Comparison of the Range of Lumbar Cerebrospinal Fluid Pressure in Adults With Normal Cerebrospinal Fluid Pressure and in Idiopathic Intracranial Hypertension.

Background/methods: Lumbar puncture CSF pressure measurements in a large group of adults (116) having lumbar puncture (LP) for diagnostic reasons with no clinical indication of raised intracranial pressure were used to establish the normal range of CSF pressure. The cerebrospinal fluid (CSF) pressure was also measured in a smaller unselected series of patients (35) with the syndrome of idiopathic intracranial hypertension (IIH). All the lumbar punctures were performed by the same highly skilled operator, a consultant nurse, to ensure accuracy of measurement.

Results: The results showed that the mean CSF pressure was 18.7 cm H 2 O with a range of 1-29 cm H 2 O in the group with normal CSF pressure. Ninty-five percentage of values was below 29 cm H 2 O in the group with normal CSF pressure. In the series with IIH, the mean and range were 37.7 cm H 2 O and 29.5-66 cm H 2 O, respectively. The lowest recorded pressure in the IIH group was 29.5 cm H 2 O with 95% of values above 31.

Conclusions: This is the first time that the normal range of CSF pressure and that found in a group of patients with IIH has been reported after LP performed by the same operator to ensure inaccuracy of measurement has not biased the results. It suggests that the current upper limit of normal adopted by the revised diagnostic criteria for IIH (25 cm H 2 O) may be too low. The range of normal CSF pressure and that found in patients with IIH in our study suggests that consideration should be given to revising the upper limit of normal CSF pressure to around 30 cm H 2 O.