Case Report

Use of the diffusion-weightED magnetic resonance imaging for early diagnosis of herpes simplex encephalitis in the ED: a case report

Herpes simplex encephalitis (HSE) is a rare neUrologic emergency. The early recognition and administration of acyclovir is important to reduce the mortality rate. It is well known that the diffusion-weighted magnetic reso- nance imaging (DWI) may visualize the lesion of HSE in the typical areas such as the temporal lobes, the insular cortex, and the cingulate gyri. However, the evaluation of HSE using DWI has not yet been prevalent in the emergency department. We believe that the DWI should be considered for the evaluation of the patient suspected of HSE, and the emergency physician should be familiar with its typical findings.

A 47-year-old man was brought to the emergency department (ED) with Seizure activity. He has been deaf and mute ever since he had measles at 4 years of age. He had experienced several episodes of seizure, and he has not taken any anticonvulsant. Three days before admission, he was transported to a private hospital with generalized tonic clonic seizures of 1- to 2-minute duration. He was then transferred to our ED because of his persistent symptom.

On initial examination, he had stable vital signs without fever. He was disoriented. The cerebrospinal fluid (CSF) study showed 102 white blood cells, 6 erythrocytes, glucose levels of 56 mg/dL, and protein levels of 61 mg/dL. The diffusion-weighted magnetic resonance imaging (DWI) was performed, which showed typical findings of HSE (Fig. 1). The acyclovir administration was started, and the patient was admitted to the neurology department. The herpes simplex encephalitis (HSE) was confirmed by CSF poly- merase chain reaction for herpes simplex virus (HSV) type

1. He was discharged after 12 days in improved state except a mild cognitive impairment.

Herpes simplex encephalitis is the most common cause of sporadic acute encephalitis occurring worldwide. The HSV type 1 is responsible for over 95% of herpetic encephalitis in adult. The mortality rate of untreated HSE reaches 70%, but the use of intravenous acyclovir signifi- cantly decreases the 6-month mortality and morbidity [1]. The early administration of acyclovir is considered the only modifiable parameter to improve the prognosis of patients with HSE. They often present as an acute febrile enceph- alopathy with altered mentation and focal cerebral signs.

However, HSE has broad spectrum of clinical manifestation, and atypical forms occur in up to 20% of patients [2]. Although HSV DNA amplification by polymerase chain reaction analysis of CSF has been the reference standard, it is not yet widely available in the ED. The DWI has become more widely available in emergency situations; however, there are only few reports on the use of DWI for the early diagnosis of HSE in the ED.

The typical neuroPathologic findings of HSE include severe edema and massive tissue necrosis with petechial and some confluent hemorrhages. The computed tomographic scan, which is widely available in the ED, has been known to be less useful. The abnormal computed tomographic findings such as parenchymal or meningeal enhancement are rarely detected before the second week of clinical symptoms [3]. Magnetic resonance imaging (MRI) has become important in the early evaluation of patients with HSE because of its higher sensitivity in identifying the manifestations of the disease. They are shown as low signal intensity on the T1-weighted images and as high signal intensity on the T2-weighted images. The HSE damages the blood-brain barrier and can be detected as regions of Contrast enhancement. The DWI, which is useful in the early diagnosis of acute ischemic stroke, can also visualize the lesions of HSE [4].

The HSV has a tropism for limbic cortex, which includes the temporal lobes, the insular cortex, the subfrontal area, and the cingulate gyri. This characteristic location of lesions indicates the probable mechanism of intracranial spread along the small meningeal branches of the trigeminal nerve

Fig. 1 diffusion-weighted MRI findings. The high signal intensity is shown in both medial temporal lobes (A), and both insular cortex and the cingulate gyri of frontal lobes (B).

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from the trigeminal ganglion. The involvement of cingulate gyrus may be associated with involvement of the efferent connections of the hippocampus. Involvement may initially appear unilaterally, but is typically followed by bilateral disease. This sequential bilateral involvement is almost pathognomonic for HSV encephalitis, particularly when asymmetrical. We also experienced the patients who clinically suspected HSE but yielded normal MRI. There- fore, empirical acyclovir was initiated based on the clinical suspicion, followed by an appropriate consultation for further diagnostic evaluation [5].

Herpes simplex encephalitis should be considered as a diagnostic possibility any time a febrile patient exhibits acute neurologic signs. It is the only form of sporadic encephalitis that has a specific antiviral therapy, acyclovir. Diffusion-weighted magnetic resonance imaging may visu- alize the lesion of HSE in the limbic cortex. Therefore, the DWI should be taken into account for the evaluation of the patient suspected of HSE, and the emergency physician should be familiar with its typical findings.

Sung Pil Chung MD, PhD

Je Sung You MD Hahn Shick Lee MD, PhD Department of Emergency Medicine Yonsei University College of Medicine Seoul 135-720, Republic of Korea

E-mail address: [email protected] doi:10.1016/j.ajem.2007.02.034

References

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2. Fodor PA, Levin MJ, Weinberg A, et al. Atypical herpes simplex virus encephalitis diagnosed by PCR amplification of viral DNA from CSF. Neurology 1998;51:554 - 9.
3. Davis JM, Davis KR, Kleinman GM, et al. Computed tomography of herpes simplex encephalitis with clinicopathological correlation. Radiology 1978;129:409 - 17.
4. Schaefer PW, Grant PE, Gonzalez RG. Diffusion-weighted MR imaging of the brain. Radiology 2000;217:331 - 45.
5. Benson PC, Swadron SP. Empiric acyclovir is infrequently initiated in the emergency department to patients ultimately diagnosed with encephalitis. Ann Emerg Med 2006;47:100 - 5.