intractable seizure disorder associated with chronic herpes infection hsv1 detection in tissue by...

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Introduction We describe persistent herpetic infection leading to a pro- gressive and intractable seizure disorder necessitating sur- gical intervention for seizure control in three children. Herpes simplex (HSV1) encephalitis had been previously diagnosed and treated several years before surgical resec- tion in each patient. In all three cases there was evidence of ongoing active inflammation in addition to the seque- lae of previous encephalitis and genomic sequences for HSV1 were detected in the brain tissue by the polymerase chain reaction (PCR). Clinical summary Case 1 This 8.5-year-old, left-handed girl was evaluated for refractory sei- zures and developmental delay. The perinatal course was unremark- able. She was the fourth child in her family. Family history was non- Child’s Nerv Syst (1998) 14: 15–20 © Springer-Verlag 1998 ORIGINAL PAPER Intractable seizure disorder associated with chronic herpes infection HSV1 detection in tissue by the polymerase chain reaction Venita Jay Paul Hwang Harold J. Hoffman Laurence E. Becker Maria Zielenska Abstract We describe the patholog- ical findings and report the detection of herpes simplex virus 1 (HSV1) in the brain in three patients who pre- sented with intractable seizures. All three patients had a previous history of HSV1 encephalitis and went on to develop a medically refractory sei- zure disorder necessitating surgical intervention. HSV1 encephalitis was clinically diagnosed and treated at 6 months, 3 years, and 7 months and surgical resection was done at 8.5 years, 6 years, and 3 years, in cases 1, 2 and 3, respectively. Pathological examination revealed chronic en- cephalitis in all three cases, with mi- croglial nodules, intraparenchymal, perivascular and meningeal lympho- cytic infiltrates, and gliosis. While immunohistochemical and ultrastruc- tural studies were negative for viral pathogens, polymerase chain reac- tion (PCR) analysis revealed HSV1 genome. These cases represent ex- amples of chronic herpes encephal- itis and seizure disorder with pres- ence of viral genome in the brain long after the initial episode of treated herpes encephalitis. Key words Brain · Encephalitis · Epilepsy · Herpes simplex virus · Temporal lobe · Polymerase chain reaction Received: 15 September 1997 V. Jay · P. Hwang Bloorview Epilepsy Program, University of Toronto, Toronto, Ontario, Canada V. Jay () · L. E. Becker Division of Pathology, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada Tel.: (416) 813-5938 Fax: (416) 813-5974 e-mail: [email protected] P. Hwang Division of Neurology, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada H. J. Hoffman Division of Neurosurgery, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada M. Zielenska Molecular Diagnostic Laboratory, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada

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Page 1: Intractable seizure disorder associated with chronic herpes infection HSV1 detection in tissue by the polymerase chain reaction

Introduction

We describe persistent herpetic infection leading to a pro-gressive and intractable seizure disorder necessitating sur-gical intervention for seizure control in three children.Herpes simplex (HSV1) encephalitis had been previouslydiagnosed and treated several years before surgical resec-tion in each patient. In all three cases there was evidenceof ongoing active inflammation in addition to the seque-lae of previous encephalitis and genomic sequences for

HSV1 were detected in the brain tissue by the polymerasechain reaction (PCR).

Clinical summary

Case 1

This 8.5-year-old, left-handed girl was evaluated for refractory sei-zures and developmental delay. The perinatal course was unremark-able. She was the fourth child in her family. Family history was non-

Child’s Nerv Syst (1998) 14: 15–20© Springer-Verlag 1998 ORIGINAL PAPER

Intractable seizure disorder associated with chronic herpes infectionHSV1 detection in tissue by the polymerase chain reaction

Venita JayPaul HwangHarold J. HoffmanLaurence E. BeckerMaria Zielenska

Abstract We describe the patholog-ical findings and report the detectionof herpes simplex virus 1 (HSV1) inthe brain in three patients who pre-sented with intractable seizures. Allthree patients had a previous historyof HSV1 encephalitis and went on todevelop a medically refractory sei-zure disorder necessitating surgicalintervention. HSV1 encephalitis wasclinically diagnosed and treated at 6months, 3 years, and 7 months andsurgical resection was done at 8.5years, 6 years, and 3 years, in cases1, 2 and 3, respectively. Pathologicalexamination revealed chronic en-cephalitis in all three cases, with mi-croglial nodules, intraparenchymal,perivascular and meningeal lympho-cytic infiltrates, and gliosis. Whileimmunohistochemical and ultrastruc-tural studies were negative for viralpathogens, polymerase chain reac-tion (PCR) analysis revealed HSV1genome. These cases represent ex-amples of chronic herpes encephal-

itis and seizure disorder with pres-ence of viral genome in the brainlong after the initial episode oftreated herpes encephalitis.

Key words Brain · Encephalitis ·Epilepsy · Herpes simplex virus ·Temporal lobe · Polymerase chainreaction

Received: 15 September 1997

V. Jay · P. HwangBloorview Epilepsy Program,University of Toronto,Toronto, Ontario, Canada

V. Jay (½) · L. E. BeckerDivision of Pathology,The Hospital for Sick Children,555 University Avenue,Toronto, Ontario M5G 1X8, CanadaTel.: (416) 813-5938Fax: (416) 813-5974e-mail: [email protected]

P. HwangDivision of Neurology,The Hospital for Sick Children,555 University Avenue,Toronto, Ontario M5G 1X8, Canada

H. J. HoffmanDivision of Neurosurgery,The Hospital for Sick Children,555 University Avenue,Toronto, Ontario M5G 1X8, Canada

M. ZielenskaMolecular Diagnostic Laboratory,The Hospital for Sick Children,555 University Avenue,Toronto, Ontario M5G 1X8, Canada

Page 2: Intractable seizure disorder associated with chronic herpes infection HSV1 detection in tissue by the polymerase chain reaction

contributory. Early development was normal until 6 months of age,when she developed acute partial seizures and a clinical diagnosis ofherpes encephalitis was made. She was treated with phenobarbitol,phenytoin and acyclovir.

However, the patient had recurrence of partial motor seizures withtonic head deviation to the right and right arm extension. On one oc-casion, seizures were secondarily generalized. She was tried on ni-trazepam and clobazam, but these were stopped because of severeside effects. She was then given valproic acid. She still had one ortwo of the tonic partial seizures with right arm extension and headand eyes deviated to the right, with some supplementary motor areatype seizures about five times a day. She developed precocious pu-berty, which was treated with lupron. She also had developmentaldelay with a behavioral disturbance involving regressive behavior.At the age of 8.5 years, she was in grade 1, but was functioning atkindergarten level.

Clinical examination revealed a right hemiatrophy of the handand foot with hemiplegia and impairment of fine finger movementsof the right hand, which she only used as a helper hand. There wasright hemianopsia, but the pupils were briskly reactive and fundi wereunremarkable. There was a right upper motor facial paresis. Deeptendon reflexes were brisk, graded 3+ in the right biceps and brachi-oradialis and 3+ in the right quadriceps, with an extensor plantar re-sponse on the right side. She had fluent communication with goodvocabulary and only occasional stuttering of the words, but her print-ing with the left hand showed reversal of letters and poor placementof letters of her own name. She had occasional headaches but no ev-idence of increased intracranial pressure.

The EEG findings were suggestive of a partial seizure originat-ing from the left supplementary motor area, but the possibility of atemporal lobe focus with secondary spread to the frontal lobe couldnot be excluded. At this time vigabatrin therapy was started. CT andMRI scans of the head showed marked loss of brain substance in-volving the left temporal, parietal and occipital lobes, with some min-imal sparing of the left frontal lobe. The MRI scan revealed alteredsignal in the left thalamus and dilatation of the left lateral ventricleconsistent with volume loss. There was also decreased volume of theright cerebellar hemisphere consistent with the left cerebral atrophy.On SPECT brain perfusion scanning, the right cerebral hemispherehas a normal appearance, while there was a marked reduction in per-fusion throughout the cortex, involving the frontal, parietal and oc-cipital cortex.

The patient was felt to be a good surgical candidate. She under-went a left frontotemporal parietal craniotomy with left frontalhemicorticectomy under neuroleptic anesthesia. The postresectionintraoperative electrocorticography revealed no evidence of seizureactivity. Postoperatively she developed a coagulopathy thought tobe secondary to valproic acid, which was discontinued. Dilantinwas started. Within a week postoperatively, the patient was stablewith her normal baseline neurological function. A postoperativeEEG confirmed no seizure activity. She continued with dilatin as maintenance therapy and was still seizure free at follow-up at 17 months.

Case 2

This 6-year-old girl presented to our center for evaluation of refrac-tory seizures following previous treated herpes encephalitis. She hadbeen normal prior to the age of 3 years, when she was diagnosed clin-ically as having herpes encephalitis and was treated with acyclovir.She became developmentally delayed after the onset of a seizure dis-order following the encephalitis episode. She was in a prolonged sei-zure and hospitalized for over a month. She remained seizure freewith anticonvulsants for about 8 months and then began to have com-plex partial seizures characterized by a motionless stare, crying andautomatisms an average of 2–8 times a day. These continued despitecarbamapazine, valproic acid and clonazepam. The EEG showed aright temporal focal slow wave with PLEDS (periodic lateralized epi-

leptiform discharges), in addition to generalized spike wave dis-charges. The MRI scan initially showed cerebral edema with hem-orrhage, but subsequent MRI showed increased signal on T2-weight-ed images in the right frontal, temporal and parietal regions and somebifrontal signal changes.

The patient was refractory to standard antiepileptic medications,including carbamazepine, phenobarbitol, clonazepam, vigabatrin,primidone, valproic acid and lamotrigine. She also had prolongedbouts of seizures averaging about 45 min in duration and suggestiveof status epilepticus.

Evaluation in the epilepsy monitoring unit at our center showedfour different types of seizures: myoclonic seizures with startle, gen-eralized tonic clonic seizures with duration averaging 2–3 min, ton-ic clonic seizures lasting 2 min 4–6 times a day on average, and 4complex partial seizures preceded by an aura, followed by automa-tisms, with or without a headache.

The patient underwent a right frontotemporal parietal cranioto-my. The intraoperative electrocorticography showed widespread epi-leptiform discharges, maximally from the anterior temporal region,which was excised back to 6.5 cm from the temporal tip, includingthe hippocampus. Residual epileptiform activity appeared over theinferior and midfrontal regions, and posterior parietal and posteriortemporal regions behind the line of excision.

The patient had a couple of postoperative seizures with a gener-alized myclonic jerk, but did not have any further complex partialseizures. The postoperative EEG showed mild residual epileptiformactivity in the right frontal and left temporal regions independent-ly, but was much improved in comparison with the preoperativeEEG. She had no postoperative motor or sensory deficit. Her sei-zures were much improved and she appeared calmer and had betterattention.

Case 3

The detailed clinical and pathological findings in this patient havealready been reported [11] and will be presented here only in brief.The patient was a 3-year-old, left-handed boy who initially present-ed at 7 months with atypical febrile seizures with lethargy and irri-tability. CT of the brain demonstrated a low-intensity, swollen, lefttemporal lobe without hemorrhage. SPECT scan demonstrated ac-cumulation of radiotracer activity in the left temporal lobe and rightbasal ganglia. The EEG revealed seizure activity with focal slowwave activity. Serum HSV titers were 1:8 and >1:128 dilution 1month apart, while the initial cerebrospinal fluid HSV antibody tit-er was <1:4. No virus was isolated on culture, and PCR analysis ofthe CSF sample for HSV1 was negative. Nonetheless, the infant wastreated for HSV encephalitis with 3 weeks of intravenous acyclo-vir.

At the age of 18 months, he had partial onset, complex partialseizures with secondary generalization, and episodes of day dream-ing and unresponsiveness. He also had diminished attention span andhyperactive behavior. The ictal EEG showed a left temporal epilep-tiform focus, while the interictal EEG showed multifocal general-ized abnormality. The CT and MR scans demonstrated left temporalvolume loss and altered signal intensity in the parenchyma on MRIconsistent with gliosis. Nuclear SPECT scan demonstrated nonaccu-mulation of activity in the left temporal lobe. The patient was refrac-tory to a number of anticonvulsant medications, including clobazam,carbamazepine, valproic acid, and phenobarbitol. A left temporal lo-bectomy was performed.

Materials and methods

The preoperative evaluation and surgical management of epilepsywas according to published protocols [3, 8–10].

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Page 3: Intractable seizure disorder associated with chronic herpes infection HSV1 detection in tissue by the polymerase chain reaction

Tissue preparation

The specimens were submitted in toto for pathological examinationincluding conventional histology, immunohistochemistry, electronmicroscopy, and PCR analysis. Immunohistochemical staining wasperformed by the peroxidase-antiperoxidase technique using theHSV1 and HSV2 antibodies (HSV1, Dakopatts, 1:100, polyclonal;HSV2, Dakopatts, 1:100, polyclonal). Immunostaining for glial fi-brillary acidic protein (GFAP, DAKO, 1:200, polyclonal) was alsodone to assess the degree of gliosis. For electron microscopy, tissuewas fixed in the universal fixative (equal parts of 4% formaldehydeand 1% glutaraldehyde), postfixed in 1% OsO4 and embedded in Ep-on. Semithin sections were stained with uranyl acetate and examinedunder a Philips 400 transmission electron microscope for the pres-ence of viral particles.

Polymerase chain reaction

The material submitted for PCR was retrieved from sections of par-affin-embedded tissue. Five 20-µm sections were cut from each par-affin block. The microtome was cleaned with 17% SDS (sodiumdocecyl sulfate, Sigma Chemical Company, St. Louis, Mo.) thenwith 95% ethanol between the blocks, as reported elsewhere [13].The PCR method was based on the procedure described by Rozen-berg and Lebon [18]. DNA for PCR was extracted from formalin-fixed, paraffin-embedded tissues according to the methods de-scribed previously [6]. PCR reaction mixtures contained 50 mMKCl, 10 mM Tris-HCl (pH 8.3), 1.5 mM MgCl2, 0.01% (wt/vol) gel-atin, 5% dimethylsulfoxide, 200 µM (each) deoxynucleoside tri-phosphates, 10 pmol of each oligonucleotide primer and 2.5 U ofTaq polymerase (Perkin-Elmer Cetus, Norwalk, Conn.). The reac-tions were performed in an automated thermal cycler (Perkin-ElmerCetus); the cycle, which consisted of 1 min of denaturation at 94°C,1 min of annealing at 60°C, and 1 min of elongation at 72°C, wasrepeated 40 times. Ten percent of each amplified product (10 µl)was loaded onto a 1.5% agarose gel containing ethidium bromideand was subjected to electrophoresis before and after digestion withthe restriction enzymes SmaI and BamHI (Bethesda Research La-boratories), which were used under the conditions recommended bythe supplier. Negative controls, including other DNA sources such

as human genomic DNA (no virus present), and positive controls(DNA from patient with known viral infection) and also a reactionmixture without any DNA were run in each experiment. Precautionsto avoid carryover of the PCR products included physical separa-tion of pre-PCR and post-PCR mixtures, aliquoting of reagents, theuse of positive displacement pipettes, and the avoidance of aerosol.PCR analysis for herpes viruses was also performed in brain tissuesfrom five patients without encephalitis as controls, as previously re-ported [12].

Results

Case 1

The specimen consisted of cortical resections measuring5×7.5×0.5 cm, 1.2×1.2×0.6 cm and 1×1×2 cm, along withcavitron aspirate. Microscopic sections revealed lympho-cytic perivascular cuffing, meningeal lymphocytic infil-trate, scattered microglial nodules and gliosis (Fig. 1). Noviral inclusions were observed. Immunostaining for HSV1and HSV2 was negative. Electron microscopy did not re-veal viral particles. PCR analysis revealed HSV1 se-quences in brain tissue (Fig. 2).

Case 2

The specimen consisted of temporal lobectomy with hip-pocampectomy measuring 5.5×4×1.2 cm, and cavitron as-pirate. Microscopy (Fig. 3) revealed extensive inflamma-tion with microglial nodules, histiocytes, occasional mul-tinucleated giant cells, perivascular lymphocytic and his-tiocytic cuffing, extensive neuronal loss and severe glio-

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Fig. 1 Case 1: immunostain-ing for glial fibrillary acidicprotein (GFAP) highlights theextensive gliosis. Perivascularlymphocytic cuffing is also evi-dent. (Immunoperoxidase,×500)

Page 4: Intractable seizure disorder associated with chronic herpes infection HSV1 detection in tissue by the polymerase chain reaction

sis, and foci of cerebral necrosis with dystrophic calcifi-cation. There was also evidence of gliosis in the end-fo-lium of the hippocampus. Immunostaining for HSV1 andHSV2 was negative. Electron microscopy did not revealviral particles. PCR analysis revealed HSV1 sequences inbrain tissue (Fig. 2).

Case 3

Sections of the left temporal lobe revealed severe activeencephalitis with marked neuronal loss, severe gliosis, andextensive chronic inflammatory infiltrates of lymphocytes,plasma cells and macrophages, microglial nodules, neuro-nophagia and scattered mineralization, as previously de-scribed [11]. This case was similar to case 2, in that scat-tered multinucleated giant cells were seen. No viral inclu-sions were identified, and immunostaining for HSV1 andHSV2 was negative. Electron microscopy also failed to re-veal viral particles. The PCR assay revealed HSV1 se-quences in brain tissue.

Discussion

The exquisitely sensitive technique of PCR is particularlyuseful for the detection of infectious agents that do notgrow in vitro, require prolonged incubation for recognitionin cell cultures, or are present in very low levels in tissuespecimens [4, 19]. Recently, PCR screening for HSV in ce-rebrospinal fluid (CSF) samples has been extensively em-ployed as a diagnostic tool for suspected HSV encephal-itis [1, 7, 17, 20]. The above studies have confirmed theusefulness of CSF PCR analysis for rapid detection andconfirmation of suspected HSV encephalitis.

In the study by Troendle-Atkins et al. [20], which en-tailed evaluation of the CSF for herpes infection in 8 neo-nates, 11 infants and children with suspected HSV enceph-alitis, and 105 controls (using primers specific for bothHSV1 and HSV2), HSV PCR had a sensitivity of 75%, a

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Fig. 2 PCR analysis: characterization of PCR products generatedfrom DNA obtained from case 1 in panel a (top) and case 2 in panel b (bottom): a (left to right) lines 1 and 10 100-bp ladder, lines 2–4 EBV control (undigested, digested with SmI and BamHI),line 5 HSV1 control (undigested), line 6 HSV1 control (digested withSma1), lines 7–9 case 1 (undigested, digested with SmaI and BamHI);b (left to right) lines 1 and 8 100-bp ladder, line 2 CMV control (notdigested), line 3 HSV2 control (undigested), line 4 HSV2 control (di-gested with BamHI), lines 5–7 case 2 (undigested, digested with SmaIand BamHI). PCR analysis results in case 3 are not shown and havealready been reported [11]

Fig. 3 Case 2: extensive cere-bral necrosis with dystrophiccalcification and mononuclearinflammatory infiltrate. (Hematoxylineosin, ×250)

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specificity of 100% and a negative predictive value of 98%.These authors detected viral DNA in the CSF in 3 of 4 neo-nates with HSV2 infection and central nervous system in-volvement and 3 of 4 patients with proven HSV1 enceph-alitis. These authors reiterated that CSF PCR was a usefulnoninvasive test in establishing the diagnosis of acute HSVencephalitis, but that a negative result did not exclude thediagnosis. In our series, PCR analysis of cerebrospinalfluid was negative for HSV1 in case 3, and was not per-formed in cases 1 and 2. Despite the negative CSF PCR re-sults, case 3 showed the typical clinical picture of HSV en-cephalitis, and examination of the pathological specimenfrom the temporal lobectomy performed 27 months laterconfirmed the presence of HSV1 encephalitis with HSV1detection by PCR.

The three patients in the present report exemplifychronic ongoing active encephalitis and a progressive sei-zure disorder with the presence of HSV1 genome in thebrain. Cases 2 and 3 showed especially active inflamma-tion, with numerous microglial nodules, neuronophagia,and prominent lymphocytic infiltrate around vessels, in themeninges and in the parenchyma. Multinucleated giantcells were also found. Case 2, and to a lesser extent case3, showed extensive cerebral necrosis and dystrophic cal-cification. There was extensive neuronal loss and gliosiscorresponding to scarring related to the old encephaliticepisode. The inflammatory reaction was less marked incase 1, which revealed gliosis, scattered microglial nod-ules, and perivascular lymphocytic infiltrates. Screeningfor a viral etiology by morphologic examination, immu-nostaining and electron microscopy was unsuccessful, butproof of persistence of HSV1 in the tissue was providedby PCR.

Despite acyclovir therapy for HSV1 encephalitis, ourpatients exhibited a prominent active inflammatory re-sponse in the brain tissue, which was resected years afterthe initial episode of encephalitis. The pathology in cases2 and 3 was that of a severe encephalitis, the chronicity ofwhich was indicated by the extensive neuronal dropout,gliosis, and mineralization, while the presence of active in-flammation was evident in the neuronophagia and wide-spread microglial nodules. Counsell et al. [2] described twopatients with necrotizing HSV encephalitis who had rela-tively mild disease at presentation but, despite treatmentwith acyclovir (3 days in one patient and 10 days in thesecond patient), developed dramatic radiographic progres-sion that mimicked mass-occupying lesions. Each of thetwo patients described in this report received a further 10-day course of acyclovir [2]. The presence of an active in-flammatory component in our patients suggests that theircases may not simply represent “burnt-out” HSV enceph-alitis. This raises the issue of further antiviral therapy inpatients who prove to have active herpes encephalitis whensurgical resection is performed for intractable epilepsy.

Esiri [5] studied 29 autopsied cases of HSV encephal-itis and applied the immunoperoxidase technique to detect

viral antigen in brain tissue. In this study, viral antigen wasfound in the brain tissue in all cases of patients dying within3 weeks of onset of neurological disease, but in none dy-ing after 3 weeks. Viral antigen was plentiful in the first 2 weeks, and inflammation and necrosis reached a peakwhen detectable virus was waning. Viral antigen wasmainly concentrated in the medial and inferior temporallobes, hippocampus, amygdala, olfactory cortex, insulaand cingulate gyrus, and was invariably present on bothsides of the brain.

Nicoll et al. [14–16] used PCR analysis to detect HSVDNA in brain tissues of patients with acute as well aschronic burnt out HSV encephalitis. In a PCR study of au-topsy brains, Nicoll et al. [15] detected HSV1 genome inbrains of 6 patients who had died of acute HSV1 enceph-alitis, but not in those of 6 other patients with other neu-rological diseases, including varicella zoster, and HSV2encephalitis. In our laboratory, we have applied viral PCRto autopsy specimens and have been successful in detect-ing viral antigen in formalin-fixed paraffin-embedded au-topsy material [11, 12], indicating that PCR is a simple andspecific technique that makes it possible to assess viralantigen even in routinely processed autopsy tissues. Nicollet al. [16] reported on detection of HSV1 DNA by PCRanalysis in 8 patients who had each survived a previous at-tack of HSV1 encephalitis. This series included the 3 casespreviously reported by the same authors [14] in anotherpaper describing autopsy findings and PCR analysis inburnt out HSV encephalitis. PCR analysis by Nicoll et al.[16] in 8 patients surviving 4 months to 17 years after aprevious episode of HSV encephalitis revealed HSV1DNA in the cerebrum in 6 cases and in the brain stem in 4 cases. Thus, the observations of Nicoll et al. [16] and ourpresent study indicate that HSV1 genome can persist in thenervous system of a surviving patient long after an acuteattack of HSE encephalitis. Nicoll et al. [14, 16] also founda variable degree of persistent inflammation in the braintissue, in addition to the destructive lesions and reactivegliosis. In their study [16] the distribution of viral DNAcorrelated better with the distribution of the inflammatoryinfiltrate than with that of neuronal loss and gliosis.

In our three patients, immunohistochemistry for HSV1antigen and electron microscopy were negative. Viral anti-gen was not detectable by Esiri [5] in patients dying 3 weeks after the episode of acute HSV encephalitis. Sim-ilarly, Nicoll et al. [14] found no staining with antibodiesto HSV1 in postmortem temporal lobe tissue in three survivors of HSV1 encephalitis, two of whom died 5 and7 years after the attack of acute encephalitis. In the thirdpatient in this series [14], who died at the age of 26 years,detailed clinical information was not available. However,in these same patients, viral DNA was detected by PCR[14]. These studies and our own cases underline the diag-nostic importance of PCR for viral detection even whenmorphological and immunohistochemical studies revealno evidence of a viral pathogen. As previously reported by

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Jay et al. [11], PCR analysis was useful in detecting the vi-ral etiology even when no inflammatory response was ev-ident, as in the example of an infant with intractable sei-zures whose brain biopsy revealed cerebral calcificationand gliosis and an absence of inflammation.

In summary, three cases of chronic HSV1 encephalitispresenting as a seizure disorder are described. While ex-amination by other modalities failed to detect viral anti-gen, HSV1 genome was detectable in the surgically re-

sected tissue by PCR. Our cases underscore the fact thatHSV1 may persist in the brain long after the acute episodeof herpes encephalitis and after treatment with acyclovir,and the ongoing chronic encephalitis may contribute tothe development of a medically refractory seizure dis-order.

Acknowledgements We thank Blair Gerrie for technical assistanceand Mike Starr for photographic assistance.

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