Neuropathology of the spinal cord in the acquired immunodeficiency syndrome

Infection-Related Myelopathies

Recent years have seen growing attention to inflammatory and infectious disorders of the spinal cord, not only due to the discovery of autoantibody-mediated disorders of the spinal cord [e.g., aquaporin-4 immunoglobulin G (IgG) antibodies and myelin oligodendrocyte glycoprotein IgG antibodies], but also due to the emergence of clusters of infection-related myelopathy, now known as acute flaccid myelitis. We review the spectrum of infection-related myelopathies and outline a nosological classification system based on association with infection. We describe the epidemiology and definitions of myelopathies, with a discussion of clinical presentation and neuroimaging features, and then turn to specific discussion of myelopathies due to direct pathogen invasion and those considered to be post- or parainfectious. Expected final online publication date for the Annual Review of Pathology: Mechanisms of Disease, Volume 17 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Infections of the Spine and Spinal Cord

PURPOSE OF REVIEW

Infections of the spine and spinal cord are associated with a high risk of morbidity and mortality and, therefore, require prompt clinical recognition, efficient diagnostic evaluation, and interdisciplinary treatment. This article reviews the pathophysiology, epidemiology, clinical manifestations, diagnosis, and treatment of infections of the spine and spinal cord to help practicing clinicians recognize, evaluate, and manage patients with such infections.

RECENT FINDINGS

Aging of the population, increasing use of immunosuppressive medications, and other factors have contributed to increasing rates of spinal infections. Although the most common agents responsible for spinal infections remain bacteria and viruses, fungal infections occur in individuals who are immunocompromised, and parasitic infections are common in endemic regions, but patterns are in evolution with migration and climate change. Recent outbreaks of acute flaccid myelitis in children have been associated with enteroviruses A71 and D68.

SUMMARY

Infections of the spine and spinal cord can be challenging to diagnose, requiring a thorough history and neurologic examination, laboratory studies of serum and CSF, neuroimaging (particularly MRI), and, in some instances, biopsy, to establish a diagnosis and treatment regimen. Interdisciplinary management including collaboration with experts in internal medicine, infectious disease, and neurosurgery is important to improve clinical outcomes.

Infectious Myelopathies

PURPOSE OF REVIEW

This article reviews infectious etiologies of spinal cord dysfunction, emphasizing the importance of recognizing common clinicoradiographic syndromes and interpreting them in the context of exposure risk and individual host susceptibilities.

RECENT FINDINGS

This article discusses the shifting spectrum of neurologic infectious diseases, the growing population of patients who are immunocompromised, and the emergence of effective antiretroviral therapies. In addition, it discusses new molecular and serologic tests that have the potential to enhance our ability to rapidly and accurately diagnose infectious diseases of the spine.

SUMMARY

When evaluating patients with suspected infectious myelopathies, it is imperative to narrow the range of pathogens under consideration. The geography, seasonality, and clinicoradiographic presentation and immunocompetence status of the patient define the range of potential pathogens and should guide testing and initial management.

HIV and spinal cord disease

The epidemiology of spinal cord disease in human immunodeficiency virus (HIV) infection is largely unknown due to a paucity of data since combination antiretroviral therapy (cART). HIV mediates spinal cord injury indirectly, by immune modulation, degeneration, or associated infections and neoplasms. The pathologies vary and range from cytotoxic necrosis to demyelination and vasculitis. Control of HIV determines the differential for all neurologic presentations in infected individuals. Primary HIV-associated acute transverse myelitis, an acute inflammatory condition with pathologic similarities to HIV encephalitis, arises in early infection and at seroconversion. In contrast, HIV vacuolar myelopathy and opportunistic infections predominate in uncontrolled disease. There is systemic immune dysregulation as early as primary infection due to initial depletion of gut-associated lymphoid tissue CD4 cells and allowance of microbial translocation across the gut that never fully recovers throughout the course of HIV infection, regardless of how well controlled. The subsequent proinflammatory state may contribute to spinal cord diseases observed even after cART initiation. This chapter will highlight an array of spinal cord pathologies classified by stage of HIV infection and immune status.

HIV neuropathology

Primary human immunodeficiency virus (HIV) neuropathologies can affect all levels of the neuraxis and occur in all stages of natural history disease. Some, like HIV encephalitis, HIV myelitis, and diffuse infiltrative lymphocytosis of peripheral nerve, reflect productive infection of the nervous system; others, like vacuolar myelopathy, distal symmetric polyneuropathy, and central and peripheral nervous system demyelination, are not clearly related to regional viral replication, and reflect more complex cascades of dysregulated host immunity and metabolic dysfunction. In pediatric patients, the spectrum of neuropathology is altered by the impacts of HIV on a developing nervous system, with microcephaly, abundant brain mineralization, and corticospinal tract degeneration as examples of this unique interaction. With efficacious therapies, CD8 T-cell encephalitis is emerging as a significant entity; often this is clinically recognized as immune reconstitution inflammatory syndrome, but has also been described in the context of viral escape and treatment interruption. The relationship of HIV neuropathology to clinical symptoms is sometimes straightforward, and sometimes mysterious, as individuals can manifest significant deficits in the absence of discrete lesions. However, at all stages of the natural history disease, neuroinflammation is abundant, and critical to the generation of clinical abnormality. Neuropathologic and neurobiologic investigations will be central to understanding HIV nervous system disorders in the era of efficacious therapies.

Spinal cord toxoplasmosis in human immunodeficiency virus infection/acquired immunodeficiency syndrome

Neurological complications in patients with human immunodeficiency virus infection/acquired immunodeficiency syndrome (HIV/AIDS) are still common, even in the era of highly active antiretroviral therapy. Opportunistic infections, immune reconstitution, the virus itself, antiretroviral drugs and neurocognitive disorders have to be considered when establishing the differential diagnosis. Toxoplasmic encephalitis remains the major cause of space-occupying lesions in the brain of patients with HIV/AIDS; however, spinal cord involvement has been reported infrequently. Here, we review spinal cord toxoplasmosis in HIV infection and illustrate the condition with a recent case from our hospital. We suggest that most patients with HIV/AIDS and myelitis with enhanced spine lesions, multiple brain lesions and positive serology for Toxoplasma gondii should receive immediate empirical treatment for toxoplasmosis, and a biopsy should be performed in those cases without clinical improvement or with deterioration.

Neuroinflammation and virus replication in the spinal cord of simian immunodeficiency virus-infected macaques

Studies of neurologic diseases induced by simian immunodeficiency virus (SIV) in Asian macaques have contributed greatly to the current understanding of human immunodeficiency virus pathogenesis in the brain and peripheral nervous system. Detailed investigations into SIV-induced alterations in the spinal cord, a critical sensorimotor relay point between the brain and the peripheral nervous system, have yet to be reported. In this study, lumbar spinal cords from SIV-infected pigtailed macaques were examined to quantify SIV replication and associated neuroinflammation. In untreated SIV-infected animals, there was a strong correlation between amount of SIV RNA in the spinal cord and expression of the macrophage marker CD68 and the key proinflammatory mediators tumor necrosis factor and CCL2. We also found a significant correlation between SIV-induced alterations in the spinal cord and the degree of distal epidermal nerve fiber loss among untreated animals. Spinal cord changes (including elevated glial fibrillary acidic protein immunostaining and enhanced CCL2 gene expression) also were present in SIV-infected antiretroviral drug-treated animals despite SIV suppression. A fuller understanding of the complex virus and host factor dynamics in the spinal cord during human immunodeficiency virus infection will be critical in the development of new treatments for human immunodeficiency virus-associated sensory neuropathies and studies aimed at eradicating the virus from the central nervous system.

Spinal Cord Lesions in Congenital Toxoplasmosis Demonstrated with Neuroimaging, Including Their Successful Treatment in an Adult

Neuroimaging studies for persons in the National Collaborative Chicago-Based Congenital Toxoplasmosis Study (NCCCTS) with symptoms and signs referable to the spinal cord were reviewed. Three infants had symptomatic spinal cord lesions, another infant a Chiari malformation, and another infant a symptomatic peri-spinal cord lipoma. One patient had an unusual history of prolonged spinal cord symptoms presenting in middle age. Neuroimaging was used to establish her diagnosis and response to treatment. This 43 year-old woman with congenital toxoplasmosis developed progressive leg spasticity, weakness, numbness, difficulty walking, and decreased visual acuity and color vision without documented re-activation of her chorioretinal disease. At 52 years of age, spinal cord lesions in locations correlating with her symptoms and optic atrophy were diagnosed with 3 Tesla MRI scan. Treatment with pyrimethamine and sulfadiazine decreased her neurologic symptoms, improved her neurologic examination, and resolved her enhancing spinal cord lesions seen on MRI.

Diffusion tensor MR imaging (DTI) metrics in the cervical spinal cord in asymptomatic HIV-positive patients

INTRODUCTION

This study was conducted to compare diffusion tensor MR imaging (DTI) metrics of the cervical spinal cord in asymptomatic human immunodeficiency virus (HIV)-positive patients with those measured in healthy volunteers, and to assess whether DTI is a valuable diagnostic tool in the early detection of HIV-associated myelopathy (HIVM).

METHODS

MR imaging of the cervical spinal cord was performed in 20 asymptomatic HIV-positive patients and in 20 healthy volunteers on a 3-T MR scanner. Average fractional anisotropy (FA), mean diffusivity (MD), and major (E1) and minor (E2, E3) eigenvalues were calculated within regions of interest (ROIs) at the C2/3 level (central and bilateral anterior, lateral and posterior white matter).

RESULTS

Statistical analysis showed significant differences with regard to mean E3 values between patients and controls (p = 0.045; mixed-model analysis of variance (ANOVA) test). Mean FA was lower, and mean MD, mean E1, and mean E2 were higher in each measured ROI in patients compared to controls, but these differences were not statistically significant.

CONCLUSION

Asymptomatic HIV-positive patients demonstrate only subtle changes in DTI metrics measured in the cervical spinal cord compared to healthy volunteers that currently do not support using DTI as a diagnostic tool for the early detection of HIVM.

Nontumor lesions of spinal cord and spine

Nontumor lesions of the spinal cord and spine include developmental disorders, cystic tumor-like lesions, vascular disorders, infective diseases, demyelinating diseases, degenerative diseases, metabolic and toxic disorders, and spinal cord injury. In addition, diseases of the spine and extradural spaces secondarily cause spinal cord injury. Aside from tumors, these include developmental abnormalities, inflammatory diseases, nontumor space-occupying lesions, and tumor-like lesions such as lipomas, vascular malformations, and cysts. Awareness is required of hemostatic agents used during surgery and subsequently presenting as space-occupying lesions, which have to be differentiated from recurrent lesions. On the therapeutic front, stem cell transplantation into spinal cord for treatment of neurodegenerative disorders, spinal cord injury, and multiple sclerosis is a challenging prospect.

Diffusion-weighted imaging, diffusion-tensor imaging, and fiber tractography of the spinal cord

In the brain, diffusion-weighted imaging (DWI) is an established and reliable method for the characterization of neurologic lesions. Although the diagnostic value of DWI in the early detection of ischemia has not diminished with time, many new clinical applications of DWI have also emerged. Diffusion-tensor imaging and fiber tractography have more recently been developed and optimized, allowing quantification of the magnitude and direction of diffusion along three principal eigenvectors. Diffusion-tensor imaging and fiber tractography are proving to be useful in clinical neuroradiology practice, with application to several categories of disease, and to be a powerful research tool. This article describes some of the applications of DWI and diffusion-tensor imaging in the evaluation of the diseases of the spinal cord.

Unusual presentations of nervous system infection by Cryptococcus neoformans

Nervous system infections by Cryptococcus neoformans may occur not only in congenital or acquired immunodeficiency syndromes, but also in immunocompetent hosts. Neurological manifestations of C. neoformans infection include meningitis and, less commonly, parenchymal CNS granulomatous disease. This paper provides detailed clinical descriptions of highly unusual neurological manifestations of cryptococcal nervous system infections. Medical records and diagnostic data including magnetic resonance imaging, histopathology, serology, and CSF analysis were reviewed. A conus medullaris abscess was found in a patient infected with the human immunodeficiency virus (HIV). A patient with Hodgkin's disease was diagnosed with cryptococcal meningitis and dermatitis mimicking ophthalmic zoster. An immunocompetent patient presented with recurrent cerebral infarctions in the setting of cryptococcal meningitis. Cryptococcal infections of the nervous system can cause severe neurological disability when diagnosis is delayed. Sensitive and specific tests are readily available and should be considered when an unusual clinical presentation is encountered.

Spinal epidural cavernous hemangioma in an HIV-positive patient

BACKGROUND

Spinal epidural cavernous hemangioma is rare.

PURPOSE

Here, we report a case of spinal epidural cavernous hemangioma in an HIV-positive patient.

STUDY DESIGN

Single case report.

METHOD

A 40-year-old known HIV-positive woman presented with a 6-month history of slowly progressive bilateral leg weakness and pain. Neuroimaging showed an epidural mass lesion, which was isointense on T1-WI, hyperintense on T2-WI, and homogenously enhanced with gadolinium diethylenetriamine pentaacetate (Gd-DTPA), from T8 to T10.

RESULTS

The patient underwent T8-T10 laminectomy and removal of this lesion. Pathological diagnosis was cavernous hemangioma.

CONCLUSION

Although soft-tissue tumors such as Kaposi's sarcoma and lymphomas have been well documented in association with HIV infection, this is the first reported case of spinal epidural cavernous hemangioma. This may be an incidental finding or perhaps a causal relationship exists, suggesting that cavernous hemangioma could be a differential diagnosis of a spine lesion in HIV-positive patients.

Progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) was a rare disease until the advent of the HIV/AIDS pandemic. Recent interest in the disorder has been spurred by its appearance in patients treated with the monoclonal antibodies natalizumab and rituximab. Unless the accompanying underlying immune deficit can be reversed, PML typically progresses to death fairly rapidly. Treatment directed against the JC virus has been unhelpful, but an increased understanding of disease pathogenesis may result in effective therapeutic strategies.

Demyelinating and infectious diseases of the spinal cord

Spinal cord diseases generally have distinctive clinical findings that reflect dysfunction of particular sensory or motor tracts. The abnormalities on MR images reflect the pathologic changes that occur in the affected pathways. The complexity and the wide spectrum of diseases affecting the spinal cord require a profound knowledge of neuropathology and exactly tuned imaging strategies. This article describes and illustrates the clinical and imaging characteristics in various demyelinating and infectious conditions of the spinal cord.

Natalizumab treatment for multiple sclerosis: recommendations for patient selection and monitoring

Natalizumab is a new treatment option for patients with active relapsing-remitting multiple sclerosis. In phase III studies, natalizumab was highly effective and well tolerated; however, three cases of progressive multifocal leucoencephalopathy (PML) were identified (estimated incidence of one per 1000; 95% CI 0.2-2.8; mean treatment period 17.9 months). In this Review we summarise the current information on PML, the three confirmed cases of PML, and the results of an extensive safety assessment of all patients treated with natalizumab. On the basis of these reviews, we make recommendations for appropriate selection of candidates for natalizumab and pretreatment assessments. In addition, a three-step diagnostic and management algorithm was developed to monitor natalizumab-treated patients with multiple sclerosis for PML and other opportunistic infections. The algorithm includes strategies for clinical, MRI, and laboratory assessments. Maintaining clinical vigilance allows for early suspension of natalizumab in potential cases of PML, thereby increasing the opportunity for immune reconstitution, which may improve prognosis if PML is confirmed.

Natalizumab and progressive multifocal leucoencephalopathy

Current data suggest that as many as 1 in 1000 treated individuals may develop progressive multifocal leucoencephalopathy (PML) in concert with the use of natalizumab. Natalizumab was withdrawn in early 2005. The present paper provides a comprehensive description of PML and reviews the role of natalizumab in the pathogenesis of PML. It is likely that use of drugs which cause specific perturbations of the immune system will be accompanied by similar rare infections. Thus researchers should be on the alert when using such agents in clinical trials.

Viral diseases of the central nervous system

Viral diseases of the central nervous system encompass a wide range of different processes, mainly inflammation affecting the brain (encephalitis), the meninges (meningitis), or a combined meningoencephalitis. The spinal cord can be affected as well (myelitis). Another group of viral-related disorders, sometimes without a clear pathophysiological mechanism disclosed, include post-viral illnesses. All of these groups of diseases are discussed in this article, with an emphasis on their imaging presentation, using magnetic resonance imaging.

Discriminatory features of acute transverse myelitis: a retrospective analysis of 45 patients

Acute transverse myelitis (ATM) is a pathogenetically heterogeneous inflammatory disorder of the spinal cord. Therefore, the identification of clinical and paraclinical features providing clues of the underlying etiologies is needed. The clinical presentation, blood and cerebrospinal fluid (CSF) findings as well as magnetic resonance imaging (MRI) and neurophysiological features were retrospectively analyzed in 45 unselected consecutive patients with ATM. Parainfectious ATM was diagnosed in 38% of patients. The underlying infectious agent, however, was identified only in a minority of patients. In 36% of patients, the etiology remained uncertain ("idiopathic" ATM) and in 22% ATM was the first manifestation of possible multiple sclerosis (ATM-MS) according to recently published diagnostic criteria. Spinal cord MRI showed signal alterations in 96% of the patients. In ATM-MS, monosegmental involvement of the spinal cord was most frequent while spinal cord involvement of two or more segments was more common in ATM of other etiologies. Of particular note, neurophysiological examinations showed evidence of peripheral nervous system (PNS) involvement in 27% of patients with ATM but not in patients with ATM-MS. Therefore, neurophysiological evidence of PNS involvement may provide additional discriminatory features between ATM-MS and ATM of other etiologies.

Intramedullary abscess resulting from disseminated cryptococcosis despite immune restoration in a patient with AIDS

We report on a case of cryptococcal intramedullary abscess, which occurred three years after a disseminated cryptococcosis and two years after a lymph node cryptococcal recurrence in a HIV-infected patient who exhibited a long-standing immune restoration. At the time of diagnosis, CD4(+) lymphocyte-count was 640x10(6)/l and HIV viral load was undetectable. Spinal involvement is rare during cryptococcosis of the central nervous system. As far as we are aware, there is only one case of proven intramedullary cryptococcal abscess reported in the literature and this case is then the second one. The significant and sustained increase in CD4 count following effective antiretroviral therapy was probably associated with only a partial immune restitution that did not allow to avoid the occurrence of the cryptococcal medullar abscess. Finally, this case raises the question of when to stop secondary prophylaxis of cryptococcal disease after increase in CD4 cell count under antiretroviral therapy.

[HIV-associated myelopathy: an uncommon indicator of AIDS]

INTRODUCTION

Spinal cord lesions are an uncommon mode of discovering acquired immunodeficiency syndrome because they usually appear at a later stage.

EXEGESIS

We report a 58-year-old patient who had a spastic paraparesia and sphincter dysfunction. The spinal cord magnetic resonance imaging showed spontaneous hypersignals on T2-weighted images at the cervical and thoracic levels, enhanced with gadolinium, and without swelling. No cause was found. The HIV serology was positive and allowed us to consider an HIV-associated myelopathy. The antiretroviral therapy led to functional recovery.

CONCLUSION

An HIV serology is suggested whenever an unexplained intramedullary lesion is discovered. Indeed, the diagnosis of HIV-associated myelopathy implies a specific therapeutic approach.

[Progressive multifocal leukoencephalopathy]

PATHOGENESIS

Progressive multifocal leukoencephalopathy is a demyelinating disease of the central nervous system caused by infection and reactivation of JC-virus. About 5% of all HIV-infected patients develop this fatal disease. Although pathogenesis is not completely understood, progressive multifocal leukoencephalopathy is thought to be a persistent infection. The kidneys, bone marrow, peripheral blood lymphocytes and the brain itself are candidates for latency sites of JC-virus. Loss of T-helper-cells in the course of HIV-infection or other immunosuppressive states result in reactivation of JC-virus.

DIAGNOSIS

Progressive multifocal leukoencephalopathy can be diagnosed by focal neurological symptoms, radiographic signs in magnetic resonance imaging and detection of JC-virus in brain tissue or cerebrospinal fluid.

TREATMENT

A specific therapy is not yet available or established. Highly active antiretroviral therapy (HAART) and cidofovir are promising and may prove useful in the near future.

Spinal cord pathology and viral burden in homosexuals and drug users with AIDS

Unless treated with effective antiretroviral therapy many AIDS patients develop a characteristic vacuolar myelopathy of the spinal cord associated with moderate clinical disability. Opinion is divided as to whether vacuolar myelopathy is causally linked to HIV myelitis. To investigate this further, spinal cord pathology was assessed in 41 drug users, 33 homosexual men and 16 other patients, all with AIDS. Previous work has shown that HIV encephalitis is more common in Edinburgh drug users than in homosexual men. In the present study HIV myelitis (10% overall) was more common in drug users (17%) than in homosexual men (3%) (P = 0.05), whereas the incidence of opportunistic infections (7% v. 9%) and lymphomas (2% v. 6%) was comparable in the two groups, but with a slight trend in the reverse direction, reflecting similar findings in the brain. However, moderate or severe vacuolar myelopathy was equally represented in both groups (20% of drug users and 21% of homosexual men). The HIV proviral load, assessed by polymerase chain reaction in frozen samples of thoracic spinal cord in 37 cases, correlated closely with the presence of giant cells and/or with immunocytochemical evidence of productive HIV infection. In 13 cases, the proviral load was measured in cervical, thoracic and lumbar samples and proved to be uniformly high or low in individual cases. This study provides no evidence for direct involvement of HIV, cytomegalovirus, papovavirus or human foamy virus in the pathogenesis of vacuolar myelopathy.

Cellular localization of tumor necrosis factor mRNA in neurological tissue from HIV-infected patients by combined reverse transcriptase/polymerase chain reaction in situ hybridization and immunohistochemistry

HIV-induced neurological disease is postulated to be caused by indirect mechanisms. Tumor necrosis factor (TNF)alpha is increased in the brains in human immunodeficiency virus (HIV)-associated dementia and in the spinal cord in vacuolar myelopathy and may play a pathogenetic role in these diseases. Microglia, astrocytes and infiltrating macrophages can be induced to produce TNF alpha and each has been identified as a source of TNF alpha in neurological disease. Reverse transcriptase synthesis of cDNA and polymerase chain reaction amplification of the cDNA was combined with immunocytochemistry to identify the cellular source of TNF alpha in HIV-induced neurological disease. Cells positive for TNF alpha mRNA were more abundant in white matter than gray matter of the brain from demented individuals. TNF alpha mRNA-positive cells in brains and spinal cords were almost exclusively macrophage-lineage cells. Only rare TNF alpha mRNA-positive cells were astrocytes. We conclude that macrophage-lineage cells are the primary source of elevated central nervous system TNF alpha mRNA in providing further evidence that macrophage activation is an important element in the pathogenesis of HIV-associated neurological disease.

Incarceration and the acquired immunodeficiency syndrome: autopsy results in Texas prison inmates

The Texas Department of Criminal Justice (TDCJ) houses many subjects with acquired immunodeficiency syndrome (AIDS) who receive medical care in a comprehensive AIDS treatment center. In this case-control autopsy survey, we compared pathological outcomes of TDCJ inmates treated at the center (n = 155) with nonincarcerated patients who died during the same period (n = 155). Using multiple regression analysis and a proportional hazards model, survival time in the prisoners was equivalent to that in the controls. With few exceptions, the prevalences of opportunistic viral, fungal, protozoal, and bacterial infections contributing to mortality were equivalent between groups. Mycobacterium tuberculosis was isolated more frequently in the inmates, and M avium intracellulare was isolated less frequently (P < .0001). The inmates had a higher prevalence of bacterial infection of the central nervous system (CNS) (9.1% v 1.4%; P < .006); half of all CNS bacterial infections were caused by M tuberculosis. Inmates had significantly lower prevalences of vacuolar myelopathy (P < .006) and severe wasting disease (P < .0009). We conclude that survival of prison inmates with AIDS treated in a comprehensive AIDS treatment center was equivalent to that of nonincarcerated subjects with AIDS. Prevalences of certain complications of AIDS differed in the inmates, showing that the prison environment influenced some of the underlying causes of AIDS morbidity and mortality.

Vacuolar myelopathy in transgenic mice expressing human immunodeficiency virus type 1 proteins under the regulation of the myelin basic protein gene promoter

Vacuolar myelopathy is a common neurological complication in AIDS patients. The pathogenesis of this spinal cord white matter disease remains unclear and it is still debated whether infection of spinal cord with the human immunodeficiency virus type 1 (HIV-1) is causing the disease. We have generated transgenic mice expressing the entire HIV-1 genome under the regulation of an oligodendrocyte-specific promoter. These mice develop spinal cord vacuolar lesions similar to those found in AIDS patients. This animal model provides in vivo evidence linking the expression of HIV-1 proteins in oligodendrocytes to the spinal cord damage found in vacuolar myelopathy.

AIDS-associated vacuolar myelopathy and tumor necrosis factor-alpha (TNF alpha)

The spinal cords from 15 patients with AIDS-associated vacuolar myelopathy (VM), 4 AIDS patients without VM, and 5 HIV-seronegative controls, were studied with immunocytochemistry for TNF alpha. CSF and blood from HIV-seropositive patients with VM (n = 16), non-vacuolar myelopathies (n = 8), CNS infection but no clinical myelopathy (n = 31), no clinical or radiological evidence of CNS disease (n = 9), and from 7 HIV-seronegative controls with motor neurone disease were assayed for TNF alpha using an ELISA technique. TNF alpha was present on immunostaining in all the 15 cords with VM studied. The stained cells were macrophages, microglia and endothelial cells. The amount of immunostaining was higher in cords with VM compared with cords from HIV-seropositive patients without VM (p = 0.001). The distribution of staining corresponded to the areas of pathology but did not correlate with the severity of the VM. Immunostaining was also higher in the HIV-seropositive group compared to the HIV-seronegative controls (p = 0.001). There was no significant difference in the levels of TNF alpha in the CSF of patients with VM compared to any of the other groups studied. Blood levels of TNF alpha were lower in the HIV-seropositive controls without CNS disease and in the HIV-seronegative MND controls, than in patients with VM, non-vacuolar myelopathies, and CNS disease. CSF TNF alpha levels did not appear to be a reliable indicator of intramedullary levels. The findings support the hypothesis that TNF alpha may be relevant in the pathogenesis of vacuolar change in VM.

Histologic classification and immunophenotype of lymphosarcomas in cats with naturally and experimentally acquired feline immunodeficiency virus infections

Lymphosarcoma (malignant lymphoma) is the commonest hematopoietic tumor in the cat. Many cases are associated with feline leukemia virus (FeLV) infection, but epidemiologic and experimental data suggest that feline immunodeficiency virus (FIV) may also have a role in lymphomagenesis. In this paper, we describe the clinical presentation, histologic classification, and immunophenotype of lymphosarcoma in eight domestic cats with natural or experimental FIV infections. The tumors were often of unusual distribution, with the majority of cases conforming to the least common anatomic classification of "miscellaneous." Histopathologic and immunophenotypic analysis using a panel of anti-cat and cross-reactive anti-human monoclonal and polyclonal antibodies identified seven of these tumors as high-grade B cell lymphomas of the centroblastic or immunoblastic subtypes. The remaining case was a T-cell tumor associated with a concurrent FeLV infection. Our findings, together with the results of an analysis of FIV proviral DNA in these tumors, indicate that the B-cell lymphosarcomas were comparable to those observed in human and simian immunodeficiency virus infections and that the role of FIV in lymphomagenesis is indirect and related to the potential for malignant transformation during polyclonal B cell activation.

Isolated toxoplasmosis of the thoracic spinal cord in a patient with acquired immunodeficiency syndrome. Case report

Toxoplasmosis and lymphoma are the two most common causes of intraparenchymal cerebral mass lesions in patients with acquired immunodeficiency syndrome (AIDS). The clinical and radiographic features of the intracranial lesions have been well described. Because of the high frequency of toxoplasmosis in the AIDS population, common therapy for patients presenting with intracranial mass lesions consists of an empirical trial of anti-Toxoplasma chemotherapy, with biopsy reserved for cases demonstrating features considered to be more consistent with lymphoma, or for lesions that do not improve despite adequate anti-Toxoplasma treatment. A similar treatment algorithm does not exist for intramedullary lesions of the spinal cord. The authors describe a patient who presented with paraparesis resulting from an isolated thoracic intramedullary lesion. An open biopsy of the lesion revealed characteristic structures containing Toxoplasma tachyzoites. The clinical and radiographic presentation of the lesion is discussed, the available literature is reviewed, and a treatment strategy for spinal cord lesions in AIDS patients is proposed.

Spinal tract pathology in AIDS: postmortem MRI correlation with neuropathology

Vacuolar myelopathy (VM) and tract pallor are poorly understood spinal tract abnormalities in patients with the acquired immunodeficiency syndrome (AIDS). We studied the ability of magnetic resonance imaging (MRI) to detect these changes in spinal cord specimens postmortem and whether criteria could be formulated which would allow these conditions to be differentiated from other lesions of the spinal cord in AIDS, such as lymphoma, cytomegalovirus (CMV) and human immunodeficiency virus (HIV) myelitis. We imaged 38 postmortem specimens of spinal cord. The MRI studies were interpreted blind. The specimens included cases of VM myelin pallor, CMV myeloradiculitis, HIV myelitis, lymphoma as well as normal cords, both HIV+ve and HIV-ve. MRI showed abnormal signal, suggestive of tract pathology, in 10 of the 14 cases with histopathological evidence of tract changes. The findings in VM and tract pallor on proton-density and T2-weighted MRI were increased signal from the affected white-matter tracts, present on multiple contiguous slices and symmetrical in most cases. The pattern was sufficiently distinct to differentiate spinal tract pathology from other spinal cord lesions in AIDS.

Histopathologic features in the central nervous system of 400 acquired immunodeficiency syndrome cases: implications of rates of occurrence

Histopathologic lesions in the central nervous system (CNS) of 400 autopsy cases of the acquired immunodeficiency syndrome (AIDS) collected from 1982 to 1990 were studied. Lesions most closely associated with human immunodeficiency virus (HIV) infection in the CNS (perivascular macrophages, nodular encephalomyelitis, diffuse leukoencephalopathy, necrotizing encephalitis, and long-tract degeneration) were found in 20% of the cases. The group of vascular and inflammatory lesions and of opportunistic infections was seen in 25% of cases. These two lesion groups were found together in 32% of cases, and none of these lesions was present in 23% of cases (most of the latter having no significant CNS lesions). Length of survival increased in the last group of 100 cases compared with the first 300 cases. The homosexual and bisexual risk groups showed continuously increasing lengths of survival for each category of HIV-associated CNS lesions throughout the study, while the lengths of survival in the other risk groups varied. Patients in the last group of 100 autopsy cases with any HIV-associated lesion survived longer than patients without these lesions. The AIDS patients with no CNS lesions had the shortest mean length of survival. The results suggest that although survival is prolonged as specific therapy is given, there is an increase in CNS lesions in AIDS patients with longer survival. This may indicate that CNS lesions in AIDS are generally dependent on systemic disease progression over many months as immune function decreases.