OBJECTIVE: To explore the extent and nature of cognitive deficits in patients with idiopathic intracranial hypertension (IIH) at the time of diagnosis and after 3 months of treatment.

DESIGN: Prospective case-control study.

SETTING: Neurological department, ophthalmological department and a tertiary headache referral clinic at a Danish university hospital.

PARTICIPANTS: 31 patients with definite IIH referred from June 2011 to February 2013 and included within 1 week of diagnostic intracranial pressure (ICP) measurement. 29 patients completed re-examination at the 3-month follow-up. At the time of testing, none of the patients took medication potentially affecting cognitive function. Controls were 31 healthy age-matched and sex-matched volunteers from the local community.

OUTCOME MEASURES: Executive function, working memory, visuospatial memory, processing speed, attention and reaction time assessed by a comprehensive neuropsychological test battery consisting of validated computerised (Cambridge neuropsychological test automated battery) and paper-and-pencil tests.

RESULTS: Patients with IIH performed significantly worse than controls in four of six cognitive domains (p≤0.02). Deficits were most pronounced in reaction time (1.45 SD below controls 95% CI 2.10 to 0.85) and processing speed (1.48 SD below controls 95% CI 2.08 to 0.81). Despite marked improvement in ICP and headache, re-examination showed persistent cognitive dysfunction 3 months after diagnosis and start of treatment.

CONCLUSIONS: We demonstrate for the first time in a well-defined cohort of patients that IIH may be associated with cognitive dysfunction. This could explain the functional disability of patients with IIH. A focused multidisciplinary approach including neuropsychological rehabilitation, therefore, might be relevant in the treatment of patients with IIH.