Diabetes insipidus following HHV-6 encephalitis after cord blood transplantation in acute myeloid leukemia

A Systematic Review of Sodium Disorders in HHV-6 Encephalitis

Human herpesvirus 6 (HHV-6) encephalitis has a high mortality rate. Among those who survive, ~80% develop some type of permanent neurologic disorder. Early diagnosis and treatment may help prevent long-term sequelae. There have been several case reports as well as retrospective and prospective studies associating HHV-6 encephalitis with some form of sodium imbalance, either hyponatremia or hypernatremia; however, the exact frequency post-HCT is unknown, with reports ranging from 30% to 100%. We performed a systematic review of the literature and found 34 cases of HHV-6 encephalitis reported in conjunction with sodium imbalance that documented the timing of that imbalance relative to the onset of encephalitis. Sodium imbalance occurred before or at the onset of HHV-6 encephalitis in all but 2 cases (94%). This finding supports previous suggestions that sodium imbalance can be considered an early indicator of the potential development or presence of HHV-6 encephalitis in at-risk patient populations.

Human herpesvirus 6 encephalitis in a patient treated with everolimus for renal cell carcinoma

INTRODUCTION

Everolimus is a mammalian target of rapamycin inhibitor and is approved as second-line treatment or beyond for renal cell carcinoma. We report a case of a 75-year-old male treated with everolimus for metastatic renal cell carcinoma, after sunitinib treatment, who was diagnosed with human herpesvirus 6 encephalitis.

CASE REPORT

After 39 months of everolimus, 10 mg per day, our patient was admitted with fever, consciousness disorders and a partial epileptic crisis. Laboratory tests revealed lymphopenia (170 lymphocytes/mm³), and polymerase chain reaction in cerebrospinal fluid was positive for human herpesvirus 6. Brain magnetic resonance imaging study demonstrated hippocampal abnormality and a pontine lesion.

MANAGEMENT AND OUTCOME

The patient stopped everolimus treatment indefinitely. He received ganciclovir initially intravenously, with a rapid clinical improvement, as well as polyvalent immunoglobulins were given to correct hypogammaglobulinemia. Two months later, antiviral therapy was switched to oral ganciclovir, which was never stopped. A new lumbar puncture was performed one month after the initiation of antiviral treatment, which did not reveal human herpesvirus 6 DNA anymore.

DISCUSSION

Human herpesvirus 6 encephalitis is more common in hematopoietic stem cell transplant recipients and HIV patients. This is the first case probably associated to everolimus treatment. In contrast to most patients diagnosed with this infection, who either die or develop neurologic sequelae, our patient almost fully recovered two months later.

Child and adult forms of human herpesvirus 6 encephalitis: looking back, looking forward

PURPOSE OF REVIEW

This review evaluates publications on human herpesvirus 6 (HHV-6) encephalitis recognizing firstly that HHV-6A and HHV-6B are separate species with differing properties, and secondly the phenomenon of chromosomal integration; this occurs in a minority of persons and the complete viral genome of either HHV-6A or HHV-6B is present in every nucleated cell in the body. Although chromosomal integration has not been associated with disease, the resulting very high level of viral DNA in human tissues and blood has sometimes been wrongly misinterpreted as active infection.

RECENT FINDINGS

No disease has been linked to HHV-6A, whereas HHV-6B may cause encephalitis. Encephalitis due to primary HHV-6B infection in young children is commonly reported from Japan, but very rarely elsewhere in the world, suggesting a genetic predisposition. Reports of HHV-6A or HHV-6B encephalitis in immunocompetent older children/adults are most likely due to chromosomal integration and not active infection. HHV-6B reactivation is well established as causing limbic encephalitis after haematopoietic stem cell transplantation, particularly after receipt of cord blood; the outcome is poor and preventive strategies are ineffective.

SUMMARY

Understanding the pathophysiology of HHV-6B encephalitis remains incomplete, especially regarding young children. Clinical trials of antiviral therapy are warranted for treatment and prevention of HHV-6B encephalitis after transplantation.

Central diabetes insipidus in an HHV6 encephalitis patient with a posterior pituitary lesion that developed after tandem cord blood transplantation

A 60-year-old myelodysplastic syndrome patient underwent tandem cord blood transplantation. The primary cord blood graft was rejected, and human herpesvirus 6 (HHV6) encephalitis developed after engraftment of secondary cord blood. Polyuria and adipsic hypernatremia were observed during treatment of the encephalitis. The patient died of bacteremia caused by methicillin-resistant Streptococcus epidermis. HHV6 infection in the posterior pituitary was confirmed on autopsy, as was infection of the hippocampus, but not of the hypothalamus. This is the first case report of central diabetes insipidus caused by an HHV6 posterior pituitary infection demonstrated on a pathological examination.