[Bipolar disorder: inter-episode symptoms]

The importance of inter-episode symptoms in bipolar disorder can be traced back to the middle of the 19th century, at a time when the two fathers of the concept in France, Falret and Baillarger were opposed on the issue as to whether the presence of free intervals between the episodes had to be part or not of the disease's definition. Modern studies have reported rates between 50 and 68% for those symptoms which refer to subsyndromal manifestations present between affective episodes but that do not meet the required criteria for episodes definition. These manifestations comprise residual symptoms, prodromes, axis I comorbid psychiatric disorders, side effects of treatment, temperamental features, and comorbidity with personality disorders. Inter- episodes symptoms represent a risk factor for the occurrence of relapses and recurrences and are usually associated with impairments in functioning in almost all domains of psychosocial and family life. As they are easy to miss, it is important in clinical practice, to draw the attention of clinicians, patients and relatives to the role they have in the course of the illness. As far as their management, it may be crucial to achieve a full remission of the episodes, using adequate dosages of psychotropic drugs. Residual symptoms, prodromes as well as other inter-episode symptoms may respond to strategies based on cognitive-behaviour therapy, and/or psychoeducation.