Mixed symptoms and syndromes of anxiety and depression: diagnostic, prognostic, and etiologic issues.

Patients with comorbid symptoms of anxiety and depression are common in clinical practice, and yet they continue to pose a diagnostic and therapeutic challenge to clinicians and researchers alike. This article is intended as a comprehensive review of current knowledge derived from a vast body of clinical research regarding the diagnostic interrelationships of anxiety and depressive disorders at both syndromal and subsyndromal levels. The prognostic implications of comorbidity are also reviewed. Biological linkages between the two disorders are explored, and recent biological theories attempting to explain and integrate the two disorders are presented as well. The article concludes with suggestions for further research.