Though the lifetime risk of bipolar disorder is frequently cited as being around 1%, that relates only to bipolar I. The true overall risk is closer to 4%, Allan Young (Institute of Psychiatry and King’s College, London, UK) said in his “State of the Art” lecture. So the disease is common. There are cases of late onset, but the highest rates of incidence are in adolescence and early adulthood.

Allan Young described the disorder as highly toxic to psychosocial functioning, and highly complex, with many subtypes and mixed features.

The bulk of the clinical issue is depression.

Much confusion with unipolar depression

People eventually classified as bipolar generally present with depression. And it may be many years before there is an episode of mania that is recognised and diagnosed as such. And throughout the disease course, depressive episodes predominate in both bipolar I and II (perhaps to a greater extent in bipolar II). The consequence is that probably a third of bipolar patients are misdiagnosed as having major depressive disorder (MDD).

With the exception of mania, there are no pathognomonic features, though it is possible that brain scans will one day be used to reveal the differing neural circuitry that distinguishes bipolar disorder from MDD.

The overlap with borderline personality disorder is also a problem. There is sometimes a clue in the fact that patients with bipolar disorder are more likely to endorse the concept of “depressed mood” rather than “emptiness”.

Mixed states complicate matters

The prevalence of psychiatric comorbidities and mixed states contributes to the uncertainties of diagnosis. Psychiatric residents are slow to grasp that depression can co-exist with mania, but this happens frequently – and the same is true of anxiety. Though people find it difficult to match anxiety and mania, probably half of all bipolar patients experience anxiety and it is frequently a troubling residual symptom.

Bipolar disorder is a valid diagnosis

In recognising the broad extent of mixed features involving depression and anxiety, the bipolar chapter of DSM 5 is a helpful advance. In field testing of the new manual, the inter-rater reliability for the bipolar I diagnosis was relatively good, and ahead of schizophrenia. The inter-rater reliability for bipolar II was better than that for MDD. So these are valid diagnostic criteria.

In those who suffer from the disease, the risk of a clinical recurrence within twelve months is around 75%. Remissions tend to be incomplete, and relapse rates are high. With each relapse, there seems to be a stepwise decline in cognitive capacity.

Even so, those facing the diagnosis should be told that the clinical course of the disease is highly variable, and that some patients do well. Good adherence to treatment may play a part in this.

Individual and social costs are considerable

In additional to the heavy personal burden carried by patients, family and friends, the economic impact of bipolar disorder is staggering. In 2011, the overall annual cost of the disease in Europe was estimated at 114 billion euros.

This includes impact on employment and money spent in the criminal justice system. But much of the burden to society arises from direct healthcare costs, and the bulk of those – in the UK at least – is accounted for by hospitalisation for manic episodes. Comparatively little (less than 10%) is spent on the medication that could keep patients out of hospital.

Although antidepressants are generally of little help, pharmacotherapy with other agents has a useful role. This should be combined with psychoeducation – which is of proven benefit, especially when conducted in groups rather than on an individual basis. But perhaps of greatest importance is that patients with bipolar disorder should be managed by specialist mood disorder clinics.