Study suggests LEMS is often missed in people with small cell lung cancer
Claims data show diagnosis rates far below what earlier research has reported
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Despite causing serious symptoms and having available treatments, Lambert-Eaton myasthenic syndrome (LEMS) may be frequently missed in people with lung cancer, a new study suggests.
While previous studies have suggested that about 3% to 6% of people with small cell lung cancer (SCLC) develop LEMS, this claims analysis found that fewer than 0.3% of patients with presumed SCLC had a LEMS diagnosis. These patients were less often diagnosed by oncologists.
“Further efforts to understand and address this discrepancy are warranted,” researchers wrote in the study, “Marked under-diagnosis of Lambert–Eaton myasthenic syndrome in small cell lung cancer: an analysis of real-world claims data,” which was published in Frontiers in Oncology.
Why LEMS can be hard to spot in cancer patients
LEMS is a rare autoimmune disease in which the immune system mistakenly attacks calcium channels that help nerve cells communicate with muscles. This can interfere with muscle signaling and lead to symptoms such as muscle weakness, fatigue, and difficulty with everyday activities.
In more than half of patients, LEMS is associated with cancer. SCLC accounts for most cancer-related LEMS cases.
Earlier research suggests that about 3% to 6% of SCLC patients develop LEMS, possibly because antibodies produced in response to the tumor can also mistakenly target calcium channels involved in muscle control.
Diagnosing LEMS can be difficult because its symptoms can overlap with cancer-related weakness and chemotherapy side effects. As a result, LEMS may be overlooked and diagnosed less often than expected.
To learn more, researchers at the University of Texas analyzed U.S. health insurance claims from Symphony Health Patient Source database, which includes more than 300 million people.
Claims data suggest LEMS is rarely diagnosed in presumed SCLC
The study analyzed claims data from 2017 to 2022. Because SCLC is not always clearly labeled in insurance records, the researchers used treatment patterns to identify likely cases of SCLC.
Out of 867,170 people with lung cancer claims, 46,995 (5.4%) received platinum-based chemotherapy plus etoposide and were classified as having presumed SCLC. These patients were, on average, about two years younger than those without presumed SCLC (66.3 vs. 68.3 years). Among them, only 77 (0.16%) had a claim for LEMS, far below the 3% to 6% reported in earlier studies.
When the researchers limited the analysis to people with at least one year of medical records before and after a cancer diagnosis, results were similar. In this smaller group, 0.19% had a claim for LEMS. Additional analyses using stricter or looser definitions of LEMS produced estimates ranging from 0.12% to 0.25%.
Based on estimates that about 10% to 15% of all U.S. lung cancer cases are SCLC, the researchers calculated that LEMS occurred in no more than 0.3% of patients with SCLC.
“Over 90% of SCLC-associated LEMS cases appear to go undetected,” the researchers wrote.
LEMS was most often diagnosed by neurologists (42%), followed by oncologists (18%) and internists (15%), who specialize in adult primary care.
LEMS diagnosis timing varied before and after lung cancer
The timing of diagnosis varied. One in four patients was diagnosed with LEMS before lung cancer, usually within three months. More than half (53%) were diagnosed with LEMS after lung cancer, including 45% diagnosed more than three months later. Seventeen patients (22%) were diagnosed with both lung cancer and LEMS on the same day.
Although immune checkpoint inhibitors have been linked to autoimmune side effects, this claims analysis did not find a higher prevalence of LEMS among patients treated with these therapies. Immune checkpoint inhibitors target molecules that cancer cells can use to evade the immune system.
Overall, the findings suggest that LEMS is diagnosed less often than expected in people with presumed SCLC.
“This marked underdiagnosis occurs despite availability of effective LEMS treatment that can improve patients’ quality of life. To address this care gap, efforts to understand and mitigate the reasons for this profound and persistent under-recognition are clearly needed,” the researchers concluded.
