Study of the Week: Lambert-Eaton Myasthenic Syndrome Found in Merkel Cell Carcinoma

Welcome to Study of the Week from Patient Worthy. In this segment, we select a study we posted about from the previous week that we think is of particular interest or importance and go more in-depth. In this story we will talk about the details of the study and explain why it’s important, who will be impacted, and more.

If you read our short form research stories and find yourself wanting to learn more, you’ve come to the right place.

 

This week’s study is…

Lambert-Eaton myasthenic syndrome and paraneoplastic cerebellar degeneration associated with
Merkel cell carcinoma with unknown primary: A case report

We previously published about this research in a story titled “Researchers Find Link Between LEMS and MCC” which can be found here. The study was originally published in the Journal of the American Society of Nephrology. You can view the full study here.

What Happened?

This case study describes a situation involving a 59-year-old man. He was admitted to the emergency department’s neurology clinic after displaying symptoms such as limb weakness, ataxia, nystagmus, diplopy, and problems with walking. The patient promptly underwent a number of tests, and a motor-nerve conduction study revealed facilitation post-exercise. The doctors also discovered antibodies that targeted the P/Q-type voltage-gated calcium channel.

These findings indicated possible cerebellar degeneration and led to the initial diagnosis of Lambert-Eaton myasthenic syndrome (LEMS). The patient was then treated with the potassium channel blocker fampridine, which helped improve symptoms. A PET scan revealed a further abnormality: a lesion in the left inguinal lymph node. Other abnormalities discovered included various immunohistochemical reactions, areas of necrosis, and multiple mitoses, findings that were consistent with Merkel cell carcinoma that had spread to the lymph node.

A skin examination found no cutaneous Merkel cell lesions. The patient was treated with radiation therapy and showed improvement in walking ability after six months. Normally surgery would have been considered, but this was avoided due to the patient’s unique collection of symptoms. However, other symptoms continued to persist. This was likely due to the presence of paraneoplastic cerebellar degeneration. The doctors were unable to find the primary Merkel cell carcinoma tumor. 

About Lambert-Eaton Myasthenic Syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disease which is characterized by weakness of the limb muscles. In this autoimmune disease, the immune system develops antibodies against an ion channel that plays a vital role in neuromuscular function. Lambert-Eaton myasthenic syndrome commonly appears as the result of cancer, often small cell lung cancer. Genetic variants are often the cause when cancer is not involved. The disease presents with muscle weakness of the upper arms and legs, with the legs usually being most affected. Other symptoms include difficulty swallowing, double vision, drooping eyelids, orthostatic hypotension, ataxia, and reduced reflexes. Weakness may be temporarily relieved after exercise; hot temperatures seem to worsen symptoms. Treatment of comorbid cancer can resolve the disease; other treatments include immune system suppressors (IVIg and prednisone) and drugs that improve neuromuscular function. To learn more about Lambert-Eaton myasthenic syndrome, click here.

About Merkel Cell Carcinoma

Merkel cell carcinoma is a type of skin cancer that is known for its rarity and aggressiveness. In most cases, roughly 80 percent, the disease is caused by Merkel cell polyomavirus (MCV). Tumors of this cancer are infected with the virus when it is found to be the cause. In the remaining cases, exposure to sunlight or UV light may be part of the cause, as it can often appear alongside other more common types of skin cancer. Signs and symptoms include a small painless skin nodule, that may be red or blue in color and enlarge rapidly. Merkel cell carcinoma can metastasize rapidly to the lymph nodes or other internal organs. Treatments for this cancer include surgery, chemotherapy, and radiation therapy. More targeted therapies are currently being tested. Curing the cancer is very difficult once metastasis has occurred. The five-year survival rate for this disease is around 60 percent. To learn more about Merkel cell carcinoma, click here.

Why Does it Matter?

The case study described represented a unique situation in medical history. Though Merkel cell carcinoma is primarily known as a skin cancer, other cases have been recorded in which a lesion has been discovered in another area without a definite primary; it is especially unusual, however, for this situation to occur in a lymph node. However, the most significant discovery from this case was the presence of paraneoplastic cerebellar atrophy and Lambert-Eaton myasthenic syndrome in association with this cancer.

While this is not the first time that paraneoplastic syndromes have been associated with Merkel cell carcinoma, only a very small number of such cases have been recorded. In the past, the association of these two conditions with this cancer has only been cases with an unknown primary and metastasis affecting the axilla (area around the shoulder/armpit). Ultimately, the case serves to highlight the connection between this cancer and these conditions and the importance of a multidisciplinary approach in treating Merkel cell carcinoma.

Dermatologists that treat this cancer should be informed about the possibility of cerebellar atrophy and Lambert-Eaton myasthenic syndrome occurring alongside the disease. It is likely that these conditions were triggered by the immune response to the cancer.

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