Epidemiology of the psychiatric comorbidities of headache

Abstract

“Comorbidity” refers to the occurrence of two conditions in the same individual at a frequency greater than would be expected by chance. [1] Migraine is comorbid with a number of medical, neurologic, and psychiatric disorders. Examples of medical comorbidities include asthma, [2] coronary heart disease, [3] and chronic pain disorders. [4–7] Neurologic comorbidities include stroke and epilepsy, [8] and psychiatric comorbidities include anxiety, depression, panic disorder, and bipolar disorder. [9,10,] Comorbidities are best studied in representative samples because the prevalence of disease and the association among disorders is sometimes altered in clinicbased samples. This phenomenon, known as Berkson bias, can lead to under-estimates or over-estimates of the rates of co-occurrence for various disorders. Berkson bias arises when patterns of symptoms influence patterns of care seeking for a range of medical disorders. For example, someone with migraine and depression may be more likely to seek medical care with complaints of head pain and sadness than someonewho experiences only one of these disorders. Clinicbased studies of comorbidities are useful for generating hypotheses about comorbidities and for characterizing patient groups. They cannot be relied upon to determine if two conditions are actually occurring together with frequency greater than chance. Both clinic and population studies suggest that migraine is comorbid with a number of psychiatric disorders including depression, [11,12] anxiety [11,13,14] posttraumatic stress disorder, [15] chronic pain, [6] fibromyalgia, [16] and other medical disorders such as asthma. [2] In addition, rates of a number of comorbid conditions increase with the frequency of migraine attacks, and are higher for episodic migraine (EM) than for chronic migraine (CM). In the American Prevalence and Prevention (AMPP) study, persons with CM (n = 655) are about twice as likely than persons with EM (11,249) to have depression, anxiety, and various chronic pain disorders. [2] Respiratory disorders including asthma, bronchitis, and COPD, and cardiac risk factors including hypertension, diabetes, high cholesterol, and obesity are significantly more likely to be reported by those with CM. The broad range of comorbidities associated with headache, and the increasing risk of comorbidity with headache frequency, have important implications for healthcare professionals. Research indicates comorbidities negatively impact headache-related disability and health-related quality-of-life, further justifying an enhanced understanding of co-existing conditions to inform clinical practice. This chapter focuses on the psychiatric comorbidities of migraine and other headache disorders. The nature of epidemiologic research, the importance in differentiating between population and clinic-based studies, the clinical relevance of comorbidity, and the potential mechanisms that link migraine to its psychiatric comorbidities are discussed. Several key studies are examined as to what they reveal about psychiatric comorbidities and headache disorders.