LEMS Affects 2.7 of Every 1M People in Japan, Similar to Other Countries
Patients with cancer-associated LEMS more likely to be male
The prevalence of Lambert-Eaton myasthenic syndrome (LEMS) in Japan is similar to that of other countries, affecting approximately 2.7 out of every one million people in the country.
That is according to a study, “Nationwide survey of Lambert-Eaton myasthenic syndrome in Japan,” published in the journal BMJ Neurology Open.
LEMS is an autoimmune disorder that causes muscle weakness. Studies done in the U.S. and Europe have estimated that the prevalence of this rare disease is about 2.5 out of every one million people.
In the new study, the scientists conducted surveys to estimate the prevalence of LEMS in Japan.
“No nationwide survey has been performed for LEMS in Japan. Thus, we conducted a national study following a standard epidemiological protocol to estimate Japanese LEMS prevalence and clinical features,” the researchers wrote.
First, they sent a survey to thousands of medical clinics in Japan, asking about the number of LEMS patients seen at their clinic in 2017. A total of 2,708 clinics completed the survey — for context, there were 8,445 medical clinics operating in Japan in 2017.
Based on the completed surveys and the size of different clinics across the country, the researchers estimated that the prevalence of LEMS in Japan is 2.7 out of every one million people. Since there are around 125 million people living in Japan, that works out to about 348 people with LEMS in the country.
“The prevalence of LEMS was similar to previous reports from other countries,” the researchers wrote.
In a second round of surveys, they asked clinics who had responded to the first survey to provide healthcare data for treated LEMS patients. The scientists obtained 30 clinical records, from 16 males and 14 females with LEMS.
Records reveal 14 of 30 LEMS patients had cancer
Of the 30 patients, 14 had cancer, including 10 with small-cell lung cancer — the most common form of LEMS-related cancer. The mean age at LEMS onset was 62.2 years. Patients who had a tumor developed LEMS at a more advanced age compared with those who did not have cancer (67.1 vs. 57.8 years).
Patients with cancer-associated LEMS — also called paraneoplastic LEMS, or P-LEMS — were significantly more likely to be male, whereas those without cancer — called primary autoimmune LEMS or AI-LEMS — were more likely to be female.
Cigarette smoking is generally more common in males than females in Japan, which may help explain these results since smoking is a major risk factor for small-cell lung cancer, the researchers noted.
Disease duration was significantly longer in patients with AI-LEMS than in those with P-LEMS (median 7.5 vs. 2 years). Patterns of symptoms, as well as clinical and laboratory tests, were similar in both groups. The researchers noted that these similarities highlight the importance of explicitly testing for cancer in patients with LEMS of unclear origin, since the presence or absence of cancer may not be obvious from other data.
Treatment patterns were also similar between AI-LEMS and P-LEMS. The use of amifampridine — which is approved to treat LEMS in the U.S. under the brand name Firdapse — was limited in this study, likely because the therapy is not commercially available in Japan.
“The lack of commercially available medicine prevents physicians from subscribing [amifampridine] for patients with LEMS,” the team wrote, adding that this situation has to change.
Similar studies in the future are important to track how the prevalence of LEMS in Japan changes over time, the researchers wrote.
“A nationwide periodical survey will contribute to understanding LEMS and help improve the treatment and welfare of patients,” they added.
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