A Stubborn Course

A 52-year-old man with end-stage renal disease from diabetic nephropathy underwent deceased-donor kidney transplantation ten months ago. Pre-transplant CMV serology showed a seropositive donor and seronegative recipient (D+/R−). He received valganciclovir prophylaxis for six months post-transplant, which was discontinued two months ago. His current immunosuppressive regimen includes tacrolimus (trough 7.2 ng/mL), mycophenolate mofetil 1000 mg twice daily, and prednisone 5 mg daily. Three weeks ago, he developed watery diarrhea with mild periumbilical cramping after a course of amoxicillin for a dental abscess. Stool testing was positive for Clostridioides difficile by PCR, and he completed a 10-day course of oral vancomycin 125 mg four times daily.

He returns to the transplant clinic with two additional weeks of persistent diarrhea — now four to six bloody stools per day — and crampy left lower abdominal pain. He reports no fever. An unintentional weight loss of 5 kg has occurred over the past month. He has not started any new medications. A repeat stool C. difficile PCR and enzyme immunoassay are both negative. His tacrolimus trough is 7.5 ng/mL, within the target range. Serum CMV quantitative PCR is sent and returns at 800 IU/mL.

On examination, temperature is 37.3°C, heart rate 88, blood pressure 134/82 mmHg. The abdomen is soft with mild tenderness to deep palpation in the left lower quadrant and no peritoneal signs. Laboratory studies: WBC 6.1 k/mcL with lymphopenia (absolute lymphocyte count 0.4 k/mcL), hemoglobin 10.1 g/dL (microcytic), serum creatinine 2.0 mg/dL (baseline 1.5 mg/dL). He is admitted and undergoes colonoscopy, which reveals diffuse mucosal erythema, edema, and multiple linear ulcerations extending from the cecum to the sigmoid colon. Biopsies are sent for histopathology with immunohistochemistry. The result is shown below.