A prediction rule for diagnosing hypomania.

BACKGROUND: Missing the diagnosis of past hypomania, and thus of bipolar II disorder, is common. Study aim was to find a 'prediction rule' for facilitating the diagnosis of past hypomania.

METHODS: In an outpatient psychiatry private practice (non-tertiary care), a consecutive sample of 275 bipolar II disorder (BP-II) remitted patients, and consecutive, independent, sample of 138 major depressive disorder (MDD) remitted patients, had been interviewed for different study goals during follow-up visits by a senior bipolar-trained psychiatrist. Using the Structured Clinical Interview for DSM-IV, modified and validated by Benazzi and Akiskal [Benazzi F (2007). Lancet 369: 935-945] to improve the probing for past hypomania, patients had been questioned about the most common symptoms and duration of recent threshold and subthreshold hypomanic episodes. The sample was retrospective in nature. A prediction rule was tested. This is a score resulting from the sum of the weighted scores of each hypomanic symptom which was an independent predictor of hypomania. Its cutoff score for discriminating hypomania was based on the highest figure of correctly classified hypomanias and on the most balanced combination of sensitivity and specificity. A second, independent sample of 138 BP-II and 71 MDD remitted outpatients was tested to replicate the findings.

RESULTS: By univariate logistic regression, hypomanic symptoms distinguishing BP-II and MDD included 'increase in goal-directed activity' (overactivity) (OR=28.3), 'elevated mood' (OR=14.9), 'increased talkativeness' (OR=9.2), 'inflated self-esteem', 'decreased need for sleep', 'excessive risky activities', and 'irritable mood'. By multivariable logistic regression, the independent predictors of hypomania resulted 'increase in goal-directed activity' (OR=14.9, weighted score=15), 'elevated mood' (OR=7.5, weighted score=7), 'increased talkativeness' (OR=3.6, weighted score=4); 'irritable mood', 'inflated self-esteem', 'decreased need for sleep', and 'excessive risky activities' had ORs between 2.04 and 2.39, with a weighted score=2. The prediction rule showed that the cutpoint score > or = 21 had the highest figure of correctly classified hypomanias (88%, ROC area=0.94), showing the most balanced combination of sensitivity (87%) and specificity (89%). This prediction rule, tested on the second sample, found that the same cutoff score > or =21 correctly classified the highest figure of hypomanias (94%, ROC area=0.97), showing the most balanced combination of sensitivity (93%) and specificity (95%). To cross this cutoff score, overactivity was always required (as the sum of the scores of elevated mood and of the other symptoms did not reach this cutoff). However, scores 10 to 20 correctly classified only slightly lower figures of hypomanias.

CONCLUSIONS: A prediction rule for hypomania was tested. The scores of overactivity plus at least some hypomanic symptom (among elevated mood, irritability, inflated self-esteem, less sleep, talkativeness, excessive risky activities) correctly classified 88% of hypomanias. Instead, elevated mood without overactivity, plus even all the other symptoms, did not reach the best figure of correctly classified. However, lower cutoff scores, up to 10, classified slightly lower figures of hypomanias, but with less balanced combinations of sensitivity and specificity. These findings may have diagnostic utility, because BP-II versus MDD is likely to be a more severe disorder. This prediction rule, if replicated and fine-tuned in different settings, may help clinicians better probing past hypomania, thus reducing the common misdiagnosis of BP-II as MDD.