Gracile tract degeneration in patients with sensory neuropathy and AIDS

Higher Levels of Cerebrospinal Fluid and Plasma Neurofilament Light in Human Immunodeficiency Virus-Associated Distal Sensory Polyneuropathy

BACKGROUND

Neurofilament light (NFL) chain concentrations, reflecting axonal damage, are seen in several polyneuropathies but have not been studied in human immunodeficiency virus (HIV) distal sensory polyneuropathy (DSP). We evaluated NFL in cerebrospinal fluid (CSF) and plasma in relation to DSP in people with HIV (PWH) from 2 independent cohorts and in people without HIV (PWoH).

METHODS

Cohort 1 consisted of PWH from the CHARTER Study. Cohort 2 consisted of PWH and PWoH from the HIV Neurobehavioral Research Center (HNRC). We evaluated DSP signs and symptoms in both cohorts. Immunoassays measured NFL in CSF for all and for plasma as well in Cohort 2.

RESULTS

Cohort 1 consisted of 111 PWH, mean ± SD age 56.8 ± 8.32 years, 15.3% female, 38.7% Black, 49.6% White, current CD4+ T-cells (median, interquartile range [IQR]) 532/µL (295, 785), 83.5% with plasma HIV RNA ≤50 copies/mL. Cohort 2 consisted of 233 PWH of similar demographics to PWH in Cohort 1 but also 51 PWoH, together age 58.4 ± 6.68 years, 41.2% female, 18.0% Black, Hispanic, non-Hispanic White 52.0%, 6.00% White. In both cohorts of PWH, CSF and plasma NFL were significantly higher in both PWH with DSP signs. Findings were similar, albeit not significant, for PWoH. The observed relationships were not explained by confounds.

CONCLUSIONS

Both plasma and CSF NFL were elevated in PWH and PWoH with DSP. The convergence of our findings with others demonstrates that NFL is a reliable biomarker reflecting peripheral nerve injury. Biomarkers such as NFL might provide, validate, and optimize clinical trials of neuroregenerative strategies in HIV DSP.

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.

Sensory Neuronopathies

PURPOSE OF REVIEW

The sensory neuronopathies are sensory-predominant polyneuropathies that result from damage to the dorsal root and trigeminal sensory ganglia. This review explores the various causes of acquired sensory neuronopathies, the approach to diagnosis, and treatment.

RECENT FINDINGS

Diagnostic criteria have recently been published and validated to allow differentiation of sensory neuronopathies from other polyneuropathies. On the basis of serial electrodiagnostic studies, the treatment window for the acquired sensory neuronopathies has been identified as approximately 8 months. If treatment is initiated within 2 months of symptom onset, there is a better opportunity for improvement of the patient's condition. Even though sensory neuronopathies are rare, significant progress has been made regarding characterization of their clinical, electrophysiologic, and imaging features. This does not hold true, however, for treatment. There have been no randomized controlled clinical trials to guide management of these diseases, and a standard treatment approach remains undetermined.

Animal models of HIV peripheral neuropathy

The use of animal models in the study of HIV and AIDS has advanced our understanding of the underlying pathophysiologic mechanisms of infection. Of the multitude of HIV disease manifestations, peripheral neuropathy remains one of the most common long-term side effects. Several of the most important causes of peripheral neuropathy in AIDS patients include direct association with HIV infection with or without antiretroviral medication and infection with opportunistic agents. Because the pathogeneses of these diseases are difficult to study in human patients, animal models have allowed for significant advancement in the understanding of the role of viral infection and the immune system in disease genesis. This review focuses on rodent, rabbit, feline and rhesus models used to study HIV-associated peripheral neuropathies, focusing specifically on sensory neuropathy and antiretroviral-associated neuropathies.

Pathogenesis of HIV-associated sensory neuropathy: evidence from in vivo and in vitro experimental models

HIV-associated sensory neuropathy (HIV-SN) is a frequent neurological complication of HIV infection and its treatment with some antiretroviral drugs. We review the pathogenesis of the viral- and drug-induced causes of the neuropathy, and its primary symptom, pain, based on evidence from in vivo and in vitro models of HIV-SN. Viral coat proteins mediate nerve fibre damage and hypernociception through direct and indirect mechanisms. Direct interactions between viral proteins and nerve fibres dominate axonal pathology, while somal pathology is dominated by indirect mechanisms that occur secondary to virus-mediated activation of glia and macrophage infiltration into the dorsal root ganglia. The treatment-induced neuropathy and resulting hypernociception arise primarily from drug-induced mitochondrial dysfunction, but the sequence of events initiated by the mitochondrial dysfunction that leads to the nerve fibre damage and dysfunction are still unclear. Overall, the models that have been developed to study the pathogenesis of HIV-SN, and hypernociception associated with the neuropathy, are reasonable models and have provided useful insights into the pathogenesis of HIV-SN. As new models are developed they may ultimately lead to identification of therapeutic targets for the prevention or treatment of this common neurological complication of HIV infection.

Neuromuscular complications in HIV: effects of aging

There has been speculation that chronic HIV infection is a condition of accelerated aging that may lead to early onset of disease in multiple organ systems. The neuromuscular disorders of HIV, in particular distal symmetric polyneuropathy and myopathies, are also seen in the general population among older patients. As the HIV-infected population ages, there may be deleterious synergistic effects of age and chronic HIV infection on the brain, peripheral nerve, and muscle. In this review, we explore commonalities between the clinical features and putative mechanisms of neuromuscular disorders and HIV.

HIV-1 viral protein R causes peripheral nervous system injury associated with in vivo neuropathic pain

Painful peripheral neuropathy has become the principal neurological disorder in HIV/AIDS patients. Herein, we investigated the effects of a cytotoxic HIV-1 accessory protein, viral protein R (Vpr), on the peripheral nervous system (PNS). Host and viral gene expression was investigated in peripheral nerves from HIV-infected individuals and in HIV-infected human dorsal root ganglion (DRG) cultures by RT-PCR and immunocytochemistry. Cytosolic calcium ([Ca(2+)]) fluxes and neuronal membrane responses were analyzed in cultured DRGs. Neurobehavioral responses and cytokine levels were assessed in a transgenic mouse model in which the vpr transgene was expressed in an immunodeficient background (vpr/RAG1(-/-)). Vpr transcripts and proteins were detected in peripheral nerves and DRGs from HIV-infected patients. Exposure of rat or human cultured DRG neurons to Vpr rapidly increased [Ca(2+)] and action potential frequency while increasing input resistance. HIV infection of human DRG cultures caused neurite retraction (P<0.05), accompanied by induction of interferon-α (IFN-α) transcripts (P<0.05). vpr/RAG1(-/-) mice expressed Vpr together with increased IFN-α (P<0.05) in the PNS and also exhibited mechanical allodynia, unlike their vpr/RAG1(-/-) littermates (P<0.05). Herein, Vpr caused DRG neuronal damage, likely through cytosolic calcium activation and cytokine perturbation, highlighting Vpr's contribution to HIV-associated peripheral neuropathy and ensuing neuropathic pain.

Differential effects of HIV infected macrophages on dorsal root ganglia neurons and axons

Human immunodeficiency virus-associated distal-symmetric neuropathy (HIV-DSP) is the most common neurological complication of HIV infection. The pathophysiology of HIV-DSP is poorly understood and no treatment is available for this entity. The dorsal root ganglia (DRG) are the principal sites of neuronal damage and are associated with reactive mononuclear phagocytes as well as HIV-infected macrophages. To determine the role of HIV-infected macrophages in the pathogenesis of HIV-DSP, we developed a technique for culturing human DRG's. When the dissociated DRG neurons were exposed to supernatants from macrophages infected with CXCR4 or CCR5 tropic HIV-1 strains axonal retraction was observed without neuronal cell death but there was mitochondrial dysfunction in the neuronal cell body. Even though CXCR4 and CCR5 were expressed on the DRG neurons, the effects were independent of these receptors. Antioxidants rescued the neuronal cell body but not the axon from the toxic effects of the culture supernatants. Further, peripheral nerves of HIV-infected patients obtained at autopsy did not show evidence of increased oxidative stress. These observations suggest a differential effect on the axon and cell body. Different mechanisms of injury may be operative in these two structures.

Regulation of neural cell survival by HIV-1 infection

Infection by the lentivirus, human immunodeficiency virus type 1 (HIV-1), results in a variety of syndromes involving both the central (CNS) and the peripheral (PNS) nervous systems. Productive HIV-1 infection of the CNS is chiefly detectable in perivascular macrophages and microglia. HIV-1 encoded transcripts and proteins have also been detected in the PNS; however, productive viral replication appears to be sparse and restricted to the macrophage cell population. Despite the absence of productive infection of neurons, HIV-1 infection has been associated with neuronal loss in distinct regions of the brain. Neuronal cell loss may occur through both necrosis and apoptosis, although neuronal apoptosis appears to be a feature of AIDS, as only rare apoptotic neurons have been demonstrated in a few pre-AIDS cases. Although there is no clear consensus as to the underlying mechanism of HIV-induced neuropathogenesis, two complementary concepts predominate. Firstly, HIV-1 encoded proteins injure neurons directly without requiring the intermediary functions of nonneuronal cells. Alternatively, neuronal apoptosis may result indirectly from the secretion of neurotoxic host molecules by resident brain macrophages or microglia in response to HIV-1 infection, stimulation by viral proteins or immune activation. Herein, we review the neurological disorders and their underlying mechanisms associated with HIV infection, focusing on HIV-associated dementia (HAD) and HIV sensory neuropathy (HIV-SN). The evidence that neuronal loss in HIV-1-infected individuals may be due to neuronal apoptosis is then discussed. This review also summarizes the current data supporting both the direct and indirect mechanisms by which neuronal death may occur during infection with HIV-1 or the closely related lentiviruses SIV and FIV. Lastly, strategies are examined for treating or preventing HAD by targeting specific neurotoxic mechanisms.

Neurological complications of HIV infection

Cognitive disorders, vacuolar myelopathy, and sensory neuropathies associated with HIV are the most common disorders in patients with HIV AIDS, and are the focus of this review. These disorders are treatable and of those associated with HIV AIDS the pathogenic mechanisms are the most understood. Although triggered by productive HIV macrophage infections, aberrant immune activation plays a major role in inducing the CNS disorders. Novel therapies aimed at these inflammatory mechanisms can be effective. The sensory neuropathies associated with HIV infection are a major cause of morbidity; incidence may be increased by the toxic effects of specific antiretroviral drugs within the peripheral nervous system.

Sensory neuron diseases

Sensory neuron diseases (SND) are a distinct subgroup of peripheral-nervous-system diseases, first acknowledged in 1948. Acquired SND have a subacute or chronic course and are associated with systemic immune-mediated diseases, vitamin intoxication or deficiency, neurotoxic drugs, and life-threatening diseases such as cancer. SND are commonly idiopathic but can be genetic diseases; the latter tend to involve subtypes of sensory neurons and are associated with certain clinical pictures. The loss of sensory neurons in dorsal root ganglia causes the degeneration of short and long peripheral axons and central sensory projections in the posterior columns. This pathological process leads to a pattern of sensory nerve degeneration that is not length dependent and explains distinct clinical and neurophysiological abnormalities. Here we propose a comprehensive approach to the diagnosis of acquired and hereditary SND and discuss clinical, genetic, neurophysiological, neuroradiological, and neuropathological assessments.

Cutaneous silent period in human immunodeficiency virus-related peripheral neuropathy

The aim of this work was first to determine whether the cutaneous silent period (CSP), a marker of small-nerve-fibre function, was altered in human immunodeficiency virus (HIV)-positive subjects with predominantly sensory symmetrical polyneuropathy and, second, to assess whether such alterations were predictive of an impairment in the largest calibre sensory and motor nerve fibres of the upper limb (UL) peripheral nerves. CSP was assessed in three groups of subjects: healthy control subjects, HIV-positive subjects with peripheral neuropathy (PN) of the lower limbs, and HIV-positive patients with clinical and neurophysiological involvement of the four limbs. CSP study showed a significant increase of the latency compared to the controls both in HIV-positive cases with no impairment in the UL (p=0.006) and in patients with four-limb neuropathy (p=0.002). CSP study in HIV-positive patients with mild lower limb distal sensory polyneuropathy can detect an early involvement of the UL peripheral nerves. CSP latency increase could therefore be addressed as the first sign of PN spreading to the UL.

Symptomatic distal sensory polyneuropathy in HIV after age 50

OBJECTIVE

To determine if aging changes the frequency, severity, or manifestations of symptomatic distal sensory polyneuropathy (SxDSPN) in patients with HIV-1.

METHODS

Prospective observations of 70 older (age < or = 50) and 56 younger (age 20 to 40) patients with HIV, and a control group of 48 older non-HIV patients, were conducted utilizing neurologic examination, neuropsychological testing, lumbar puncture, laboratory, and medical history.

RESULTS

The frequency of SxDSPN among older HIV patients was 50.4%, compared to 19.6% among younger HIV patients (p < 0.001). SxDSPN among control patients occurred in 4.2%, similar to the general population. Older compared to younger HIV patients demonstrated more severe symptoms (p = 0.02) and greater deficits for vibration (p < 0.01). Increasing numbers of neuropathic comorbidities among older compared to younger HIV patients were associated with increasing severity of deficits to pinprick (p = 0.003). Dementia and SxDSPN coexisted in 36% of the older HIV patients and in none of the younger HIV patients (p = 0.021). Older HIV patients with nadir CD4 < or =200 cells/mL were 4.23 times as likely to have SxDSPN than older patients with nadir CD4 >200 cells/mL (p = 0.007). Vibratory deficits excessive to pinprick deficits predicted SxDSPN among older (OR 2.83) but not younger seropositive patients (p = 0.036).

CONCLUSIONS

Age > or = 50 increases the frequency of SxDSPN, and is associated with both vibratory loss as the predominant sensory deficit and increased severity of pinprick loss among symptomatic patients with neuropathic comorbidities. SxDSPN is associated with both dementia and low nadir CD4 in HIV-positive patients aged 50 and greater.

The peripheral nerve complications of human immunodeficiency virus (HIV) infection

Peripheral nerve complications occurring in patients with human immunodeficiency virus (HIV) infection are frequent and challenging. This review discusses these various complications according to the degree of advancement of HIV disease. Particular emphasis is placed upon emerging causes of neuropathy found in the context of HIV disease, such as infection with hepatitis C and human T-lymphotropic virus type I, as well as neuropathies related to antiretroviral medications.

Neuroimmune and neurovirological aspects of human immunodeficiency virus infection

Like most lentiviruses, HIV-1 causes both immune suppression and neurological disease. Neurological disease may occur at any stage of HIV infection but is most apparent with severe immune suppression. Cognitive impairment, reflected strikingly by HIV-associated dementia, has attracted intense interest since the outset of the HIV epidemic, and understanding of its pathogenesis has been spurred on by the emergence of several hypotheses outlining potential pathogenic mechanisms. The release of inflammatory molecules by HIV-infected microglia and macrophages and the concurrent neuronal damage play central roles in the conceptualization of HIV neuropathogenesis. Many inflammatory molecules appear to contribute to the pathogenic cascade and their individual roles remain undefined. At the same time, the abundance of virus in the brain and the type or strain of virus found in the brain may also be important codeterminants of neurological disease, as shown for other neurotropic viruses. Coreceptor use by HIV found in the brain appears to closely mirror what has been reported in systemic macrophages. The impact of HAART on viral genotype and phenotype found in the brain, and its relationship to clinical disease, remain uncertain. Several interesting animal models have been developed, using other lentiviruses, transgenic animals, and HIV-infected SCID mice, that may prove useful in future pathogenesis and therapeutic studies. Despite the progress in the understanding of HIV neuropathogenesis, many questions remain unanswered.

HIV-associated neuropathies: role of HIV-1, CMV, and other viruses

The role of the human immunodeficiency virus (HIV) and other viruses in the development of neuropathies associated with HIV infection is controversial. Distal symmetric polyneuropathy (DSP), the most common subtype of HIV-associated neuropathy, is characterized by an abundance of reactive macrophages within the peripheral nerve, but HIV replication is limited to a small percentage of the macrophages. Thus, the pathological destruction may be mediated by pro-inflammatory signals amplified by activated glial elements within the nerve, similar to the proposed mechanism of damage caused by HIV within the central nervous system. In contrast, in mononeuropathy multiplex (MM) and progressive polyneuropathy (PP), cytomegalovirus (CMV) replication in the peripheral nerve is consistently demonstrable, and this replication likely results in direct damage to the infected cells (neurons and glia). The rarest form of HIV-associated neuropathy, the diffuse infiltrative lymphocytosis syndrome (DILS), is characterized by an intense CD8+ T lymphocyte infiltration into the nerve and abundant HIV infection of macrophages. Finally, while other viruses (varicella zoster, herpes simplex) are associated with myelitis in HIV-infected individuals, there is little support for a role for these viruses in HIV-associated neuropathy.

HIV neuropathy: insights in the pathology of HIV peripheral nerve disease

HIV-associated neuropathies (HIV-N) have become the most frequent neurological disorder associated with HIV infection. The most common forms of HIV-N are the distal sensory polyneuropathy (DSP) and antiretroviral toxic neuropathies (ATN), disorders characterized mostly by sensory symptoms that include spontaneous or evoked pain that follow a subacute or chronic course. The main pathological features that characterize DSP and ATN include "dying back" axonal degeneration of long axons in distal regions, loss of unmyelinated fibers, and variable degree of macrophage infiltration in peripheral nerves and dorsal root ganglia. Marked activation of macrophages as well as the effect of pro-inflammatory cytokines appear to be the main immunopathogenic factors in DSP. Interference with DNA synthesis and mitochondrial abnormalities produced by nucleoside antiretrovirals have been hypothesized as pathogenic factors involved in ATN. The use of skin biopsy has become a useful tool in the evaluation of HIV-N. Reduction in fiber density, increased frequency of fiber varicosities and fiber fragmentation are prominent features of skin biopsies from patients with HIV-N. Other forms of HIV-N include acute or chronic inflammatory polyneuropathies, uncommon disorders that may ocur during seroconversion or early stages of HIV infection. Opportunisitic infections, mostly associated with cytomegalovirus or herpes zoster virus infection occur in late stages of AIDS and produce characteristic clinical features such as mononeuritis multiple or radiculopathies.

HIV-associated peripheral neuropathy: epidemiology, pathophysiology and treatment

Peripheral neuropathy is the most frequent neurological complication associated with human immunodeficiency virus type 1 (HIV) infection and advanced acquired immunodeficiency syndrome (AIDS). There are at least 6 patterns of HIV-associated peripheral neuropathy, although these diagnoses are often overlooked or misdiagnosed. Distal symmetrical polyneuropathy (DSP) is the most common form of peripheral neuropathy in HIV infection. DSP occurs mainly in patients with advanced immunosuppression and may also be secondary to the neurotoxicity of several antiretroviral agents. Treatment of painful DSP is primarily symptomatic, while pathogenesis-based therapies are under investigation. Reduction or discontinuation of neurotoxic agents should be considered if possible. Inflammatory demyelinating polyneuropathy (IDP) can present in an acute or chronic form. The acute form may occur at the time of primary HIV infection or seroconversion. Cerebrospinal fluid lymphocytic pleocytosis (10 to 50 cells/mm3) is helpful in the diagnosis of HIV-associated IDP. Treatment consists of immunomodulatory therapy. Progressive polyradiculopathy (PP) most commonly occurs in advanced immunosuppression and usually is caused by cytomegalovirus (CMV) infection. Rapidly progressive flaccid paraparesis, radiating pain and paresthesias, areflexia and sphincter dysfunction are the cardinal clinical features. Rapid diagnosis and treatment with anti-CMV therapy are necessary to prevent irreversible neurological deficits resulting from nerve root necrosis. Mononeuropathy multiplex (MM) that occurs in early HIV infection is characterised by self-limited sensory and motor deficits in the distribution of individual peripheral nerves. In advanced HIV infection, multiple nerves in two or more extremities or cranial nerves are affected. Treatment includes immunomodulation or anti-CMV therapy. Autonomic neuropathy may be caused by central or peripheral nervous system abnormalities. Treatment is supportive with correction of metabolic or toxic causes. Diffuse infiltrative lymphocytosis syndrome (DILS) presents as a Sjögren's-like disorder with CD8 T cell infiltration of multiple organs. Antiretroviral therapy and steroids may be effective treatments.

HIV-1-Associated Neuropathies

Peripheral neuropathy associated with human immunodeficiency virus type 1 (HIV-1) infection is a major cause of morbidity in this patient population. Due to the associated chronic pain, its management has come within the purview of neuropsychiatrists. This paper will focus on the primary pathogenic aspects of HIV-1-associated peripheral neuropathies. The specific syndromes of greatest concern are distal sensory polyneuropathy, toxic neuropathy, inflammatory demyelinating polyradiculoneuropathy, and cytomegalovirus-related progressive polyradiculoneuropathy. The treatments available for these conditions and their efficacy are discussed.

Progressive peripheral and central sensory tract lesion in HIV-infected patients evidenced by evoked potentials (a three-year follow-up study)

OBJECTIVE

To investigate progression of peripheral and central sensory tract lesion and its correlation to immunological deterioration.

METHODS

Clinical and neurophysiological investigation (evoked potentials of the median and tibial nerve) and immunological parameters (CD4-cells, beta 2-microglobuline) were followed up in 160 patients (24 females, 136 males, HIV infection for 2.7 +/- 2.3 years, mv +/- 1 sd) up to four times over approximately 3 years regardless of disease stage and evidence of neurological symptoms. Recordings were done using needle electrodes over the Th12 and C7 spinous process and from the scalp (10/20 system) in the conventional manner. Statistical analysis was performed intraindividually and in comparison to normal laboratory values (n = 96).

RESULTS

All parameters deteriorated during the follow-up period. Statistical analysis showed significant differences between probands and patients for evoked potentials, but also a significant deterioration for evoked potentials after three years at the end of the follow-up study. A significant correlation between progressive impairment of evoked potentials and laboratory data was found.

CONCLUSION

HIV infection induces a progressive lesion of the ascending sensory tracts. The results indicate a peripheral neuropathy as well as a progressive lesion of the ascending central sensory tracts. Pathogenesis of polyneuropathy and of central sensory tract lesion is up to now conjectural. Laboratory investigations indicate a clear-cut correlation between immunological alterations induced by HIV infection and its neurologic manifestation on ascending sensory tracts.

HIV-associated distal symmetrical polyneuropathy: clinical features and nursing management

DSPN is a common manifestation of HIV infection and/or its treatment that can have adverse effects on quality of life and functional status. The pathogenesis remains unclear but likely involves the elaboration of neurotoxic inflammatory cytokines and their metabolites. DSPN is often refractory to available pharmacological treatments, although new treatments involving NGF hold promise for effecting sustained symptom relief and reversing axonal degeneration. Further research is needed to determine the efficacy of nonpharmacological treatments, such as cognitive-behavioral therapies, to alleviate DSPN-associated pain.

Human immunodeficiency virus infection of dorsal root ganglion neurons detected by polymerase chain reaction in situ hybridization

A predominantly sensory peripheral neuropathy is common with human immunodeficiency virus (HIV) infection, but the cause is unknown. Formalin-fixed dorsal root ganglia (DRG), obtained at postmortem from patients with neuropathy and HIV infection and from control subjects, were examined for the presence of HIV DNA by using polymerase chain reaction (PCR)-amplified in situ hybridization. Viral message RNA was detected using reverse transcription in situ PCR with gag-specific primers. HIV DNA and RNA sequences were detected in many satellite cells, mononuclear cells, and occasional neurons in 5 of 5 patients with HIV and neuropathy. HIV DNA was detected only in rare interstitial and satellite cells from 3 of 4 patients with HIV infection without neuropathy and was not detected in 6 patients without HIV infection. HIV infection of DRG neurons and supporting cells may contribute to the HIV-associated sensory neuropathy.

Cerebrospinal fluid and nerve conduction abnormalities in HIV positive individuals

We studied whether there was an association between nerve conduction studies (NCS), CSF, and CD4-T lymphocyte parameters in a large cohort of HIV positive individuals. Two hundred and twenty-eight HIV positive individuals underwent motor and sensory nerve conduction studies, CSF evaluation, peripheral CD4-T lymphocyte count, and neurologic evaluation to determine the presence or absence of peripheral neuropathy. We compared NCS of HIV positive subjects with and without abnormal CSF parameters in the entire cohort. We also compared CSF parameters in a subset of CD4-matched patients with and without neuropathy. CSF abnormalities (in excess of laboratory norms) occurred frequently in the entire study group. There was no statistically significant relationship between NCS and CSF parameters. In addition, there was no significant difference in the CSF findings in the group of patients with clinical neuropathy compared to the group without neuropathy. However, there was an association (p < 0.05) between lower CD4 counts and NCS parameters. In general, abnormal CSF findings are not associated with deteriorating peripheral nerve function in HIV infected patients and are just as likely to be found in an HIV positive patient whether or not a peripheral neuropathy is present.

Role of HIV in the pathogenesis of distal symmetrical peripheral neuropathy

We report the results of a clinical, electrophysiological and pathological study conducted in 18 AIDS patients presenting a distal symmetrical predominantly sensory polyneuropathy (DSPN) characterized by painful dysesthesias as main complaint. Onset of the neuropathy was at CDC (Center for Disease Control) stage II in 2 patients, at CDC stage III in 5 patients and at CDC stage IV in the remainder. Electrophysiological investigation confirmed the presence of an axonal alteration in the sensory nerves, but also revealed motor involvement in all cases. The neuropathological features of sensory nerves were fiber loss and axonal degeneration with macrophagic activation. The expression of monocyte-macrophage markers and of major histocompatibility complex class II antigens appeared up-regulated in endoneurial ramified cells, while expression of CR3, a complement receptor involved in the process of phagocytosis, was down-regulated. In six nerve biopsy samples and in two out of five DSPN dorsal root ganglia we found HIV-related mRNA and protein located in scattered cells of the endoneurium which we presume to be macrophages. These data suggest that: (a) DSPN may occur early in the course of the disease and is not limited to later stages; (b) DSPN is not a ganglionitis but is actually a sensory-motor neuropathy; (c) the virus enters the peripheral nervous system and induces changes in the immunocompetent cell population with activation of macrophages. Storage of the virus inside macrophages may act both as a reservoir for the virus and as a putative cause of nerve damage, probably through release of cytotoxins and/or interaction with trophic factors.

Are there separate central nervous system pathways for touch and pain?

Information about bodily events is conveyed by primary sensory fibres to higher brain centres through neurons in the dorsal column nuclei (DCN) and spinal dorsal horn. The DCN route is commonly considered a 'touch pathway', separate from the spinal pain pathway', in part because DCN neurons respond to gentle tactile stimulation of small skin areas. Here we report that DCN neurons can additionally respond to gentle and noxious stimulation of viscera and widespread skin regions. These and other experimental and clinical data suggest that the DCN and spinal routes cooperate, rather than operate separately, to produce the many perceptions of touch and pain, an ensemble view that encourages novel approaches to health care and research.

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.

Early detection of distal symmetrical polyneuropathy during HIV infection by paired stimulation of sural nerve

In 203 HIV infected patients in various clinical stages neurological examination, paired stimulation (LPSS), nerve conduction velocity (NCVS) and amplitude (AMPS) of the sural nerve, distal latency (DLP), nerve conduction velocity (NCVP), amplitude (AMPP) and F waves of the peroneal nerve were recorded. Neurological examination revealed symptoms and clinical signs of polyneuropathy in 67 (33%) (WR 1-6) of the patients. LPSS after paired stimulation was abnormal in 25.5%, NCVS in 14.2%, AMPS in 9.8%, NCVP in 11.8%, DLP in 11.2%, AMPP in 5.9% and FWP in 14.6%. Our findings indicate a high incidence of peripheral nerve system involvement during HIV infection. In 11.5% of all patients only LPSS proved polyneuropathy. Neurophysiological results from HIV infected patients with symptoms and clinical signs of polyneuropathy were statistically significantly different from HIV infected patients without symptoms and clinical signs of polyneuropathy. The delay of LPSS represents the most sensitive neurophysiological indicator of polyneuropathy during HIV infection and announces the onset of peripheral nerve disease even in early stages of infection, according to Walter Reed staging classification 1 and 2 (approx. 20%).

AIDS-myelopathy. A neuropathological study

Vacuolar myelopathy belongs to the AIDS-associated diseases. It is characterized by vacuolation and infiltration of the long tracts of the spinal cord by macrophages. The clinical and morphological findings of 8 AIDS-patients with vacuolar myelopathy are reported here. The syndrome developed during the final stages of AIDS and was associated with HIV-encephalopathy in 5 cases. The vacuoles were mainly due to intramyelinic swelling and vacuolation. Vacuolated macrophages and axons contributed only to a minor degree. In one case only, HIV-antigens were detected immunohistochemically. The results are discussed in the light of modern pathogenetical concepts of HIV-related diseases.

[Involvement of the peripheral nervous system in HIV infection: electromyographic study and nerve conduction velocity]

Disorders of the peripheral nervous system occur at all stages of HIV1 infection. Acute and subacute inflammatory demyelinating polyneuropathies are mainly observed in otherwise asymptomatic HIV+ patients and in patients with ARC (AIDS-related complex): clinical and electrophysiological features are similar to those observed in Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyneuropathy (CIDP), but CSF examination usually shows pleocytosis, and an infiltration of the endoneurium and/or the epineurium is commonly seen in nerve biopsies. Mononeuropathy multiplex is a rare complication occurring in ARC-patients: electrophysiological studies are consistent with an axonopathy and nerve biopsies may show vasculitis. Distal predominantly sensory polyneuropathies are the most frequent peripheral neuropathies in HIV1 infection and are usually reported in patients with AIDS and severe immunosuppression: electrophysiological features are of an axonopathy with signs of acute denervation. Meningoradiculitis is observed at the late stages of the disease and is mainly due to a cytomegalovirus infection. On the other hand, systematic electrophysiological studies in HIV+ cases reveal a high percentage of abnormalities concerning sensory and less frequently motor nerve conduction velocities. The severity of this asymptomatic involvement of the peripheral nervous system seems to be related to the degree of the immunodeficiency. The mechanism of these peripheral neuropathies remains hypothetical in most cases.

Neuropathology of the spinal cord in the acquired immunodeficiency syndrome

The neuropathologic findings in the spinal cord were reviewed in 138 consecutive autopsies of patients with the acquired immunodeficiency syndrome. In all cases both the brain and spinal cord were examined by conventional histologic techniques, and in 63 cases immunohistochemistry was used to detect human immunodeficiency virus (HIV), Toxoplasma gondii, cytomegalovirus, and JC papovavirus antigens. The most common observation was a normal spinal cord (60%). Vacuolar myelopathy (VM) was observed in 23 (17%) cases. Human immunodeficiency virus myelitis was evident in 8% of cases. Human immunodeficiency virus myelitis was associated with HIV encephalitis in 65% of the cases. Opportunistic infections of the spinal cord were uncommon, consisting of cryptococcosis (five cases), cytomegalovirus (four cases), toxoplasmosis (one case), and progressive multifocal leukoencephalopathy (one case), and almost always were seen with cerebral and/or systemic infection by these agents. Malignant lymphoma rarely involved the spinal cord (four cases); all were B-cell lymphomas and were associated with cerebral and/or systemic lymphoma. Other abnormalities rarely observed were Wallerian degeneration of the corticospinal tracts or posterior columns (6%) and focal microinfarcts. Most cases of VM (78%) were not associated with HIV myelitis, and in the five patients with both VM and HIV myelitis, HIV-infected cells were not found in the regions affected by VM. In contrast, 65% of cases with VM were associated with HIV encephalitis. The pathogenesis of VM remains unknown; it is probably not due to direct infection by HIV.

The pathology of the posterior root ganglia in AIDS and its relationship to the pallor of the gracile tract

The spinal cord and the thoracic and lumbar posterior root ganglia (PRGs) of 14 HIV-positive men and 7 age- and sex-matched controls were studied by routine histology, morphometric analysis of the number of nodules of Nageotte (nN) and the diameters of sensory ganglion cells, immunohistochemistry and in situ hybridization. In 7 patients (2 of whom had evidence of cytomegalovirus ganglionitis) there were increased numbers of nN and diffuse, mild infiltration with CD45R+ T lymphocytes; no B lymphocytes were observed. Macrophages were increased in number in all cases. Whenever more than one ganglion was examined from the same patient, the appearances were similar in all. There was no alteration in the distribution of ganglion cell diameters. Changes in the spinal cord included vacuolar myelopathy (5 cases), HIV myelitis (1 case), microglial nodules (3 cases) and pallor of the gracile tracts (GTP) in 7 cases, in 6 of whom it co-existed with increased numbers of nN. Seven cases had no abnormalities, except the increase in number of macrophages in PRGs. In spite of a correlation between sensory nerve cell loss and GTP our findings suggest that other mechanisms, such as 'dying back' may contribute to the pathogenesis of GTP. Moreover, sensory disturbances were found most commonly in association with nerve cell loss; however, loss of sensory ganglion cells was not necessarily associated with evidence of sensory impairment.

Human nerve growth factor prevents degeneration of basal forebrain cholinergic neurons in primates

Basal forebrain cholinergic neurons respond to nerve growth factor (NGF), and it has been suggested that the administration of NGF might prevent their degeneration in patients with Alzheimer's disease. One major prerequisite to be fulfilled before the consideration of clinical trials of NGF in patients with Alzheimer's disease is the demonstration that human NGF affects basal forebrain cholinergic neurons in primates. In the present study, we used a recombinant human nerve growth factor (rhNGF), which we previously showed to be active on rat basal forebrain cholinergic neurons, in nonhuman primates with a unilateral transection of the fornix (a well-established model for the induction of retrograde degenerative changes in septal cholinergic neurons). After the lesion, one group of animals received rhNGF and a second group received vehicle solution for 2 weeks. In animals receiving vehicle, the medial septal nucleus ipsilateral to the lesion showed reductions in number (55%) and size of cell bodies immunoreactive for NGF receptor and choline acetyltransferase. In Nissl stains, many cells showed reduced size and basophilia. The rhNGF completely prevented alterations in the number and size of NGF receptor- and choline acetyltransferase-immunoreactive neurons in the medial septal nucleus and reversed atrophy in a subpopulation of large, basophilic medial septal nucleus neurons, as identified by Nissl stains. The effects of rhNGF were identical to those of mouse NGF, which we have previously used in the same primate lesion paradigm. The restoration of the phenotype of injured cholinergic septal neurons by rhNGF in the monkey raises the possibility that this factor may be used to ameliorate acetylcholine-dependent memory impairments that occur in aged nonhuman primates. In concert, results of the present investigation provide critical information for the future use of NGF in patients with neurological disorders that affect NGF-responsive cells in the peripheral and central nervous systems.

Idiopathic myelopathies with white matter vacuolation in non-acquired immunodeficiency syndrome patients

Postmortem examination of 21 patients showed a vacuolar myelopathy resembling that associated with the acquired immunodeficiency syndrome. Underlying diseases included six cases of leukemia or lymphoma, five of carcinoma, three of systemic lupus erythematosus, two of chronic lung disease, and one each of cadaveric renal transplant, cirrhosis, diabetes, hemophagocytic syndrome, and viral encephalitis. Fourteen patients were on long-term steroid therapy and 10 of these also had immunosuppressive chemotherapy. No patient had the acquired immunodeficiency syndrome, although one received blood transfusions in 1978. Signs and symptoms consistent with myelopathy included paraparesis in seven patients, ataxia in one, and bilateral extensor plantar reflexes in one. Microscopic examination showed vacuolation in spinal cord white matter primarily located in posterior and lateral columns. Lipid-laden macrophages and axonal changes were proportional to the severity of the vacuolation, which was severe in five patients, moderate in 10, and mild in six. Eight patients had coexistent viral diseases elsewhere in the central nervous system, but viral-associated antigens or genomic material was not found in regions of vacuolated spinal cord white matter. Although the etiology of these myelopathies is unknown, their association with immune suppression and coexistent viral infection of the central nervous system suggests that an opportunistic viral infection may be important.

Multifocal multinucleated giant cell myelitis in an AIDS patient

A 19-year-old male intravenous drug abuser, was admitted to hospital with a one-week history of lower limb weakness and urinary retention. He was known to have been HIV-seropositive for 3 years and had been treated for cerebral toxoplasmosis. Neurological examination confirmed flaccid paraparesis with weak ankle jerks and bilateral extensor plantar responses. There was no obvious sensory deficit. Neurological examination was otherwise normal. CSF contained 63 mg/dl protein and 10 leucocytes/mm3. Myelography was normal. He died 1 month later from septic peritonitis. Neuropathological examination showed chronic lesions of toxoplasmosis in brain. Small necrotic foci with myelin loss, proliferation of microglia, macrophages and multinucleated giant cells (MGC) were disseminated in the whole spinal cord, mostly in the white matter, but the brain was spared. Immunohistochemistry demonstrated p24 and p17 HIV antigens in macrophages, MGC and microglial cells. These lesions resemble those of so called 'multifocal giant cell encephalitis'. The present case demonstrates that HIV-related multifocal inflammatory changes may be restricted to the spinal cord and may be a cause of myelopathy in AIDS patients.

Spinal cord disease in children with HIV-1 infection: a combined molecular biological and neuropathological study

An autopsy study was performed on spinal cords from 18 children who died with HIV-1 infection, using standard histopathologic techniques as well as in situ hybridization and immunocytochemistry for HIV-1. Of 16 spinal cords examined by histology, nine had inflammatory cell infiltrates and six had multinucleated cells; both types of lesion are associated with the presence of HIV-1 in central nervous system tissue. HIV-1 type lesions were often present in the spinal cord and brain from the same patient. Pallor of myelin in corticospinal tracts in the cord was present in half of the cases; this change correlated with diffuse myelin pallor in the corresponding brains, but not with the HIV-1 associated changes in the cords. In situ hybridization for HIV-1 nucleic acid sequences gave positive results in seven of 18 spinal cords, with hybridizing signal usually localized to inflammatory cell infiltrates and multinucleated cells. Positive in situ hybridization, on frozen sections, correlated with the presence of HIV-1 associated changes on paraffin sections from the same cases. Immunocytochemistry for p25 core protein of HIV-1, using a monoclonal antibody on frozen sections, was positive in multinucleated cells, macrophages, and microglia. In this series there were two cases of vacuolar myelopathy, one a 30-month-old boy who had concomitant measles virus in the spinal cord grey matter, and the other nine-year-old girl who had severe HIV-1 infection of the cord. Other than the single case of measles virus, there were no opportunistic infections in the cords in this series. HIV-1 frequently involves the spinal cord in children with AIDS, while opportunistic infections are rare. Vacuolar myelopathy occurs in children with HIV-1 infection, although its occurrence is much less frequent than in adults with AIDS.

Vacuolar myelopathy in AIDS. A morphological analysis

Between 1986 and 1988 we studied the spinal cord of 40 patients dying of AIDS. Transverse and longitudinal sections from a minimum of four levels of the spinal cord were examined by means of conventional histology, immunohistochemistry and electron microscopy. Out of 22 cases there were 6 showing a mild, 11 a moderate and 5 a severe myelopathy. Among these cases with severe myelopathy, vacuolar degeneration of the posterior, lateral, and anterior columns of the white matter, which are typical findings of vacuolar myelopathy (VM), were present. Cervical and thoracic cords were affected in all cases, the lumbal cord, however, in only two. Fusiform vacuoles, 30 to 180 microns in diameter and 200 to 500 microns in length, could be seen rising between the axolemma and the myelin sheath. Most of them were still containing an axon cylinder. Foamy phagocytic cells, phagocytosing axons of apparently preserved structure were found within the vacuoles. These foamy macrophages contained rests of axons in their cytoplasm. However, only one case with severe tissue disruption exhibited myelin debris as well. Our morphological findings suggest that in VM of AIDS a process of phagocytosis directed against the axon cylinders occurs simultaneously with vacuolar degeneration of the white matter of the spinal cord. The results suggest furthermore that VM, especially its moderate form, appears to be a more frequent condition than previously assumed.