Bipolar disorder affects approximately 2-8% of the population, depending on how it’s defined. People who are not familiar with bipolar disorder may only know about those who experience true mania and severe depression. This is known as bipolar I and only affects about 1% of the population. Bipolar disorder is now being characterized as a spectrum disorder, meaning there is a range of severity up to bipolar I. Part of the range of symptoms for some people includes symptoms that do not qualify as full-blown episodes. These symptoms are known as subthreshold.
In addition to bipolar I, bipolar spectrum disorders also include bipolar II disorder, cyclothymia and bipolar not otherwise specified (NOS). In bipolar II, patients experience full depressive disorders, but never full manic disorders. Cyclothymia consists of short episodes that are not as severe as those in bipolar I or II.
Subthreshold bipolar disorder can be included in a diagnosis of bipolar disorder not otherwise specified (NOS). While there is not a solid definition for subthreshold bipolar disorder or bipolar disorder NOS, it basically means that the person is experiencing some symptoms of bipolar disorder, but not enough to qualify for the other three types of the disorder.
Subthreshold bipolar disorder may often be misdiagnosed as major depressive disorder. This is because symptoms of hypomania may be missed. Patients might not realize they are experiencing symptoms of hypomania because they do not realize what they are experiencing is syndromal. Doctors may miss the diagnosis because the patient doesn’t report the symptoms or because they are simply not looking for bipolar disorder when diagnosing major depressive disorder.
The latter is problematic because according to one study approximately 2.5% of people with major depressive disorder show signs of subthreshold hypomania, meaning they met one of three criteria including one full week of feeling abnormally elated or hyper, one week of acting abnormally elated or hyper so that others were concerned or at least one week of being extraordinarily irritable or annoyed.
If a person is experiencing subthreshold hypomania, it is important to screen them for bipolar disorder. People with subthreshold hypomania often experience higher rates of anxiety disorders, impulse control disorders and substance use disorders. At this point, receiving proper treatment is important, but must be done carefully as antidepressants can induce hypomania or full mania in some people.
On the other hand, diagnosing more people with bipolar disorder may be problematic simply because their symptoms are subthreshold enough that they do not have a full illness, but merely the potential for having bipolar disorder.
Treatment for bipolar disorder is incredibly serious. The medications used are potent and come with risks. If a person does not need these medications to function well or the person is not in distress, they might not need the diagnosis in the first place.
Similarly, a diagnosis of bipolar disorder is serious and life-altering. It is not an illness that can be cured, and once given will follow the person for the rest of their life. It also still comes with a fair amount of stigma that is simply no longer experienced by those with mental illnesses such as major depressive disorder or anxiety disorders.
While subthreshold bipolar disorder may not need to be diagnosed or treated, the patient should be regularly screened in order to catch any signs of progression. It is absolutely possible that the patient could develop cyclothymia, bipolar II or bipolar I and with those, the sooner the treatment begins the better off the patient will be.
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