A rare case of pleural localisation of both metastatic Merkel cell carcinoma and chronic lymphocytic leukaemia

Cytology coupled with immunocytochemistry nails Merkel cell carcinoma: a rare intruder in the cerebrospinal fluid

Merkel cell carcinoma is an uncommon aggressive skin tumor which is well known for its recurrence and metastasis. Leptomeningeal metastasis involving the cerebrospinal fluid is extremely rare. The diagnosis may easily be missed as it simulates other much common small round blue cell tumors. A history of primary diagnosis may not always be available. Awareness and cytomorphological vigilance with judicious employment of appropriate immunomarkers on limited cerebrospinal fluid samples is indispensable for nailing the diagnosis. The tumor cells are usually monotonous small round cells, singly scattered or as loosely cohesive clusters. Cells have round to elongated nuclei with coarsely granular chromatin, nuclear molding at places and scanty basophilic cytoplasm. A limited immunocytochemistry panel employing CK20 and CD56 for which the tumor is positive is confirmatory. We herein present a case of infiltration of cerebrospinal fluid by Merkel cell carcinoma.

Merkel cell carcinoma presenting as a malignant pleural effusion post-COVID-19 hospitalization: A case report and literature review

Merkel cell carcinoma (MCC) is a rare, highly aggressive neuroendocrine carcinoma of the skin, associated with immunosuppression, UV light exposure, and the Merkel cell polyomavirus (MCPyV). Cases of metastatic MCC diagnosed in body fluid cytology are extremely rare; only five cases have been reported previously in the English literature. We present a case of a 65‐year‐old male with acute respiratory failure and an enlarged right pleural effusion. He had two hospitalizations for COVID‐19 pneumonia 2 months prior, for which he received steroid treatment and tocilizumab. Emergent thoracentesis was done, with pleural fluid sent for cytologic evaluation. Both the Papanicolaou stained ThinPrep slide and cell block demonstrated clusters of predominantly small to medium sized blue round cells with hyperchromatic nuclei, scant cytoplasm and fine chromatin, in a background of rare mesothelial cells, macrophages and numerous lymphocytes. Tumor cells were positive for CD56, chromogranin, synaptophysin, SAT2B, MCPyV, and CK20 in perinuclear dot like pattern, while negative for TTF‐1 and CD45 immunostains. Ki67 proliferative index was approximately 40%. The patient had a history of MCC of the right ulnar forearm 4 years before the current presentation, which was unknown to us at the time of cytologic evaluation. To the best of our knowledge, this is the sixth case of metastatic MCC diagnosed by fluid cytology and the first reported in a patient receiving immunosuppressive treatment for COVID‐19. Further reporting of such cases may increase awareness, especially when prior history is not readily available, such as in our case.