Human Herpes Virus-6 Limbic Encephalitis

Case history: A 32-year-old Caucasian female with newly diagnosed acute myeloid leukemia (AML) was treated with induction chemotherapy and attained complete remission. She underwent hemopoietic allogenic stem cell transplant (HSCT) from a 10/10 matched unrelated stem cell donor. She returned to ED day+32 post-transplant with fever, headache and new-onset confusion.

On examination patient had a fever of 101.5 degrees. She had mild confusion which was thought to be from delirium. She has no nuchal rigidity and rest of the exam was normal. Blood culture was obtained and was started on broad spectrum antibiotics.

During the hospital stay she had worsening mental status and on repeat exam, she is disoriented with disconjugate eye movements and severe short-term memory impairment with intact long term memory. She also had a new onset of seizure during the hospital stay.

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Initial MRI Diffusion – 1

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Initial MRI Diffusion – 2

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Initial MRI Diffusion – 3

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Initial MRI FLAIR – 1

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Initial MRI FLAIR – 2

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Initial MRI FLAIR – 3

An initial MRI showed that the medial aspects of both temporal lobes, including the uncus, medial temporal lobe white matter, and hippocampi having a gyriform swelling with associated FLAIR hyperintensity. The area of signal abnormality on the FLAIR images demonstrated a restricted diffusion.

Initial differential diagnosis included herpes encephalitis and a lumbar puncture was performed with CSF analysis ordered.

CSF analysis was acellular with normal protein and glucose levels. Bacterial and fungal culture was negative. HSV PCR was also found to be negative. A HHV-6 PCR was found to be positive with a consecutive positive serum HHV-6 PCR . She was immediately started on IV ganciclovir.

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Repeat MRI – 1

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Repeat MRI –2

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Repeat MRI – 3

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Repeat MRI – 4

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Repeat MRI – 5

A repeat MRI a month later depicted an interval increase in FLAIR hyperintensity within the periventricular white matter of both cerebral hemispheres. There was a slightly decrease FLAIR hyperintensity seen in the temporal lobes with associated progressive atrophy of the hippocampi. The patient however, had persistent memory problems despite the resolution of fevers, CSF and blood viremia.

Diagnosis: Human herpes virus-6 limbic encephalitis

HHV-6 (Human Herpes Virus -6) causes exanthema subitum in infants and infectious mononucleosis like symptoms in adults. Its reactivation is associated with limbic encephalitis in patients who underwent transplantation, particularly bone-marrow transplantation which is often associated with severe immunosuppression. Prevalence of HHV-6 reactivation post stem cell transplantation (SCT) range from 2 percent in allogenic stem cell transplantation versus 8.3 percent among those received cord blood stem cell transplant for various hematological malignancies. This viral reactivation is associated with various neurological presentations including headache, disconjugate eye movements, hyponatremia secondary to diabetes insipidus and commonly with profound short term memory loss.

Involvement of the limbic system leads to profound short term memory loss with often retained long term memory function. This memory loss can be permanent. An initial FLAIR hyperintensity is often noted on MRI with avid FDG uptake on PET scan suggesting inflammatory changes with hypermetabolism. Eventual sclerosis of the hippocampi leads to the atrophy and subsequent regressions in the FDG uptake on PET scans suggesting hypoactiveness.

Elevated serum and CSF IL-6 levels are associated with HHV-6 encephalopathy and may predict neurological sequelae as well. Initial treatments include either IV ganciclovir, oral valganciclovir or foscarnet. Patients usually develop recurrence after cessation of therapy secondary to the genomic integration of viral DNA.

Pavan Kumar Bhamidipati, MD
Clinical instructor, Division of Hospital Medicine,
Barnes-Jewish Hospital at Washington University School of Medicine in St. Louis