Polymerase chain reaction and the diagnosis of viral central nervous system diseases

Nervous system infections in patients with cancer

The diagnostic approach to the patient with cancer with suspected CNS infection depends on an analysis of the patient's immune defect, the time course of development of manifestations of infection, and the type of clinical syndrome with supportive evidence for a specific diagnosis coming from laboratory and neuroradiographic data. Most patients with CNS infections can be grouped into those with signs of meningitis or meningoencephalitis and those with focal mass lesions. A smaller group presents with stroke-like onset. Except for the group with strokes, those with focal deficits usually present in a more indolent fashion, whereas those with meningitis and encephalitis present more acutely [63]. Patients with B-lymphocyte dysfunction are susceptible to encapsulated bacterial pathogens. Patients with T-lymphocyte impairment develop CNS infections that are caused by intracellular pathogens, particularly viruses (HSV, JC, CMV, HHV-6), Nocardia, Aspergillus, and Toxoplasma. Many noninfectious entities, such as drug treatment complications, radiation effects, recurrent tumor, and paraneoplastic syndromes, can mimic CNS infections. Although cryptococcosis, bacterial meningitis, and some viral infections are easily diagnosed from Gram's stain, culture, or PCR, patients with mass lesions may require tissue biopsy to confirm diagnosis. Patients with cancer differ from normal hosts in the distribution of pathogens, and there is a wider range of differential diagnostic issues, both infectious and noninfectious, for the relatively few clinical syndromes that present as potential CNS infections.

Molecular analysis of cerebrospinal fluid in viral diseases of the central nervous system

The use of nucleic acid (NA) amplification techniques has transformed the diagnosis of viral infections of the central nervous system (CNS). Because of their enhanced sensitivity, these methods enable detection of even low amounts of viral genomes in cerebrospinal fluid. Following more than 10 years of experience, the polymerase chain reaction or other NA-based amplification techniques are nowadays performed in most diagnostic laboratories and have become the test of choice for the diagnosis of several viral CNS infections, such as herpes encephalitis, enterovirus meningitis and other viral infections occurring in human immunodeficiency virus-infected persons. Furthermore, they have been useful to establish a viral etiology in neurological syndromes of dubious origin and to recognise unusual or poorly characterised CNS diseases. Quantitative methods have provided a valuable additional tool for clinical management of these diseases, whereas post-amplification techniques have enabled precise genome characterisation. Current efforts are aiming at further improvement of the diagnostic efficiency of molecular techniques, their speed and standardisation, and to reduce the costs. The most relevant NA amplification strategies and clinical applications of to date will be the object of this review.

Use of PCR for the diagnosis of herpesvirus infections of the central nervous system

Polymerase chain reaction (PCR) analysis of cerebrospinal fluid (CSF) has revolutionized the diagnosis of nervous system viral infections, particularly those caused by human herpesviruses (HHV). The PCR technique allows the detection of minute quantities of DNA or RNA in body fluids and tissues. Both fresh-frozen and formalin-fixed tissues may be utilized for PCR assays, with the latter making archival studies possible. CSF PCR has now replaced brain biopsy as the gold standard for the diagnosis of herpes simplex virus (HSV) encephalitis. PCR analysis of both CSF and nervous system tissues has also broadened our understanding of the spectrum of disease caused by HSV-1 and -2, cytomegalovirus (CMV), Epstein-Barr virus (EBV), varicella zoster virus (VZV) and HHV-6. PCR results obtained from tissue specimens must be interpreted cautiously, since this highly sensitive technique may detect portions of viral genomic material that may be present even in the absence of active viral infection. Tissue PCR results in particular must be corroborated with clinical and neuropathologic evidence of central nervous system (CNS) infection. In several neurological diseases, negative PCR results have provided evidence against a role for herpesviruses as the causative agents. This review summarizes the role of CSF PCR in the diagnosis and therapeutic management of herpesvirus infections of the nervous system, particularly those caused by HSV and VZV.

Polymerase chain reaction as a diagnostic adjunct in herpesvirus infections of the nervous system

Polymerase chain reaction (PCR) is a powerful technique that allows detection of minute quantities of DNA or RNA in cerebrospinal fluid (CSF), vesicle and endoneurial fluids, blood, fresh-frozen, and even formalin-fixed tissues. Various infectious agents can be detected with high specificity and sensitivity, including bacteria, parasites, rickettsia and viruses. PCR analysis of CSF has revolutionized the diagnosis of nervous system viral infections, particularly those caused by human herpesviruses (HHV), and has now replaced brain biopsy as the gold standard for diagnosis of herpes simplex virus (HSV) encephalitis. PCR analysis of both CSF and nervous system tissues has also broadened our understanding of the spectrum of disease caused by HSV-1 and -2, cytomegalovirus (CMV), Epstein-Barr virus (EBV), varicella zoster virus (VZV), and HHV-6. Nonetheless, positive tissue PCR results must be interpreted cautiously, especially in cases that lack corroborating clinical and neuropathologic evidence of infection. Moreover, positive PCR results from tissues do not distinguish latent from productive (lytic) viral infections. In several neurological diseases, negative PCR results have provided strong evidence against a role for herpesviruses as the causative agents. This review focuses on the use of PCR tests to diagnose HSV and VZV infections of the nervous system.

Characterization of La Crosse virus RNA in autopsied central nervous system tissues

A reverse transcription-PCR (RT-PCR) technique was used to detect La Crosse (LAC) virus RNA in the central nervous system (CNS) tissues of two patients who died of LAC encephalitis in 1960 and 1978. Viral RNA was readily detected by RT-PCR although the tissues had been stored frozen for up to 37 years. LAC virus was detected in the cerebral cortex but not in other CNS tissues. RT-PCR allowed detection of replicative forms of the virus, indicating that the virus was actively replicating in the specific CNS tissues. The small (S) RNA segments of the viruses from the CNS samples were demonstrated to be genetically similar by single-strand conformation polymorphism analyses. These S RNA segments were then sequenced; only two base changes were demonstrated between the 1960 and the 1978 samples, suggesting that LAC virus is genetically stable in areas of endemicity. The RT-PCR analyses of analyte directly from CNS tissues allows study of the virus without passage in cell culture.

The value of cerebrospinal fluid antiviral antibody in the diagnosis of neurologic disease produced by varicella zoster virus

We studied four patients with subacute to chronic varicella zoster virus (VZV) infection of the central nervous system (CNS). VZV infection was verified by detecting antibody to VZV in the cerebrospinal fluid (CSF). VZV caused myelitis in two patients and encephalitis in two patients. In one of the patients with VZV encephalitis, in addition to VZV IgM antibody, VZV DNA was found in the CSF. Among the four patients with VZV infection of the CNS, CSF antibody to VZV was the crucial diagnostic laboratory test which corroborated the clinical features, and indicated that VZV caused neurologic disease. In addition to looking for amplifiable VZV DNA in the CSF of patients with neurologic disease whose clinical and radiologic features suggest VZV infection, we also recommend a search for CSF antibody to VZV, particularly in patients with intervals of weeks to months between zoster and the onset of neurologic disease, or in those patients without rash in whom the tempo of illness is unknown.

Cognitive impairment after acute encephalitis: comparison of herpes simplex and other aetiologies

OBJECTIVE

To compare the cognitive defects after acute acyclovir treated herpes simplex encephalitis with those after other types of acute encephalitis.

METHODS

Seventy seven consecutive patients between 1985 and 1995 and 29 normal controls were studied. Of the 77 patients without concomitant neurological conditions, 17 had herpes simplex, one virus encephalitis (HSVE group), 27 had some other identified aetiology (non-HSVE group), and in 33 patients the cause was unknown. Acyclovir treatment was started less than four days after the first mental symptoms in 12 of 17 patients with HSVE. A thorough neuropsychological assessment was carried out about one month after the onset.

RESULTS

The HSVE group had deficits in verbal memory, verbal-semantic functions, and visuoperceptual functions more often than the non-HSVE group. The risk for cognitive defects was twofold to four-fold in the patients with HSVE compared with the non-HSVE patients. Two (12%) of the patients with HSVE and 12 (44%) of the non-HSVE patients were cognitively intact. Six patients with HSVE (46%) and 17 (89%) non-HSVE patients later returned to work. The lesions on CT or MRI were bilateral only in one patient with HSVE. The defects in the three patients with adenovirus infection were severe and resembled the amnesia after HSVE. Cognitive impairment, not previously reported, was found in encephalitis after rotavirus infection and epidemic nephropathy.

CONCLUSION

The recovery in the HSVE group was better than expected based on the medical literature. On the other hand there were surprisingly severe cognitive defects in encephalitis after other viruses. With early acyclovir treatment patients with the least severe HSVE were equivalent to those with non-HSV encephalitis with good outcome whereas those with the most severe non-HSV encephalitis were equivalent to those with HSVE with poor outcome.

Acyclovir treatment of relapsing-remitting multiple sclerosis. A randomized, placebo-controlled, double-blind study

Acyclovir treatment was used in a randomized, double-blind, placebo-controlled clinical trial with parallel groups to test the hypothesis that herpes virus infections are involved in the pathogenesis of multiple sclerosis (MS). Sixty patients with the relapsing-remitting form of MS were randomized to either oral treatment with 800 mg acyclovir or placebo tablets three times daily for 2 years. The clinical effect was investigated by an extensive test battery consisting of neurological examinations, neuro-ophthalmological and neuropsychological tests, and evoked potentials. Results were based on "intent-to-treat" data and the primary outcome measure was the exacerbation rate. In the acyclovir group (n = 30), 62 exacerbations were recorded during the treatment period, yielding an annual exacerbation rate of 1.03. The placebo group (n = 30) had 94 exacerbations and an annual exacerbation rate of 1.57. Thus, 34% fewer exacerbations were encountered during acyclovir treatment. This difference in exacerbation rate between the treatment groups was not significant (P = 0.083). However, this trend to a lower disease activity in acyclovir-treated patients was supported in subsequent data analysis. If the patients were grouped according to exacerbation frequencies, i.e. into low (0-2), medium (3-5) and high (6-8) rate groups, the difference between acyclovir and placebo treatment was significant (P = 0.017). Moreover, in a subgroup of the population with a duration of the disease of at least 2 years providing an exacerbation rate base-line before entry, individual differences in exacerbation rates were compared between the 2-year pre-study period and the study period in acyclovir-treated (n = 19) and placebo (n = 20) patients and acyclovir-treated patients showed a significant reduction of exacerbations (P = 0.024). Otherwise, neurological parameters were essentially unaffected by acyclovir treatment and there were no convincing signs of reduced neurological deterioration in the acyclovir group. This study indicates that acyclovir treatment might inhibit the triggering of MS exacerbations and thus suggests that acyclovir-susceptible viruses might be involved in the pathogenesis of MS. This possibility warrants further investigation.

Herpes encephalitis is a disease of middle aged and elderly people: polymerase chain reaction for detection of herpes simplex virus in the CSF of 516 patients with encephalitis. The Study Group

OBJECTIVE

To assess the diagnostic potential of the polymerase chain reaction (PCR) in herpes simplex virus (HSV) encephalitis.

METHODS

Samples of CSF from 516 patients with encephalitis were studied for HSV-DNA by PCR.

RESULTS

Samples taken one to 29 days from the onset of symptoms from 38 patients (7.4%) were positive, 32 (6.2%) for HSV-1 and six (1.2%) for HSV-2. At follow up, eight of 28 patients studied were still HSV-PCR positive. A diagnostic serum:CSF antibody ratio to HSV but not to other viruses was detected in 25 of the 38 HSV-PCR positive patients thus supporting the initial PCR findings. Patients positive by HSV-PCR were concentrated in the age group > or = 40 years, and especially in patients aged 60-64 years, of whom nine of 24 (37.5%) were positive. The HSV-PCR was negative in all other patients with encephalitis of known or unknown aetiology. This group included 34 patients with a diagnostic serum:CSF antibody ratio to other viruses. A dual infection, HSV and another microbe, was considered possible in seven patients.

CONCLUSIONS

The HSV-PCR is a rapid and useful diagnostic method during the early phase of encephalitis. It may be useful in monitoring the efficacy of treatment and allowing the recognition of new features in the appearance of herpes encephalitis. The HSV-PCR test and antibody determinations from serum and CSF are complementary methods, which should both be applied in pursuit of clinical laboratory diagnosis of these conditions.

Cerebrospinal fluid

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