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 imaging, four months after completion of initial treatment, suggestive of early relapse. Serological testing for toxoplasma gondii, however, showed evidence of a recently reactivated or newly acquired infection. Three weeks after immediate antibiotic treatment with Daraprime and Sulfadiazin, the splenic lesions had completely resolved. Additionally, serological titers for toxoplasma gondii were normalized and whole body FDG-PET imaging showed no metabolic 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 show low glucose metabolism, activated granulocytes and macrophages may display significantly increased glucose consumption. In conclusion, our case report shows that although therapeutic decisions are often based on the results of imaging modalities, the taking of a detailed history and the acquisition of histological confirmation of the suspected lymphoma relapse are also advisable where possible. Cellular immunodeficiency can result in severe infections even in patients with intermediate stage Hodgkin's lymphoma in remission after combined modality treatment. Therefore, despite the high sensitivity of FDG-PET imaging for the detection of recurrent lymphoma, the differential diagnosis of infectious lesions should be kept in mind, in particular in immunocompromised patients.