COPENHAGEN – Sleep spindle density is diminished in euthymic patients with bipolar disorder, suggesting that this sleep architecture abnormality might offer potential for early differentiation of bipolar from unipolar depression, Philipp S. Ritter, MD, said at the annual congress of the European College of Neuropsychopharmacology.
“Hopefully in the future our finding, if replicated, might have clinical utility. It might be a kind of soft biomarker that could be used in early detection, or, in people having their first depressive episode, you could perhaps use this to risk-stratify. And if you see there’s a great reduction in spindle density then a patient might have a higher likelihood of a bipolar disorder, so you might not want to treat with antidepressants that have a high switch rate,” explained, a psychiatrist at Technical University of Dresden (Germany).
are a specific sleep architecture formation evident on the sleep EEG. They are sudden high-amplitude bursts occurring in stage N2 sleep. They are thought to be associated with sensory gating and memory processes. Other investigators have repeatedly demonstrated that patients with schizophrenia, as well as their asymptomatic first-degree relatives, have a reduced density of fast spindles greater than 13 Hz, compared with the general population. In contrast, patients with unipolar depression do not display this polysomnographic abnormality.
These findings prompted Dr. Ritter and his coinvestigators to conduct an all-night polysomnographic study in 24 euthymic patients with bipolar disorder and 25 healthy controls. The bipolar patients demonstrated a reduced density and mean frequency of fast sleep spindles, but not slow spindles ().
These sleep spindle findings implicate thalamic dysfunction as a potential neurobiologic mechanism in bipolar disorder, since spindles are generated in the thalamus and spun off in thalamocortical feedback loops, Dr. Ritter observed.
Which came first: the chicken (bipolar disorder) or the egg (sleep disturbance)?
Sleep problems are a prominent issue in patients with bipolar disorder, even when they are euthymic.
“Anybody who deals with bipolar patients knows that sleep is a constant issue. You are always talking to your patients about their sleep. They’re sleeping too much, or not enough, or they’re sleeping just about right but it’s unsatisfactory. They do not sleep well. And if there’s something that disrupts their sleep, it can precipitate episodes,” Dr. Ritter said.
He wondered whether sleep problems are an intrinsic part of the bipolar illness, or a byproduct of the stress of having a severe mental disorder, perhaps a medication side effect, or whether the disordered sleep actually precedes the clinical expression of the mood disorder. So he and his coinvestigators turned to a Munich-based cohort sample of 3,021 adolescents and young adults assessed via the standardizedfour times during 10 years of prospective follow-up.
Among 1,943 participants in the epidemiologic study who were free of major mental disorders at entry, the presence of sleep disturbance at baseline as quantified using thedoubled the risk of developing bipolar disorder within the next 10 years. After the researchers controlled for potential confounders, including parental mood disorder, gender, age, and a history of alcohol or cannabis dependence, poor sleep quality at baseline remained independently associated with a 1.75-fold increased chance of subsequently developing bipolar disorder ( ).
“This is a little bit higher, actually, than the odds ratio usually found for depressive disorders,” said Dr. Ritter.
Dr. Ritter reported having no financial conflicts regarding these studies.