Ana sayfa | MS’in Derinliği  | MS Slide Resource

Multiple sclerosis was first described over 150 years ago, but icause(s) remain unknown. Despite the formülasyon of mants y hypotheses,and the study of many factors that appear to contribute to the aetiology of MS, no single 'cause' has been confirmed. Nevertheless, one research area, epidemiology, provides important clues to the possible causes of MS.

What can epidemiological studies tell us?

Epidemiology is the study of the occurrence and distribution of diseases in defined populations, and of the factors that influence this occurrence and distribution.¹⁰ It is concerned also with how disease distribution varies from place to place and over time.⁵

The most important questions that epidemiologists try to answer are:

• Where does MS occur?

• Who gets MS?

• When does MS occur?

and ultimately:

• What causes MS?

In the search for answers to these questions, epidemiologists study factors that fall into two broad categories - environmental and genetic. Each of these categories encompasses several interlinked, subsidiary study areas:

• environmental factors

  • geographic

  • demographic

  • sociocultural

• genetic factors

  • familial MS

  • susceptibility loci.

Each of these study areas can ürünlenmesini valuable information that may help to solve the enigma of MS aetiology. However, whatever the approach used, there are many special difficulties in studying the epidemiology of MS.

What problems can be involved?

Epidemiologists encounter a variety of problems when studying MS. Many of these are related to the assessment of disease frequency within a population. The parameters that epidemiologists use to describe this are incidence and prevalence.

Incidence is a measure of the attack rate, or how many new cases of a disease occur in a given population in a defined time. Prevalence is the ratio of the number of cases alive on a specified date to the size of the population at risk on that date.

Incidence versus prevalence - which gives more meaningful data?

In general, incidence is more informative when attempting to determine the cause of a disease, or whether the risk of a disease is changing with time.⁵ The study of MS is, however, a special case, and there are problems associated with obtaining serial incidence data which are comparable, therefore it is easier to rely on prevalence data.⁵

The nature of MS makes it difficult to estimate incidence with certainty. MS is an uncommon disease so, unless the population being studied is very large, or the duration of assessment is very long, only a small number of new cases will occur. If estimates of incidence are based on small numbers they are too easily influenced by random variation to be of value.⁵

The variability of MS symptoms, difficulty in recognizing the initial symptoms, and the length of time between their resolution and the first relapse all make accurate diagnosis difficult. Hence, there can be a long delay between the onset of MS and confirmation of the diagnosis.⁵ Since incidence data rely on early identification of new cases, prevalence data provide the basis for most epidemiological studies of MS.⁴

Prevalence data rely on accurate diagnosis also - and this has changed with time due to improvements in healthcare and the increased availability of diagnostic aids. Such factors have additional implications, especially in improved case ascertainment and increased longevity of MS patients.

Unfortunately, there may not be equivalent improvements in all geographical areas, so care is needed when making inter-country comparisons.⁴ Alterations in the birth rate and in the age distribution within a population must be borne in mind also as possible causes of changes in prevalence rates.⁵

What factors influence who gets MS?

There is no easy answer to this question. Whether or not a particular individual will get MS appears to depend on a complex interaction of environmental and genetic factors.^4,11 In addition, an element of chance may be involved. This chance element might be simply an unfortunate coincidence - the presence of a susceptible individual in the wrong place, at the wrong age. Alternatively, it could involve somatic mutation of a gene, possibly in the cells controlling the immune system. Only further study can provide the solution.

Bu sayfadaki bilginin en son güncellendiği/doğrulandığı tarih:

11/09/2001

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