BLUNTED PHASE-SHIFT RESPONSES TO MORNING BRIGHT LIGHT IN PREMENSTRUALDYSPHORIC DISORDER

Patients with premenstrual dysphoric disorder (PMDD) respond therapeut ically to sleep deprivation and light therapy. They have blunted circa dian rhythms of melatonin. The authors sought to test the hypothesis t hat these disturbances are a reflection of a disturbance in the underl ying circadian pacemaker or, alternatively, that they reflect a distur bance in the input pathways to the clock. To test these hypotheses, af ter a 2-month diagnostic evaluation, 8 patients who met DSM-IV criteri a for PMDD and 5 normal control (NC) subjects underwent two studies to determine whether PMDD subjects showed (1) altered melatonin sensitiv ity to light suppression (Study 1) and (2) altered phase-shift respons es to morning light as a measure of the functional capacity of the und erlying pacemaker (Study 2). In both studies, measurements were made d uring asymptomatic follicular and symptomatic luteal menstrual cycle p hases in PMDD patients. The results of Study 1 showed no significant e ffect of group or menstrual cycle phase on the amount or percentage of suppression of melatonin by light. The results of Study 2 showed that with respect to the variable of offset time, PMDD subjects, when symp tomatic, showed a reduced and directionally altered melatonin phase-sh ift response to a morning bright light stimulus; in 4 of 5 NC subjects , melatonin offset was advanced by bright morning light, whereas in PM DD subjects, it was delayed (3 subjects) or not shifted (5 subjects) ( group effect, p = .045). Study 2 also revealed that area under the cur ve also changed differentially in PMDD versus NC subjects. In summary, the primary findings from this pilot study suggest that in PMDD there is a maladaptive (directionally altered and blunted) response to ligh t in the symptomatic luteal phase. Because the suppressive effects of light were similar in PMDD and NC subjects, the previously observed lo w melatonin levels in this disorder do not likely represent a disturba nce in pineal reactivity to suprachiasmatic nucleus efferents. Instead , the findings support a possible disturbance in PMDD in the clock its elf or its coupling mechanisms.