (CSF) were calculated.

Of 65 subjects, 25 converted to AD during a follow-up of 19.2±7.4 months and 40 remained stable. Converters had significantly more WML in periventricular regions and the temporal lobe as well as lower volume of WM and a higher volume of CSF. In contrast, ROI analysis of iron deposits showed higher iron concentration in the globus pallidus, the insula, the hippocampus and the substantia nigra in non-converters compared to converters.

Our results suggest that the validity of the measurement of iron deposits as a biomarker for the imminent conversion from MCI to AD may be limited by the presents of WML pathology.