Phenotypic spectra of bipolar disorder in responders to lithium versus lamotrigine

Objective: We conducted a study of clinical presentation and family history in patients responsive to either of two commonly used mood stabilizers, lithium and lamotrigine. Methods: The sample included 164 subjects from 21 families of bipolar probands, 14 responders to lithium and seven to lamotrigine. Diagnostic information on first-degree relatives was obtained in a blind fashion through a combination of direct interviews (SADS-L) and family history assessments (FH-RDC). Results: The probands differed with respect to clinical course (episodic in the lithium group, rapid cycling in the lamotrigine group), and comorbidity (panic attacks and substance abuse in the lamotrigine group). The relatives of lithium responders had significantly higher risk of bipolar disorder while relatives of lamotrigine responders had higher prevalence of schizoaffective disorder, major depression and panic attacks. Conclusions: These findings suggest that lithium- and lamotrigine-responsive patients differ with respect to course of illness, comorbidity and family history and may represent distinct subtypes of bipolar disorder.