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Case Reports

Abstract

Nevoid melanoma, a rare variant of melanoma mimicking benign nevi, poses diagnostic
challenges and carries a high mortality rate. We present a case of a 46-year-old female with
rheumatoid arthritis managed with JAK and TNF-α inhibitors since 2019. She initially presented
with worsening pelvic pain, prompting imaging studies that revealed a hypointense bone marrow
signal in the lumbar spine, suggestive of an infiltrative process. Subsequent bone marrow biopsy
demonstrated numerous large, atypical cells with vacuoles and cherry red nucleoli, replacing
most of the marrow space. Immunohistochemical studies confirmed the neoplastic cells were
positive for SOX10 and S100, consistent with metastatic melanoma. A thorough skin
examination identified a pink dome-shaped papule with dark ink spots near the sternum.
Histologic examination revealed an asymmetric melanocytic lesion with a lateral junctional
component, a cellular epithelioid component that exhibited no maturation with descent and
cytologic atypia, and a deeper spindled component with bland cytology. All three components
were positive for SOX10, supporting a diagnosis of melanoma with a mixed nevoid and
desmoplastic phenotype. Follow-up PET CT confirmed metastatic disease involving the liver,
spleen, and bone marrow. This presentation of metastatic melanoma as diffuse bone marrow
involvement is exceedingly rare. Long-term JAK and TNF-α inhibitor therapy may have
contributed to the aggressive clinical course. While research on their association with melanoma
risk is ongoing, some studies suggest a potential link, highlighting the need for
dermatopathologists to consider this in diagnosis. Regular skin exams and prompt reporting of
changes are crucial for patients on such therapies.