Two cases of 18F-FDG PET/CT findings in HIV-negative Kaposi's sarcoma. Original presentation of one case favorably treated with interferon.

To the Editor: Kaposi’s sarcoma (KS) is a rarely seen angioproliferative tumor associated with human herpes virus 8 (HHV-8) infection, also known as Kaposi sarcoma herpes virus (KSHV) [1-3]. Four epidemiological types of KS have been described: a) The classic type originally described by Kaposi, which is typically found in midaged or in the elderly, b) The endemic type, several subtypes of which have been described in sub-Saharan indigenous Africans prior to the acquired immune deficiency syndrome (AIDS) epidemic after 2000s, c) The iatrogenic type associated with immunosuppressive drug treatment, typically seen in organ transplant recipients, and d) AIDS-associated, epidemic KS, which is usually aggressive in HIV-related or in post transplant patients, but may be more indolent. Clinically, in KS we find dark blue or purplish macular or spindleshaped nodular skin lesions. The same lesions are found in pathology in the lymphoid, respiratory, and/or in the gastrointestinal tissues [4-7]. The disease carries a variable clinical course ranging from minimal mucocutaneous disease to extensive organ involvement. Treatment for localized pathology is surgery or radiation treatment, while widespread disease may be treated by systemic chemotherapy or immunomodulators [8-14]. Currently, fluorine-18-fluorodesoxyglucose positron emission tomography/computed tomography (18F-FDGPET/CT) is used as a very effective tool in monitoring treatment response for many 18F-FDG avid tumors. To our knowledge, the role of 18F-FDG-PET/CT , in HIV-negative KS of the skin and soft tissues was documented in only one case report [8]. In that report, the authors documented a case of human immunodeficiency virus (HIV)-negative classic KS, which responded to target of rapamycin (mTOR), a kinase delivering phosphate groups to amino acid residues of downstream proteins. The treatment response to rapamycin was well demonstrated by PET-CT. No published report refering to the interferon (INF) response in a HIV-negative KS using 18F-FDG-PET/CT could be found in current literature till January 2010. In case 1, a 76 years old man with violaceous plaques and nodular skin lesions diffusely involving the lower thigh, legs and upper extremities was admitted. He had no significant medical history except for asthma. His blood tests were normal. The histopathological diagnosis obtained from skin lesions of the thigh revealed low grade KS. Before starting INF treatment, he was referred to us for a 18F-FDG-PET/CT test for staging and treatment response. Fluorine-18-FDG-PET scan using 444MBq activity showed multifocal increased dermal and subdermal 18F-FDG uptake in the distal parts of the lower extremities more intense on the dorsal surface of the left foot (Fig. 1A and C). The lesions on the scan were fewer than lesions seen on physical examination. Upper extremities’ lesions showed no 18F-FDG avidity. Bilateral 18F-FDG positive axillary lympadenopathy was an unexpected finding which may be due to benign or malignant lymphoprolipherative disease related or unrelated with KS (Fig. 1E). No change in axillary lymph nodes sizes as compared to previous thorax CT findings was found indicating a benign course. A control PET/CT scan after 6 months revealed dimished metabolic activity in both axillas (Fig. 1B and F) and in the lower extremities (Fig. 1B and D). New lesions on the upper extremities were 18F-FDG negative.