Complicated Case of DLBCL Shows Limits of 18F-FDG PET/CT Imaging

Fluorine-18-fluorodeoxyglucose positron emission tomography/CT (18F-FDG PET/CT) is an important tool to guide the management of lymphoma, but it also has limitations that can complicate the assessment of patients who simultaneously have an infection, according to the authors of a new case report.

The authors, both of the University of Queensland, in Australia, detailed the case in Radiology Case Reports. It involved a 43-year-old woman with diffuse large B-cell lymphoma (DLBCL) who also had a fungal infection.

The woman sought emergency care due to abdominal discomfort and chronic fatigue lasting 6 months; she had a history of untreated hepatitis C. Her primary care physician sent her to the hospital after she had abnormal liver function tests and was found to have diffuse abdominal lymphadenopathy.

Subsequent imaging revealed extensive abdominal lymphadenopathy and splenomegaly. She was referred to the hospital’s Hematology Department for further testing. There, she underwent her first staging PET/CT scan, which showed mild diffuse increased FDG activity, the authors said, indicating splenic involvement. After biopsies and cytometry, the patient was found to have with stage IVb DLBCL with liver, spleen, and bone marrow involvement.

The patient underwent 6 cycles of chemotherapy, after which PET/CT indicated a complete metabolic response. Both the upper abdominal lymphadenopathy and the spleen were reduced in size, the authors added.

However, 2 months later she returned to the emergency department, this time complaining of drowsiness and extreme lethargy, the investigators reported. She underwent an urgent head CT, which showed new solid enhancing lesions in the interventricular, ependymal, and suprasellar regions of her brain, which the authors said indicated relapsed DLBCL with central nervous system involvement. A subsequent PET/CT scan showed liver involvement.

A multidisciplinary team decided to treat her with combination chemotherapy and targeted therapy, followed by autologous stem cell transplantation. However, stem cell collection was delayed when the patient asked to be discharged until her collection appointment, but later returned with persistent fevers. A new restaging PET/CT scan was performed, “which showed multiple tiny scattered hypodensities throughout the spleen, with some of the lesions demonstrating subtle increased FDG uptake to the diffusely increased background splenic FDG avidity concerning for multiple splenic abscesses in the current clinical context.”

The patient also had new cerebral abscesses, but the lesions were too small to biopsy, and a surgeon recommended total splenectomy. During surgery, multiple lesions were seen in the spleen that were densely adherent to surrounding structures, the authors said.

“Histopathological examination of the spleen revealed multiple small and round cream-colored lesions showing foci of necrosis and suppuration consistent with suppurative granulomatous inflammation scattered throughout the spleen,” the authors wrote.

Microbiological culture results indicated she had a fungal infection. The patient was given voriconazole for the infection, and a postsplenectomy vaccine was planned after 6 to 12 months of rituximab, the authors said.

They added that this patient was a particularly challenging case, both because of her cancer and illness and that she had a complex social background, including ongoing intravenous drug use and nonoptimal treatment adherence.

The authors said that although 18F-FDG PET/CT scans are “essential” in evaluating lymphoma, clinicians should consider the individual patient’s clinical context and be aware of factors that can mimic or obscure disease progression.

“High nonspecificity of elevated FDG uptake is often seen in inflammatory processes and physiological uptake throughout the body, which can also confound interpretation,” they said. “Therefore, it is crucial to have strong knowledge of the physiological and abnormal FDG uptake seen in different processes to provide accurate clinical interpretation of the scan.”

In this case, they said, it could have been easy to miss the tiny hypodensities in the patient’s spleen or to dismiss them as posttherapy reactive changes. If they had, they said, it “could have resulted in a very different clinical outcome for the patient.”

Reference

Goh SC and Ngai S. The clinical challenge of relapsed diffuse large b-cell lymphoma with disseminated infection. Radiol Case Rep. Published online June 25, 2023. doi:10.1016/j.radcr.2023.05.068