By Christian Duffin
Up to a fifth of primary care patients with depression may have an undiagnosed bipolar disorder, a UK study suggests.
The researchers argue that their findings have important implications for GP diagnosis and assessment, because prescribing antidepressants as monotherapy for patients with bipolar disorder may result in mania and frequent mood swings.
The researchers believe that their study is the first to investigate the extent to which bipolar disorder is misdiagnosed as major depressive disorder among UK primary care patients.
The study involved a two-phase sampling technique to produce three estimates of unrecognised bipolar disorder.
The researchers initially collected diagnostic, clinical, psychosocial functioning and quality of life data from 11 GP practices in south Wales for patients with a diagnosis of unipolar depression.
576 of the 3,117 patients contacted sent back completed Hypomania Checklist (HCL-32) and Bipolar Spectrum Diagnostic Scale (BSDS) screening tool questionnaires, both used to test for bipolar disorder.
Of these, 154 were then given a comprehensive diagnostic and clinical assessment. 29 met the diagnostic criteria for bipolar disorder.
The researchers calculated three estimates of the prevalence of previously undiagnosed bipolar disorder, ranging from 3.3% up to 21.6%.
The estimates were based on different assumptions. The most conservative estimate assumed that all individuals who dropped out of the study did not have bipolar disorder.
Assuming that all of those who were invited to interview but did not attend did not have bipolar disorder resulted in a prevalence of 9.6%, while assuming all who were invited and attended had bipolar disorder resulted in a prevalence of 21.6%.
Lead researcher Dr Daniel Smith, a clinical senior lecturer in psychiatry at Cardiff University, said: ‘Although challenging, these are findings with potentially considerable implications for they way in which GPs approach the diagnosis and treatment of their patients with depression, especially when we consider how commonly antidepressants are prescribed in primary care and the potential for harm when antidepressants are used as monotherapy for bipolar disorder.’
He added: ‘It will be important that GPs are supported in developing strategies to ensure that their patients with depression receive the correct diagnosis with regard to the possibility of a primary bipolar illness.’
Dr Thomas Shackleton, a GP from Bottisham, near Cambridge with an interest in depression, said the research should serve as a reminder to GPs that they should screen for manic symptoms when they make they make a diagnosis for depression and during the follow-up at 5-12 weeks.
Dr Shackleton, also an advisor to NICE for its guidelines on depression, added: ‘This is a big issue because the majority of first presentations are depressive, and if you prescribe antidepressants you can induce a manic episode in someone who has bipolar disorder.
‘It can be difficult for GPs because if patients have impulsive or risky behaviour, such as risky sex or gambling, they tend you hide it from GPs. But GPs can explore patients’ histories and ask them if their family have had any concerns about them.’
Professor Richard Morriss, a professor of psychiatry at the University of Nottingham, said: ‘In people with depression who score highly on hypomania questionnaires there is a high prevalence of people with impulse control problems such as borderline personality disorder and intermittent explosive disorder who may superficially look like people with bipolar disorder.’
NICE guidelines on bipolar disorder
– GPs should fully involve patients in decisions about their treatment and care, and determine treatment plans in collaboration with the patient’s preference.
– GPs should discuss contraception and the risks of pregnancy with all women of child-bearing potential, regardless of whether they are planning a pregnancy.
– People experiencing a manic episode, or severe depressive symptoms, should normally be seen again within a week of their first assessment, and then regularly at appropriate intervals, for example, every 2–4 weeks in the first 3 months and less often after that, if response is good.
– The treatment of bipolar disorder is based primarily on psychotropic medication, but side effects and potential harms will determine the choice of drug. A range of psychological and psychosocial interventions can also have a significant impact.
CG38 Bipolar disorder: NICE guideline, October 2006