Subthreshold manic symptoms (subM) are a risk factor for onset and recurrence of bipolar disorder (BD). Individuals with subM may benefit from preventive interventions, however, their development is hampered by a lack of knowledge on subM prevalence and subsequent course. This study examines subM characteristics, course, and risk factors for an unfavourable course.
In a Dutch representative, population-based sample aged 18-64 (N=4618), we assessed subM, defined as the occurrence of manic core symptoms (elation/irritability), without meeting full DSM-IV criteria for BD I or II in the past three years. Comparison groups had either no manic symptoms (noM); or hypomania/mania in the context of BD (mBD) in the past three years. Furthermore, we differentiated a mild and moderate type of subM, based on the number of manic symptoms. Subsequent three-year course was assessed prospectively.
SubM had a three-year prevalence of 4.9%. Its prevalence, characteristics, and course were in between noM and mBD, and there were few differences between mild and moderate subM. Over three-year follow-up, 25.0% of individuals with subM had persistent subM and another 6.1% transitioned to mBD. Eleven significant risk factors for this unfavourable course were found. The most important were history of depression/dysthymia (OR 3.75, p≤0.001), living alone (OR 2.61, p≤0.01), and elevated neuroticism score (OR 1.21, p≤0.001).
This study supports the validity and clinical relevance of subM as a BD prodrome. It demonstrates that subM symptoms often persist or increase during follow-up and identifies eleven risk factors that are associated with unfavourable course.