Pitfalls in imaging Hodgkin's disease with computed tomography and positron emission tomography using fluorine-18-fluorodeoxyglucose

We report on a patient with Hodgkin's disease who presented with hypodense splenic lesions and corresponding increased glucose metabolism in FDG-PET i maging, four months after completion of initial treatment, suggestive of ea rly relapse. Serological testing for toxoplasma gondii, however, showed evi dence of a recently reactivated or newly acquired infection. Three weeks af ter immediate antibiotic treatment with Daraprime and Sulfadiazin, the sple nic lesions had completely resolved. Additionally, serological titers for t oxoplasma gondii were normalized and whole body FDG-PET imaging showed no m etabolic activity. Although the positive predictive value of PET imaging to indicate lymphoma is reported to be higher than CT, hypermetabolic lesions are not specific for malignant tissue. Whereas benign tumors typically sho w low glucose metabolism, activated granulocytes and macrophages may displa y significantly increased glucose consumption. In conclusion, our case repo rt shows that although therapeutic decisions are often based on the results of imaging modalities, the taking of a detailed history and the acquisitio n of histological confirmation of the suspected lymphoma relapse are also a dvisable where possible. Cellular immunodeficiency can result in severe inf ections even in patients with intermediate stage Hodgkin's lymphoma in remi ssion after combined modality treatment. Therefore, despite the high sensit ivity of FDG-PET imaging for the detection of recurrent lymphoma, the diffe rential diagnosis of infectious lesions should be kept in mind, in particul ar in immunocompromised patients.