Background
Aseptic meningitis is an inflammation of the meninges associated with acute onset of headache, fever and neck stiffness, with pleocytosis of the cerebrospinal fluid, and no growth on routine bacterial culture [
1]. The leading recognizable causes of aseptic meningitis include non-polio human enteroviruses, mumps virus, lymphocytic choriomeningitis virus and herpesviruses [
2]. Varicella zoster virus (VZV) reactivation is recognized as one of the most common neurological infectious diseases and VZV the second most frequent virus causing encephalitis [
3]. VZV meningitis were less described in the literature, most of which involved adolescent or elderly patients and meanwhile the viruses were detected by means of polymerase chain reaction (PCR) [
4].
We here described cases of 4 immunocompetent adults with aseptic meningitis due to VZV reactivation diagnosed by next-generation sequencing (NGS).
Discussion and conclusions
VZV, belonging to the group of alpha-herpes viruses, causes varicella (chickenpox) and herpes zoster. Varicella usually results in mild to moderate illness in mainly childhood or immunocompetent patients with disseminated vesicular rash. After primary infection, VZV remains latent in sensory cranial nerve ganglia or dorsal root ganglia, when reactivated, replicates along the course of the nerve and appears as a localized vesicular skin rash. Viral reactivation can cause a wide range of neurologic disease, most frequently manifesting as herpes zoster and post-herpetic neuralgia [
3]. Older age, immunocompromised state, bone marrow transplant recipients and possibly pregnancy are risk factors associated with higher severity of VZV. Aseptic meningitis is usually regarded as an uncommon complication of the cutaneous primary infection in patients with impaired cellular immunity. Recently, many studies reported that VZV was an important cause of aseptic infection in central nervous system (CNS), with the frequencies ranging from 5 to 27% [
5,
6].
The etiology of acute meningoencephalitis remains undiagnosed in approximately 60% of cases despite extensive clinical laboratory testing for infectious pathogens [
7]. Till now, many diagnostic assays are based on polymerase chain reaction (PCR), which relies on sequence-specific primers. NGS has been applied as a diagnostic method to detect the pathogens for CNS infectious diseases in recent years. Many successful applications of NGS to the diagnosis with CNS infections have been reported [
8,
9]. The case series included 4 male adult patients who were diagnosis with VZV meningitis by NGS. Interestingly, all 4 patients presenting in this study were less than 50 years of age, although VZV reactivation were reported more commonly occurred in older adults [
10]. This finding was similar to that in another study in which 5 of the 8 patients with VZV meningitis were presented before the fifth decade of life. None of them had traditional risk factors for VZV infection. The only one who had epilepsy history took antiepileptic drugs, rather than immunosuppressant drugs, which indicated that reactivation of VZV may be a more frequent cause of aseptic meningitis than previously anticipated in immunocompetent individuals. Koskiniemi et al. reported that 27 and 65% of patients with encephalitis and meningitis, respectively, had no skin manifestations, suggesting VZV could reactivate independently of vesicular eruptions, and spread directly to the leptomeninges [
11]. In the present study, 3 patients (75%) had no cutaneous zosteriform lesions, which was consistence with the previous study [
11,
12].
Lumbar puncture revealed increased opening pressure of CSF (235–400 mm H
2O) in three patients, and it was also on the high side (165 mm H
2O) for the other one. All cases showed elevation in CSF WBC, ranging from 147 to 478 × 10
6/L, and the CSF cytology indicated lymphocytic inflammation. It was regarded that mild elevation in CSF protein levels would been observed in aseptic meningitis. However, the relatively high CSF protein levels were reported seen in patients with VZV infection which were significantly higher than those seen in patients with enteroviral infection [
12,
13]. Protein levels (median 1.41 g/L) in this study were higher than previously reported. All patients received acyclovir intravenously for 1–2 weeks resulting in full recovery, suggesting that VZV meningitis tends to be mild symptom, good response to treatment and benign prognosis.
The difficulty in meningitis diagnosis is to distinguish whether it’s a viral or bacterial etiology, because this is crucial for treatment decisions. The treatment threshold is usually set low in clinical work, so that antibiotics, even anti-tuberculosis treatment, are often prescribed in cases of doubt, as were patients in this study. The patient of case No. 2 had vesicular rash before admission which made the diagnosis with aseptic meningitis relatively easy. However, the other 3 patients never showed cutaneous zosteriform lesions. Additionally, the T-cell spot test was positive for the second and fourth cases, meanwhile the protein levels in CSF elevated significantly for both these 2 patients, which implied possible tuberculosis infection, therefore anti-tuberculosis treatment as well as antibiotics were administrated. However, all the cases in our study were pathogen diagnosis within 72 h after admission. Once the sequences of VZV were detected by NGS, inappropriate treatment were stopped.
NGS is a rapid and accurate approach for the molecular diagnosis with diseases compared to traditional clinical testing. It could dramatically reduce the diagnostic period to less than 3 days [
14]. Pathogen-specific PCR is widely used to detect common viruses like herpes simplex virus, VZV and enterovirus because of its high sensitivity and specificity. The turn-around time, which is the time taken from CSF collection to receipt result report, is often 2 days for PCR, and is comparable to that of the NGS test. Most centers around the world would consider NGS only for samples that have been tested negative by pathogen-specific PCR. However, our center opted for direct NGS instead of PCR in this study, for 3 of the cases were difficult to distinguish between viral and bacterial etiology from CSF characteristic or clinical feature. The main limitation of PCR is the level to which assays can be multiplexed, which constrains the number of targets that can be assessed per reaction. For cases of common virus infection, the diagnosis will be quickly confirmed by PCR; for cases of other microorganism infection which are out of the PCR test range, the diagnosis time would be extended. In contrast, NGS is a high-throughput approach that can interrogate all genetic material in a biologic sample simultaneously [
15]. It enable sequencing the total DNA or ribonucleic acid (RNA) from a human sample and identify all possible microorganism present in the specimen. Besides, NGS is an untarged assay as it can amplify and sequence the entire DNA content of a sample without using any primers or probes. The NGS results were further validated by Sanger sequencing in our cases, which was consistent with our expectation, and indicated the reliability of the results and the great practical guiding value of NGS.
VZV reactivation leading to aseptic meningitis in immunocompetent adults with or without cutaneous zoster is more common that previous regarded. Relatively high CSF protein levels could be observed in VZV meningitis. This study highlighted the feasibility of using NGS of CSF as a diagnostic tool for CNS infection. Unbiased NGS could facilitate identification of all the potential pathogens in a single assay theoretically, which is of great importance for providing the rapid and accurate diagnosis and the targeted antimicrobial therapy for CNS infection.
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