Merkel Cell Carcinoma Should Be Considered in Differential Diagnosis of LEMS Patients, Report Suggests

Merkel cell carcinoma (MCC) should be included in the differential diagnosis of patients with Lambert-Eaton myasthenic syndrome (LEMS) who do not have lung cancer, a case report says.

The case study, “Lambert-Eaton Myasthenic Syndrome and Merkel Cell Carcinoma,” was published in Cutis MDedge Dermatology.

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 often is associated with cancer, as 50% t0 60% of LEMS patients have an underlying tumor. The  tumors usually are small cell lung cancer (SCLC), as between 40% to 62% of patients diagnosed with LEMS are found to have SCLC.

Histologically, SCLC is very similar to MCC, a rare form of aggressive skin cancer. However, reports of patients with LEMS associated with MCC are extremely rare.

In this case study, physicians described the clinical case of a man with LEMS associated with MCC.

The 63-year-old man visited a neurology clinic complaining he had been having difficulty walking, climbing stairs and doing push-ups for the past month. He also experienced constipation, had episodes of urinary urgency, dry mouth, difficulty swallowing (dysphagia), lack of sensation below the knees, and nasal speech.

Neurological examination revealed he had mild muscle weakness in his upper arms, shoulders and hips, consistent with LEMS. In addition, nerve conduction studies — tests used to measure nerves’ ability to send electrical signals — also were consistent with the diagnosis.

However, a computed tomography (CT) scan of the chest revealed two enlarged lymph nodes in his left armpit and found no signs of lung cancer. Biopsies of the enlarged lymph nodes revealed the presence of cancer cells, which were identified as MCC.

The man underwent surgery to remove the enlarged lymph nodes. One month after the operation, he noticed a significant improvement in muscle strength and no longer experienced constipation, dry mouth, nasal speech, difficulty swallowing, or episodes of urinary urgency.

He started radiation therapy two months after the surgery, and four months later reported his physical strength had returned to 95% of what it had been before being diagnosed with MCC. He was able to resume his normal physical activity routine and did not experience any further symptoms, neurologic deficits or weakness, and did not show any signs of skin lesions or abnormal lymph nodes suggestive of MCC.

“A thorough search for an underlying malignancy is highly recommended in patients with diagnosed LEMS without clear cause. Early identification and treatment of the primary tumor can lead to improvement of neurologic symptoms,” the authors wrote.

“In cases of LEMS without pulmonary malignancy, we recommend considering MCC in the differential diagnosis during the workup of an underlying malignancy,” they added.