Speculating the timing of iron deposition in the putamen in multiple system atrophy

Background & objective: Although iron accumulation is thought to be associated with neurodegenerative processes, the timing of putaminal iron deposition during the disease course of multiple system atrophy (MSA) remains unclear. We sought to investigate the temporal pattern of iron deposition in the putamen of MSA patients by calculating the conditional probabilities (CPs) of multimodal MRI changes. Methods: We simultaneously measured putaminal R2*, volume and MD values of 39 probable MSA patients and 22 control subjects. The presence of significant MRI changes was defined as higher R2* and MD values, or lower volumes than cut-off values derived from mean values in control putamen. The CPs of R2* changes without MD or volume changes were then compared with those of MD or volume changes without R2* changes. Results: Regardless of the cut-off values, the CPs of R2* increments without MD or volume changes were significantly lower than those for MD or volume changes without R2* increments. The associations of R2* with volume and MD values appeared in non-linear exponential and quadratic patterns, respectively. Conclusions: Our findings suggest that putaminal iron accumulation would occur under volume atrophy or MD increments. Thus, iron deposition in the putamen of MSA patients is likely a secondary byproduct of neurodegeneration.