Multiple sclerosis (MS) is the most common progressive neurological disease of young adults and currently affects 5000 persons in Portugal. Typically, the course of MS starts with random exacerbations and then slowly becomes progressive. Psychiatric symptoms are common in MS and affect mood, behaviour and cognition.

Affective disturbances in MS were first noted by Charcot in 1874, when he observed that the intellectual and emotional faculties of patients with MS were “blunted in their totality”. Major depression is the most common neuropsychiatric disorder in MS with an approximate 50% lifetime prevalence rate.

The association between psychotic symptoms and MS has been described in the literature, although not yet well understood. About 5% of MS patients develop psychotic symptoms in the disease course, usually coinciding with an relapse, but in less than 1% of the cases, they are the onset of the disease. Several studies have suggested a relationship between psychosis and MS through demonstrating their higher comorbidity, their temporal relationship, and their association with particular structural abnormalities in the brain (periventricular white matter and temporal demyelination). Besides regional demyelination, the use of corticosteroids and interferon, have been implicated in the presence of psychotic symptoms. the authors make a subsequent review of the neuropsychiatric manifestations of MS, with special attention to the psychotic symptoms, the differential diagnosis between these two conditions and the psychiatric treatment.