Amelanotic melanoma detected by 18F-FDG PET-CT

Amelanotic/hypomelanotic melanoma is an extremely rare cancer and accounts for less than 1/10,000 in the population. For losing and hypomelanotic pigment, amelanotic melanoma can lead to misdiagnosis with benign skin lesions. Therefore, early recognition and diagnosis is important to avoid a delay in treatment. A 73-year-old man presented for a gradually enlarged nodule on the surface skin of the left crus, with no color change, ulceration, or bleeding. Malignant lesion was suspected based on computed tomography (CT) and magnetic resonance imaging (MRI), and biopsy was scheduled. Immunohistochemical (IHC) revealed amelanotic melanoma followed by biopsy.18Florine-fluoro-2-deoxy-2-d-glucose (18F-FDG) positron emission tomography-computed tomography (PET-CT) was employed to explore whether there are metastases or not. 18F-FDG PET-CT showed increased FDG accumulation with standardized uptake value max (SUVmax) of 5.6 of the lesion, and no other lesions were detected. The patient refused to be hospitalized and died 12 months later. This case highlights the need of considering melanoma even if there is no color change. Increased FDG uptake from PET-CT is prone to be consistent with malignant disease as well as whole body scan is crucial in determining the accurate TNM stage. Moreover, prompt treatment according to guidelines is necessary even if the disease is at its early stage.