CSF / BMI

Q: The normal cerebrospinal fluid (CSF) pressure should be adjusted with patients' body mass index to avoid false positive or false negative results? (select one) 

A) True

B) False

Answer: B

The normal CSF pressure in most healthy people is usually less than 150 mm H20. Although the upper limit up to 250 mm H20 has been described. The  CSF pressure should be measured with a manometer in a patient lying flat in the lateral decubitus position with the legs extended. 

Said that, there are many factors that can alter the CSF measurement. It includes an improper patient's position, the experience of an operator, and the degree of relaxation of a patient's other body muscles. Although patients' BMI may cause a little elevation in CSF opening pressure, studies have failed to show a strong correlation. 

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References:

Whiteley W, Al-Shahi R, Warlow CP, et al. CSF opening pressure: reference interval and the effect of body mass index. Neurology 2006; 67:1690.