Distinct developmental trajectories for bipolar disorder and schizophrenia

By Eleanor McDermid, Senior medwireNews Reporter

Early diagnoses given to patients with a final diagnosis of bipolar disorder are markedly different from those given to patients with schizophrenia, a study shows.

A diagnosis of bipolar disorder tended to be preceded by other affective diagnoses, report Søren Martin Andersen (Aalborg University Hospital, Denmark) and co-workers. Schizophrenia patients also often received early affective diagnoses, but were more commonly diagnosed with psychoses other than schizophrenia, or with substance use disorders.

In all, 69.3% of 784 patients with bipolar disorder, drawn from a national database, had a preceding psychiatric diagnosis, as did 76.6% of 1667 patients with schizophrenia. The high prevalence of previous diagnoses reflects the fact that bipolar disorder and schizophrenia “are serious mental disorders that gradually unfold,” the researchers write in BMC Psychiatry.

Notably, very few of the preceding diagnoses were made during childhood or adolescence, with the first diagnoses not made until patients were about 22 to 23 years old. The researchers say this may not reflect missed diagnoses, but rather a substantial number of patients previously having unclear psychiatric symptoms “that may not exactly have met defining diagnostic criteria, but might later have been considered as prodromal features of a disorder.”

They also point out the low rate of preceding attention deficit hyperactivity disorder (ADHD) diagnoses among bipolar disorder patients (4.2%), which is not consistent with the view that bipolar disorder in childhood is often mistaken for ADHD.

Among the bipolar patients, 46.6% had a preceding affective disorder diagnosis, most commonly depression, at 41.5%. Schizophrenia patients were more often diagnosed with a psychotic disorder, at 41.5% compared with 14.2% of bipolar patients, but also had a high rate of affective diagnoses, at 28.0%, with depression again being most common.

However, schizophrenia patients were more likely to be diagnosed with a substance use disorder, at 26.9%, compared with 16.1% of bipolar patients.

Overall, the team believes that patients with affective diagnoses should be monitored for emerging bipolarity, and those with psychosis or substance use disorders for schizophrenia.

Diagnoses of reactions to severe stress were common in both bipolar and schizophrenia patients, at 26.3% and 26.6%, which the researchers suggest may “reflect a generally heightened vulnerability” of these patients. They also highlight the high prevalence of personality disorders, diagnosed in about 22% of both groups, and say it may be worth investigating how many of these disorders prove to be comorbid conditions rather than just preceding diagnoses.

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