As many as one in four patients diagnosed with depression in primary care were found to have had episodes of mania when questioned, the latest study showed.
It focused on 790 patients with a diagnosis of unipolar depression who attended a GP practice in Darlington, Cleveland.
Patients were sent the mood disorder questionnaire (MDQ). Of 278 patients who returned the questionnaire, 24 per cent had an episode of mania or mild mania. Subsequent assessment of the patients showed that half had bipolar disorder.
Lead researcher Dr Stuart Watson, from the psychiatric department of the University of Newcastle, said treating bipolar patients as though they had depression could exacerbate the condition.
'The guidelines say that bipolar patients shouldn't be on an antidepressant drug without an antimania drug,' he said.
The concern is that treating bipolar disorder with antidepressants alone can exacerbate the mania side of the disorder.
Dr Dave Tomson, a Tyneside GP who has an interest in mental health, said his practice was already trying out the MDQ.
'Some people who are being treated for depression may have bipolar disorder,' he said.
But, Dr Tomson said as bipolar disorder is not a single condition, outcomes may vary: 'What we're not sure about is how often a different diagnosis will help. It's not clear it'll help everyone.'
The latest research was presented at Faculty of General and Community Psychiatry Annual Meeting in Newcastle last week.
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