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⚃ 1.2.8.1 Takeaway: IBM is an extraordinarily rare disease. Based on recent studies, it is estimated that there are roughly 20,000 to 26,000 people diagnosed with IBM today in the United States (Greenberg, 2021).
⚃ 1.2.8.2 Prevalence of IBM:
⚄ The prevalence of IBM is very difficult to establish for several reasons:
⚄ There is no system of collection of statistics for
rare diseases.
≻ When your doctor diagnoses you, this information generally is not
shared in any database.
⚄ This is a very difficult disease to diagnose and it is clear that many cases are misdiagnosed, or undiagnosed.
⚄ Because the illness is related to aging, many patients assume that mild symptoms are simply signs of getting older and do not seek medical diagnosis.
⚄ Summary: Numbers reflecting the prevalence of IBM are hard to establish and are probably underestimated because of the high rates of misdiagnosis and undiagnosed cases.
⚃ 1.2.8.3 IBM and aging.
⚄ When you look at IBM numbers you have to
look at the age profile because IBM is an age-related disease…the
rate of IBM in the population goes up with age.
≻ This means that how you measure IBM in the population will affect
how many cases you will find.
≻ If you surveyed just people under 30, there would be virtually no
cases.
≻ If you survey people over 50 there will be many more cases.
⚄ Greenberg (2021) summarized research by Shelly et al.
(2021) that reviewed IBM in cases in Olmstead County, Minnesota.
≻ One of the paper's main findings is that the over age 30 IBM
prevalence rates for years 1990, 2000, and 2010 were 127.8, 104.3, and
97.2 per million, respectively.
≻ Over age 50 prevalence rates at these decades were 278.2, 223.9,
and 182.0 per million people.
≻ Annual incidence rates for the over 30 population were also
provided and ranged from 1.2 - 10.3 per million per year.
≻ These rates are the highest reported to date globally.
≻ Previously reported over age 50 prevalence rates have been 10.7 -
139.3 per million so that rates identified by Shelly et al. (2021) are as
much as twice as large as the highest rate previously reported.
≻ The authors note several reasons for the much higher prevalence
rates they identified, including less reliance on insurance diagnostic
codes (no specific ICD-9 code existed for IBM prior to 2010), improved
diagnostic methods and criteria affecting IBM case ascertainment, and
increased disease awareness.
≻ The study suggests that increases in IBM prevalence may largely be
the result of improved diagnostic methods.
⚄ It is now recognized that about 20 percent of cases
will occur in individuals younger than 50.
≻ IBM should be considered in patients with appropriate symptoms who
are older than 40 years.
From: Greenberg, S. A. (2016). Inclusion Body Myositis.
CONTINUUM: Lifelong Learning in Neurology, 22(21), 1871-1888.
https://journals.lww.com/continuum/abstract/2016/12000/inclusion_body_myositis.11.aspx
⚄ IBM is rare in African Americans and in non-Caucasians (Dimachkie & Barohn, 2013).
⚄ Men get IBM more often than females, about on average 2 times (so for every 33 women there will be 66 men with IBM).
https://ysph.yale.edu/ibmregistry/questionandanswer/
⚃ 1.2.8.4 Appendix. Terminology: It is important to understand some terminology. This Information is from the New York State Department of health.
⚄ A.1 What is incidence? Incidence is a measure of
disease that allows us to determine a person's probability of being
diagnosed with a disease during a given period of time.
≻ Therefore, the incidence is the number of newly diagnosed disease
cases.
≻ An incidence rate is the number of new disease cases divided by
the number of persons at risk for the disease.
≻ If five women are diagnosed with breast cancer over one year, out
of a total female study population of 200 (who do not have breast cancer
at the beginning of the study period), then we would say the incidence of
breast cancer in this population was 0.025 (or 2,500 per 100,000
women-years of study).
⚄ A.2 What is prevalence? Prevalence is a measure of
disease that allows us to determine a person's likelihood of having a
disease.
≻ Therefore, the number of prevalent cases is the total number of
cases of disease existing in a population.
≻ A prevalence rate is the total number of disease cases existing in
a population divided by the total population.
≻ So, if a measurement of cancer is taken in a population of 40,000
people and 1,200 were recently diagnosed with cancer and 3,500 are living
with cancer, then the prevalence of cancer is 0.118 (or 11,750 per 100,000
persons).
⚄ A.3 What is morbidity? Morbidity is another term for
illness.
≻ A person can have several co-morbidities simultaneously. So,
morbidities can range from Alzheimer's disease to cancer to traumatic
brain injury.
≻ Morbidities are NOT deaths.
≻ Prevalence is a measure often used to determine the level of
morbidity in a population.
⚄ A.4 What is mortality? Mortality is another term for
death.
≻ A mortality rate is the number of deaths due to a disease divided
by the total population.
≻ If there are 25 lung cancer deaths in one year in a population of
30,000, then the mortality rate for that population is 83 per 100,000.
⚃ 1.2.8.5 References:
⚄ Greenberg, S. A. (2021). Counting People with Inclusion Body Myositis. Neurology, 10.1212/WNL.0000000000011994. https://doi.org/10.1212/WNL.0000000000011994.
⚄ Shelly, S., Mielke, M. M., Mandrekar, J., Milone, M., Ernste, F. C., Naddaf, E., & Liewluck, T. (2021). Epidemiology and Natural History of Inclusion Body Myositis: A 40-Year Population-Based Study. Neurology, 10.1212/WNL.0000000000012004. https://doi.org/10.1212/WNL.0000000000012004.