Subsyndromal depressive symptoms are associated with functional impairment in patients with bipolar disorder: Results of a large, multisite study

Objective: Studies of patients with unipolar depression have demonstrated a relationship between subthreshold depressive symptoms and impairment in role functioning. Research examining this relationship in persons with bipolar disorder is rare. This study sought to evaluate the association between subsyndromal depressive symptoms and role functioning in subjects with bipolar disorder. Method: 759 adult outpatients with a DSM-IV diagnosis of bipolar disorder were entered into this study at 7 different sites in the Stanley Foundation Bipolar Network (SFBN) beginning in March 1996 and ending in November 2002 and were followed longitudinally for assessment of their course of illness. Subsyndromal depression was operationalized using cutoff scores on the Inventory for Depressive Symptomatology-Clinician Rated (IDS-C), and patients were divided into 3 groups: not depressed (IDS-C score < 13), subsyndromally depressed (IDS-C score 13 to 27), and syndromally depressed (IDS-C score ≥ 28). Groups were compared using a series of χ² analyses on degree of role function impairment across 4 role domains (work, home duties, family life, and friendships) from the Life Functioning Questionnaire. Logistic regression was used to estimate the probability of any impairment in life functioning based on severity of depressive symptoms. Results: Subsyndromally depressed patients were significantly more likely than those not depressed to report impairment in their work and home functioning roles, as well as impairment in relations with family and friends (p < .001). Across all domains of role function, the proportion of patients impaired in the subsyndromally depressed group was more similar to the syndromally depressed group than to the not depressed group. Conclusions: These findings clearly demonstrate the public health significance of subsyndromal depression in the bipolar population. The most appropriate interventions for subsyndromal depressive symptoms in patients with bipolar disorder remain to be determined.