Subclinical peripheral nerve involvement in AIDS: an electrophysiological and pathological study

HIV peripheral neuropathy

Peripheral neuropathies are the most common neurological manifestations occurring in HIV-infected individuals. Distal symmetrical sensory neuropathy is the most common form encountered today and is one of the few that are specific to HIV infection or its treatment. The wide variety of other neuropathies is akin to the neuropathies seen in the general population and should be managed accordingly. In the pre-ART era, neuropathies were categorized according to the CD4 count and HIV viral load. In the early stages of HIV infection when CD4 count is high, the inflammatory demyelinating neuropathies predominate and in the late stages with the decline of CD4 count opportunistic infection-related neuropathies prevail. That scenario has changed with the present almost universal use of ART (antiretroviral therapy). Hence, HIV-associated peripheral neuropathies are better classified according to their clinical presentations: distal symmetrical polyneuropathy, acute inflammatory demyelinating polyradiculoneuropathy (AIDP) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), mononeuropathies, mononeuropathies multiplex and cranial neuropathies, autonomic neuropathy, lumbosacral polyradiculomyelopathy, and amyotrophic lateral sclerosis (ALS)-like motor neuropathy. Treated with ART, HIV-infected individuals are living longer and are at a higher risk of metabolic and age-related complications; moreover they are also prone to the potentially neurotoxic effects of ART. There are no epidemiological data regarding the incidence and prevalence of the peripheral neuropathies. In the pre-ART era, most data were from case reports, series of patients, and pooled autopsy data. At that time the histopathological evidence of neuropathies in autopsy series was almost 100%. In large prospective cohorts presently being evaluated, it has been found that 57% of HIV-infected individuals have distal symmetrical sensory neuropathy and 38% have neuropathic pain. It is now clear that distal symmetrical sensory neuropathy is caused predominantly by the ART's neurotoxic effect but may also be caused by the HIV itself. With a sizeable morbidity, the neuropathic pain caused by distal symmetrical sensory neuropathy is very difficult to manage; it is often necessary to change the ART regimen before deciding upon the putative role of HIV infection itself. If the change does not improve the pain, there are few options available; the most common drugs used for neuropathic pain are usually not effective. One is left with cannabis, which cannot be recommended as routine therapy, recombinant human nerve growth factor, which is unavailable, and topical capsaicin with its side-effects. Much has been done to and learned from HIV infection in humans; HIV-infected individuals, treated with ART, are now dying mostly from cardiovascular disease and non-AIDS-related cancers. It hence behooves us to find new approaches to mitigate the residual neurological morbidity that still impacts the quality of life of that population.

Processing of nerve biopsies: a practical guide for neuropathologists

Nerve biopsy is a valuable tool in the diagnostic work-up of peripheral neuropathies. Currently, major indications include interstitial pathologies such as suspected vasculitis and amyloidosis, atypical cases of inflammatory neuropathy and the differential diagnosis of hereditary neuropathies that cannot be specified otherwise. However, surgical removal of a piece of nerve causes a sensory deficit and – in some cases – chronic pain. Therefore, a nerve biopsy is usually performed only when other clinical, laboratory and electrophysiological methods have failed to clarify the cause of disease. The neuropathological work-up should include at least paraffin and resin semithin histology using a panel of conventional and immunohistochemical stains. Cryostat section staining, teased fiber preparations, electron microscopy and molecular genetic analyses are potentially useful additional methods in a subset of cases. Being performed, processed and read by experienced physicians and technicians nerve biopsies can provide important information relevant for clinical management.

Differential sensitivity of thick and thin fibers to HIV and therapy-induced neuropathy

The study assessed HIV-related and anti-retroviral therapy-induced neuropathy in myelinated and unmyelinated nerve fibers. One hundred consecutive HIV patients were examined clinically and standard nerve conduction velocities were measured. In addition, electrically induced sympathetic skin response (SSR) was assessed in the palms and soles. The difference in delay of SSR in palms and soles (DeltaSSR) was calculated as an indirect measure of C-fiber conduction velocity. Thick fiber conduction velocities significantly decreased with age and increasing stage of the disease, whereas no effect of stage was found for DeltaSSR (p=0.6). In contrast, medication of at least one of the most known neurotoxic drugs zalcitabine, stavudine, or didanosine did not result in significantly lower conduction velocities in thick fibers (51.29+/-3.4 m/s vs. 50.86+/-3.5 m/s), but was related to an increased DeltaSSR. DeltaSSR allows an indirect measurement of C-fiber conduction velocity. In HIV this measure of unmyelinated sympathetic fibers was most sensitive to anti-viral treatment whereas conduction velocity of myelinated somatic fibers was more sensitive to disease-related neuropathy. The results suggest that HIV neuropathy preferably affects myelinated and anti-retroviral therapy unmyelinated fibers.

Epidermal nerve fiber density, axonal swellings and QST as predictors of HIV distal sensory neuropathy

We investigated the associations of baseline epidermal nerve fiber (ENF) densities and morphology (percent ENF swellings) and quantitative sensory testing (QST) with clinically defined human immunodeficiency virus (HIV)-associated distal polyneuropathy (DSP) and whether these measures are predictive of development of symptomatic DSP over time. Fifty-seven HIV-infected subjects with and without DSP and 19 controls participated. Mean ENF densities were lower at the distal leg and proximal thigh in asymptomatic or symptomatic DSP than in controls. Mean ENF densities did not differ significantly among the HIV groups. Percent ENF swellings was higher in patients with symptomatic DSP than controls at the distal leg, and was also greater at the proximal thigh in patients with asymptomatic or symptomatic DSP than in controls. The percent ENF swellings at the distal leg correlated with the thresholds for both minimal (HP 0.5) and intermediate (HP 5.0) heat pain (HP) intensity. A higher percent ENF swellings in the distal leg [hazard ratio (HR) 1.16, 95% CI 1.02-1.31] and HP 0.5 thresholds (HR 1.03, 95% CI 1.01-1.05) were the only two measures associated with a shorter time to development of symptomatic DSP. Quantitation of ENF swellings and heat pain thresholds deserve further study as predictors of symptomatic neuropathy.

Sensory evoked potentials in SIV-infected monkeys with rapidly and slowly progressing disease

Human immunodeficiency virus (HIV-1) infects the central nervous system (CNS) early in the course of disease progression and leads to some form of neurological disease in 40-60% of cases. Both symptomatic and asymptomatic HIV-infected subjects also show abnormalities in evoked potentials. As part of an effort to further validate an animal model of the neurological disease associated with lentiviral infection, we recorded multimodal sensory evoked potentials (EPs) from nine rhesus macaques infected with passaged strains of SIVmac (R71/E17), prior to and at 1 month intervals following inoculation. The latencies of forelimb and hindlimb somatosensory evoked potentials (SEP) and flash visual evoked potentials (VEP) were measured. Within 14 weeks of inoculation, all but two animals had progressed to end-stage disease (rapid progressors). The two animals with slowly progressing disease (AQ15 and AQ94) had postinoculation life spans of 109 and 87 weeks, respectively. No significant changes were observed in evoked potentials recorded during the control period or at any time in the animals with slowly progressing disease. However, all of the monkeys with rapidly progressing disease exhibited increases in latency for at least one evoked potential type. The overall mean increases in somatosensory and visual evoked potential peak latencies for the rapid progressors were 22.4 and 25.3%, respectively. For comparison, the changes in slow progressors were not significant (1.8 and -1.9%, respectively). These results, coupled with our previous finding of slowed motor evoked potentials in the same cohort of macaques (Raymond et al.: J Neurovirol 1999;5:217-231), demonstrate a broad and somewhat variable pattern of viral injury to both sensory and motor system structures, resembling the findings in HIV-infected humans. These results coupled with our earlier work demonstrating cognitive and motor behavioral impairments in the same monkeys support the use of the SIVmac-infected rhesus macaque as a model of AIDS-related neurological disease.

Neuromuscular Complications of HIV-1 Infection

Neuromuscular disorders are the most frequent neurologic complications that occur in patients with HIV infection. The distinction among the different forms of peripheral neuropathy (ie, distal symmetrical polyneuropathy, polyradiculopathy, mononeuritis multiplex) is crucial in determining their potential etiology and treatment. Distal symmetrical polyneuropathy is most common in HIV-infected patients with advanced immunosuppression and may also result from neurotoxicity of several antiretroviral agents. Myopathy may occur at any stage of HIV disease, and has also been described as a toxic side effect of zidovudine. This paper reviews current knowledge of pathogenesis, clinical manifestations, and treatment of HIV-associated neuromuscular disorders.

Peripheral neuropathy with nucleoside antiretrovirals: risk factors, incidence and management

Distal symmetrical peripheral neuropathy is a common adverse experience in persons with HIV infection. This condition, which presents as a pain, numbness. burning and/or dysaethesia initially in the feet, is often multi-factorial in its origin. Nucleoside analogue reverse transcriptase inhibitors represent an important contributor to peripheral neuropathy. Specifically, around 10% of patients receiving stavudine or zalcitabine and 1 to 2% of didanosine recipients may have to discontinue therapy with these agents due to neuropathy. Prompt withdrawal of these therapies enables gradual resolution of signs and symptoms in most patients, although a period of symptom intensification may occur shortly after withdrawal. Risk factors for developing peripheral neuropathy during nucleoside analogue therapy include low CD4+ cell count (<100 cells/mm3), a prior history of an AIDS defining illness or neoplasm, a history of peripheral neuropathy, use of other neurotoxic agents including high alcohol (ethanol) consumption and nutritional deficiencies such as low serum hydroxocobalamin levels. Thus, patients at increased risk of peripheral neuropathy should potentially avoid the use of the neurotoxic nucleoside analogues or be more carefully monitored during therapy. Management of this problem includes patient education. prompt withdrawal of the likely causative agent (giving consideration not to leave the patient on a sub-optimal therapy regimen) and simple analgesia. with augmentation with tricyclic antidepressants or anticonvulsant agents when pain is severe. New agents that may assist in managing this condition include levacecarnine (acetyl-L-carnitine) and nerve growth factors such as recombinant human nerve growth factor.

The reliability and validity of the subjective peripheral neuropathy screen

Painful sensory neuropathy (PSN) is the most common neurological disorder associated with HIV infection and affects up to 30% of HIV-positive individuals. PSN may develop as a consequence of HIV infection or from the toxic effect of the antiretrovirals. Although several tools have been developed to screen for PSN, their validity and reliability has yet to be established among HIV-positive patients. The Subjective Peripheral Neuropathy Screen (SPNS) is a brief self-report tool that is currently being administered in the AIDS Clinical Trials Group. The objective of this study was to establish the psychometric properties of the SPNS screening tool for the correct identification of PSN in HIV-positive individuals. Specifically the goals were to determine the reliability, the validity, and the diagnostic efficiency of the SPNS in the detection of PSN. Data were abstracted on subjects enrolled in an ongoing natural history cohort. The SPNS was administered to a convenience sample of 39 HIV-positive individuals with PSN and 44 HIV-positive controls. Results showed the SPNS to be internally consistent (Cronbach's alpha = .86). SPNS score differences assessed by t-test were significantly different for individual symptoms of parasthesias, numbness, and pain of the lower extremities, and for severity measures (the Clinical Severity Grade, and the Average Severity Score) between the HIV-positive groups (p < .05). Using Spearman's rank, significant correlations were demonstrated between the neurological exam and the Clinical Severity Grade and the Average Severity Score, the neurological exam and vibratory quantitative sensory testing (QST) only, and the severity measures and vibratory QST only. Sensitivity and specificity analysis demonstrated that numbness of the lower extremities was the symptom with the highest efficiency for correctly classifying PSN. Thus, internal consistency, construct validity, and criterion related validity were confirmed with the SPNS for the correct classification of PSN in HIV-positive individuals.

Parvalbumin and calbindin D-28 k immunoreactivity in dorsal root ganglia in acquired immunodeficiency syndrome

Various degrees of neuronal degeneration have been found in lumbosacral dorsal root ganglia of patients with acquired immunodeficiency syndrome (AIDS). To characterize the subpopulations of primary sensory neurons affected in AIDS, we immunostained dorsal root ganglion tissues from 11 AIDS patients and six controls using antibodies to the calcium binding proteins, parvalbumin and calbindin D-28 k. In controls, the proportion of neurons containing parvalbumin and calbindin was 18.0% and 22.4%, respectively. The majority of parvalbumin-positive neurons, which are thought to be proprioceptive neurons, were of medium to large size, while calbindin was found in both large- and small-sized neurons. The density of parvalbumin-immunoreactive neurons was reduced by 7.3% in AIDS patients, but the density of calbindin-immunoreactive neurons was preserved. Furthermore, in AIDS cases, the number of parvalbumin-positive neurons was reduced more in dorsal root ganglia in which human immunodeficiency virus (HIV) antigen was detected than in HIV-negative ganglia. These results suggest that specific subpopulations of sensory neurons positive for parvalbumin may be differentially affected over the course of AIDS, and that this could be related to peripheral neuropathy which frequently occurs in the late stages of AIDS.

Neurophysiological assessment of peripheral nerve and spinal cord function in asymptomatic HIV-1 infection: results from the UCMSM/Medical Research Council neurology cohort

As part of the Medical Research Council prospective study of the neurological complications of HIV infection, neurophysiological tests of spinal cord and peripheral nerve function were recorded in a cohort of homosexual or bisexual men. The studies included motor and sensory nerve conduction studies, vibration perception thresholds, somatosensory evoked potentials and motor evoked potentials elicited by magnetic stimulation. The results were compared with markers of immune function. The findings from 114 volunteers were analysed in a cross-sectional study. Fifty-nine were HIV-seropositive but asymptomatic, 26 had progressed to the symptomatic stages of HIV disease and 29 were persistently HIV-seronegative. There was some evidence of a mild sensory axonopathy in the symptomatic HIV-seropositive group. No differences were detected between the asymptomatic HIV-seropositive group and the HIV-seronegative comparison group. There were no consistently significant correlations between the neurophysiological measurements and CD4 counts and beta 2-microglobulin levels. On repeated testing, there was no evidence of a trend towards deterioration over a mean period of approximately 3 years in 36 HIV-seropositive subjects who remained asymptomatic compared with 22 HIV-seronegatives. These findings have failed to demonstrate neurophysiological evidence of spinal cord or peripheral nerve dysfunction in the asymptomatic stages of HIV infection.

Spinal cord disease due to vacuolar myelopathy in AIDS

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AAEM minimonograph #41: neuromuscular diseases associated with HIV-1 infection

Neuromuscular diseases occur in as many as 50% of patients infected with human immunodeficiency virus type 1 (HIV-1). All forms of neuromuscular disease have been reported, including axonal neuropathy, demyelinating neuropathy, mononeuropathy multiplex, polyradiculitis, ALS-like syndromes, disorders of neuromuscular transmission, myopathy, and toxic neuropathies due to medication side effects. Neuromuscular disease is often the presenting manifestation of HIV-1 infection. Infection with cytomegalovirus (CMV) is associated with different types of neuropathy including mononeuritis multiplex and polyradiculopathy. There is effective treatment for many of the associated disorders including chronic inflammatory demyelinating neuropathy, CMV-mediated neuropathies, and myopathy. Treatment of CMV-mediated mononeuropathy multiplex may be life saving. The different neuromuscular syndromes associated with different stages of HIV-1 infection may be due, in part, to different levels of immunocompetence.

Neurological dysfunction in asymptomatic HIV-1 infected men: evidence from evoked potentials. HNRC Group

Neurological function in 159 subjects infected by the human immunodeficiency virus (HIV) who had no neurological symptoms or signs (129 asymptomatic, 30 with ARC/AIDS) was compared to that of 62 controls by means of pattern-reversal evoked potentials (PREPs), brain-stem auditory evoked potentials (BAEPs), median nerve somatosensory evoked potentials (MSEPs), tibial nerve somatosensory evoked potentials (TSEPs) and nerve conduction studies (NCSs). Central nervous system somatosensory conduction from lumbar cord to cortex was prolonged in both asymptomatic seropositive and ARC/AIDS groups, while peripheral somatosensory conduction, NCSs and PREP delays occurred only in the ARC/AIDS group. BAEPs did not show significant differences among groups. TSEPs were abnormal in 8% of asymptomatic carriers and 43% of patients with ARC/AIDS, MSEPs in 7% and 20%, PREPs in 4% and 0%, and BAEPs in 1% and 0% respectively. One or more evoked potentials were abnormal in 18 of 129 (14%) asymptomatic carriers and 13 of 30 (43%) subjects with ARC/AIDS as compared with 1 of 62 (2%) seronegative controls. We conclude that asymptomatic HIV carriers have subclinical neurological impairment of central somatosensory function and that the neurological impairment increases with disease progression to involve peripheral nerves and visual system.

Total reaction time: a new approach in early HIV encephalopathy?

In an attempt to develop better methods for diagnosis, screening and serial assessment of HIV-1-associated cognitive/motor complex, we have added a motor component to tests of reaction time, defining the new parameter as total reaction time. Thirty-four non-drug-using, HIV-positive men underwent four different tests of total reaction time. All four tests reached a level of statistical significance, both for a group of patients with early disease and for a group of patients with symptoms, compared with a control group. Total reaction time had a better discriminatory ability than standard reaction time, particularly for patients with early disease. It is suggested that neuropsychological studies of HIV-1-associated cognitive/motor complex should include tests of total reaction time.

Neuropathies and HIV infection

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Nature and incidence of peripheral nerve syndromes in HIV infection

Fifty four patients with peripheral nerve syndromes were seen during a 15 month period in a population of about 1500 HIV infected patients at all stages of the disease. Distal symmetrical peripheral neuropathies were seen in 38 of the 54 patients, (11.5% of AIDS patients) and could be distinguished into two forms. The most common (n = 25) was a painful peripheral neuropathy during AIDS, which is distinct clinically and pathologically, having axonal atrophy, and is associated with cytomegalovirus infection at other sites. The 13 non-painful neuropathies seen were more heterogeneous. Lumbosacral polyradiculopathy associated with cytomegalovirus and lymphomatous mononeuritis multiplex occurred in fewer than 1% of AIDS patients. Mononeuropathies were seen in 3% of AIDS patients. No patients with acute or chronic inflammatory demyelinating polyradiculoneuropathies were seen. The annual incidence of neuropathies during the AIDS related complex stage was less than 1%; none were seen in asymptomatic HIV seropositive patients.

Longitudinal study of EEG and evoked potentials in neurologically asymptomatic HIV infected subjects

Serial electroencephalograms (EEGs) and multimodality evoked potentials (EPs) were performed along with neurological and neuropsychological evaluation, cerebrospinal fluid assessment and magnetic resonance imaging at 6 month intervals in 73 neurologically asymptomatic HIV infected subjects. The results were compared with 50 age- and sex-matched controls. EEG was abnormal in 2 subjects (3%) initially and was abnormal in 7 (9%) subjects by the last examination. EEG abnormality (diffuse slowing) correlated significantly with slowed reaction time in neuropsychological testing (P < 0.05). VEP and BAEP provided low yields of 1.3% and 4% respectively. SEP was abnormal in 7 (9%) of the subjects initially and in 10 (13%) subjects by the last testing, with 80% of the abnormalities seen on the posterior tibial study. In 3 subjects, initial SEP abnormalities predicted later development of myelopathy and peripheral neuropathy. Event-related auditory evoked potentials were performed in 39 subjects. They were abnormal in 5 subjects initially (12%) and in 6 subjects (15%) by the last examination and more commonly in advanced stages of the illness with lower T4 counts. This data shows the evolution and association of electrophysiological abnormalities in early HIV infection and suggests a predictive value for SEP in HIV infected asymptomatic individuals.

Electrophysiological study of neurologically asymptomatic HIV1 seropositive patients

EEGs, brainstem auditory evoked potentials (BAEPs) and auditory event-related potentials (ERPs) were recorded from 33 individuals infected with the human immunodeficiency virus, type 1 (HIV1+ patients: 13 CDC Class II or III; 20 Class IV). All were neurologically asymptomatic, non-demented, and had a past history of intravenous drug abuse. Sixteen age- and sex-matched normals and 10 HIV1- former drug addicts served as controls. Half of the HIV1+ and HIV1- subjects displayed mild EEG anomalies and, except for one HIV1+ patient, BAEPs were normal in both groups. ERPs were normal in all HIV1- subjects but anomalous (longer latencies of components P2, N2, P3; reduced amplitude of P3) in 9 HIV1+ patients (27%), the incidence of such anomalies being higher for Class IV than Class II/III patients. Auditory ERPs proved the most sensitive and specific of these electrophysiological procedures in detecting subclinical central nervous system involvement in HIV1 infection.

[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.

Peripheral and central nervous system anomalies in HIV-1 infection: an electrophysiological study

This study explored the neurophysiological changes in 87 HIV1+ (20 AIDS, 24 ARC, 24 LAS and 19 AC) patients showing no clinical evidence of neurological impairment. Tracing somatosensory responses by recording SEPs from upper and lower limbs, we found a slowing of both peripheral and central nerve conduction. Peripheral alterations occurred in virtually all patients of the AIDS group. Central anomalies, confined largely to the lower spinal cord, manifested themselves only during the later stages of the disease (ARC and AIDS) and then only in about half of our sample. More marked neurotropic varieties of HIV1 may account for these differences. We feel that SEP studies can serve to reveal pre-clinical NS involvement in HIV1+ subjects and should be included among research strategies aimed at tracing the evolution of AIDS.

Correlation of neuromuscular pathology in acquired immune deficiency syndrome patients with cytomegalovirus infection and zidovudine treatment

Peripheral nerve and skeletal muscle specimens from 115 autopsied adult AIDS patients were examined for types and incidence of histological abnormalities. Focal perivascular chronic inflammatory infiltrates featuring plasma cells were found in 85% of nerve and muscle specimens. These foci were specifically associated with cytomegalovirus (CMV)-infected capillary or venous endothelial cells in neuromuscular specimens of 31/115 patients, with increasing incidence in patients surviving longer with the diagnosis of AIDS. Neuromuscular CMV was identified histologically in 19% of AIDS patients with an AIDS-defining illness for 3 months or less, with the incidence increasing to 46% of patients who had the diagnosis for 2 years or longer. Vascular damage from CMV endothelial infection may result in regional ischemic and/or inflammatory damage to nerves, producing myelinated fiber loss and axonal degeneration, leading to denervation atrophy of myofibers found in skeletal muscle specimens in a majority of the patients. Myelinated fiber loss within the sural nerve was determined by morphometric quantitation for a subset of 50 patients, and correlated with the presence of histologically identifiable neuromuscular CMV, clinical history of zidovudine administration, and chemotherapy for alleviation of Kaposi's sarcoma. CMV infection and zidovudine treatment were both positively correlated with myelinated fiber loss, while Kaposi's sarcoma chemotherapy did not independently increase the incidence of myelinated fiber loss.

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.