Past is Prologue

A broad differential diagnosis should be considered when acute fever develops in a patient who has undergone solid organ transplantation. Causes may include opportunistic and nonopportunistic infections as well as noninfectious etiologies such as malignancy, organ rejection, inflammatory conditions, and medication toxicity.^1,2 As the discussant noted, more than one infection, or both infection and malignancy, can coexist in immunocompromised patients. For example, while viral pathogens such as EBV, CMV, and respiratory syncytial virus can cause illness due to direct tissue infection, they can also exert indirect effects in transplant recipients: acting as cofactors for and enabling other infections by causing immunosuppression (eg, Aspergillus or PCP developing after CMV infection), triggering graft rejection by upregulating proinflammatory cytokines, and inducing oncogenesis (eg, EBV-related PTLD).^1,3-5

PTLD is a rare but serious complication of solid organ transplantation and immunosuppression. Most cases are driven by EBV infection and subsequent transformation of infected lymphoid tissue in a variety of organs in the context of reduced T-cell surveillance.⁶ The incidence of PTLD varies based on the organ transplanted, ranging from 0.8%-2.5% in those who have undergone renal transplantation to 1.0%-5.5% in liver transplant recipients and 3.0%-10% in lung transplant recipients.³ The incidence has increased over the past decade. This may be due to a greater number of solid organ transplantations being performed, aging of the transplant donor/recipient population, new immunosuppressive regimens, and improved PTLD diagnosis due to superior diagnostic tools and clinician awareness.³ However, the mortality rate among solid organ transplant recipients with PTLD remains high, ranging from 40% to 70%.⁶

Risk factors for PTLD include a greater intensity of T-cell immunosuppression,⁷ history of pretransplant malignancy, recipient EBV seronegativity and donor seropositivity, and younger age at the time of transplantation.^8-10 EBV-related PTLD incidence in solid organ transplant recipients is greatest in the early posttransplantation course (the period of most intense immunosuppression) with over 80% of cases occurring in the first posttransplant year.¹¹

A high index of suspicion for PTLD is warranted in any solid organ transplant recipient who presents with constitutional symptoms, adenopathy, or cytopenias. Clinical suspicion of PTLD can be informed by risk factors, constitutional symptoms, elevated serum LDH, a detectable or rising serum EBV viral load, and radiologic adenopathy or visceral tissue infiltration.¹² The clinical presentation of PTLD is heterogeneous and varies in accordance with the organs affected. Extranodal involvement, such as pulmonary, gastrointestinal, and bone marrow involvement, is more common in PTLD than in other types of lymphoma.¹³ In this patient, the cytopenias, elevated serum LDH level, lung infiltrates, and radiologic pancreatic tail abnormality served as early clues to the presence of underlying PTLD.

The standard approach to diagnosing PTLD is biopsy of a suspicious lesion (adenopathy or an infiltrated visceral organ) with histopathological examination. Pathology may demonstrate distorted tissue architecture, clonal lymphocytes, or EBV-positive lymphocytes.¹⁴ Conventional CT is the most commonly used imaging modality to detect adenopathy or tissue infiltration related to PTLD,³ though 18F-fluorodeoxyglucose position-emission tomography (FDG-PET) is also used. Although FDG-PET has high diagnostic accuracy, with an overall sensitivity of 89% and specificity of 89%, false-negative results have been reported, particularly in cases of early PTLD lesions and diffuse large B-cell lymphoma.¹⁵ The majority of patients with EBV-associated PTLD demonstrate significant elevations in the serum EBV viral load compared with immunosuppressed controls without PTLD.¹⁶ An elevated EBV viral load can support a diagnosis of PTLD, though the absence of EBV viremia does not rule it out.¹⁷ Some transplant centers perform posttransplantation monitoring of the serum EBV viral load to aid in PTLD risk assessment and early diagnosis.

Management of PTLD is patient-specific and may involve reduction of immunosuppressive therapy, rituximab, chemotherapy, surgical excision, and/or radiation.¹³ Reduction of immunosuppression is the cornerstone of treatment.¹⁸ In patients who do not respond to the reduction of immunosuppression, rituximab and immunochemotherapy are second-line treatment options. A prospective, multicenter phase 2 trial (the PTLD-1 trial) demonstrated a complete response rate of 40% among patients with PTLD managed with rituximab.¹⁹

In summary, this case illustrates the importance of maintaining a broad differential diagnosis when acute fever develops in a patient who has undergone solid organ transplantation. The presence of more than one condition should be considered when the clinical presentation cannot be explained by a single diagnosis, as infections and malignancies can coexist in immunocompromised hosts. This case also highlights an unusual clinical presentation of PTLD, which was heralded mainly by its immunomodulatory effects rather than by compatible symptoms or obvious mass lesions.

Carefully reviewing the patient’s medical history and understanding how it sets the stage for the present illness is an essential step in clinical problem solving, because what is past is prologue.