Antiretroviral therapy may improve sensory function in HIV-infected patients: a pilot study

Article Topic: Neuropathies Due to Infections and Antimicrobial Treatments

Purpose of eview

The aim of this review is to discuss the presentation, diagnosis, and management of polyneuropathy (PN) in selected infections. Overall, most infection related PNs are an indirect consequence of immune activation rather than a direct result of peripheral nerve infection,  Schwann cell infection, or toxin production, though note this review will describe infections that cause PN through all these mechanisms. Rather than dividing them by each infectious agent separately, we have grouped the infectious neuropathies according to their presenting phenotype, to serve as a guide to clinicians. Finally, toxic neuropathies related to antimicrobials are briefly summarized.

Recent findings

While PN from many infections is decreasing, increasing evidence links infections to variants of GBS. Incidence of neuropathies secondary to use of HIV therapy has decreased over the last few years.

Summary

In this manuscript, a general overview of the more common infectious causes of PN will be discussed, dividing them across clinical phenotypes: large- and small-fiber polyneuropathy, Guillain-Barré syndrome (GBS), mononeuritis multiplex, and autonomic neuropathy. Rare but important infectious causes are also discussed.

Update of HIV-Associated Sensory Neuropathies

PURPOSE OF REVIEW

HIV-sensory neuropathy (HIV-SN) remains a common complication of HIV infection and may be associated with significant morbidity due to neuropathic pain. The overall purpose of this review is to discuss trends in the changing epidemiology in HIV-SN, new data regarding the pathophysiology of the condition, and discuss approaches to management.

RECENT FINDINGS

While HIV-SN has been historically considered the most common neurological complication of HIV infection, improved accessibility to effective combination antiretroviral therapy (cART), use of less neurotoxic antiretroviral medication regimens, and trends towards earlier introduction of treatment have impacted the condition: overall incident HIV-SN is likely decreased compared to prior rates and patients afflicted by HIV-SN may more frequently have asymptomatic or subclinical disease. Traditional predictors of HIV-SN have also changed, as traditional indices of severe immune deficiency such as low CD4 count and high viral load no longer predict HIV-SN. Emerging evidence supports the contention that both peripheral and central mechanisms underlying the generation as well as persistence of neuropathic pain in HIV-SN exist. It is important to recognize that even mild neuropathic pain in this clinical population is associated with meaningful impairment in quality of life and function, which emphasizes the clinical importance of recognizing and treating the condition. The general approach to management of neuropathic pain in HIV-SN is the introduction of symptomatic analgesic therapy. There exist, however, few evidence-based analgesic options for HIV-SN based on available clinical data. Symptomatic treatment trials are increasingly recognized to have been potentially confounded by more robust placebo response than that observed in other neuropathic pain conditions. In the authors' experience, use of analgesic therapies with proven efficacy in other neuropathic pain conditions is appropriate, bearing in consideration potential pharmacokinetic interactions with the cART regimen. Combination analgesic regimens may also achieve meaningful analgesic responses, particularly when drugs with differing mechanisms of action are utilized. It is paramount that the patient is appropriately counseled regarding expectations and the anticipated benefit of analgesic therapy, as pain relief is often incomplete but clinically meaningful improvement in pain and function can be achieved.

[Successful treatment of HIV-associated chronic inflammatory demyelinating polyneuropathy by early initiation of highly active anti-retroviral therapy]

A 47-year-old man with HIV infection presented with lower leg dominant dysesthesia, muscle weakness and sensory ataxia of 3 month's duration. Nerve conduction studies (NCS) showed demyelination change in the median and tibial nerves and sensory nerve action potential (SNAP) in the sural nerve was not evoked. Somatosensory evoked potential (SEP) showed the delayed N9 latency. Diagnose of HIV-associated chronic inflammatory demyelinating polyneuropathy (CIDP) was made. Although the CD4 lymphocyte counts were relatively preserved (466/μl), highly active anti-retroviral therapy (HAART) was started according to a new guideline for the use of antiretroviral agents in HIV-1-infected adults and adolescents recommending early initiation of treatment. After six months, HIV1-RNA was not detected and the CD4 lymphocyte counts showed a recovering trend (585/μl). His symptoms had disappeared, except for dysesthesia in the tip of a toe. Repeated NCS demonstrated full recovery from the demyelination and appearance of SNAP in the sural nerve. The improvement of his symptoms and NCS findings has been maintained for two years. Although effectiveness of immunotherapies such as oral prednisone, high-dose immunoglobulins and plasmapheresis have been reported in HIV-associated CIDP, early initiation of HAART may be also important for favorable prognosis in HIV-associated CIDP.

Neuromuscular manifestations of HIV/AIDS

The human immunodeficiency virus (HIV) epidemic, now entering its fourth decade, affects approximately 33 million people living in both developed and resource-limited countries. Neurological complications of the peripheral nervous system are common in HIV-infected patients, and neuromuscular pathology is associated with significant morbidity. Peripheral neuropathy is the most common neuromuscular manifestation observed in HIV/AIDS, and in the antiretroviral era, its prevalence has increased. The purpose of this review was to describe the clinical spectrum of neuromuscular disorders in the setting of HIV infection and to provide an approach to diagnosis and management.

Influence of Age and Neurotoxic HAART Use on Frequency of HIV Sensory Neuropathy

Background. Sensory neuropathy (SN) is one of the most common AIDS-associated neurologic disorders especially in the era of highly active antiretroviral therapy (HAART). The aim of this study was to determine the prevalence of SN among highly-active-antiretroviral-therapy- (HAART-) experienced and HAART-naïve HIV-positive individuals and to investigate the relationship to demographic, clinical, and laboratory factors. Methods. 323 patients with HIV infection (142 on HAART and 181 HAART naïve) were enrolled in a cross-sectional neuropathy screening program. Data was collected using structured questionnaires which contained the brief peripheral neuropathy screening tool of AIDS Clinical Trial Group protocol. Neuropathy was defined by the presence of at least 1 clinical sign in a distal, symmetrical pattern. Patients were classified as symptomatic if they described aching, stabbing, or burning pain, paresthesia, or numbness in a similar distribution. Demographic, clinical, and laboratory details were documented as risk factors. Result. The prevalence of sensory neuropathy was 39.0% (126/323), (of which 29/126 (23%)) were symptomatic. Amongst those on HAART, 60/142 (42.3%) had SN compared to 66/181 (36.5%) HAART-naïve individuals (P = 0.29). On multivariate analyses, the independent associations with SN were increasing age (P = 0.03) and current exposure to stavudine (P = 0.00). Gender (P = 0.99) height (P = 0.07) use of HAART (P = 0.50), duration of HAART treatment (P = 0.10), and lower CD4 count (P = 0.12) were not associated with an increased SN risk. Conclusion. HIV SN remains common despite improved immunologic function associated with HAART and decreased neurotoxic HAART use. In this cross-sectional analysis, age and stavudine-based therapies were the independent risk factors.

Brain-derived neurotrophic factor modulates antiretroviral-induced mechanical allodynia in the mouse

Nucleoside reverse transcriptase inhibitors (NRTIs) are key components of HIV/AIDS treatment to reduce viral load. However, these drugs can induce chronic neuropathic pain, leading to increased morbidity in HIV patients. This study examines the role of brain-derived neurotrophic factor (BDNF) in the spinal dorsal horn (SDH) in development of mechanical allodynia in male C57BL/6J mice treated with the NRTI stavudine (d4T). After d4T administration, mice developed increased neuronal activity and BDNF expression in the SDH and hind paw mechanical allodynia that was exacerbated by intrathecal BDNF administration. Intrathecal BDNF alone also increased neuronal activity and caused mechanical allodynia. Because excess BDNF amplified d4T-induced mechanical allodynia and neuronal activity, the impact of decreasing BDNF in the SDH was investigated. After d4T, BDNF heterozygous mice were less allodynic than wild-type littermates, which was negated by intrathecal BDNF administration. Finally, pretreatment with intrathecal trkB-Fc chimera prior to d4T or administration of the tyrosine kinase inhibitor K252a 3 days after d4T blocked BDNF-mediated signaling, significantly attenuated the development of mechanical allodynia (trkB-Fc), and decreased neuronal activity (trkB-Fc and K252a). Taken together, these findings provide evidence that BDNF in the SDH contributes to the development of NRTI-induced painful peripheral neuropathy and may represent a new therapeutic opportunity.

[HIV-associated neuropathies]

Human immunodeficiency virus (HIV)-associated polyneuropathy has become the most common neurological complication of HIV infection and is one of the main risk factors for development of a neuropathy worldwide. Therefore HIV should always be considered as an underlying cause in patients with neuropathy. Many types of peripheral neuropathies are seen in HIV infection depending on the stage of infection. The inflammatory demyelinating neuropathies both acute (Guillain-Barré syndrome, GBS) and chronic (chronic inflammatory demyelinating neuropathy, CIDP) occur mainly at the time of seroconversion or early in the course of the disease while syndromes associated with opportunistic infections like CMV (i.e. polyradiculoneuropathy) occur in the late phase of HIV infection and are related to the loss of immune function. Distal symmetrical polyneuropathy (DSP) is the most common neuropathy in HIV-infected patients. We review the clinical manifestations, epidemiology, clinical diagnostics, pathophysiology and management strategies for HIV-associated polyneuropathies.

Benefits and risks of stavudine therapy for HIV-associated neurologic complications in Uganda

BACKGROUND

The frequency of HIV dementia in a recent study of HIV+ individuals at the Infectious Disease Institute in Kampala, Uganda, was 31%. Coformulated generic drugs, which include stavudine, are the most common regimens to treat HIV infection in Uganda and many other parts of Africa.

OBJECTIVE

To evaluate the benefits and risks of stavudine-based highly active antiretroviral therapy (HAART) for HIV-associated cognitive impairment and distal sensory neuropathy. The study compared neuropsychological performance changes in HIV+ individuals initiating HAART for 6 months and HIV- individuals receiving no treatment for 6 months. The risk of antiretroviral toxic neuropathy as a result of the initiation of stavudine-based HAART was also examined.

METHODS

At baseline, 102 HIV+ individuals in Uganda received neurologic, neuropsychological, and functional assessments; began HAART; and were followed up for 6 months. Twenty-five HIV- individuals received identical clinical assessments and were followed up for 6 months.

RESULTS

In HIV+ individuals, there was improvement in verbal memory, motor and psychomotor speed, executive thinking, and verbal fluency. After adjusting for differences in sex, HIV+ individuals demonstrated significant improvement in the Color Trails 2 test (p = 0.025) compared with HIV- individuals. Symptoms of neuropathy developed in 38% of previously asymptomatic HIV+ patients after initiation of the stavudine-based HAART.

CONCLUSIONS

After the initiation of highly active antiretroviral therapy (HAART) including stavudine, HIV+ individuals with cognitive impairment improve significantly as demonstrated by improved performance on a test of executive function. However, peripheral neurotoxicity occurred in 30 patients, presumably because of stavudine-based HAART, suggesting the need for less toxic therapy.

Human immunodeficiency virus protease inhibitors and risk for peripheral neuropathy

OBJECTIVE

Two recent analyses found that exposure to protease inhibitors (PIs) in the context of antiretroviral (ARV) therapy increased the risk for distal sensory polyneuropathy (DSPN) in subjects with human immunodeficiency virus (HIV) infection. These findings were supported by an in vitro model in which PI exposure produced neurite retraction and process loss in dorsal root ganglion sensory neurons. Confirmation of peripheral nerve toxicity with PIs could substantially limit their long-term use in highly active ARV therapy.

METHODS

We evaluated current and past exposure to PIs as a risk factor for DSPN in 1,159 HIV-infected individuals enrolled in a large, prospective, observational, multicenter study. Signs of DSPN were ascertained by neurological examination. Subjects were grouped into categories according to past and current exposure to any ARV and to PIs. We included disease indicators such as nadir CD4, plasma viral load, and duration of HIV infection, as well as advancing age and exposure to dideoxynucleoside ARVs in multivariate models.

RESULTS

In univariate analyses, both past and current PI exposure significantly increased the risk for DSPN. However, after adjusting for previously validated concomitant risk factors in multivariate models, none of the PI exposure groups was more likely to have DSPN than ARV naive subjects. A secondary evaluation of duration of PI use and exposure to individual PI drugs was similarly nonsignificant in multivariate models, except for small effects of amprenavir and lopinavir.

INTERPRETATION

Evaluation of concomitant risks for HIV DSPN suggests that the independent risk attributable to PIs, if any, is small. This risk must be weighed against the important role of PIs in modern ARV therapy regimens.

[Treatment of neuropathic pain in HIV-infected patients]

Neuropathic pain of various etiologies is a frequent symptom in HIV-infected patients that is underdiagnosed and inadequately treated. It requires a multidisciplinary pain approach based on psychosocial factors, diet and exercise, etiologic treatment whenever possible, symptomatic medical treatment, and sometimes, interventional techniques. Medical treatment should be individualized and introduced gradually, with a mind to potential drug interactions. Neuropathic pain responds poorly to conventional analgesics, such as nonsteroidal antiinflammatory drugs and opiates; tricyclic antidepressants and anticonvulsants are the drugs of choice. Before establishing an analgesic treatment, possible drug interactions should be ruled out, mainly those occurring with antiretroviral agents.

Initiation of antiretroviral therapy at CD4 cell counts >/=350 cells/mm3 does not increase incidence or risk of peripheral neuropathy, anemia, or renal insufficiency

BACKGROUND

US guidelines recommend deferring initiation of highly active antiretroviral therapy (HAART) for most patients with CD4 counts >350 cells/mm in part because of concerns about antiretroviral toxicity.

METHODS

Incidence rates of peripheral neuropathy, anemia, and renal insufficiency in a cohort of 2165 patients followed more than 3 years (mean) were analyzed in multivariate Cox proportional hazards models by CD4 cell counts at initiation of HAART. A nested cohort of 895 patients restricted to study participants who did or did not start HAART within a CD4 cell count stratum were also compared.

RESULTS

Incidence and risks of all 3 comorbidities decreased with initiation of HAART at CD4 counts >200 cells/mm versus <200 cells/mm. Incidence and risks of renal insufficiency were similar with HAART initiation at CD4 counts >/=350 cells/mm versus 200 to 349 cells/mm, but risk of peripheral neuropathy and anemia were further decreased in persons starting HAART at a CD4 count >/=350 cells/mm. The incidence of these conditions was highest during the first 6 months of treatment at any CD4 cell count and declined up to 19-fold with further therapy.

DISCUSSION

Initiating HAART at CD4 cell counts >/=200 cells/mm reduced the incidence and risk of the 3 comorbid conditions and for anemia and peripheral neuropathy as well by starting at CD4 counts >/=350 cells/mm. The incidence of each condition decreased rapidly and remained low with increasing time on HAART.

The Risk of Developing Peripheral Neuropathy Induced by Nucleoside Reverse Transcriptase Inhibitors Decreases over Time: Evidence from the Delta Trial

Background

Peripheral neuropathy (PN) in HIV-infected individuals is thought be due to a toxic effect on mitochondria induced by some nucleoside reverse transcriptase inhibitors (NRTI).

Methods

A time-to-event analysis was performed using data from the Delta trial to study the incidence of PN in HIV-infected individuals receiving zidovudine (AZT) alone or in combination with didanosine (ddI) or zalcitabine (ddC). In an on-treatment analysis, changes in the incidence of PN by duration of treatment were directly estimated using a flexible parametric survival model.

Results

A total of 3,195 patients (total follow-up 4,593 person-years) were included in the analysis. AZT+ddC was associated with a higher incidence of PN (6.2 cases/100 person-years) compared with AZT monotherapy (3.0 cases/100 person-years) and AZT+ddI (2.2 cases/100 person-years). The risk of PN peaked around day 90 following randomization (at 8.9 events/100 person-years in the AZT+ddC arm). PN was also associated with age at entry (hazard ratio (HR)=2.35 for those aged 35–44 years compared with <30) and current CD4+ T-cell count (HR=2.27 for CD4+ T-cell counts <150 cell/mm3 compared with >350).

Conclusion

Our findings challenge the common supposition that PN arises from cumulative exposure to NRTIs. We found that patients who developed PN tended to do so shortly after exposure to antiretroviral therapy. Therefore, our results support the hypothesis of a susceptibility in a subgroup of patients. These results will be of direct interest to those working in resource-limited countries where potentially neurotoxic dideoxynucleosides are still widely used.

Managing HIV peripheral neuropathy

Peripheral nerve disorders are frequent complications of HIV disease. Distal symmetrical polyneuropathy (DSP) is the most common peripheral nerve disorder associated with HIV and occurs in over one third of infected patients but may occur in up to 67% if asymptomatic patients are included. Risk factors for DSP include increased age, advanced HIV disease, and history of "d-drugs" or other neurotoxic drugs. The primary manifestations of polyneuropathy are slowly progressive numbness and paresthesias, with burning sensations in the feet usually in a symmetrical pattern. The etiology of HIV-associated DSP is unknown, although neurotoxic effects of cytokines, toxicity of HIV proteins, and mitochondrial damage have been implicated. The current treatment for HIV-associated DSP is symptomatic, with pain modifying medications, including anti-inflammatory agents, opioids, antidepressants, antiepileptics, topical anesthetics, and capsaicin. Sustained virologic control may improve DSP. Novel therapies such as -acetyl-l-carnitine or neurotrophic factors are being studied for treatment of DSP.

Neurologic and psychiatric complications of antiretroviral agents

Advances in highly active antiretroviral therapy (HAART) aim to improve the efficacy of HIV drugs as well as the quality of life in HIV-infected patients. Neurologic and psychologic disturbances that occur because of HIV disease and therapy are of great concern, and because they can overlap and are often difficult to distinguish, their pathogenesis is not clearly understood. Furthermore, these complications can lead to decreased adherence, thereby interfering with treatment outcomes. Antiretrovirals, including nonnucleoside reverse transcriptase inhibitors, can penetrate the central nervous system (CNS) and suppress viral replication, but they can also exacerbate CNS side effects and neuropsychiatric symptoms. When deciding which HAART drug combination is most appropriate for a patient, clinicians must consider the individual's risk of CNS complications together with the efficacy of the specific HAART regimen.

HIV-associated neuropathic pain: epidemiology, pathophysiology and management

Peripheral neuropathy is associated with numerous systemic illnesses including HIV infection. Neuropathic pain constitutes approximately 25-50% of all pain clinic visits. Distal symmetrical polyneuropathy (DSP) is the most common form of peripheral neuropathy in individuals with HIV infection. DSP is distinguished from other forms of neuropathy on the basis of history and neurological examination. The pain associated with DSP can be debilitating. Therefore, it is important to diagnose HIV-associated DSP properly and treat the neuropathic pain in order to improve quality of life. We review the clinical manifestations, epidemiology, pathophysiology and management strategies for HIV-associated DSP.

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.

Painful and non-painful neuropathy in HIV-infected patients: an analysis of somatosensory nerve function

Fifteen to 50% of AIDS-patients suffer from distal predominantly sensory neuropathy (DSP), which is commonly associated with painful symptoms. In the present study, we have focused on the function of fine calibre nerve channels, in 36 consecutive HIV-1-infected patients with painful (PPN) (n=20; 54%) and non-painful (PN) (n=16) sensory neuropathy, assessed by clinical, quantitative thermal testing (QTT) (31/36), and peripheral nerve conduction examination (32/36). Control QTT data were obtained from 49 healthy subjects with a corresponding age- and sex distribution. Demographics, antiviral treatment, immunological status, and nerve conduction examination did not differ between patients with and without painful symptoms. Hypoaesthesia to warmth, cold, and heat pain was observed in both neuropathy groups when compared to healthy controls. However, the perception threshold to warmth was more often impaired (p<0.01) and the level of impairment was more pronounced (p<0.001) in patients with painful neuropathy. Furthermore, increased pain sensitivity to cold was found only in patients with painful symptoms (p<0.05). An abnormal outcome of any QTT parameter was found in all patients with pain, but only among 62% of patients without pain, p<0.01, and the cumulative frequency of abnormalities in any of the four thermal percepts (warmth, cold, heat pain, and cold pain) was higher in patients with painful symptoms, p<0.0001. This study demonstrates a more pronounced impairment of C-fibre-mediated innocuous warm perception in patients with painful neuropathy, which in the setting of impaired or absent heat pain perception suggests a more generalised loss of function in somatosensory C-fibre channels.

Medication-induced peripheral neuropathy

Although not very common, medication-induced neuropathy is a treatable condition and, therefore, is important to identify. Medications continue to grow in number and expand in usage; consequently, toxic neuropathy continues to be relevant to neurologists. Many agents have toxicities that are tolerated because the treatments are necessary, such as therapies for HIV and malignancy. Additional agents to prevent or ameliorate the toxic neuropathy are being sought and trials are ongoing. Certain patients, however, may be at high risk for peripheral nerve toxicity due to genetic factors or another underlying neuropathy. Newer drug-delivery methods, such as viral transfection, may produce less toxicity in the future. The underlying pathomechanisms remain incompletely elucidated; however, apoptosis is emerging as an important final pathway in some forms of toxic neuropathy. Although most cases demonstrate acute or subacute onset after exposure, recent experiences with statin drugs raise the possibility of occult toxic causes of chronic idiopathic neuropathy.

AIDS and AIDS-treatment neuropathies

AIDS and AIDS-treatment neuropathies are common in individuals infected with HIV. As patients live longer due to improved antiretroviral therapies, the impact of painful neuropathy on patients' lives may increase. Several antiretroviral medications are known to cause toxic neuropathy in patients with AIDS, but this may be outweighed by the beneficial effects of viral suppression. Current theories on the pathogenesis of AIDS neuropathies include mitochondrial toxicity secondary to gamma-DNA polymerase inhibition and subsequent abnormal mitochondrial DNA synthesis. Treatment of AIDS neuropathies is directed toward relief of symptoms; however, new evidence suggests that aggressive antiretroviral therapy may also be effective.

Severity of HIV-associated neuropathy is associated with plasma HIV-1 RNA levels

OBJECTIVE

To determine if there is an association between plasma HIV-1 RNA levels and severity of HIV-associated distal symmetrical polyneuropathy (DSP).

DESIGN

Substudy of AIDS Clinical Trials Group Protocol 291, a double-blind, placebo-controlled study of recombinant human nerve growth factor for the treatment of painful DSP.

METHODS

Two-hundred and thirty-six subjects had plasma HIV-1 RNA load assayed at baseline. Mean and maximum neuropathic pain was assessed once daily by the Gracely Pain Scale. Other measures included subjects' global pain assessment and quantitative sensory tests (QST). These values were correlated with baseline HIV-1 RNA levels.

RESULTS

Among 168 subjects with detectable plasma HIV-1 RNA, there was a significant correlation between plasma HIV-1 RNA and the severity of maximum and global pain, and toe cooling thresholds. Maximum and global pain assessment correlated with plasma HIV-1 RNA in individuals with detectable viral load (r, 0.162 and 0.194; P = 0.04 and 0.01, respectively).

CONCLUSIONS

There is an association between plasma HIV-1 RNA levels and the severity of pain and QST results in HIV-associated DSP. Further studies are needed to determine if aggressive use of antiretroviral drugs, including the use of dideoxynucleosides, may be of benefit to prevent or improve peripheral neuropathy.

Neurological manifestations of HIV-1 infection in the HAART era

Neurologic complications in patients with AIDS are diverse and include opportunistic infections and lymphoma, as well as HIV-related peripheral neuropathy, myelopathy, and dementia. Improved prophylaxis and antiretroviral therapies have modified the approach to neurologic disease in the setting of AIDS.

AIDS and AIDS-treatment neuropathies

AIDS and AIDS-treatment neuropathies are common in individuals infected with HIV. As patients live longer due to improved antiretroviral therapies, the impact of painful neuropathy on patients' lives may increase. Several antiretroviral medications are known to cause toxic neuropathy in AIDS patients; but this may be outweighed by the beneficial effects of viral suppression. Current theories on the pathogenesis of AIDS neuropathies include mitochondrial toxicity secondary to gamma-DNA polymerase inhibition and subsequent abnormal mitochondrial DNA synthesis. Treatment of AIDS neuropathies is directed toward relief of symptoms, however, new evidence suggests that aggressive antiretroviral therapy may also be effective.

Peripheral neuropathy and antiretroviral drugs

Patients treated with nucleoside analogue reverse transcriptase inhibitors (NRTIs) develop a varying degree of myopathy or neuropathy after long-term therapy. Zidovudine (AZT) causes myopathy; zalcitabine (ddC), didanosine (ddl) and lamuvidine (3TC) cause neuropathy; stavudine (d4T) and fialuridine (FIAU) cause neuropathy or myopathy and lactic acidosis. The tissue distribution of phosphorylases responsible for phosphorylation of NRTIs relates to their selective tissue toxicity. The myopathy is characterized by muscle wasting, myalgia, fatigue, weakness and elevation of CK. The neuropathy is painful, sensory and axonal. In vitro, NRTIs inhibit the gamma-DNA polymerase, responsible for replication of mtDNA, and cause mtDNA dysfunction. In vivo, patients treated with AZT, the best studied NRTI, develop a mitochondrial myopathy with mtDNA depletion, deficiency of COX (complex IV), intracellular fat accumulation, high lactate production and marked phosphocreatine depletion, as determined with in vivo MRS spectroscopy, due to impaired oxidative phosphorylation. Animals or cultured cells treated with NRTIs develop neuropathy, myopathy, or cell destruction with similar changes in the mitochondria. There is evidence that the NRTI-related neuropathy is also due to mitochondrial toxicity. The NRTIs (AZT, ddC, ddl, d4T, 3TC) contain azido groups that compete with natural thymidine triphosphate as substrates of DNA pol-gamma and terminate mtDNA synthesis. In contrast, FIAU that contains 3'-OH groups serves as an alternate substrate for thymidine triphosphate with DNA pol-gamma and is incorporated into the DNA causing permanent mtDNA dysfunction. The NRTI-induced mitochondrial dysfunction has an influence on the clinical application of these agents, especially at high doses and when combined. They have produced in humans a new category of acquired mitochondrial toxins that cause clinical manifestations resembling the genetic mitochondrial disorders.

Neuropathy in HIV infection

Peripheral nerve complications in patients infected with HIV usually result from the virus itself, or are due to some of the antiretroviral drugs (zalcitabine, didanosine or stavudine). It may be difficult to distinguish between these two aetiologies on clinical or neurophysiological criteria. Since they are a significant cause of morbidity, a number of studies have looked at agents used for symptomatic control. More recently, there has been a focus on treatments that improve nerve function, including recombinant human nerve growth factor and the reduction of HIV viral load with antiretroviral drugs.