MRI evaluation of brain iron in earlier- and later-onset Parkinson's disease and normal subjects

Tissue iron levels in the extrapyramidal system of earlier- and later-onset Parkinson's disease (PD) subjects were evaluated in vivo using a magnetic resonance imaging (MRI) method. The method involves scanning subjects in bo th high- and low-field MRI instruments, measuring tissue relaxation rate (R -2), and calculating the field-dependent R-2 increase (FDRI) which is the d ifference between the R-2 measured with the two MRI instruments. In tissue, only ferritin iron is known to increase R-2 in a field-dependent manner an d the FDRI measure is a specific measure of this tissue iron pool. Two grou ps of male subjects with PD and two age-matched groups of normal control ma les were studied. The two groups of six subjects with PD consisted of subje cts with earlier- or later-onset (before or after age 60) PD, FDRI was meas ured in five subcortical structures: the substantia nigra reticulata (SNR), substantia nigra compacta (SNC), globus pallidus, putamen, and caudate nuc leus, and in one comparison region; the frontal white matter. Earlier-onset PD subjects had significant (p < 0.05) increases in FDRI in the SNR, SNC, putamen, and globus pallidus, while later-onset PD subjects had significant ly decreased FDRI in the SNR when compared to their respective age-matched controls. Controlling for illness duration or structure size did not meanin gfully alter the results. Published post-mortem studies on SN iron levels i ndicate decreased ferritin levels and increased free iron levels in the SN of older PD subjects, consistent with the decreased FDRI observed in our la ter-onset PD sample, which was closely matched in age to the post-mortem PD samples. The FDRI results suggest that disregulation of iron metabolism oc curs in PD and that this disregulation may differ in earlier- versus later- onset PD, (C) 1999 Elsevier Science Inc.