Objectives: The authors investigated the relationship between brain lithium, serum lithium and age in adult subjects treated with lithium. In addition, the authors investigated the association between brain lithium and serum lithium with frontal lobe functioning and mood in a subgroup of older subjects.
Design: Cross-sectional assessment.
Setting: McLean Hospital's Geriatric Psychiatry Research Program and Brain Imaging Center; The Division of Psychiatry, Boston University School of Medicine.
Participants: Twenty-six subjects, 20 to 85 years, with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition-TR bipolar disorder (BD), currently treated with lithium.
Measurements: All subjects had measurements of mood (Hamilton Depression Rating Scale [HDRS] and Young Mania Rating Scale) and serum and brain lithium levels. Brain lithium levels were assessed using lithium Magnetic Resonance Spectroscopy. Ten subjects older than 50 years also had assessments of frontal lobe functioning (Stroop, Trails A and B, Wis. Card Sorting Task).
Results: Brain lithium levels correlated with serum lithium levels for the group as a whole. However, this relationship was not present for the group of subjects older than 50. For these older subjects elevations in brain (but not serum) lithium levels were associated with frontal lobe dysfunction and higher HDRS scores. The higher HDRS were associated with increased somatic symptoms.
Conclusion: Frontal lobe dysfunction and elevated depression symptoms correlating with higher brain lithium levels supports conservative dosing recommendations in bipolar older adults. The absence of a predictable relationship between serum and brain lithium makes specific individual predictions about the "ideal" lithium serum level in an older adult with BD difficult.