FDG-PET in childhood Hodgkin's lymphoma: Reports on the false-negative, false-positive and unexpected results during a five-year experience

Abstract

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Objectives: FDG-PET has been shown as an efficient tool to stage the disease and monitor therapy in Hodgkin's lymphoma, both in adults and children. We report on a five-year experience of FDG-PET in childhood Hodgkin's lymphoma, focusing on the limitations of FDG-PET or the unexpected results in this context.

Methods: Between January 2000 and December 2005, 172 FDG-PET examinations have been performed in 72 children (age: 5 to 18 years, mean: 12.8) for staging (n = 44), restaging (n = 4) or assessment of therapy or residual masses (n = 124). Two PET systems were successively used: a C-PET NaI Philips from January 2000 to July 2004 then the Gemini PET-CT Philips system.

Results: Among the 172 examinations, 163 were evaluable according to histology or a follow-up > 3 months. Global results, on patient basis, corresponded to a sensitivity of 72/76 = 95%, a specificity of 80/87 = 91% and an accuracy of 152/163 = 93%. One false negative result occured at diagnosis, before chemotherapy in a child whose very aggressive disease required corticosteroid therapy that did not induced hyperglycaemia. The 3 other false negative results occurred during follow-up, with recurrences becoming obvious 1 to 2 months after the negative FDG-PET. The 7 false positive results corresponded to 4 cases of lung pathologic foci due to infection, an unexpected splenic uptake appearing during follow-up without therapy, a case of axillary uptake by probable activation of brown fat or muscles(PET without CT) and a case of lymph node uptake visualised on PET-CT, corresponding to a reactive adenitis at biopsy. Finally, one unexpected negative result was observed at initial staging, explained by the spontaneous apoptosis of the lymphoma tissue in a child with a renal graft. The reduction of the immunosuppressive therapy allowed a spontaneous recovery, confirmed by the prolonged disappearance of tumor masses at CT.

Conclusions: Our results confirm, in rather large series of examinations, the very good diagnostic performance of FDG-PET in childhood Hodgkin's lymphoma. However, some limitations of the technique must remain in mind. Even if new PET-CT acquiring have reduced the number of false positive results due to brown fat or muscles activation and now allows to detect infracentimetric disease, FDG-PET remains limited by microscopic disease or infectious or inflammatory disease. An important point to remind is the induction of false negative results of PET-FDG by corticosteroid therapy due to its major anti-inflammatory effect, even in the absence of hyperglycaemia.