Role of MR spectroscopy and Structural MRI in MDD and BPAD

Abstract

ABSTRACT

BACKGROUND:

Major (Unipolar) depressive disorder (MDD) and Bipolar Associative disorder ( BPAD) are both major health issues associated with increased morbidity and mortality rates. There is an overlapping symptomatic spectrum between both these conditions, especially during the depressive phase of BPAD. Apt and early diagnosis of the condition can help prevent misdiagnosis and ensure that the patient receives the appropriate treatment mandated for the condition. Studies have shown that neuro imaging and monitoring of brain metabolites using functional MRI (MRS) could be used as a potential tool for understanding the pathophysiology of depression and prove as a diagnostic tool in differentiating unipolar and bipolar depression.[2] This study combines the role of structural imaging: hippocampal volumetry and white matter changes, with the biochemical concentration of metabolites using MR spectroscopy, in the differentiation of both these conditions.

AIMS &OBJECTIVES OF THE STUDY: To utilize MRI to evaluate structural and metabolic changes in the anterior cingulate, medial prefrontal cortex, parietal cortex, and posterior cingulate cortex [using MR spectroscopy] in patients diagnosed with depressive disorder. To differentiate between unipolar depressive disorder and bipolar disorder presenting in the depressive phase, using the above structural and metabolic changes.

MATERIALS AND METHODS: Written informed consent was taken from all the subjects included in the study. The study was conducted after approval from the ethics committee.

METHOD OF EVALUATION: Patients clinically diagnosed with major depressive and bipolar affective disorder and referred from the Department of Psychiatry at Vydehi Institute of Medical Sciences and Research Centre from January 2019 to June 2020. Patients who met the inclusion and exclusion criteria were recruited after written informed consent is taken for the study. All the MRI was performed on a 1.5 T full body system (Achieva, Phillips, The Netherlands) with the use of a standard eight-channel head coil. MR volumetry was performed for bilateral hippocampi, and total hippocampal volume was generated in both cases and controls for comparison among cases and controls. Multi voxel PRESS (Spin – echo point resolved) spectroscopy (Repetition time TR = 1750 ms, echo time [ TE = 24 ms], matrix = 320x 224,, field of view : 240 x 240 , number of excitation = 8 ) with chemical - shift selective saturation (CHESS) water suppression will be used for proton MR spectra.

RESULT: Patients with Bipolar Affective Disorder showed significantly higher levels of Choline, Phospho Creatine, Glutamic acid/ Glutamine in their anterior cingulate cortex, lower Myo Inositol, and N- Acetyl Aspartate in their Posterior cingulate cortex, and lower N- Acety l Aspartate , Myo Inositol in their medial pre-frontal cortex, compared to healthy controls, Patients with Major depressive disorder presented significantly lower Phosphocreatine and N- acetyl aspartate levels in their Posterior cingulate cortex and lower Glutamic acid/ Glutamine in their medial pre-frontal cortex. Mean hippocampal volumetry was found to be reduced in patients with major depressive disorder compared to those with bipolar affective disorder and the control group. The occurrence of white matter changes in all three groups was inconclusive.

CONCLUSION: MRI has a significant advantage over other imaging modalities in the differentiation of unipolar and bipolar affective disorder. MR-based hippocampal volumetry combined with H1 MRS has a significant role in enabling early differentiation between these conditions

OBSERVATIONS AND RESULTS

Statistical analysis: Data was entered into Microsoft excel data sheet and was analyzed using SPSS 22 version software. Categorical data was represented in the form of Frequencies and proportions. Chi- square test was used as test of significance for qualitative data. Continuous data was represented as mean and standard deviation. ANOVA (Analysis of Variance) was the test of significance to identify the mean difference between more than two groups for quantitative data.

Graphical representation of data: MS Excel and MS word was used to obtain various types of graphs such as bar diagram. p value (Probability that the result is true) of <0.05 was considered as statistically significant after assuming all the rules of statistical tests. Statistical software: MS Excel, SPSS version 22 (IBM SPSS Statistics, Somers NY, USA) was used to analyze data.