Trends in survival and cause of death in Danish patients with multiple sclerosis
Bronnum-Hansen H, Koch-Henriksen N and Stenager E;
Commented by , 24 May 2004
Background
The epidemiologist of multiple sclerosis (MS) has been extensively described, although basic information such as survival after disease onset, and degree of MS related death varies considerably. Few studies have been comprehensive enough to provide data of cause specific mortality, compared to a background population. The current study aims at addressing these questions in a large population based study. The authors use data from The Danish Multiple Sclerosis Registry. This database is unique, since it holds a complete record of all Danish MS patients diagnosed over half a century.
Aim
To analyze trends in survival and causes of death in MS compared to the general population.
Methods
Patients with initial MS symptoms between 1949 – 1996 were included and classified as clinically definite, probable or possible. Follow up ended January 2000 for emigration and death, and January 1999 for cause specific deaths.
Expected number of deaths was estimated by multiplying age- and time- specific person-years of observation by the age- and time- specific population death rate. Standardized mortality ratios (SMR) was estimated as the quotient of observed to the expected number of death. Excess death rates (EDR) was estimated as the observed minus the expected number of deaths. Cox regression was used to analyze the trends in 10-year probability.
Results
1. The study comprised 9881 MS patients of which 84.4% was classified as clinically definite, and 15.6% possible.
2. Before follow up, 4254 MS patients had died compared with 1471 in the matched general population. SMR was 2.89 (95% CI: 2.81-2,98) for the whole group, 2.66 (95% CI: 2.54-2.78) for men and 3.14 (95% CI: 3.01-3.27) for women.
3. Median survival time from onset was 28 years for men and 33 years for women, compared with 38 and 45 years for the general population, respectively.
4. The survival probability improved significantly during the observation period (p £ 0.001). The 10-year EDR was almost halved during the study period.
5. MS was quoted as the underlying cause of death in 56.4% of death certificates. EDR was found for other diseases (except cancer) as well as suicide or accidents.
Discussion
The authors found that median survival time from onset, was reduced approximately 10 years in MS patients, compared with an age matched population, which is quite low in the range of previously reported results.
Survival improved during the study, which is suggested to be a consequence of improved treatment of complications and rehabilitation, since the effect of the general decline in mortality in the population was drawn out of the data. The effect of immuno-modulatory treatment was not contributing to these results since e.g. beta-interferon (BIF) treatment was introduced in Denmark in 1996. In this way the study provide an excellent basis for evaluating effect of BIF and other recently introduced treatment regimens in MS.
Although EDR was reduced, there was an increased risk of cardiovascular death and accidents/suicide, which can be explained by the disabling nature of the disease. The lower frequency of cancer is more questionable and is thought to mask a reduced medical surveillance of MS patients in the primary health care.
The results generally speak for themselves, and it is refreshing to see interesting new data in the field of MS epidemiology.