Long-term effectiveness of lithium in bipolar disorder: a multicenter investigation of patients with typical and atypical features.

Objective: Poor response to long-term lithium treatment has been reported to be associated with atypical features of bipolar disorder. The purpose of this study was to investigate the influence of atypical symptoms on the effectiveness and stability of long-term lithium treatment in a prospective, multicenter cohort of bipolar patients in a naturalistic setting. Method: Patients were initially selected according to International Classification of Diseases, 8th Revision, criteria for bipolar disorder and required long-term treatment. Their diagnoses were reconfirmed according to DSM-IV upon its publication. They were prospectively followed for an approximately 20-year period ending in 2004 in 5 centers participating in the International Group for the Study of Lithium-Treated Patients. Examinations included a comprehensive psychiatric evaluation, an assessment of typical and atypical features on an 8-item scale, and an evaluation of clinical course using the morbidity index. Unbalanced repeatedmeasures regression models with structured covariance matrices were used to assess the extent to which the morbidity index was influenced by atypical symptoms, duration of treatment, and pretreatment features. Results: A total of 242 patients were followed for a mean period of 10 years. In 142 patients, the number of typical features was greater than the number of atypical features, whereas in 100 patients the number of atypical features was greater than or equal to the number of typical features. The mean morbidity index remained stable over a period of 20 years in both groups of patients and was not significantly associated with the presence of atypical features, the duration of lithium treatment, the number or frequency of episodes, or latency from the onset of bipolar disorder to the start of lithium treatment. Conclusion: Our study suggests that long-term response to lithium maintenance treatment is stable both in patients with typical and in patients with atypical features. The predominance of either typical or atypical features did not result in different responses to longterm lithium treatment in this sample of bipolar patients. (J Clin Psychiatry 2008;69:1860–1868)