Altered plasma dexamethasone and cortisol suppressibility in patients with panic disorders

Some abnormalities in the hypothalamic-pituitary-adrenal (HPA) axis in patients with panic disorders were recently reported. The possibility that the disposition of dexamethasone, which has been reported to influence the Dexamethasone Suppression Test (DST), might be altered in this subgroup of patients has not, as yet, been reported. We report that 4:00 pm dexamethasone plasma concentrations following a 1-mg oral DST were significantly (p < 0.01) lower in 23 patients with panic disorders (0.49 ± 0.44 ng/ml) compared to 52 normal control subjects (1.09 ± 0.64 ng/ml). This is in addition to the significantly higher (p < 0.05) 4:00 pm postdexamethasone cortisol values per nanogram per milliliter of dexamethasone in the panic disorder patients compared to normal controls (17.7 ± 29.6 versus 5.0 ± 11.2 μg/dl). The mean percent suppression of cortisol from baseline in panic disorder was normal despite one-half the dexamethasone concentrations in these subjects. The cortisol suppression versus dexamethasone concentration curve was also shifted lower (greater fraction of cortisol suppression) and to the left (toward lower dexamethasone concentrations). These results further suggest that the HPA system is indeed altered in panic disorders, but in a manner that is not readily apparent from the DST alone.