Iron accumulation in the substantia nigra of patients with Alzheimer disease and parkinsonism

Abstract

Background: Preliminary studies have shown an increase in iron accumulation in the substantia nigra but not in the hippocampus in patients with Parkinson disease without dementia and the reverse in patients with Alzheimer disease (AD) and no parkinsonism.

Objective: To determine whether iron levels (measured as T2 shortening on magnetic resonance images) are greater in the substantia nigra of patients with AD who have parkinsonism than in those with AD alone.

Design: Case-control study.

Setting: Albany Medical College, Albany, New York.

Participants: Fifteen patients with only AD (controls) and 18 with AD as well as parkinsonism, aged 56 to 89 years, and with a total Clinical Dementia Rating of 5.0 to 11.5. Patients were selected according to the purity of their disease; patients with a Unified Parkinson's Disease Rating Scale motor score of 15 or greater were considered to have parkinsonism. Main Outcome Measure Area under the curve for short T2 (30 milliseconds) in patients with only AD vs patients with AD who developed parkinsonism.

Results: Patients who developed parkinsonism along with their existing dementia had significantly more iron in their substantia nigra than did patients with AD alone (P = .03, 2-sample t test).

Conclusions: Iron accumulation may be a predictor of parkinsonism. The development of parkinsonism during the course of AD appears to be associated with the accumulation of iron, which in turn may contribute to the pathogenesis of neurologic decline.