^Ferri, Fred F. Ferri's differential diagnosis : a practical guide to the differential diagnosis of symptoms, signs, and clinical disorders 2nd ed. Philadelphia, PA: Elsevier/Mosby. 2010: Chapter U. ISBN 0323076998. 引文格式1维护：冗余文本 (link)
^Global Burden of Disease Study 2013, Collaborators. Global, regional, and national incidence, prevalence, and years lived with disability for 301 acute and chronic diseases and injuries in 188 countries, 1990-2013: a systematic analysis for the Global Burden of Disease Study 2013.. Lancet (London, England). 5 June 2015. PMID 26063472.