Dr. Ahearn and Colleagues Reply

To the Editor: We appreciate Dr. Garside and colleagues’ letter regarding our report of MRI lesions in a family with bipolar disorder. The authors are correct in noting that white matter lesions are common in the elderly. Our study found no age effect when comparing family members with MRI lesions to those without.

While we did not have an active comparison group in this study, our research group did a previous study of comparison subjects (1), using the same spin-echo pulse sequences, the same classification system for reporting the data, and the same raters who were blind to information about the study subjects. These data were reported in the introduction and indicate a low incidence of MRI lesions (1%) in subjects under age 45 and a higher incidence of lesions in the elderly.

The purpose of this study was not to look for correlations between the clinical manifestations of bipolar disorder and MRI lesions. Other researchers have already documented such findings (2–5). Rather, we were specifically looking at the prevalence of MRI lesions in affected and unaffected family members in a family with a substantial history of bipolar disorder. As noted in the article, the prevalence of white matter and subcortical lesions was high in unaffected family members and those with bipolar disorder. In the absence of other diseases that could explain these findings (the family had few risk factors), we postulate that they may correlate with a genotypic risk factor for the disorder.