HHV-6 might be one of the most important causes of pulmonary dysfunction in compromised hosts, such as bone marrow transplant recipients. Ogata et al [7
] determined the incidence and clinical relevance of active HHV-6 infection among 50 allogeneic stem cell transplant recipients [7
]. In their study, HHV-6 DNA was most frequently observed 14–27 days post transplantation; an increased risk of a positive finding of HHV-6 DNA was associated with transplantation from an allelic-mismatched donor. In addition, these authors reported that steroid therapy is associated with an increased incidence of infection and accelerated viral replication [7
]. Although our case received an allogeneic bone marrow transplant from a related HLA-matched donor, the steroid medication might have triggered his pulmonary dysfunction in agreement with the findings of Ogata et al.
There are very few previous reports of HHV-6 infection after bone marrow transplantation with radiological findings.
Carrigan et al [8
] reported two cases of severe interstitial pneumonitis associated with HHV-6 infection in bone marrow transplant recipients. The radiological findings were described only as progressive bilateral interstitial infiltrates on chest radiographs. Meanwhile, Merk et al [9
] reported fatal pulmonary failure in a healthy 19-year-old woman. The chest radiographs showed developing pulmonary infiltration at the basal region of both lungs, with large amounts of pulmonary effusions; however, no previous reports have published CT images.
In our case, transverse thin-section CT images showed bilateral ground-glass attenuation and consolidation with peripheral lung sparing and interlobular reticular opacity. These CT findings are similar to those seen in patients with Pneumocystis jirovecii
]. In addition, our CT images revealed centrilobular nodules in both lungs and bilateral pleural effusions, which are similar to findings in patients with cytomegalovirus pneumonia [4
]. Therefore, we initially diagnosed this case as concurrent Pneumocystis jirovecii
pneumonia with cytomegalovirus. However, no pathogens other than HHV-6 were found in plasma specimens or in BALF. In our case, lung biopsy was not performed; therefore, a correlation between the CT findings and pathological findings could not be determined.
In 1993, Cone et al [10
] reported that bone marrow transplant recipients with high levels of HHV-6 DNA in lung tissue tended to have idiopathic pneumonitis, a favourable outcome, severe graft vs
host disease and changes in HHV-6 antibody titres, suggesting an association between HHV-6 infection and idiopathic pneumonitis. However, it would be difficult to differentiate HHV-6-pneumonitis from other opportunistic infections. Therefore, to better understand the characteristics of HHV-6 infection and the radiological findings, further studies with larger patient groups are needed. The final diagnosis is made by bacteriological and virological analysis using the plasma and BALF materials of patients.
In the present case, HHV-6 encephalitis developed 24 days after bone marrow transplantation, which was diagnosed by serological studies. The T2
weighted images, FLAIR images and DWI (b
factor = 1000 s mm–2
) showed symmetrical regions with high signal intensity in the lateral lobes and insular cortex. Provenzale et al [6
] reported that the presence of MR signal intensity abnormalities in the medial temporal lobe should be recognised as HHV-6 encephalitis in immunosuppressed patients, especially when hyperintense lesions on FLAIR images and DWI are seen in the insular region and inferior frontal lobe. The MR images in our case were similar to those in the previous report.
In summary, we have presented a case of pneumonitis and encephalitis associated with HHV-6 infection after bone marrow transplantation with thin-section CT findings. In patients with immunosuppression after bone marrow transplantation who have acute respiratory symptoms, such as fever or cough, together with abnormal thin-section CT findings, HHV-6 pneumonitis should be considered in differential diagnosis.