NEURO-EPIDEMIOLOGY The accuracy of discharge diagnosis coding for Amyotrophic Lateral Sclerosis in a large teaching hospital Federica Edith Pisa Æ Lorenzo Verriello Æ Laura Deroma Æ Daniela Drigo Æ Paolo Bergonzi Æ Gian Luigi Gigli Æ Fabio Barbone Received: 2 January 2009 / Accepted: 17 July 2009 / Published online: 6 August 2009 Ó Springer Science+Business Media B.V. 2009 Abstract To evaluate the accuracy of hospital discharge data as a source of Amyotrophic Lateral Sclerosis (ALS) cases for epidemiological studies or disease registries, a validation study was performed. All records of patients discharged in 2005 and 2006 with principal or secondary International Classification of Diseases, 9th rev., Clinical Modification (ICD 9 CM) diagnosis code of ALS (335.20), other anterior horn cell disease (335), spinal cord disease (336), hereditary and idiopathic peripheral neuropathy (356), inflammatory and toxic neuropathy (357), myoneu- ral disorders (358), muscular dystrophies and myopathies (359), were selected from the electronic archive of dis- charge data of the University Hospital of Udine, Friuli Venezia Giulia Region, North East Italy. Corresponding clinical documentation was reviewed to ascertain the presence of El Escorial criteria, the gold standard. Sensi- tivity of the ICD 9 CM discharge code 335.20 was 93% (95%CI: 82–99%) and decreased to 91% (95%CI: 77–98%) when suspect ALS was excluded. Specificity was 99% (95%CI: 97–99%). The ICD 9 CM discharge code 335.20 can identify a high percentage of hospitalizations of patients truly affected by ALS and of patients with no ALS, among selected neurological diagnostic codes. To ensure complete ALS case ascertainment, prospective population- based registries or epidemiologic studies require active prospective surveillance and use of multiple sources, among them hospital discharge archives can provide accurate information. Keywords Amyotrophic lateral sclerosis Á Disease registries Á Hospital morbidity data Á Incidence Á Sensitivity Á Specificity Abbreviations ALS Amyotrophic lateral sclerosis ICD 9 CM International Classification of Diseases, 9th rev., Clinical Modification Introduction Amyotrophic lateral sclerosis (ALS) is a rare and pro- gressive neurodegenerative disease affecting cortical and spinal motor neurons, whose diagnosis is mainly based on clinical retrieval of signs and symptoms of motor neuron degeneration [1]. Studies performed in Europe and North America report a great variability in incidence for ALS, rates ranging from 0.6 to 2.4 per 100,000 person-years. This variability might be partly accounted for by study design features, since when more consistent methods are used, incidence rates show greater uniformity [2, 3]. Prospective population-based registries or studies, based on active surveillance, uniform diagnostic criteria and use of multiple sources for case ascertainment, are considered the optimal methodological approach for obtaining reli- able incidence estimates for ALS [2]. Besides active case finding and prospective surveillance, health care system F. E. Pisa (&) Á L. Deroma Á D. Drigo Á F. Barbone Institute of Hygiene and Epidemiology, DPMSC, Azienda Ospedaliero-Universitaria di Udine, Via Colugna 40, 33100 Udine, Italy e-mail: federica.pisa@uniud.it F. E. Pisa Á L. Verriello Á P. Bergonzi Á G. L. Gigli Á F. Barbone University Hospital of Udine, Udine, Italy L. Verriello Á P. Bergonzi Á G. L. Gigli Department of Neurology, University of Udine, Udine, Italy 123 Eur J Epidemiol (2009) 24:635–640 DOI 10.1007/s10654-009-9376-1