title: CT and MRI findings of human herpesvirus 6-associated encephalopathy: comparison with findings of herpes simplex virus encephalitis.
abstract: OBJECTIVE
  It is important to differentiate human herpesvirus 6 (HHV-6)-associated encephalopathy from herpes simplex encephalitis (HSE). Although these conditions are similar with regard to involvement of the mesial temporal lobe, HSE is sensitive to acyclovir but HHV-6 encephalopathy is not. We compared the imaging findings of the two conditions.
  
  
  METHODS
  We encountered eight cases of HHV-6 encephalopathy and nine cases of HSE. We divided an observation time into early, middle, and late periods defined as 0-2, 3-30, and more than 30 days from the onset of neurologic symptoms. Differences between HHV-6 encephalopathy and HSE on CT scans in the early period and in distribution and temporal changes in the affected regions on MR images in the three periods were analyzed.
  
  
  RESULTS
  At MRI in the early and middle periods, all eight patients with HHV-6 encephalopathy had exclusive involvement of the mesial temporal lobes, and all nine patients with HSE had involvement of both the mesial temporal lobes and the extratemporal regions (p < 0.01). Among patients who underwent head MRI, six of six with HHV-6 encephalopathy but none of six with HSE had resolution of high signal intensity on T2-weighted and FLAIR images (p < 0.01). Among patients who underwent head CT in the early period, none of the four with HHV-6 encephalopathy and six of the seven with HSE had abnormal findings, including parenchymal swelling, decreased attenuation of affected regions, and abnormal gyral enhancement (p < 0.05).
  
  
  CONCLUSIONS
  Serial MRI showed transient abnormal signal intensity in the mesial temporal lobes in patients with HHV-6 encephalopathy but persistent abnormal signal intensity in both the mesial temporal lobes and the extratemporal regions in patients with HSE. CT in the early period showed no abnormality in patients with HHV-6 encephalopathy but definite abnormal findings in patients with HSE. These differences may be useful in the differential diagnosis of the two conditions.
authors.affiliation: Department of Radiology, Faculty of Medicine and Graduate School of Medicine, Saga University, Saga, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Noguchi
authors.forename: Takashi
authors.initials: T
authors.lastname: Yoshiura
authors.forename: Akio
authors.initials: A
authors.lastname: Hiwatashi
authors.forename: Osamu
authors.initials: O
authors.lastname: Togao
authors.forename: Koji
authors.initials: K
authors.lastname: Yamashita
authors.forename: Eiki
authors.initials: E
authors.lastname: Nagao
authors.forename: Akira
authors.initials: A
authors.lastname: Uchino
authors.forename: Kanehiro
authors.initials: K
authors.lastname: Hasuo
authors.forename: Kazushige
authors.initials: K
authors.lastname: Atsumi
authors.forename: Takashi
authors.initials: T
authors.lastname: Matsuura
authors.forename: Toshiro
authors.initials: T
authors.lastname: Kuroiwa
authors.forename: Futoshi
authors.initials: F
authors.lastname: Mihara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Honda
authors.forename: Sho
authors.initials: S
authors.lastname: Kudo
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D015897:Comorbidity; D003287:Contrast Media; D003937:Diagnosis, Differential; D004660:Encephalitis / Q000175:diagnosis* / Q000821:virology*; D020803:Encephalitis, Herpes Simplex / Q000175:diagnosis*; D005260:Female; D019786:Gadolinium DTPA; D015654:Herpesvirus 6, Human; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D019349:Roseolovirus Infections / Q000175:diagnosis*; D014057:Tomography, X-Ray Computed
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA