[Bipolar disorder type 1 was the most stable bipolar subdiagnosis]

DSM-IV subcategorises bipolar disorders into type 1, type 2, and a third not otherwise specified (NOS) category. Although previous works suggest that these subtypes remain reasonably stable over time, it is unclear if subdiagnoses endure over time or if patients are commonly recategorized within the spectrum in a real-world clinical setting. We assessed subdiagnostic stability in 6,374 individuals with bipolar disorder using data from the Swedish national quality assurance register for bipolar disorders (BipoläR). Diagnoses at baseline registration - that could occur at any time point during the course of illness - were compared with diagnoses at follow-up registration 3 years later. Changes in subdiagnoses were analysed in relation to clinical setting, diagnostic procedure, and patient features. We found that 74 %, 67 %, and 47 % of patients diagnosed with bipolar disorder type 1, type 2, and NOS, respectively, retained the same subdiagnosis at the 3-year follow-up. The following factors were associated with higher rate of subdiagnostic transitions: previous suicide attempts, unemployment or low psychosocial function, treatment with antidepressants, and comorbid anxiety, neuropsychiatric, or personality disorder. Conversely, use and duration of mood stabilizer treatment, the use of structured diagnostic instruments, and treatment at an outpatient unit specialized in managing affective disorders were associated with lower likelihood of subdiagnostic transitions. Our findings confirm that bipolar disorder type 1 is the most stable subdiagnostic group, but findings also indicate a significant degree of subdiagnostic instability, particularly in the NOS group.