A 62-year-old renal transplant recipient presents with abdominal pain and bloody diarrhoea. Cytomegalovirus (CMV) serology is positive, but plasma viral load is negative.
a) Explain this result in this context. (10% marks)
b) How is the diagnosis of CMV colitis confirmed? (10% marks)
a) This immunocompromised patient has presented with positive serology (i.e. CMV antibodies in the blood), but no viral load per se. Positive CMV serology simply indicates that the patient had been exposed to CMV at some stage, and is itself not enough to make the diagnosis of a current active infection. Nonetheless the abdominal pain and bloody diarrhoea could still be due to CMV colitis, as in one study by Durand et al (2013), 15% of patients had biopsy-proven CMV colitis without any plasma viral load.
b) CMV colitis does not require serology or a viral load to be detected, those would be merely supportive. The diagnosis relies on colonic biopsies to demonstrate characteristic cellular features ("owl's eye" inclusions, for example), and immunohistochemistry is the gold standard.
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Vancikova, Z., and P. Dvorak. "Cytomegalovirus infection in immunocompetent and immunocompromised individuals--a review." Current drug targets. Immune, endocrine and metabolic disorders 1.2 (2001): 179-187.
Durand, Christine M., et al. "Detection of cytomegalovirus DNA in plasma as an adjunct diagnostic for gastrointestinal tract disease in kidney and liver transplant recipients." Clinical infectious diseases 57.11 (2013): 1550-1559.