A transplant patient who had serologic evidence of previous Epstein-Barr virus infection was taking high levels of immunosuppressive medications. He presents with generalized lymphadenopathy, fever, night sweats, weight loss, abdominal pain, and tonsillitis. The dosage of immunosuppressive drugs given to the patient is decreased, and the lymphadenopathy regresses. Which of the following is the best diagnosis for this patient?

**Core Concept**
The patient's presentation is suggestive of a lymphoproliferative disorder, which is a complication of immunosuppression in transplant recipients. Epstein-Barr virus (EBV) reactivation is a known risk factor for lymphoproliferative disorders, particularly in immunocompromised individuals.

**Why the Correct Answer is Right**
The patient's symptoms, including generalized lymphadenopathy, fever, night sweats, weight loss, abdominal pain, and tonsillitis, are suggestive of a lymphoproliferative disorder. The decrease in lymphadenopathy after reducing immunosuppressive medications suggests that the disorder was triggered by immunosuppression. EBV-associated lymphoproliferative disorders are often characterized by the presence of EBV-encoded small RNAs (EBERs) in lymphocytes, which can be detected by in situ hybridization. The patient's serologic evidence of previous EBV infection increases the likelihood of EBV reactivation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the patient's immunosuppressed state and EBV serology. The presentation is not typical of an infectious mononucleosis-like syndrome in a healthy individual.
**Option B:** This option is incorrect because it does not consider the patient's immunosuppressed state and the presence of EBV serology. The presentation is not typical of a malignant lymphoma in a healthy individual.
**Option C:** This option is incorrect because it does not take into account the patient's immunosuppressed state and EBV serology. The presentation is not typical of a drug-induced lymphocytosis in a healthy individual.
**Option D:** This option is incorrect because it does not consider the patient's immunosuppressed state and the presence of EBV serology. The presentation is not typical of a viral infection such as CMV or HSV in an immunosuppressed individual.

**Clinical Pearl / High-Yield Fact**
In transplant recipients, EBV-associated lymphoproliferative disorders are a known complication of immunosuppression. Reducing immunosuppressive medications can help manage these disorders. EBV serology and EBV-encoded small RNAs (EBERs) can be used as diagnostic markers for EBV-associated lymphoproliferative disorders.

**Correct Answer:** C. EBV-associated posttransplant lymphoproliferative disorder.

✓ Correct Answer: D. Lymphoproliferative disorder