Mood disorders are a cluster of mental disorders that are characterized by mood swings or an abnormally depressed (low) or manic (elevated or irritable) mood. The most common mood disorder is major depression; others include bipolar disorder (or manic-depressive disorder), cyclothymia, and dysthymia (United States Department of Health and Human Services, 2006). Major depression is characterized by persistent feelings of sadness accompanied by several symptoms related to changes in appetite or sleeping patterns, loss of interest in activities, fatigue, inability to concentrate, and hopelessness or suicidal thoughts. Bipolar disorder is characterized by at least one manic episode and often by recurring episodes of mood disturbance, including both depressed and manic episodes. Bipolar disorder typically begins in a person’s middle twenties, tends to appear in families, and is a lifelong disorder. There are few published data on an association of TBI with bipolar disorder. Suicidal behavior is one of the most serious consequences of mood disorders and may consist of suicidal ideation (thoughts), suicide attempts, or completed suicide; suicide is discussed in the next section of this chapter.

Primary Studies

The committee identified four primary studies that examined an association between TBI and mood disorders. Fann et al. (2004) conducted a prospective cohort study to determine the risk of psychiatric illness after TBI. Patients were drawn from a health maintenance organization, Group Health Cooperative of Puget Sound, and received care in its facilities in six different counties in Washington. Computerized records of 939 health-plan members, 15 years old or older who had a diagnosis of a TBI in 1993, were available. Each patient was matched on sex, age, and reference date to three randomly selected unexposed health-plan members. TBI was ascertained in an emergency room, hospital or outpatient clinic, and severity of TBI was established by using the Centers for Disease Control and Prevention criteria. Psychiatric illnesses were ascertained by using the presence of psychiatric diagnoses, filling of prescriptions for psychiatric medications, and utilization of psychiatric services. In the first year after a moderate to severe TBI, 49% of the patients had evidence of psychiatric illnesses compared with 34% in the mild-TBI group and 18% in the comparison group; this reflected a significantly increasing risk of psychiatric illness with severity of TBI. The authors also found the risk of psychiatric illness to be greatest in the 6–12 months after the TBI in analyses that separately considered whether or not psychiatric illness had occurred in the year before injury. In patients without psychiatric illness in the year before injury, there was a 4-fold increased risk for developing a psychiatric disorder in the 6 months after a moderate to severe TBI (95% confidence interval [CI], 2.4–6.8) and a 2.8-fold increased risk after a mild TBI (95% CI, 2.1–3.7) compared with the risk in patients without a TBI. In patients with prior psychiatric illness, the corresponding increases in risk of psychiatric illness were factors of 2.1 (95% CI, 1.3–3.3) and 1.6 (95% CI, 1.2–2.2), respectively. The limitations of the study include the possible lack of precision in TBI exposure measurement, uncertainty regarding past psychiatric diagnosis occurring more than 1 year before ascertainment, and possible confounding by socioeconomic status.

Holsinger et al. (2002) examined the association between TBI and lifetime and current depression in a nested case–control study of World War II veterans. Cases were World War II veterans who had been hospitalized for TBI in 1944–1945 and controls were veterans who had been hospitalized during the same period with either pneumonia or serious laceration or other

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