To describe the limitations and challenges encountered while determining the number of ALS cases in the United States. 

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neuromuscular disorder with no cure. The most recent estimates of ALS cases in the United States (U.S.) from the National ALS Registry (Registry) show over 16,000 cases or 5.2 per 100,000 persons for 2015. Unlike many communicable diseases and conditions, ALS is not reported to state and local health officials who would, in turn, notify federal health agencies. In addition, personally identifiable information (PII) data from private health insurance providers are not available to the Registry  for determining ALS cases.

In the event ALS was a reportable disease and data were available from all insurance providers, the Registry would utilize its validated algorithm for case ascertainment. This is based on International Classification of Diseases codes, visits to neurologists, prescriptions for ALS specific drugs, and death certificates. In addition, the Registry is utilizing capture-recapture methodology in order to estimate the number of missing cases. Capture-recapture allows for the correction of under-ascertainment in epidemiology.

The results are currently unknown since ALS is not notifiable to federal health officials and data from private insurance providers are not available. Though it is anticipated the addition of these  cases will increase the national prevalence estimates and counts.

Communicable diseases in the U.S. have an inherent advantage when it comes to case-ascertainment  on a national scale. The limitations of determining incidence and prevalence for non-communicable diseases are evident since reporting requirements are not available. Better data sources, data sharing, and novel case ascertainment methods are needed in order to provide an accurate estimate of national epidemiologic trends.