Microstructural changes of the nucleus accumbens due to increase of estradiol level during menstrual cycle contribute to recurrent manic episodes--a single case study.

We examined a rapid-cycling bipolar disorder patient who demonstrated manic episode regularly at around day 7 of the menstrual cycle. We hypothesize that gonadal hormones may induce a state-dependent change in cerebral microstructure and function. Following this hypothesis, the serum levels of estradiol and progesterone were analyzed and diffusion tensor imaging data were examined between the manic and euthymic states of the patient. Estradiol levels increased in the late follicular phase at manic state when compared to the luteal or early follicular phase at euthymic state. DTI results showed that the patient had increased fractional anisotropy values at manic state in the bilateral nucleus accumbens (NAc) and its connected areas, which is a major projection field of the mesolimbic dopamine (DA) system, perhaps reflecting microstructural changes due to neuronal activation related to manic episodes. According to these results, we consider that the mesolimbic DA system of this patient has hypersensitivity to estradiol, and elevation of the estradiol level increases the activity of the dopaminergic system, which in turn may contribute to recurrent manic episodes. Our findings provide a clue for understanding how fluctuations in gonadal hormone may amplify or ameliorate the symptomatology of psychiatric disorders related to the menstrual cycle.