This review addresses the methodologic issues relevant to the study of comorbidity and provides a broad overview of the medical and psychiatric conditions associated with migraine. Since the body of literature examining the comorbidity of migraine is enormous, the scope of this review will largely focus on community and case-control studies. Among the selected comorbid medical conditions, including disorders of the cardiovascular, respiratory, neurologic, gastrointestinal and immunologic systems, stroke, asthma, and allergies appear to be most strongly associated with migraine. Among the psychiatric illnesses, mood and anxiety disorders have been shown to be most strongly associated with migraine in the general population. Further research is indicated and necessary to elucidate the precise mechanism of migraine comorbidity.

This paper describes the application of prospective longitudinal data from an epidemiological sample of young adults to define subtypes of major depression. Depression was classified on a spectrum from subthreshold manifestation of symptoms and duration at one end, to cases with recurrent episodes of depression meeting duration criteria for major depressive episodes at the other. There was a direct relationship between the severity of depression over the longitudinal course and both duration and recurrence of depressive episodes. The subgroup of depression with recurrence of both brief and longer duration episodes could be discriminated on most of the indicators of validity including symptoms, impairment, family history, and suicide attempts. In light of the young age of this cohort, the strong history of suicide attempts and other complications of depression among the subjects with recurrent depression was striking. These findings underscore the importance of employing course as a classification criterion of depression, and the inclusion of subthreshold episodes of depression in the characterisation of course.

Assortative mating among 56 married in-patients with primary affective disorders and their spouses was studied by determining the prevalence of psychiatric illness among the spouses by means of direct interviews and standardized diagnostic criteria. A high degree of assortative mating among both male and female patients was observed for total psychiatric illness, broad spectrum affective illness and major depression. A significantly higher prevalence of psychiatric and affective illness was found among the first-degree relatives of the ill spouses when compared with the first-degree relatives of the well spouses. There was a high degree of diagnostic concordance between the patients and spouses for both affective illness and alcoholism, with a higher degree of assortative mating among bipolar patients than among unipolar patients. The finding in this study of an increased prevalence of psychiatric disorder in the first-degree relatives of the ill spouses would support the hypothesis that there is a tendency for individuals with a predisposition to psychiatric illness to marry, rather than the existence of a marital interaction which causes an increased concordance for psychiatric illness.