Researchers have found significant elevations of choline-containing compounds in the hippocampus and orbitofrontal cortex of euthymic patients with bipolar disorder (BD), suggesting that these regions are involved in the pathophysiology of BD.

Since metabolite concentrations in the orbitofrontal cortex and hippocampus have not been extensively studied in BD patients, Canadian researchers performed proton magnetic resonance spectroscopy in 12 euthymic BD patients and 12 age- and gender-matched controls to assess levels of N-acetyl aspartate (NAA), glutamate, and glycerophosphocholine+phosphocoline (GPC+PCh).

Patients were aged 42.1 years on average and had an average illness duration of 30.0 years, mean Young Mania Rating Scale score of 2.4, and a mean Beck Depression Inventory score of 7.5. In total, 67% were being treated with lithium, 33% with atypical antipsychotic medication, 75% with anti-convulsant medications, and 33% with antidepressants.

Geoffrey Hall (McMaster University, Ontario, Canada) and co-authors found that levels of GPC+PCh were significantly increased in the hippocampus (1.97 vs 1.61 µM) and in the orbitofrontal cortex (2.07 vs 1.79 µM) compared with controls.

As choline is a marker of membrane phospholipid metabolism, elevated choline levels may indicate increased membrane turnover and active neurodegeneration characteristic of disorders such as Alzheimer’s and Huntington’s disease, say the authors.

Glutamate levels were also significantly elevated in the occipital cortex in BD patients compared with controls (16.52 vs 13.98 µM), but not in the hippocampus or orbitofrontal cortex.

Conversely, NAA levels were comparable between the groups in all three studied brain regions ??” a result consistent with previous studies, and one that may “may reflect a lithium-induced normalization of NAA in these regions,” according to Hall et al.

Writing in the journal Psychiatry Research: Neuroimaging, the researchers caution: “An obvious limitation of the study is that patients were treated with a variety of medications and these medications may influence metabolite levels.”

They suggest that future studies should include patients with variable illness burden to determine whether the findings generalize from this chronic group of patients to those earlier in the course of illness.

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009

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