10 Poorly Understood Facts about HHV-6 Encephalitis
- HHV-6 encephalitis is most commonly seen among stem cell transplant patients who do not receive prophylactic antiviral therapy, but has been reported in immunocompetent adults as well.
- Approximately 1-4% of all HSCT patients develop post-transplant HHV-6 encephalitis; however, the rate is significantly higher—around 10-15%–following cord blood transplantation (CBT) (Hill 2011, Chevallier 2010, Mori 2010).
- Encephalitis associated with primary infection in infants has an unexpectedly poor outcome. In a nationwide survey in Japan, 48% of 81 cases had neurologic sequelae and two died. (Yoshikawa 2009)
- HHV-6 encephalitis is transplant patients causes a high rate of disability. One study found that 80% of those who survive HHV-6 encephalitis suffer from permanent neurological disability. (Sakai 2011)
- A recent study found that out of 983 cases of acute encephalopathy in Japan, 17% were caused by HHV-6. More importantly, however, is that fact that HHV-6-associated encephalitis accounted for 64% of the more severe cases with biphasic seizures in this study, of which only half survived without neurological sequelae (Hoshino 2011)
- HHV-6 reactivation is associated with cognitive decline in stem cell transplant patients, especially processing speed and executive functioning. (Zerr 2005, 2011)
- HHV-6 may be far more common than currently suspected because HHV-6 is a low copy number virus and often falls below the level of detection. The NINDS recently used an ultra-sensitive assay and found HHV-6 was found in 40% of 35 cases of encephalitis of unknown etiology. (Yao 2009)
- There is typically no pleocytosis with HHV-6 encephalitis/encephalopathy. (Zerr 2006, Yoshikawa 2009)
- Antiviral therapy should be started early to prevent brain damage. (Ogata 2011, Ishiyama 2010, 2009, Olli-Lahdesmaki 2011, Crawford 2009)
- HHV-6 encephalitis should be suspected in patients who present with abnormalities in the hippocampus, amygdala and limbic structures beyond the medial temporal lobe. (Provenzale, 2009)
Download a copy of The HHV-6 Foundation’s 2012 AAN Meeting Packet on “HHV-6 Encephalitis” which has a collection of select abstracts and publications on HHV-6 & Encephalitis.
For more information, visit the HHV-6 Foundation’s webpage on HHV-6 Encephalitis.
