HHV-6 & Cognitive Dysfunction

HHV-6 reactivation is the most common cause of mental confusion among post-transplant patients (Zerr 2011). HHV-6 limbic encephalitis occurs in 1-4% of all transplant patients, resulting in intermittent confusion, poor coordination, flat affect and somnolence.

Several cases of HHV-6-associated encephalitis have also presented retrograde and anterograde amnesia. In these cases, HHV-6 DNA was detected in the CSF by PCR, which is considered substantive evidence of active CNS infection. These patients also showed signal intensity abnormalities in the medial temporal lobes, which correlates well with the presentation of anterograde amnesia (Gorniak 2006).

A clinical association between the medial temporal lobes and dysfunction of memory formation was first documented in 1957 (Scoville & Milner).  Since then, dozens of studies have supported the concept that the medial temporal lobes, specifically the hippocampus and surrounding structures, are intrinsically important to the processing of declarative functions such as conscious memory–which is responsible for remembering specific facts and events.  Additionally, MR imaging following seizure episodes in several patients have demonstrated cerebral volume loss disproportionately prominent in the temporal lobes; these patients also displayed lesions in the hippocampus and temporal lobes (Visser 2005, Van der Flier 2005). This data suggests that HHV-6 infection may play a role in amnesia through its pathogenesis in encephalitis.