Differential responses to anxiogenic challenge studies in patients with major depressive disorder and panic disorder.

Anxiogenic challenge studies (intravenous lactate infusion and oral fenfluramine challenge) were conducted in 17 patients with panic disorder (PD), 12 patients with major depressive disorder and a history of panic attacks (MDD-PD), 27 patients with major depression and no history of panic (MDD), and 12 normal controls. PD and MDD-PD patients revealed significantly greater anxiogenic responses to lactate infusion and fenfluramine administration than either MDD patients or controls. PD patients revealed the most robust anxiogenic responses to both challenges as well as associated significant prolactin and cortisol responses to fenfluramine. The findings suggest that the predisposition to panic attacks as seen in PD and MDD-PD patients may represent a distinct neurobiological diathesis which may coexist with a major depressive diathesis in some patients. The delineation of subgroups within the more heterogenous groups of patients with MDD and/or PD will lead to greater precision in the development of clinical treatment strategies. Thus, MDD-PD patients (better called panic-depressives) may have a more severe illness than patients with MDD alone which must be accounted for in the course of pharmacotherapy and psychotherapy.