Separation of affective disorder into seasonal and nonseasonal types using motion sickness susceptibility as a marker.

A sample of 133 candidates for antidepressant or mood-stabilizing medication treatment, with acute onset or a new phase of illness between the autumnal and vernal equinoxes, was gathered over a 3-year period from a private outpatient practice. All patients were diagnosed using DSM-III-R criteria, rated on a standard motion sickness (MS) questionnaire, and asked whether they had experienced cardinal symptoms of seasonal affective disorder (SAD). There was a positive relationship between greater MS and SAD in the entire patient sample. When a subsample of 23 patients was given a 2-week trial of phototherapy and rated for improvement, MS-susceptible patients responded better than MS-resistant patients.