Lambert-Eaton Myasthenic Syndrome Underdiagnosed Alongside SCLC in the U.S.

PHOENIX — While Lambert-Eaton myasthenic syndrome (LEMS) is known to be associated with small cell lung cancer (SCLC), researchers here suggested the autoimmune disorder is underdiagnosed in the U.S.

Using claims from a large U.S. database, 16% to 21% of patients who were diagnosed with LEMS on the basis of ICD-9 or -10 codes were also diagnosed with SCLC, reported David Morrell, MBA, of Catalyst Pharmaceuticals in Coral Gables, Florida, during the American Association of Neuromuscular & Electrodiagnostic Medicine meeting.

“SCLC has been reported among half of LEMS patients in prospective international studies,” Morrell told MedPage Today at his poster presentation. “These findings suggest patients with SCLC are not screened for LEMS, and, as a result, the observed prevalence of SCLC in this analysis was approximately half of that previously reported in the literature.”

Morrell said his team’s working hypothesis was that when an oncologist diagnoses SCLC, which has similar symptoms to LEMS — a relatively rare autoimmune disorder characterized by proximal muscle weakness, loss of tendon reflexes, and autonomic dysfunction that can occur as a paraneoplastic disorder, most commonly in association with SCLC — the oncologist doesn’t screen the patient for LEMS.

On the other hand, neurologists who encounter a LEMS case usually screen people for lung cancer since they know that the two diseases often occur together, said Michael Schwartzman, DO, of the University of Missouri-Kansas City.

“When I find a patient with LEMS, typically I will do a CT scan of the chest, as well as a PET scan, and then refer the patient to an oncologist for follow-up,” Schwartzman told MedPage Today. “I then let the oncologist handle the cancer side of the therapy and then I treat the patient for LEMS.”

“It makes perfect sense that the claims data are so low compared to international studies because oncologists aren’t looking for LEMS in these SCLC patients,” he added, noting that if a patient with SCLC is diagnosed with LEMS, there are treatments for the two diseases that may improve quality of life.

For this analysis, Morrell and team used the Symphony Health PatientSource database from 2014 through mid-2022 to identify 1,836 patients with LEMS. Patients with two or more claims 30 or more days apart were considered to have a LEMS diagnosis.

Mean age was 60.2, and 57% were women; 62% had commercial health insurance, while 24% had Medicare or Medicaid. Of these patients, 38% were from the South, 25% were from the Midwest, and 20% were from the Northeast.

Morrell and team also identified 390 patients with both LEMS and SCLC. These patients had ICD codes for LEMS and lung cancer and/or SCLC-related therapies.

Mean age was 65.7, and 54% were women; 54% had commercial health insurance, and 26% had Medicare or Medicaid. Cases by U.S. region were similar to those with only LEMS diagnoses.

Of the patients with LEMS, 56% were subsequently diagnosed with SCLC within 90 days of the LEMS diagnosis.

Morrell noted that the study was limited by its reliance on ICD coding and may not have captured all patients with LEMS or SCLC.