Human Herpesvirus 6 (HHV-6) Infection Workup

Updated: Aug 16, 2019
  • Author: John L Kiley, MD; Chief Editor: Burke A Cunha, MD  more...
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Workup

Approach Considerations

Workup in infants and children is often directed at causes of fever, rash, and or febrile seizures, depending on the clinical scenario.

Diagnosis in recipients of organ transplants or patients with immunodeficiency, encephalitis, or hepatitis is often made using a combination of PCR and antibody detection. This diagnosis can be very difficult because of the paucity of evidence concerning the clinical significance of HHV-6 detection in serum via PCR. Many questions have been raised by researchers, including the significance in the setting of chromosomally integrated HHV-6. Further studies will be needed to move from associative to causative arguments about HHV-6.

Testing for HHV-6 disease is complicated by multiple factors, not the least of which is that serum HHV-6 DNA levels do not necessarily correlate with disease burden at the tissue level. Guidelines for diagnosis of HHV-6 infection in allogeneic stem cell transplant recipients have been published and should be referenced for an approach to diagnosis. [27, 32, 4]

Other studies used in the diagnosis of HHV-6 infection include diagnostic imaging, bronchoscopy, and tissue biopsy.

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Laboratory Studies

Testing for HHV-6 disease requires a careful assessment of the pretest probability of disease, clinical syndrome, and the host.

The complete blood count (CBC) may show leukopenia and varying degrees of cytopenia (thrombocytopenia or anemia), especially in the setting of transplantation. In active infection, a CBC with differential may show leukopenia with relative leukocytosis.

Electrolytes should be evaluated and renal function tests performed, especially when considering treatment for HHV-6 encephalitis. Liver function tests may reveal hepatitis or liver dysfunction.

Culture

Standard peripheral cell culture, which takes 5-21 days and is labor-intensive, and shell vial assay culture are available in research settings for isolation of HHV-6. [33]

Immunohistochemistry

Immunohistochemical stains are available for detecting HHV-6 in formalin-fixed paraffin-embedded tissues. Only cells with active infection, as opposed to latent infection, stain positively with these antibodies. Immunohistochemical staining can be performed on tissue and cytologic samples. Depending on the pathology laboratory processing the samples, this can usually be completed in 1-3 days.

Serology

Primary infection can be demonstrated by seroconversion from immunoglobulin G (IgG)-negative to IgG-positive or by the presence of immunoglobulin M (IgM) to HHV-6 and a four-fold rise in titers from baseline over 4-6 weeks. Interpretation of antibodies in older children and adults is difficult given high seroprevalence and cross-reactivity and should not be used for diagnosis. [23]

Polymerase chain reaction assay

Rapid diagnosis of HHV-6 primary infections or reactivations can be facilitated by using quantitative PCR assays. [34] Detection of co-infections with multiple herpesviruses can also be accomplished, with quantitative results enabling monitoring of virus load during antiviral therapy.

Neither qualitative nor quantitative PCR of plasma is sufficient to distinguish between active viral replication and chromosomal integration with HHV-6. A higher specificity may be obtained by using reverse transcriptase PCR (RT-PCR) for viral messenger RNA when evaluating samples for active HHV-6 replication. [33, 35] However, this type of testing is not often readily available clinically.

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Radiography and Computed Tomography

Chest radiography or computed tomography (CT) of the chest should be performed in patients with respiratory symptoms. These may show evidence of pneumonitis or pneumonia.

Brain MRI can be helpful and should be considered in the workup of HHV-6 encephalitis.

Indications for these and other diagnostic procedures depend on the clinical presentation, especially in immunocompromised patients.

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Other Studies

In patients with central nervous system (CNS) symptoms, lumbar puncture can be performed to rule out other etiologies. In cases of febrile seizures due to HHV-6 infection, the cerebrospinal fluid (CSF) may reveal a mild pleocytosis with elevated protein levels, but it is often noteworthy for a lack of inflammatory response. [28, 8, 2] CSF can be sent for HHV-6 PCR studies. A positive result may indicate active HHV-6 infection in the CNS.

Tissue biopsy is especially relevant in solid-organ or bone-marrow transplant recipients who have evidence of graft rejection and in immunocompromised patients with severe hepatitis or hepatic failure. Samples should be sent for immunohistochemical staining.

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