A new study, published in the journal Harvard Review of Psychiatry, has revealed two patterns of antecedent or "prodromal" psychiatric symptoms that could be used to predict the development of bipolar disorder in young people.

Early signs of BD can fall into a relatively characteristic "homotypic" pattern, consisting mainly of symptoms or other features associated with mood disorders; or a "heterotypic" pattern of other symptoms including anxiety and disruptive behavior. Environmental risk factors and exposures can also contribute to BD risk, according to the meta-analysis review.

The authors reviewed and analyzed data from 39 studies of prodromal symptoms and risk factors for later development of BD. Their analysis focused on high-quality evidence from prospective studies in which data on early symptoms and risk factors were gathered before BD was diagnosed.

BD is commonly preceded by early depression or other symptoms of mental illness, sometimes years before BD develops, as indicated by onset of mania or hypomania. Nevertheless, the authors note that "the prodromal phase of BD remains incompletely characterized, limiting early detection of BD and delaying interventions that might limit future morbidity."

The evidence reviewed suggested two patterns of early symptoms that "precede and predict" later BD. A homotypic pattern consisted of affective or mood-associated symptoms that are related to, but fall short of, standard diagnostic criteria for BD: for example, mood swings, relatively mild symptoms of excitement, or major depression, sometimes severe and with psychotic symptoms.

The authors note that homotypic symptoms have "low sensitivity" — that is, most young people with these mood symptoms do not later develop BD. However, this symptom pattern also had "moderate to high specificity" — homotypic symptoms do occur in many patients who go on to develop BD.

The heterotypic pattern consisted of other types of prodromal symptoms, such as early anxiety and disorders of attention or behavior. This pattern had low sensitivity and specificity: relatively few patients with such symptoms develop BD, while many young people without heterotopic symptoms do develop BD.

The study findings also associate several other factors with an increased risk of developing BD, including preterm birth, head injury, drug exposures (especially cocaine), physical or sexual abuse, and other forms of stress. However, for most of these risk factors, both sensitivity and specificity are low.

Although many elements of the reported patterns of prodromal symptoms and risk factors have been identified previously, the study increases confidence that they are related to the later occurrence of BD. The researchers note that the findings of high-quality data from prospective studies are "encouragingly similar" to those of previous retrospective and family-risk studies.

"There was evidence of a wide range of [psychiatric] symptoms, behavioral changes, and exposures with statistically significant associations with later diagnoses of BD," the authors concluded.