[Low-dose (0.5 mg) DST in manic and major depressive episodes: in relation to the severity of symptoms].

BACKGROUND Results of previous studies and our own preliminary study suggest that the dexamethasone suppression test (DST) using 1 mg of dexamethasone might result in lower sensitivity in Japanese and Asian people with major depressive episodes, when compared to Caucasian people. We investigated the clinical utility of low-dose (0.5 mg) DST in Japanese patients with manic or major depressive episodes. METHODS Low-dose (0.5 mg) DST was performed 276 times in 122 patients with bipolar disorder (manic or depressed) or major depressive disorder who visited the Department of Psychiatry of Osaka Prefectural General Hospital. After strict exclusion criteria were applied, the remaining 225 test results in 98 patients were analyzed. The severity of symptoms was estimated in accordance with the DSM-IV, namely, severe, moderate, mild, or in remission. A 0.5 mg dose of dexamethasone was administered orally at 20:30, and blood samples were taken the following day at 8:00 (9:00 in outpatients) and 13:00. Serum cortisol levels were measured by radioimmunoassay. Nonsuppression was considered to have occurred when at least one of the postdexamethasone cortisol values was 4.0 micrograms/dl or over. RESULTS In manic episodes, the postdexamethasone cortisol levels were significantly correlated with the severity of the symptoms, and the postdexamethasone cortisol levels in patients with severe symptoms were significantly higher than in those in remission. The rates of nonsuppression in manic episodes with severe, moderate, mild symptoms, and in remission, were 7/8 (88%), 1/4 (25%), 1/3 (33%) and 2/7 (29%), respectively. In major depressive episodes, the postdexamethasone cortisol levels were significantly correlated with the severity of the symptoms. The rates of nonsuppression in major depressive episodes with each grading of severity were 47/58 (81%), 28/52 (54%), 14/40 (35%), 10/53 (19%), respectively. In major depressive episodes, patients aged 50 or over showed significantly higher postdexamethasone cortisol levels than patients aged under 50. In particular, patients aged between 30 and 49 showed significantly lower postdexamethasone cortisol levels than those in the other age groups. There was no significant difference between male and female patients (two-way ANOVA), but female patients with severe depressive symptoms showed significantly higher postdexamethasone cortisol levels than male patients with severe symptoms. There was no significant difference between bipolar and unipolar patients with major depressive episodes (two-way ANOVA), with the exception that the rate of nonsuppression in remission in bipolar patients was significantly different than that in unipolar patients (9/33 (27%), 1/20 (5%), respectively). Among major depressive disorders, the rate of nonsuppression was highest in those with psychotic features, followed by those with melancholia, and then by those without melancholia. Re-evaluating the cut-off point discriminating nonsuppression from suppression, it was suggested that the optimal cut-off point might differ according to age and gender, but a fixed cut-off point at 4.0 micrograms/dl was considered to be appropriate. The postdexamethasone cortisol levels of samples obtained at 13:00 were more sensitive than those obtained at 8:00 or 9:00. The exclusion criteria and the clinical meanings of DST were discussed. CONCLUSIONS Along with the previous studies indicating a low rate of nonsuppression in Japanese and other Asians using a standard 1 mg DST, our results suggest that low-dose (0.5 mg) DST is better in Japanese, and probably in most Asian patients, than 1 mg DST.