Decrease in rate of multiple sclerosis-related hospitalizations in Portugal

Introduction

Multiple sclerosis (MS) is a chronic, neurodegenerative autoimmune disorder of the central nervous system¹. With a prevalence of 1/800 in North America and Northern Europe, MS is the most common acquired neurological disorder in young adults¹, posing a substantialburden on healthcare systems. Recent studies have, however, suggested that MS-related hospitalization rates have been declining over the last decades^2,3.

Portugal is considered a region of medium MS prevalence⁴, but epidemiological data are limited. In the present study, we sought to investigate the difference in the rate of MS-related hospitalizations in Portugal between 2008 and 2013.

Methods

Data on the number of hospitalizations in 2008 and 2013 with an MS diagnosis [International Classification of Diseases, 9th revision (ICD 9): 340] were obtained from the National Hospital Discharge Registry, centrally held in the Portuguese Central Administration of the Health System. This database includes data about all hospitalizations in all public hospitals. In Portugal, the National Health Service provides universal access to healthcare and patients with MS are almost exclusively treated in public hospitals⁴. These years were chosen as MS prevalence data in 2008 and 2013 in Portugal were available from the Atlas of MS (http://www.msif.org/wp-content/uploads/2014/09/Atlas-of-MS.pdf)⁵. The total number of hospitalizations (1,177,048 in 2008 and 1,108,911 in 2013), as well as the estimates of the Portuguese population, were obtained from Portuguese official statistics⁶.

The incidence of hospitalizations (MS-related or all-cause hospitalizations) was calculated by dividing the number of hospitalizations in each year by the number of patients at risk in the same year. The Wald method was used to calculate 95% confidence intervals (CI). Two different definitions of MS-related hospitalizations were used: 1) where MS was the primary reason for admission — the MS ICD-9 diagnostic code was reported in the field of the primary diagnosis, and 2) where MS was reported as either a primary or a secondary reason for admission — the MS ICD 9 diagnostic code was in any position on the diagnoses fields (20 fields available). The proportion of MS-related hospitalizations in each year was obtained by dividing the number of MS-related hospitalizations in each year by the total number of hospitalizations in the same year. Demographic and clinical characteristics of patients with MS hospitalized in each year were described using number and percentage of patients for categorical variables, and mean and standard deviation (variables with a normal distribution) or median and interquartile range (variables with a skewed distribution) for continuous variables. Differences between characteristics in 2008 and 2013 were estimated using t-tests (variables with a normal distribution) or Mann–Whitney test (variables with a skewed distribution) for continuous variables, and Chi square test for other categorical variables. P values < 0.05 were considered to be statistically significant. Statistical analysis was performed using STATA software version 13.

Results

Demographic and clinical characteristics of patients with MS hospitalized in 2008 and 2013 are summarized in Table 1. Between 2008 and 2013, the incidence rate of MS-related hospitalizations decreased from 15.9/100 person-years (95% CI: 14.9–16.9) to 8.9/100 person-years (95% CI: 8.2–9.6), defined using only information recorded in the main diagnosis field, and from 25.5/100 person-years (95% CI: 24.4–26.8) to 19.4/100 person-years (95% CI: 18.5–20.4) using the main or secondary diagnoses respectively (Figure 1). In the same years, the incidence rate of all hospitalizations in Portugal decreased from 11.7/100 person-years (95% CI: 11.7–11.7) to 11.2/100 person-years (95% CI: 11.1–11.2) (Figure 1). The proportion of MS-related hospitalizations among all hospitalizations in Portugal decreased slightly from 0.07% to 0.05% between 2008 and 2013.

Figure 1. Incidence rate of MS-related and all hospitalizations in Portugal in 2008 and 2013.

The age of the patients with MS hospitalized and the length of stay in the hospital increased significantly (Table 1) between 2008 and 2013, where MS was either only a primary diagnosis or a diagnosis anywhere on the patient record. There was an increase in the proportions of females admitted to hospital but this was only significant when MS was recorded in any of the diagnosis fields (Table 1; p value = 0.062 for MS as main diagnosis and p value = 0.006 for MS as main or secondary diagnosis).

No differences were observed in the proportion of patients that died during hospitalization (Table 1). Where MS diagnosis was anywhere on the patient record, the proportion of MS patients with other diagnoses during hospitalization increased significantly between 2008 and 2013 for all groups of diseases considered, except for infectious and parasitic diseases, neoplasms, diseases of the nervous system and sense organs (excluding MS), and congenital anomalies (Table 1).