Assessing amyotrophic lateral sclerosis prevalence in Norway from 2009 to 2015 from compulsory nationwide health registers

Abstract

Objective: In Norway, diagnoses from specialist health care visits, drug prescriptions, and causes of deaths are registered in compulsory health registers. We aimed to determine amyotrophic lateral sclerosis (ALS) prevalence from 2009 to 2015 by combining these registers. Methods: We validated the Norwegian Patient Registry (NPR) through hospital files, and linked it with the Norwegian Cause of Death Registry and the Norwegian Prescription Database. Poisson regression models were fitted for estimating gender ratios, time trends and possible interactions. Similar models were used for mortality data subtracted from the dataset. Results: Eleven percent of patients with at least one ALS-related entry in NPR did not have ALS. ALS prevalence could nevertheless be reliably estimated through ascertaining cases identified in two separate registers, or with at least two entries in NPR with first entry within four years prior to prevalence date. ALS prevalence remained stable, and was 7.6/100,000 (95% CI 6.9–8.4) at 31st December 2015. Mean male:female ratio was higher for prevalence (1.8; 95% CI 1.6–2.0) than for mortality (1.5; 95% CI 1.2–1.8) (p = 0.04). There were also significant regional differences in prevalence (p < 0.01) but not in mortality. Conclusions: Norwegian compulsory health registers provide reliable tools for ALS surveillance, and suggest gender and regional differences in survival after diagnosis.

Keywords:

• Amyotrophic lateral sclerosis
• motor neuron disease
• epidemiology
• prevalence

Acknowledgements

We are grateful for data supplied by The Norwegian Patient Registry, The Norwegian Prescription Database, The Norwegian Cause of Death Registry and financial support from the Norwegian ALS Foundation.

Ethical standards

The study was approved by the Regional Committee for Medical and Health Research Ethics (REC South East, ref 2014/1987). The manuscript does not contain clinical studies. The exchange of identities from hospital files to Norwegian Patient Registry was limited to deceased individuals.

Declaration of interest

The authors report no conflicts of interest.

Supplementary material available online