Acne vulgaris: False-positive finding on integrated ¹⁸F-FDG PET/CT in a patient with melanoma

Malignant melanoma was diagnosed in approximately 59,580 patients in the United States in 2005. Appropriate treatment of patients with this tumor depends on accurate staging at presentation. CT has been used in the evaluation of melanoma at high risk of metastasis (i.e., thick, ulcerated primary tumors [stage IIC] or stage III disease). Because the accuracy of CT in the detection of occult metastatic lesions is limited, whole-body ¹⁸F-FDG PET has emerged as a complementary imaging technique and is being used with increasing frequency in examinations of patients with advanced melanoma [1, 2]. Although integration of PET and CT findings increases diagnostic accuracy, use of this combination in the detection of distant metastatic lesions is associated with a high false-positive rate [3]. Awareness of potential diagnostic pitfalls is therefore needed to avoid misinterpretation of integrated PET/CT images that can lead to inaccurate staging. In particular, accurate identification of cutaneous and subcutaneous metastasis of melanoma is important because the lesions may represent new or additional regional or distant metastatic disease. Such findings may influence the overall treatment approach. We report the case of a patient with melanoma lymph node metastasis (American Joint Committee on Cancer stage III) who had ¹⁸F-FDG accumulation at the sites of acne vulgaris that might have been misinterpreted as evidence of multiple distant cutaneous or subcutaneous metastatic lesions, potentially altering the pre-PET surgical treatment plan of regional lymph node dissection.