Hippocampal subfield volumes in short- and long-term lithium-treated patients with bipolar I disorder

Objectives: Patients diagnosed with bipolar disorder (BP) may experience hippocampal atrophy. Lithium exposure has been associated with increased hippocampal volumes. However, its effects on hippocampal subfields remain to be clarified. Methods: We investigated the effects of short- and long-term lithium exposure on the hippocampus and its subfields in patients affected by bipolar I disorder (BP-I). Hippocampal subfields and total hippocampal volumes were measured in 60 subjects divided into four groups: 15 patients with BP-I who were never exposed to lithium [no-exposure group (NE)], 15 patients with BP-I exposed to lithium for < 24 months [short-exposure group (SE)], 15 patients with BP-I exposed to lithium for > 24 months [long-exposure group (LE)], and 15 healthy control subjects (HC). Results: The SE and NE groups showed smaller total hippocampal volumes and smaller bilateral cornu ammonis CA2-3, CA4-dentate gyrus (DG), presubiculum, and subiculum volumes compared with HC. The LE group showed larger total hippocampal volumes and bilateral CA2-3, left CA4-DG, left presubiculum, and right subiculum volumes compared with the NE group, and larger volumes of the right CA2-3, left CA4-DG, left presubiculum, and right subiculum compared with the SE group. No differences were found between the LE group and HC or between the SE and NE groups. Conclusions: Long-term, but not short-term, exposure to lithium treatment may exert neuroprotective effects on specific hippocampal subfields linked to disease progression.