Economic aspects of chronic diseases : multiple sclerosis and diabetes mellitus

Abstract

This thesis contains applications of health economics on the chronic diseases multiple sclerosis (MS) and diabetes mellitus. Health economics has been defined as the science concerned with issues relating to the allocation of scarce resources to improve health. Costof-illness studies, which are one type of health economic studies, are mainly descriptive by nature. The aim of these studies is to show the total cost to society of a certain disease or group of diseases. There are two approaches for calculating the cost-of-illness: the top-down and the bottom-up approach. The top-down approach uses aggregated figures from official registers to collect diagnosis-related resources. In a bottom-up study, all resources are collected in a sub-population, for example through patient surveys, and extrapolated to the population level. Another type of health economic study is economic evaluation, the aim of which is to investigate the cost-effectiveness of different interventions.

The main aim of this thesis was to calculate the cost-of-illness of multiple sclerosis and diabetes mellitus, using both the top-down and the bottom-up approach. Multiple sclerosis was chosen as the main alternative because it is a common neurological disorder with life-long duration and significant severity, which suggests that the disease imposes a major economic burden on society. Diabetes mellitus was chosen as the alternative for comparison because it is also a chronic disease but different in many ways. The main type of diabetes (type 2) affects elderly with high co- morbidity, the disease is complex with a number of related complications and the incidence is increasing. New disease modifying drugs for treating multiple sclerosis have recently been introduced. A second aim of this thesis was to use data collected from one of the cost-of-illness studies together with several other data sources to evaluate the cost-effectiveness of one of the disease modifying drugs (interferonbeta-1b).

The results show that cost-of-illness studies are very data dependent. The availability and quality of data will have a major impact on the result of the study. The two approaches, top-down and bottom-up, rely on different data sources and will normally give different results. For a disease like multiple sclerosis, where the majority of resources are used outside the health care system, a bottom-up approach is needed to capture all resources. The total cost due to MS was calculated at 1.7 billion SEK in 1994 using a top-down method which can. be compared to a total cost of 4.9 billion SEK calculated in 1998 using a bottom-up method. How costs are defined and calculated will also affect the results. The top-down study on diabetes showed the direct costs to be 1.6 billion SEK. However, this study only used the main diagnosis to calculate costs. When both diabetes- related and non diabetes-related resources for patients of type 2 diabetes were included, the direct costs were estimated at 7 billion SEK.

The economic evaluation of interferon-beta for treating secondary progressive multiple sclerosis revealed that a simulation model is necessary for undertaking economic evaluations in a chronic disease like MS. Clinical trials seldom include economic data and the follow-up period is too short to show economic benefits of new drugs. Our evaluation showed that the result of the evaluation is dependent on the time perspective and which costs are included in the analysis. In the base-case scenario, the incremental cost per quality adjusted life year (QALY) was estimated at 342 700 SEK, and it is at the higher end of what is normally regarded as a cost-effective intervention in Swedish health care.

The thesis has shown that economic, epidemiologic and clinical data can be combined to increase the knowledge of the economic aspects of chronic diseases. This information can be used for decision-making on the allocation of scarce resources, for the benefit of both individual patients and society as a whole.