PRIMARY EARLY-ONSET DYSTHYMIA, BIOCHEMICAL CORRELATES OF THE THERAPEUTIC RESPONSE TO FLUOXETINE .1. PLATELET MONOAMINE-OXIDASE AND THE DEXAMETHASONE SUPPRESSION TEST

A subgroup of primary dysthymic patients have been reported to respond to traditional antidepressants and, more recently, to the newer serot onergic agents. Two putative biological markers of affective illness, platelet monoamine oxidase (MAO) activity and plasma cortisol levels f ollowing dexamethasone administration, were explored for their diagnos tic and predictive potential in dysthymia. Compared to controls, patie nts had significantly lower platelet MAO activity. Among patients, tho se that responded to treatment with the serotonergic agent, fluoxetine , had lower pretreatment MAO activity than nonresponders. Higher pretr eatment plasma cortisol levels following dexamethasone were also assoc iated with a positive treatment response to this medication. These fin dings support the view that there is a biological substrate for some s ubgroups of dysthymics. This biological component may involve the hypo thalamic pituitary adrenal axis and serotonergic system(s).