Systemic Sarcoidosis Mimicking Metastatic Melanoma: Unveiling the Masquerade.

The coexistence of melanoma and sarcoidosis presents significant diagnostic challenges, particularly when imaging studies reveal suspicious lesions that may represent either metastatic disease or granulomatous inflammation. This complexity is compounded by the overlapping clinical and radiological features of both conditions. We present the case of a woman in her 80s with a history of pulmonary sarcoidosis who developed a thick melanoma (5.1 mm Breslow depth) and subsequently underwent wide local excision with a negative sentinel lymph node biopsy. Surveillance imaging revealed an FDG-avid lytic lesion in the fibular head, raising suspicion for metastatic disease. Histopathological examination of the fibular lesion confirmed sarcoidosis rather than melanoma metastasis. The patient continues under clinical surveillance without evidence of melanoma progression. This case highlights the diagnostic complexity when melanoma and sarcoidosis coexist. Multidisciplinary team discussion and histopathological confirmation remain essential for accurate diagnosis and appropriate management decisions. Given Ireland's high prevalence of both conditions, clinicians must maintain awareness of this potential diagnostic pitfall.