@inbook{3411866,
author={Egilius L.H. Spierings},
editor={Warfield, Carol A. and Bajwa, Zahid H.},
title={Chapter 22. Chronic Daily Headache},
booktitle={Principles & Practice of Pain Medicine, 2e},
publisher={The McGraw-Hill Companies},
address={New York, NY},
year={2004},
url={accessanesthesiology.mhmedical.com/content.aspx?aid=3411866}
}