Interface of panic and depression: clinical and sleep EEG correlates.

Four groups of subjects were compared with respect to their clinical and demographic status and electroencephalographic (EEG) characteristics, namely: primary major depressive disorder (PRI MDD); panic disorder (Panic); "Mixed" group comprising patients meeting full syndromal criteria for MDD and panic occurring concomitantly; and normal controls. The "Mixed" (MDD + Panic) patients were characterized by earlier age of onset of psychiatric illness, longer duration of current episode, greater intensity of symptoms, higher impairment of functioning, increased miscellaneous psychopathology, and greater objective stress and anger. With respect to sleep EEG variables, PRI MDD patients were clearly different from the other three groups. The sleep profile of the "Mixed" group occupies an intermediate position between the "pure" Panic and MDD groups. Classification of the "Mixed" patients based on the discriminant function coefficients of the Schedule for Affective Disorders and Schizophrenia and sleep analysis of the "pure" groups (PRI MDD and Panic) reveals that some patients are classified as true PRI MDD while others are classified as falling somewhere along the PRI-MDD/Panic spectrum. The separation of the PRI MDD from Panic and Normals, however, is clear, suggesting that sleep can be successfully used as a physiological marker in the separation of these conditions.