Clinical diagnosis
Case 113
【Progress】We introduced her to the distant hospital where a specific neurologist works. Thereafter, we do not have any information from the neurologist.
【Discussion】
After initial infection of herpes simplex virus (HSV) to skin or mucosa, HSV permanently infects to nerve cells via peripheral nerve fibers, makes life as latent infection and sometimes reactivates. The degree of the reactivate symptom depends on the immune system of host:hypofunction of immune ability or immunosuppressive agents (1-3). In a latent infection, HSV exists as a DNA circle but not as a virus particle (1). HSV is categorized as type I and type II. HSV type I includes infection to skin and mucosa of upper body (encephalitis, eye and oral mucosa) and HSV type II includes infection to skin and mucosa of lower body (myelitis, genital mucosa) (1-3). Neonatal encephalitis is usually caused by HSV type II possibly because of infection via vagina during delivery, leading to be fatal.
While HSV infection induces apoptosis of the infected cells, HSV represses apoptosis of the host cell for preserving HSV latent life (1). HSV type I lies in trigeminal nerve ganglion situated at the edge of the petrous bone & in the trigeminal (Meckel) cave (3). Trigeminal nerve has three branches (divisions): ophthalmic nerve exits at superior orbital fissure, maxillary branch exits at rotundum foramen and mandibular branch exits at oval foramen. When inflammation of HSV type I reactivates and outbreaks at trigeminal ganglion, the swollen trigeminal ganglion may irritate these three nerve branches and cause various symptoms. In our case, she experienced pulsating headache at right temporal portion and experienced visual blurring of right eye that might be related to irritation to maxillary nerve branch and ophthalmic nerve branch, respectively.
Pathology of viral encephalitis revealed severe edema, petechial hemorrhage, diffuse necrosis, and necrotizing vasculitis with perivascular lymphocytes infiltration and eosinophilic intranuclear inclusions in ganglion cells (3). Although HSV encephalitis involves frontal lobe at times, HSV encephalitis involve mainly medial areas of temporal lobes (4). The reason why the temporal lobe is susceptible to be damaged is not clarified yet. It might be related that trigeminal ganglion situates adjacent to the temporal lobe. HSV might transmit directly to temporal lobe via cerebrospinal fluid. In our case, the localized gyrus (cortex) surrounding sulcus in the right temporal lobe was swollen with edema (Figs 1, 2).
MRI with diffusion-weighted imaging is known to be more sensitive to detect HSV encephalitis than MRI with conventional sequences. However, of the temporal lobe encephalitis, HSV encephalitis occurs in approximately 25 % (3). Then, other infectious and noninfectious diseases should be considered in differential diagnosis. In our case, temporal edema was detected by MRI with DWI, T1WI, T2WI and FLAIR (Figs 1, 2), and MRI with DWI was more clear to show the lesion rather than MRI with other sequences.
【Summary】
We present a thirty year-old female suffering from visual blur, pulsating temporal headache and dizziness. Brain MRI with DWI showed the localized edematous gyrus surrounding sulcus most clearly rather than MRI with other sequences, implying herpes simplex virus (HSV) encephalitis. We should keep in mind that HSV is categorized as type I and type II, and adult encephalitis is caused by HSV type I and neonatal encephalitis is caused by HSV type II. HSV type I lies in trigeminal nerve ganglion and reactivates. The swollen trigeminal ganglion may irritate three nerve branches: ophthalmic, maxillary and mandibular branches which cause various symptoms. Although the reason why the temporal lobe is susceptible to be damaged is not clarified yet, it might be related that trigeminal ganglion situates adjacent to the temporal lobe via cerebrospinal fluid. HSV encephalitis occurs in approximately 25 % of the temporal encephalitis. Then, other infectious and noninfectious diseases should be considered in differential diagnosis.
【References】
1.Minagawa H. Topics on herpes simplex virus pathogenesis – roles ofviral non-essential genes and host immune status. Virus 2002; 52: 109-115. (in Japanese)
2.Verjans GM, et al. Selective retention of herpes simplex virus-specific T cells in latently infected human trigeminal ganglia". Proc. Natl. Acad. Sci. U.S.A. 2007; 104 (9): 3496–501. doi:10.1073/pnas.0610847104. PMC 1805572 . PMID 17360672
3.Bradshaw MJ, et al. Herpes Simplex Virus-1 Encephalitis in Adults: Pathophysiology, Diagnosis, and Management. Neurotherapeutics. 2016 Jul; 13(3): 493–508. Published online 2016 Apr 22. doi: 10.1007/s13311-016-0433-7PMCID: PMC4965403 PMID: 27106239
4.Leonard JR, et-al. MR imaging of herpes simplex type 1 encephalitis in infants and young children: a separate pattern of findings. AJR Am J Roentgenol. 2000;174 : 1651-5.
2018.7.18