Epidemiology is a branch of medicine that looks beyond the 4 walls of a healthcare facility and tracks how a particular disease affects the general population. It is a discipline in which medicine and policymaking meet, opening the door for healthcare to become more efficient and equitable to all.
Epidemiology as a discipline began to flourish in earnest in the 20th century when medicine became less of a personal issue and more of a sociopolitical one. This change could be observed in Britain with the introduction of the National Health Service, which for the first time in British history, made healthcare free at the point of delivery. This meant that subsequent governments would have to allocate a greater proportion of public funds to healthcare, a task best carried out with the help of epidemiological data.
In fact, it is because of epidemiological studies that we are able to classify some diseases as “rare” and others as “common.” This distinction is important to make for a variety of reasons: it allows public funds to be spent on research and care in proportion to how much the disease affects the general population, and it also helps physicians determine the likelihood of a diagnosis based on its overall prevalence in the public.
In the Journal of Medicine and Life, Ana-Maria and colleagues conducted a literature review on the epidemiology of myasthenia gravis. Their findings provide an interesting snapshot of the state of myasthenia gravis in the global population today.
Rising Incidence and Prevalence
Myasthenia gravis is a neuromuscular disorder that has a highly heterogeneous presentation. Its name is derived from the base words “mus,” which means “muscle,” and “asthenia,” which means “weakness.”
“Given its pathogenetic mechanism and specific anatomical location, [myasthenia gravis] has become both a prototype for autoimmune disorders and a model for understanding the synaptic function,” Ana-Maria and colleagues wrote.
Read more about myasthenia gravis etiology
Although myasthenia gravis is one of the most common neuromuscular junction disorders in the world, it is still classified as a rare disease — neurologists are likely to only encounter a handful of myasthenia gravis cases a year.
Charting the epidemiology of rare diseases has always been challenging for a variety of reasons: small mistakes in reporting can drastically alter the overall picture, and rare diseases are naturally easier to miss, meaning that its true prevalence in a given population can never be known with the same precision as other well-known illnesses.
Nevertheless, specific facts can still be established, which, as we have seen, can be hugely beneficial for both physicians and policymakers.
Let’s start with the incidence and prevalence of the disease. There is little doubt that the number of cases of myasthenia gravis around the world is rising. When Ana-Maria and colleagues first studied the epidemiology of myasthenia gravis in 2007, the incidence was between 1.7 to 21.3, and the global rate was around 5.3 per million persons-years. When the study was repeated in 2019, the global rate of acetylcholine receptor antibody-positive myasthenia gravis was estimated to be between 4 to 8 per million persons-years.
Read more about myasthenia gravis prognosis
As for the prevalence of myasthenia gravis, it was estimated to be at 1 in 200,000 before the mid-1930s. After the introduction of anticholinesterase inhibitors, the figure rose to 1 in 20,000. In 1969, after serum antibodies against anticholinesterase receptors were detected, the figure rose again to 1 in 17,000 population.
“In the last decades, a further steady increase in prevalence has been observed,” the authors wrote. “Prolonged survival, a normal life expectancy, an aging population as well as improved diagnosis are probably the main explanations.”
In Neurologic Clinics, Hehir and Silversti arrived at a similar conclusion. In their study on the epidemiology of myasthenia gravis, they wrote, ”In general, both [incidence] and [prevalence] are increasing in nonlinear fashion over time. The biggest increase occurred around 1980. These increases are attributed to greater awareness of the disease and improvements in diagnostic antibody testing, epidemiologic methodology, and treatment of the disease leading to better survival.”
It should also be noted that studies have found a bimodal age distribution for myasthenia gravis, with peaks occurring when patients are in their 30s and again in their 50s. There have been various theories for why this is the case, but the consensus is that the number of patients with myasthenia gravis across all age groups will increase as treatment becomes more potent in reducing mortality rates.
Epidemiological studies on Alagille syndrome confirm much of what we already know: that it is a rare, debilitating disease that can be difficult to diagnose. Because Alagille syndrome is so rare, physicians would be correct to suspect an alternative diagnosis most of the time, which is why a close familiarity with the presentation and progression of the disease is much needed.
Ultimately, figures on the incidence and prevalence of a disease can be affected by many factors, including improved diagnostic testing, better public awareness, and upgraded data collection. The challenge is for physicians and policymakers to utilize the data collected to further refine diagnostic protocol and care.
Bubuioc AM, Kudebayeva A, Turuspekova S, Lisnic V, Leone MA. The epidemiology of myasthenia gravis. J Med Life. Published online October 14, 2020. doi:10.25122/jml-2020-0145
Hehir MK, Silvestri NJ. Generalized myasthenia gravis: classification, clinical presentation, natural history, and epidemiology. Neurol Clin. Published online April 11, 2018. doi:10.1016/j.ncl.2018.01.002