Abstract
Merkel cell carcinoma (MCC) is a rare and aggressive cutaneous neuroendocrine cancer with a high risk of recurrence and metastasis. MCC is generally associated with advanced age, fair skin, sun exposure, immunosuppression, and in the majority of cases, the Merkel cell polyomavirus. Neuroendocrine malignancies are associated with a variety of paraneoplastic neurological syndromes (PNS), characterized as autoimmune responses to malignancy-associated expression of neural antigens. Our literature review underscores previous case reports of MCC-associated PNS with voltage-gated calcium channel (VGCC) and anti-Hu (or ANNA-1) autoantibodies. We present the case of a 59-year-old male with regionally metastatic Merkel cell carcinoma complicated by the paraneoplastic manifestation of anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis. His primary lower neck subcutaneous MCC and metastasis were initially treated with surgery. Additional recurrent lymph node metastases were successfully treated with definitive intensity-modulated radiation therapy. His PNS improved with rituximab therapy. Although rare, this case highlights that in the setting of seizures and prominent psychiatric symptoms accompanying an MCC diagnosis, evaluation for autoimmune paraneoplastic encephalitis is warranted. Awareness and detection of preexisting PNS are crucial in the era of immune checkpoint inhibitors (ICI) for advanced MCC, where treatment with ICI has the potential to exacerbate preexisting autoimmune PNS and lead to worsened or even lethal neurologic immune-related adverse events (nirAEs).
Highlights
Paraneoplastic neurological syndromes (PNS) are a heterogenous group of immune-mediated disorders associated with neural autoantibodies directed against antigens expressed by both the tumor and the nervous system
We report the case of a 59-year-old male who developed anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis as a paraneoplastic manifestation of Merkel cell carcinoma (MCC)
This report highlights a patient who was treated with surgical therapy and intensity-modulated radiation therapy (IMRT) for regionally metastatic MCC and achieved complete regional control both clinically and radiologically, one year post definitive radiotherapy
Summary
Paraneoplastic neurological syndromes (PNS) are a heterogenous group of immune-mediated disorders associated with neural autoantibodies directed against antigens expressed by both the tumor and the nervous system These syndromes may affect any part of the nervous system and are exceptionally rare [1], with a higher incidence in small-cell lung cancer and gynecological tumors [2]. We report the case of a 59-year-old male who developed anti-NMDAR encephalitis as a paraneoplastic manifestation of Merkel cell carcinoma (MCC) This rare and aggressive cutaneous neuroendocrine cancer has a high risk of recurrence and metastasis, often occurring within the first two years after initial diagnosis [5]. His regionally metastatic MCC was Merkel cell polyomavirus (MCPyV) positive He underwent surgical-wide local excision with neck lymph node dissection and was successfully treated with definitive intensity-modulated radiation. Treatment and close monitoring of PNS, including anti-NMDAR encephalitis, before ICI therapy may reduce the possibility of worsened or even lethal neurologic immune-related adverse events [7]
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