MS diagnosis rate constant for 20 years, large UK study shows

The rate of multiple sclerosis (MS) diagnoses have remained relatively constant for almost 20 years in the U.K., according to a population-based study involving more than 22 million people.

Most MS diagnoses occurred during middle age, with women being more likely than men to receive a diagnosis.

While many autoimmune diseases occurred together, MS stood out as having few coexisting autoimmune conditions. Researchers noted this finding suggests MS may be a distinct disease compared with other autoimmune disorders.

The data also showed that about 10% of this U.K. population had an autoimmune condition, which can “consume considerable health resources,” researchers wrote.

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“There is a crucial need, therefore, to increase research efforts aimed at understanding the underlying causes of these conditions,” Geraldine Cambridge, PhD, said in a press release. Cambridge is the study’s senior author and a professor at the University College London, in the U.K.

This will “support the development of targeted interventions to reduce the contribution of environmental and social risk factors,” Cambridge said.

The population-based study, “Incidence, prevalence, and co-occurrence of autoimmune disorders over time and by age, sex, and socioeconomic status: a population-based cohort study of 22 million individuals in the UK,” was published in the journal The Lancet.

MS is considered an autoimmune disease because, instead of the immune system attacking infectious agents, it also targets and damages the myelin sheath, a fatty protective coating around nerve fibers. Such damage impairs proper nerve cell communication, leading to the onset of a wide range of neurological symptoms.

So far, more than 80 types of autoimmune diseases have been described, including rheumatoid arthritis, type 1 diabetes, lupus, myasthenia gravis, Sjögren’s syndrome, systemic sclerosis, and ankylosing spondylitis.

Although it is important to have accurate information about how common these diseases are and how that is changing over time, there is a lack of consistent information about the incidence of autoimmune diseases.

A group of specialists from various universities across the U.K. and from KU Leuven, in Belgium, now came together to investigate the incidence of 19 of the most common autoimmune diseases in the U.K. Incidence refers to the number of new diagnoses in a given period.

Searching for trends

They also looked for trends over time, relating to factors such as age, sex, socioeconomic status, season, and region, as well as whether autoimmune diseases may coexist with each other.

Anonymized (anonymous) electronic health records from 22 million individuals in the U.K., ranging from 2000-2019, were collected for analysis. Of the 19 autoimmune disorders examined, 10.2% of the entire population was affected, more of whom were women than men (13.1% vs. 7.4%).

During the study period, 15,634 people were newly diagnosed with MS, at a median age of 45, with most cases arising between 36 and 56. Women were 2.31 times more likely to receive an MS diagnosis than men. Other autoimmune diseases that peaked in middle age included psoriasis and lupus.

The incidence of MS diagnosis remained constant over the two-decade period, with an incidence rate of 10.4 per 100,000 person-years between 2000-2002 compared with 10.6 between 2017-2019. Person-years is a measurement that considers both the number of people and the amount of time each person spent in the study.

Overall, the data suggested that many autoimmune diseases occur together. Associations were highest among conditions affecting connective tissue, particularly Sjögren’s syndrome, lupus, and systemic sclerosis, after adjusting for age and sex. Other co-occurrences included childhood-onset type 1 diabetes with Addison’s disease (adrenal insufficiency), celiac disease, and thyroid diseases.

By contrast, MS was unique, with low rates of co-occurrence with other autoimmune diseases, suggesting distinct underlying disease processes. Myasthenia gravis and MS tended to co-occur, but the association was weak. The team noted it could not rule out diagnostic or diagnostic coding errors to explain this result.

MS also showed weak inverse associations with some autoimmune disorders, meaning those with MS were less likely to be diagnosed with these diseases. This finding was significant only for vitiligo, a condition marked by patches of skin losing their pigment or color.

Shared risk factors

“We observed that some autoimmune diseases tended to co-occur with one another more commonly than would be expected by chance or increased surveillance alone,” said Nathalie Conrad, PhD, first author of the study and a postdoctoral fellow at KU Leuven. “This could mean that some autoimmune diseases share common risk factors, such as genetic predispositions or environmental triggers.”

“But this phenomenon was not generalised across all autoimmune diseases — multiple sclerosis for example, stood out as having low rates of co-occurrence with other autoimmune diseases, suggesting a distinct pathophysiology [disease mechanism],” Conrad said.

While several reports have linked smoking to some autoimmune diseases such as MS, rheumatoid arthritis, or psoriasis, the team noted there were no signs of an incidence decline in these conditions despite a considerable reduction in smoking over the same period.

“Currently, the exact causes of many of the autoimmune diseases included in our study remain unknown and require further research,” the researchers wrote.

“Our study highlights the considerable burden that autoimmune diseases place upon individuals and the wider population,” Cambridge added. “Disentangling the commonalities and differences within this large and varied set of conditions is a complex task.”