Results from the largest United States study to date of Lambert-Eaton myasthenic syndrome (LEMS) have indicated that for the majority of patients, Firdapse is the most effective treatment option currently available.
Data for this investigation came from the Veterans Affairs (VA) health information system called VistA. VistA is currently the largest electronic medical record in the country. Specifically, this study utilized records from October 1999 to September 2013. The total data set was 12,523,409 patients. Of these, 48 had a LEMS diagnosis, and 9 patients were considered likely to have the condition.
The results from this study were published in Muscle & Nerve.
Findings
LEMS and SCLC
LEMS is a rare neuromuscular and autoimmune disease which causes symptoms such as weakness in the proximal muscles, breathing issues, difficulty chewing and swallowing, deficiencies in gait, and eye problems.
58% of the LEMS patients in this study were also found to have small-cell lung cancer (SCLC). For 61% of these individuals, one of these diagnoses led to the other. The association of these two diseases is well-known among oncologists and neurologists.
Unfortunately, patients with LEMS who don’t have SCLC took about a year longer to receive their LEMS diagnosis than those who had both conditions. This means that these patients were not able to receive LEMS treatment until after they have lived with the condition for a significant period of time. Other individuals who have SCLC and LEMS may never receive their LEMS diagnosis because LEMS symptoms can be misattributed to side effects of chemotherapy.
It is important to note that there may be some bias present in this data as nearly all of the VA patients in the study were men and many of them were also cigarette smokers. As smokers have a higher risk of developing SCLC, the data may not be completely accurate.
Prevalence
This study also took into account the prevalence of LEMS. Researchers found a similar incidence of disease in the United States and Europe. Fortunately, most of the documented patients experienced improvements with therapy (80%).
In the U.S., there were 2.6 confirmed cases of LEMS per 1,000,000 people. 0.6 were newly diagnosed in the country each year. That said, there were many indeterminate cases (23) and therefore, researchers believe the true incidence is actually higher.
For the individuals in this study, the average age that symptoms were first experienced was 60. From this time, it took them an average of 10 months to be diagnosed with LEMS.
83% of patients had antibodies to VGCC, which is a hallmark sign of LEMS.
Treatments
The most common treatment prescribed to these LEMS patients was Mestinon (73%). Next was Firdapse (38%), followed by glucocorticoids (35%) and intravenous immunoglobulin (27%). 6 patients underwent plasmapheresis. This treatment was effective for all 6 individuals, but unfortunately the sample size is too small to prove its effectiveness as a whole.
Firdapse however, turned out to have the greatest level of improvements for patients. It resolved all symptoms in 1 patient (out of 18 treated with the drug) and relieved symptoms in 13 out of 18 patients.
Firdapse was first approved by the FDA in November of 2018 for the treatment of adult patients diagnosed with LEMS. It became the first treatment specifically indicated for LEMS in the United States. It is a potassium channel blocker that has shown marked improvements in mobility, muscle strength, and muscle electrical activity in LEMS patients. Additionally, Firdapse has been proven to be well-tolerated.
Ultimately, “The study ‘confirms the prominent role’ of Firdapse as a ‘leading treatment modality’ for LEMS.”
You can read more about this study and its findings here.
