Subsyndromal mood symptoms: a useful concept for maintenance studies of bipolar disorder?

To explore the measurement of subsyndromal mood symptoms in relation to studies of maintenance therapy for bipolar disorder.

Literature review of the Medline database using the following selection criteria: (1) 'bipolar disorder' plus 'inter-episode or interepisode or subsyndromal or subclinical or residual or subthreshold' and (2) 'bipolar disorder' plus 'maintenance or prophylaxis or longitudinal'. Studies of children or adolescents and non-English-language reports were excluded.

Of the studies published between 1987 and October 2007, 77 articles about subsyndromal mood symptoms and 257 studies of maintenance therapy agents were found. Only 11 of the 257 studies of maintenance therapy agents discussed subsyndromal mood symptoms. Of the 77 articles, two thirds were published after 2000. Inconsistent definitions of subsyndromal mood symptoms and different evaluation tools and methodologies were used in the studies.

There is a need to standardize definitions and validate measuring approaches for subsyndromal mood symptoms. However, when measured in both naturalistic studies and clinical trials, subsyndromal mood symptoms were frequently reported by patients receiving maintenance therapy and were associated with poor functioning. As with other chronic illnesses, knowledge of the patient's perspective of daily morbidity is important for improving the clinical outcome. Studies of maintenance therapy for bipolar disorder, regardless of the approach, should measure subsyndromal mood symptoms as an additional outcome.