Validity of hospital discharge data for identifying cases of amyotrophic lateral sclerosis.

Inpatient hospital encounters and emergency department visits were examined to identify cases of amyotrophic lateral sclerosis (ALS).The ninth edition of the International Classification of Disease, clinical modification (ICD-9-CM) for ALS was confirmed for ALS was confirmed in 93% of inpatient discharges and in 91% of emergency department visits by the diagnostic standard (chart review). Yearly prevalence rates ranged from 2.94 to 3.28 per 100,000 residents. The low calculated prevalence rates suggest that this method of case identification is inadequate and must be combined with other data sets to maximize confirmation of the clinical diagnosis.