Seasonal cyclothymia to seasonal bipolar affective disorder: a double switch after stroke.

The appearance of bipolar affective disorder after stroke depends on the presence of two factors: a predisposing factor of either genetic loading or subcortical atrophy, and a lesion of specific corticolimbic pathways involving the right hemisphere. Whether cyclothymia and seasonal affective disorder further predispose to poststroke affective disorder is not clear. A case is described which highlights these issues. The aetiological factors, pathophysiology, and diagnosis are discussed.