Questions
Human herpesvirus 6 — Questions
Study questions about Human herpesvirus 6 — exam-style, clinical-scenario and FAQ.
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1 questions: 1 MCQ, 0 written.
- MCQ
Three weeks after an allogeneic stem-cell transplant, a patient develops confusion, short-term memory loss, seizures and hyponatraemia, with bilateral medial temporal lobe change on MRI. Which infection is most likely, and how is it confirmed?
- A. Human herpesvirus 6 encephalitis, confirmed by HHV-6 DNA PCR on cerebrospinal fluid and plasma, while remembering that chromosomally integrated HHV-6 can give persistently high loads without active disease
- B. Herpes simplex encephalitis, confirmed by HSV DNA PCR on cerebrospinal fluid, which is the expected cause of limbic encephalitis at this point and responds rapidly to a standard intravenous course of aciclovir
- C. Cytomegalovirus encephalitis, confirmed by CMV DNA PCR on cerebrospinal fluid, this being the commonest cause of medial temporal lobe encephalitis in the first month after a stem-cell transplant
- D. JC virus progressive multifocal leukoencephalopathy, confirmed by JC virus DNA PCR on cerebrospinal fluid, with the bilateral medial temporal MRI change being typical of this demyelinating white-matter disease
- E. Epstein-Barr virus central nervous system lymphoma, confirmed by EBV DNA PCR on cerebrospinal fluid, which characteristically presents three weeks after transplant with amnesia, seizures and hyponatraemia
Show answer
Correct answer: A
The syndrome
The picture is post-transplant acute limbic encephalitis caused by human herpesvirus 6 (HHV-6B) reactivation, which characteristically occurs early after stem-cell transplant (around weeks 2 to 4). The features are anterograde amnesia, seizures, the syndrome of inappropriate antidiuretic hormone secretion (hyponatraemia), and bilateral medial temporal lobe signal change on MRI.
Confirmation and a pitfall
Diagnosis is by HHV-6 DNA PCR on cerebrospinal fluid and plasma. The important pitfall is chromosomally integrated HHV-6: in people who carry the integrated viral genome in every nucleated cell, PCR shows a persistently very high load that does not indicate active disease. A load that falls with treatment supports a causative role.
Treatment and the distractors
Treat with ganciclovir or foscarnet; aciclovir is inactive against HHV-6. The distractors are wrong on pattern or timing: HSV encephalitis is possible but the MRI and post-transplant context favour HHV-6; CMV CNS disease is uncommon and not the typical limbic picture; JC virus causes white-matter PML, not medial temporal limbic disease; and EBV CNS lymphoma presents as a mass lesion, not this acute encephalitic syndrome.