Patients who have Lambert-Eaton myasthenic syndrome (LEMS) associated with small cell lung cancer (SCLC) are easier to diagnose and have a higher prevalence of ataxia (loss of movement control) compared to those who have LEMS unrelated to cancer, a study says.
The study, “Clinical characteristics and long term follow-up of Lambert-Eaton myasthenia syndrome in patients with and without small cell lung cancer,” was published in the Journal of Clinical Neuroscience.
LEMS is an autoimmune disease that affects the neuromuscular junction — the region where motor neurons and muscle fibers communicate — resulting in muscle weakness and reduced reflexes. The disorder is often associated with cancer, in particular SCLC, which is responsible for 40-70% of all cases of patients who have LEMS associated with cancer.
“Currently, many reported cohorts of LEMS were from Europe, America, and Japan and only a few of them compared the clinical features between non-tumor related LEMS (NT-LEMS) and SCLC related LEMS (SCLC-LEMS). Also, many of them lacked treatment responses and long-term follow-up,” the investigators stated.
In this study, a group of researchers from the Fudan University in Shanghai set out to describe the clinical features and long-term outcomes of Chinese patients with SCLC-LEMS and NT-LEMS.
The retrospective study involved 50 patients, including 23 (46%) with SCLC-LEMS, 20 (40%) with NT-LEMS and seven (14%) unclassified, who were followed between January 1997 and December 2017 at the Huashan Hospital.
Demographic and clinical data were collected retrospectively from the patients’ medical records. The Quantitative Myasthenia Gravis (QMG) score, the MG specific manual muscle testing (MG-MMT) and the MG related activities of daily living (MG-ADL) scale were used to assess patients’ clinical outcomes and quality of life during follow-up.
Results showed that patients with SCLC-LEMS received their diagnosis faster compared to patients with NT-LEMS (median time of six versus 22.5 months, respectively).
“The shorter diagnosis delay of six months in SCLC-LEMS versus that of 22.5 months in NT-LEMS, which was mentioned in many studies before, was partly due to the well awareness of association between SCLC and LEMS. This also indicated a more severe and rapid clinical course in SCLC-LEMS,” the researchers said.
Likewise, patients with SCLC-LEMS had a higher prevalence of paraneoplastic syndromes (organ or tissue changes caused by cancer), compared to patients with NT-LEMS (eight out of 23 versus zero out of 20, respectively).
From the seven patients (14%) who experienced symptoms of ataxia at baseline, six had been included in the SCLC-LEMS group, while none had been included in the NT-LEMS group.
Regarding muscle function, the only statistically significant difference found between patients with SCLC-LEMS and NT-LEMS was on the compound motor action potential (CMAP) of rest, a measure of muscle conduction, of the peroneal muscles (a group of leg muscles, 0.8 versus 1.6 mV, respectively). The reduced amplitude indicates a more greatly affected muscle.
During follow-up, most patients with NT-LEMS achieved a status of complete stable remission (CSR), pharmacologic remission (PR), or minimal manifestations (MM), after a treatment course with immunosuppressants. No statistically significant differences were found in the percentage of patients with SCLC-LEMS or NT-LEMS attaining CSR, PR, or MM during follow-up.
“In conclusion, patients with SCLC-LEMS tended to take less time to make the diagnosis and have a higher prevalence of ataxia comparing with NT-LEMS. Most NT-LEMS showed improvement or obtained CSR/PR/MM after immunosuppressive treatment,” the scientists stated.