Small Cell Lung Cancer ID’d as LEMS Cause Nearly 2 Years After Diagnosis
Man's case highlights importance of cancer checks when LEMS cause unknown
Patients diagnosed with Lambert-Eaton myasthenic syndrome (LEMS) with no identifiable cause should be continuously followed for signs of cancer, according to a recent case report.
The researchers’ suggestion was supported by the case of a 64-year-old man who was diagnosed with LEMS at their clinic, and in whom lung cancer was found nearly two years later.
“LEMS is rare and is often accompanied by malignancy [cancer],” the researchers wrote. “This case highlights the importance of being concerned about LEMS diagnoses and of long-term follow-ups for unexplained LEMS.”
The case report, “Long-Standing Lambert–Eaton Myasthenic Syndrome Caused by Undetectable Small-Cell Lung Cancer: Why We Should Follow-Up LEMS,” was published in the journal Diagnostics.
LEMS results from an erroneous immune system attack on a specific type of calcium channel found in nerve endings that are involved in muscle control. Since calcium is needed for the release of acetylcholine, a chemical needed for muscle contraction, LEMS patients do not have enough acetylcholine, and experience symptoms of muscle weakness.
LEMS and small cell lung cancer
In about 50% of cases, LEMS is associated with an underlying cancer, most often small cell lung cancer. This relationship is thought to arise through “cross reactivity.” Some cancer cells have the same calcium channels on their surface as those found in nerve endings. When the body recognizes these cells as a threat, it generates antibodies against the calcium channels to eliminate them, but these antibodies also end up attacking healthy nerve cells, causing LEMS.
A 64 year-old-man reported to the department of rehabilitation at St. Vincent’s Hospital in Seoul, South Korea, with swallowing difficulties and generalized limb weakness.
Notable in the patient’s history was a 14 kg (about 30 lbs) weight loss over the previous four years. He had also worked as a coal miner for 20 years and was an ex-smoker.
A neurological exam in the researchers’ clinic showed signs of intermittent double vision, mild weakness, and low muscle tone in all limbs.
A repetitive nerve stimulation test was administered to assess the electrical activity of nerves innervating muscles in response to stimulation. Muscles in the man’s hands and neck/shoulder area showed 40% reductions in their responses to stimulation.
When a rapid train of several stimulations were administered, nerves showed signs of facilitation, a phenomenon in which excess calcium released during repeated muscle stimulation and contraction (i.e., during exercise) temporarily improves nerve function.
While the test for calcium channel-targeting antibodies is not available in South Korea, the man did not test positive for different antibodies associated with other autoimmune neuromuscular conditions.
He was diagnosed with LEMS of unknown origin and prescribed pyridostigmine and low-dose oral steroids, to which he responded well.
An initial chest CT scan and one performed nine months later showed no signs of cancer. Twenty-one months after his LEMS diagnosis, an enlarged lymph node suggestive of small-cell lung cancer was identified during a follow-up and a cancer diagnosis given.
With a course of chemotherapy, most LEMS symptoms eased, but mild weakness and swallowing difficulty persisted, the researchers reported.
In a recent study, a team developed a lung cancer prediction model for LEMS patients based on six risk factors: muscle weakness in head or neck (bulbar muscles), a 5% or greater loss of body weight, tobacco use at onset, age of 51 or older, sexual impotence, and reduced ability to perform ordinary tasks, as measured by the Karnofsky performance test.
Researchers noted that this patient had three of these factors — bulbar weakness (difficulty swallowing), weight loss, and advanced age — giving him about a 60% probability of small-cell lung cancer. Together with his occupational and smoking history, this probability is likely even higher, the team noted.
Overall, the findings support long-term follow-up in patients with LEMS for whom a cause has not been identified, especially those with identifiable risk factors.
“When encountering patients with LEMS, a physician should decide how long to trace the disease in a patient when no culprit lesion, such as lung cancer, is initially found,” the researchers wrote.