Is skin biopsy a predictor of transition to symptomatic HIV neuropathy?: A longitudinal study

Clinical and paraclinical features of small fiber neuropathy in Sjögren's syndrome

Sjögren's syndrome is a potentially treatable cause of Small Fiber Neuropathy (SFN)-a condition that severely affects patients' quality of life. We therefore aimed to characterize patients with SFN and Sjögren's syndrome to raise awareness of this disease and facilitate its early recognition as an essential step for appropriate treatment. In 97 SFN patients (median age 48 years, 77% female), we studied the clinical features associated with Sjögren's syndrome compared to the idiopathic SFN subtype. According to the current ACR/EULAR classification criteria (Shiboski et al., Ann Rheum Dis 76:9-16, 2017), 24/97 individuals (25%, median age 48.5 years, 75% female) were diagnosed with Sjögren's syndrome. We did not observe any differences in SFN-defining sensory plus symptoms. Furthermore, intraepidermal nerve fiber densities (IENFD) were significantly lower in patients with SFN and Sjögren's syndrome (mean 2.6 ± 1.2/mm) compared to patients with idiopathic SFN (mean 3.2 ± 1.5/mm; p = 0.048). There were no significant group differences when analyzing cerebrospinal fluid (CSF) parameters. We conclude that Sjögren's syndrome-associated SFN is difficult to distinguish from idiopathic forms based on initial clinical symptoms and CSF results. However, lower IENFD values in patients with Sjögren's syndrome-associated SFN might indicate a distinct different pathomechanism in this entity compared to idiopathic SFN.

Association of painful human immunodeficiency virus distal sensory polyneuropathy with aberrant expectation of pain relief: functional magnetic resonance imaging evidence

Mechanisms underlying chronic neuropathic pain associated with HIV-associated distal sensory polyneuropathy are poorly understood, yet 40% of those with distal neuropathy (or 20% of all people with HIV) suffer from this debilitating condition. Central pain processing mechanisms are thought to contribute to the development of HIV neuropathic pain, yet studies investigating central mechanisms for HIV neuropathic pain are few. Considering the motivational nature of pain, we aimed to examine the degree to which expectation of pain onset and expectation of pain offset are altered in sixty-one male patients with HIV-related distal sensory polyneuropathy with (N = 30) and without (N = 31) chronic neuropathic pain. By contrasting painful (foot) and non-painful (hand) sites between those with and without neuropathic pain, we could identify unique neural structures that showed altered activation during expectation of pain offset or relief. Our results showed no evidence for peripheral mechanisms evidenced by lack of significant between group differences in thermo-sensation, subjective pain response or epidermal nerve fibre density. Likewise, we found no significant differences between groups in subjective or brain mechanisms underlying the expectation of pain onset. Conversely, we found significant interaction within right anterior insula during expectation of pain offset in our study in that individuals in the pain group compared to the no-pain group exhibited increased anterior insula activation on the painful compared to the non-painful site. Our findings are consistent with abnormal processing of expectation of pain offset or abnormal pain relief-related mechanisms potentially due to increased emotional distress regarding the experience of chronic endogenous pain.

Large Mitochondrial DNA Deletions in HIV Sensory Neuropathy

OBJECTIVE

The primary objective of this study was to evaluate the correlation of large mitochondrial DNA (mtDNA) deletions in skin samples of people with HIV (PWH) with measures of neuropathy and prior exposure to therapy. We hypothesized that deletions would be associated with neuropathy. As secondary objectives, we determined the correlation of deletion burden with demographic data and neuropathy measures.

METHODS

In this retrospective cohort study, we measured the accumulation of large mtDNA deletions in skin biopsies from PWH recruited as part of the AIDS Clinical Trials Group (ACTG). Our cohort includes individuals with and without sensory neuropathy, as well as individuals with normal or abnormal skin biopsies. Skin biopsies, sural and peroneal nerve conduction studies, total neuropathy score, and deletion burden scores were measured, along with baseline demographic data such as age, CD4+ cell count, viral counts, and prior nucleoside reverse transcriptase inhibitor exposures.

RESULTS

Sixty-seven PWH were enrolled in the study. The mean age of the cohort (n = 67) was 44 years (SD 6.8, range 32-65 years), and 9 participants were female. The mean CD4+ T-cell count was 168 cells/mm³ (SD 97 cells/mm³, range 1-416 cells/mm³) and mean viral load was 51,129 copies/mL (SD 114,586 copies/mL, range 147-657,775 copies/mL). We determined that there was a correlation between the total mtDNA deletion and intraepidermal nerve fiber density (IENFD) (r = -0.344, p = 0.04) and sural nerve amplitude (r = -0.359, p = 0.004).

CONCLUSIONS

Both IENFD and sural nerve amplitude statistically correlate with mitochondrial mutation burden in PWH, specifically in those with HIV-associated sensory neuropathy as assessed by skin biopsy.

Current View of Diagnosing Small Fiber Neuropathy

Small fiber neuropathy (SFN) is a disorder of the small myelinated Aδ-fibers and unmyelinated C-fibers [5, 6]. SFN might affect small sensory fibers, autonomic fibers or both, resulting in sensory changes, autonomic dysfunction or combined symptoms [7]. As a consequence, the symptoms are potentially numerous and have a large impact on quality of life [8]. Since diagnostic methods for SFN are numerous and its pathophysiology complex, this extensive review focusses on categorizing all aspects of SFN as disease and its diagnosis. In this review, sensitivity in combination with specificity of different diagnostic methods are described using the areas under the curve. In the end, a diagnostic work-flow is suggested based on different phenotypes of SFN.

Human immunodeficiency virus-related peripheral neuropathy: A systematic review and meta-analysis

BACKGROUND AND PURPOSE

Human immunodeficiency virus (HIV)-associated neurological syndromes occur in affected individuals as a consequence of primary HIV infection, opportunistic infections, inflammation and as an adverse effect of some forms of antiretroviral treatment (ART). The aim of this systematic review was to establish the epidemiological characteristics, clinical features, pathogenetic mechanisms and risk factors of HIV-related peripheral neuropathy (PN).

METHODS

A systematic, computer-based search was conducted using the PubMed database. Data regarding the above parameters were extracted. Ninety-four articles were included in this review.

RESULTS

The most commonly described clinical presentation of HIV neuropathy is the distal predominantly sensory polyneuropathy. The primary pathology in HIVPN appears to be axonal rather than demyelinating. Age and treatment with medications belonging in the nucleoside analogue reverse transcriptase class are risk factors for developing HIV-related neuropathy. The pooled prevalence of PN in patients naïve to ARTs was established to be 29% (95% CI: 9%-62%) and increased to 38% (95% confidence interval [CI]: 29%-48%) when looking into patients at various stages of their disease. More than half of patients with HIV-related neuropathy are symptomatic (53%, 95% CI: 41%-63%). Management of HIV-related neuropathy is mainly symptomatic, although there is evidence that discontinuation of some types of ART, such as didanosine, can improve or resolve symptoms.

CONCLUSIONS

Human immunodeficiency virus-related neuropathy is common and represents a significant burden in patients' lives. Our understanding of the disease has grown over the last years, but there are unexplored areas requiring further study.

Intraepidermal Nerve Fiber Analysis in Human Patients and Animal Models of Peripheral Neuropathy: A Comparative Review

Analysis of intraepidermal nerve fibers (IENFs) in skin biopsy samples has become a standard clinical tool for diagnosing peripheral neuropathies in human patients. Compared to sural nerve biopsy, skin biopsy is safer, less invasive, and can be performed repeatedly to facilitate longitudinal assessment. Intraepidermal nerve fiber analysis is also more sensitive than conventional nerve histology or electrophysiological tests for detecting damage to small-diameter sensory nerve fibers. The techniques used for IENF analysis in humans have been adapted for large and small animal models and successfully used in studies of diabetic neuropathy, chemotherapy-induced peripheral neuropathy, HIV-associated sensory neuropathy, among others. Although IENF analysis has yet to become a routine end point in nonclinical safety testing, it has the potential to serve as a highly relevant indicator of sensory nerve fiber status in neurotoxicity studies, as well as development of neuroprotective and neuroregenerative therapies. Recently, there is also interest in the evaluation of IENF via skin biopsy as a biomarker of small fiber neuropathy in the regulatory setting. This article provides an overview of the anatomic and pathophysiologic principles behind IENF analysis, its use as a diagnostic tool in humans, and applications in animal models with focus on comparative methodology and considerations for study design.

The Potential Role of Sensory Testing, Skin Biopsy, and Functional Brain Imaging as Biomarkers in Chronic Pain Clinical Trials: IMMPACT Considerations

Valid and reliable biomarkers can play an important role in clinical trials as indicators of biological or pathogenic processes or as a signal of treatment response. Currently, there are no biomarkers for pain qualified by the U.S. Food and Drug Administration or the European Medicines Agency for use in clinical trials. This article summarizes an Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials meeting in which 3 potential biomarkers were discussed for use in the development of analgesic treatments: 1) sensory testing, 2) skin punch biopsy, and 3) brain imaging. The empirical evidence supporting the use of these tests is described within the context of the 4 categories of biomarkers: 1) diagnostic, 2) prognostic, 3) predictive, and 4) pharmacodynamic. Although sensory testing, skin punch biopsy, and brain imaging are promising tools for pain in clinical trials, additional evidence is needed to further support and standardize these tests for use as biomarkers in pain clinical trials.

PERSPECTIVE

The applicability of sensory testing, skin biopsy, and brain imaging as diagnostic, prognostic, predictive, and pharmacodynamic biomarkers for use in analgesic treatment trials is considered. Evidence in support of their use and outlining problems is presented, as well as a call for further standardization and demonstrations of validity and reliability.

Clinical, histological, and biochemical predictors of postsurgical neuropathic pain

Surgical nerve injury sometimes leads to chronic postsurgical neuropathic pain (CPSNP). The risk factors for this condition are not well understood. We prospectively assessed 46 patients scheduled for iliac crest bone harvest, 2 days (D2) and 3 months (M3) after surgery, to determine the time course of nerve fiber degeneration and expression of the TNF-α and NGF genes in skin punch biopsies. Mechanical and thermal detection and pain thresholds were evaluated at D2 and M3, by quantitative sensory testing. Skin punch biopsies were also obtained from the thighs ipsilateral and contralateral to iliac crest bone harvest. Intraepidermal nerve fiber density (IENFD) and cutaneous TNF-α and NGF gene expression were analyzed. Forty-five volunteers matched for age, sex, skin color were examined as controls. Chronic postsurgical neuropathic pain was defined as pain in an area of hypesthesia with a positive Douleur Neuropathique 4 questionnaire score. Overall, 73% (N = 32) of patients developed hypesthesia and 40% (N = 13) of these patients had developed CPSNP at M3. Quantitative sensory testing results, IENFD, and skin TNF-α and NGF gene expression at D2 and M3 did not differ between patients with and without CPSNP. However, in patients with CPSNP, burning, compression, and pain provoked by brushing were correlated with IENFD at M3, suggesting a possible association between partial nerve lesions and more intense CPSNP, than with total nerve lesion. Furthermore, preoperative pain and opioid use were higher in patients who developed CPSNP than in those without CPSNP. These findings suggest that the predictors of CPSNP development are clinical rather than histological or biochemical.

Treatment of human immunodeficiency virus-related peripheral neuropathy with Scrambler Therapy: a case report

Peripheral neuropathy is one of the most common neurological complications of HIV infection with a 30-60% lifetime prevalence. Newer HIV drugs cause less peripheral neuropathy, but patients are now living long enough to develop concomitant diabetes-related, vascular-related, and chemotherapy-related neuropathy so it continues as a major debilitating issue. Recent national CDC guidelines have stressed the importance of non-opioid therapies, especially in this population that may have had drug abuse problems. We treated a 52-year-old man who had severe disabling classic peripheral neuropathy since 1998 with Scrambler Therapy (Calmare), an FDA-cleared peripheral non-invasive neuromodulation device. His pain rapidly improved, as did his motor and sensory function, with just four 45-min treatments, and he was able to come off opioids for the first time in years. When his pain returned six months later, only two treatments were needed to resolve it. This represents the first published use of this novel, inexpensive, and non-invasive pain modality in HIV peripheral neuropathy, and should engender further trials.

Small fiber neuropathy: Getting bigger!

Etiological and clinical heterogeneity of small fiber neuropathy (SFN) precludes a unifying approach and necessitates reliance on recognizable clinical syndromes. Symptoms of SFN arise from dysfunction in nociception, temperature, and autonomic modalities. This review focuses on SFN involving nociception and temperature, examining epidemiology, etiology, clinical presentation, diagnosis, pathophysiology, and management. Prevalence of SFN is 52.95 per 100,000 population, and diabetes and idiopathic are the most common etiologies. Dysesthesia, allodynia, pain, burning, and coldness sensations frequently present in a length-dependent pattern. Additional autonomic features in gastrointestinal, urinary, or cardiovascular systems are frequent but poorly objectified. SFN is diagnosed by intraepidermal nerve fiber density and quantitative sensory and autonomic tests in combination with normal nerve conduction. Pathophysiological understanding centers on sodium channel dysfunction, and genetic forms are beginning to be understood. Treatment is directed at the underlying etiology supported by symptomatic treatment using antidepressants and anticonvulsants. Little is known about long-term outcomes, and systematic cohort studies are needed.

Epidermal nerve fiber density, oxidative stress, and mitochondrial haplogroups in HIV-infected Thais initiating therapy

OBJECTIVE

We explored associations between mitochondrial DNA (mtDNA) haplogroups, epidermal nerve fiber density (ENFD), and HIV-associated sensory neuropathy (HIV-SN) in a randomized trial of Thai patients initiating antiretroviral therapy (ART).

DESIGN

The South East Asia Research Collaboration with Hawaii 003 study evaluated toxicity of nucleoside reverse transcriptase inhibitors (stavudine vs. zidovudine vs. tenofovir). We present secondary analyses of mtDNA haplogroups and ENFD changes.

METHODS

ENFD, peripheral blood mononuclear cell mitochondrial complex I and IV, and 8-oxo-deoxyguanine (8-oxo-dG) were quantified. Peripheral blood mononuclear cell mtDNA sequences were obtained for haplogroup determination. Multivariate regression of ENFD change was performed.

RESULTS

Paired ENFD was available from 118 patients. Median age, CD4 cell count, and height at entry were 34 years, 172 cells/μl, and 162 cm, respectively. Major haplogroups included M (42%), F (21%), and B (16%). Baseline ENFD, CD4 cell count, randomized ART, and biomarkers did not differ by haplogroup. Haplogroup B patients were older (P=0.02) at baseline, and had an increase in median ENFD (+1.5 vs. -2.9 fibers/mm; P=0.03) and 8-oxo-dG break frequency (+0.05 vs. 0.00; P=0.05) compared to other haplogroups. In a multivariate model, haplogroup B was associated with increased ENFD (β=3.5, P=0.009) at week 24, whereas older age (P=0.02), higher baseline CD4 cell count, (P=0.03), higher complex I level (P=0.03), and higher ENFD (P<0.001) at baseline were all associated with decreased ENFD. Three of the six HIV-SN cases were haplogroup B (P=0.05).

CONCLUSIONS

Thai persons belonging to mtDNA haplogroup B had increased ENFD and 8-oxo-dG on ART, and were more likely to develop HIV-SN. These results suggest that mtDNA variation influences early oxidative damage and ENFD changes.

Reduced intraepidermal nerve fiber density in patients with chronic ischemic pain in peripheral arterial disease

Chronic ischemic pain in peripheral arterial disease (PAD) is a leading cause of pain in the lower extremities. A neuropathic component of chronic ischemic pain has been shown independent of coexisting diabetes. We aimed to identify a morphological correlate potentially associated with pain and sensory deficits in PAD. Forty patients with symptomatic PAD (Fontaine stages II-IV), 20 with intermittent claudication (CI), and 20 with critical limb ischemia (CLI) were enrolled; 12 volunteers served as healthy controls. All patients were examined using pain scales and questionnaires. All study participants underwent quantitative sensory testing (QST) at the distal calf and skin punch biopsy at the distal leg for determination of intraepidermal nerve fiber density (IENFD). Additionally, S100 beta serum levels were measured as a potential marker for ischemic nerve damage. Neuropathic pain questionnaires revealed slightly higher scores and more pronounced pain-induced disability in CLI patients compared to CI patients. QST showed elevated thermal and mechanical detection pain thresholds as well as dynamic mechanical allodynia, particularly in patients with advanced disease. IENFD was reduced in PAD compared to controls (P<0.05), more pronounced in the CLI subgroup (CLI: 1.3 ± 0.5 fibers/mm, CI: 2.9 ± 0.5 fibers/mm, controls: 5.3 ± 0.6 fibers/mm). In particular, increased mechanical and heat pain thresholds negatively correlated with lower IENFD. Mean S100 beta levels were in the normal range but were higher in advanced disease. Patients with chronic ischemic pain had a reduced IENFD associated with impaired sensory functions. These findings support the concept of a neuropathic component in ischemic pain.

Contribution of QSART to the diagnosis of small fiber neuropathy

INTRODUCTION

We evaluated incorporation of the quantitative sudomotor axon reflex test (QSART) into the diagnostic criteria for small fiber neuropathy (SFN) as an addition to quantitative sensory testing (QST) and intraepidermal nerve fiber density (IENFD) testing.

METHODS

One hundred one patients with clinically suspected SFN underwent QSART, QST, and skin biopsy. The diagnostic yield of existing SFN criteria in these patients was compared with criteria incorporating QSART. The new combined diagnostic criteria were evaluated.

RESULTS

SFN was diagnosed in 38 of the 101 patients (38%) using current criteria. Addition of QSART existing SFN criteria resulted in an increased diagnostic yield to 67 patients (66%). Applying new SFN criteria requiring abnormality in at least 2 assessments among QSART, QST, and IENFD resulted in a diagnosis of SFN in 57 patients (56%).

CONCLUSION

Assessment of both somatic and peripheral autonomic small nerve fibers enhances diagnostic criteria for SFN.

HIV-related neuropathy: current perspectives

Distal symmetric polyneuropathy (DSP) related to human immunodeficiency virus (HIV) is one of the most common neurologic complications of HIV, possibly affecting as many as 50% of all individuals infected with HIV. Two potentially neurotoxic mechanisms have been proposed to play a crucial role in the pathogenesis of HIV DSP: neurotoxicity resulting from the virus and its products; as well as adverse neurotoxic effects of medications used in the treatment of HIV. Clinically, HIV DSP is characterized by a combination of signs and symptoms that include decreased deep tendon reflexes at the ankles and decreased sensation in the distal extremities as well as paresthesias, dysesthesias, and pain in a symmetric stocking-glove distribution. These symptoms are generally static or slowly progressive over time, and depending on the severity, may interfere significantly with the patient's daily activities. In addition to the clinical picture, nerve conduction studies and skin biopsies are often pursued to support the diagnosis of HIV DSP. Anticonvulsants, antidepressants, topical agents, and nonspecific analgesics may help relieve neuropathic pain. Specifically, gabapentin, lamotrigine, pregabalin, amitriptyline, duloxetine, and high-dose topical capsaicin patches have been used in research and clinical practice. Further research is needed to elucidate the pathogenesis of HIV DSP, thus facilitating the development of novel treatment strategies. This review discusses the epidemiology, pathophysiology, clinical findings, diagnosis, and management of DSP in the setting of HIV.

Skin matters: identifying pain mechanisms and predicting treatment outcomes

The skin acts as a complex sensory organ. The emerging new data on peripheral pain mechanisms from within the skin is presented. This data has led to new insights into the potential pain mechanisms for various pain conditions including neuropathic pain (from small fiber neuropathies) and Complex Regional Pain Syndrome. The somatosensory neurons that innervate our skin constantly update our brains on the objects and environmental factors that surround us. Cutaneous sensory neurons expressing nociceptive receptors such as transient receptor potential vanilloid 1 channels and voltage-gated sodium channels are critical for pain transmission. Epidermal cells (such as keratinocytes, Langerhans cells, and Merkel cells) express sensor proteins and neuropeptides; these regulate the neuroimmunocutaneous system and participate in nociception and neurogenic inflammation. In the past two decades, there has been widespread use of modalities such as punch skin biopsies, quantitative sensory testing, and laser-evoked potentials to evaluate small caliber nerve fibers. This paper explores these laboratory techniques as well as the phenomenon of small fiber neuropathy. Treatment using transdermal drug delivery is discussed. There is potential for these findings to predict treatment outcomes in clinical practice and to develop new therapies for different pain conditions. These findings should enhance the physician's ability to evaluate and treat diverse types of pain.

The cutaneous nerve biopsy: technical aspects, indications, and contribution

Skin biopsy with a 3mm disposable circular punch is easy to perform and allows, after proper processing, the visualization of epidermal, dermal, and sweat gland nerve fibers. A technique of sampling the epidermis alone by applying a suction capsule, the "blister" technique, has also been developed. It is most common to stain immunohistochemically for the pan-axonal marker protein gene product 9.5 (PGP 9.5), an ubiquitin C-terminal hydroxylase. The sections are then observed and analyzed with bright-field microscopy or with indirect immunofluorescence with or without confocal microscopy. Most studies report quantification of intraepidermal nerve fiber density displayed in bright-field microscopy. Normative values have been established, particularly from the distal part of the leg, 10cm above the external malleolus. In diabetes mellitus early degeneration of intraepidermal nerve fibers is induced and there is slower regeneration even when there is no evidence of neuropathy. Skin biopsy is of particular value in the diagnosis of small fiber neuropathy when nerve conduction studies are normal. It may also be repeated in order to study the progressive nature of the disease and also has the potential of studying regeneration of nerve fibers and thus the effects of treatment. Inflammatory demyelinating neuropathies may also involve loss of small-diameter nerve fibers and IgM deposits in dermal myelinated nerve fibers in anti-MAG neuropathy. In some cases the presence of vasculitis in skin may indicate a nonsystemic vasculitic neuropathy and in HIV neuropathy intraepidermal nerve fiber density is reduced in a length-dependent manner. In several hereditary neuropathies intraepidermal nerve fiber density may be reduced but other abnormalities can also be demonstrated in dermal myelinated fibers. Some small swellings and varicosities may be present in the distal leg skin biopsy of healthy individuals but large axonal swellings are considered as evidence of a pathological process affecting the normal structure of nerves. The indirect immunofluorescence technique with confocal microscopy provides the opportunity to study the complex structure of sensory receptors and cutaneous myelinated fibers and the innervation of sweat glands, arrector pilorum muscles, and vessels.

HIV neuropathy: an in vivo confocal microscopic study

Several approaches exist for quantitative assessment of human immunodeficiency virus (HIV)-associated distal sensory polyneuropathy (DSP). While useful, each has some limitations. This study evaluated non-invasive, in vivo reflectance confocal microscopy (RCM) of Meissner corpuscles (MCs) as a measure of HIV-DSP. Forty-eight adults (29 HIV-infected, 19 controls) underwent RCM of MC density (MCs/mm(2)) at the arch, fingertip, and thenar eminence (TE); ankle skin biopsy to measure epidermal nerve fiber density (ENFD); electrophysiologic studies; and tactile, vibration, and thermal threshold testing. HIV+ subjects were clinically categorized as having DSP signs or no signs. MC densities were lower in HIV+ subjects with DSP signs than in controls (arch, p = 0.0003; fingertip, p < 0.0001; TE, p = 0.0002). Tactile thresholds in the TE and foot were worse in HIV-DSP than in controls, but in this mild DSP cohort, sural amplitudes, ENFD, and vibration and thermal thresholds did not differ significantly from controls. Fingertip MC densities and tactile thresholds at the foot were also lower in HIV+ subjects without DSP signs than in controls. Other sensory measures were not significantly different in HIV+ subjects without DSP signs than in controls. MC density correlated inversely with tactile thresholds at each imaging location. The results suggest that RCM of MC density complements existing sensory DSP measures and discriminates mild HIV-DSP from controls at a stage when sural amplitudes do not. Further studies are required to determine whether RCM of MC density can establish quantitative changes in DSP, in response to treatment or disease progression.

Determinants of epidermal nerve fibre density in antiretroviral-naïve HIV-infected individuals

OBJECTIVES

Distal leg epidermal nerve fibre density (ENFD) is a validated predictor of small unmyelinated nerve fibre damage and neuropathy risk in HIV infection. As pre-existing damage may increase the risk of neuropathy following antiretroviral (ARV) therapy, particularly when the regimen contains stavudine (d4T), we assessed the relationship between ENFD and various parameters including mitochondrial factors in HIV-infected Thai individuals naïve to ARV therapy.

METHODS

Distal leg and proximal thigh ENFDs were quantified in HIV-infected Thai individuals without neuropathy prior to randomization to a HIV clinical trial that focused on mitochondrial toxicity issues. We assessed their association with various clinical and immunovirological parameters as well as with peripheral blood mononuclear cell (PBMC) mitochondrial (mt) DNA copies/cell, oxidative phosphorylation (OXPHOS) complex I (CI) and complex IV (CIV) enzyme activities, and mt 8-oxo-deoxyguanine (8-oxo-dG) break frequencies.

RESULTS

In 132 subjects, the median (interquartile range) ENFD (fibres/mm) values were 21.0 (16.2-26.6) for the distal leg and 31.7 (26.2-40.0) for the proximal thigh. By linear regression, lower CD4 count (P < 0.01), older age (P < 0.01), increased body mass index (BMI) (P = 0.04), increased height (P = 0.02), and higher PBMC OXPHOS activity as measured by CIV activity (P = 0.02) were associated with lower distal leg ENFD.

CONCLUSIONS

Older age, increased height, higher BMI, poorer immunological status and higher PBMC OXPHOS activity are associated with lower distal leg ENFD in HIV-infected subjects free of neuropathy prior to initiation of first-time ARV therapy.

Lipodystrophy and adrenal insufficiency: potential mediators of peripheral neuropathy in HIV infection?

The mechanisms behind certain co-morbid conditions associated with chronic HIV disease still remain elusive. HIV-associated peripheral neuropathy is one among those rarely studied manifestations in HIV-1 infection. Numerous underlying factors associated with peripheral neuropathy have been described in HIV disease. Herein, we hypothesized certain heretofore undescribed potential mechanisms that lead to HIV associated neuropathy. Being a multifactoral manifestation, HIV-associated neuropathy is presumed to have an association with physiological factors namely, adrenal inadequacy/steroid resistance and lipodystrophy-induced cushion-effect loss in peripheral nerves. Therefore, management of the adrenals with steroids at the time-point of high inflammatory burden thereby preventing lipodystrophy by selecting the optimum treatment regimen could markedly alleviate the severity of HIV-associated neuropathic manifestations.

Epidemiology of HIV-related neuropathy: a systematic literature review

We sought to identify and summarize the incidence and prevalence of neuropathy among HIV patients and subgroups. A systematic search of the literature was performed using MEDLINE and EMBASE. The relevant literature was identified based on predefined criteria. Prevalence data were collected from cross-sectional and cohort studies. Incidence data were collected from cohort and case-control studies. Thirty-seven studies were included of which there were 23 cohort studies, 13 cross-sectional studies, and one case-control study. The prevalence of neuropathy among HIV patients derived from 25 studies varied from 1.2% to 69.4%. Regarding the development of neuropathy among HIV-positive patients, standardized by study duration, the rates per 100 person-years ranged from 0.7 to 39.7. Among older patients there is a greater risk of neuropathy. The same seems to be the case for patients with more severe disease. Currently available studies providing information on the incidence and prevalence of neuropathy among HIV patients suggest a significant burden, but there is a great variation in results across studies. There is no definitive explanation for the variation. However, it underscores the fact that complexity of the disease, along with absence of standardized diagnostic criteria, has considerably influenced the methodologies and outcomes of the studies.

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.

European Federation of Neurological Societies/Peripheral Nerve Society Guideline on the use of skin biopsy in the diagnosis of small fiber neuropathy. Report of a joint task force of the European Federation of Neurological Societies and the Peripheral Nerve Society

BACKGROUND

Revision of the guidelines on the use of skin biopsy in the diagnosis of peripheral neuropathy, published in 2005, has become appropriate owing to publication of more relevant articles. Most of the new studies focused on small fiber neuropathy (SFN), a subtype of neuropathy for which the diagnosis was first developed through skin biopsy examination. This revision focuses on the use of this technique to diagnose SFN.

METHODS

Task force members searched the Medline database from 2005, the year of the publication of the first EFNS guideline, to June 30th, 2009. All pertinent articles were rated according to the EFNS and PNS guidance. After a consensus meeting, the task force members created a manuscript that was subsequently revised by two experts (JML and JVS) in the field of peripheral neuropathy and clinical neurophysiology, who were not previously involved in the use of skin biopsy.

RESULTS AND CONCLUSIONS

Distal leg skin biopsy with quantification of the linear density of intraepidermal nerve fibers (IENF), using generally agreed upon counting rules, is a reliable and efficient technique to assess the diagnosis of SFN (Recommendation Level A). Normative reference values are available for bright-field immunohistochemistry (Recommendation Level A) but not yet for confocal immunofluorescence or the blister technique. The morphometric analysis of IENF density, either performed with bright-field or immunofluorescence microscopy, should always refer to normative values matched for age (Recommendation Level A). Newly established laboratories should undergo adequate training in a well-established skin biopsy laboratory and provide their own stratified for age and gender normative values, intra- and interobserver reliability, and interlaboratory agreement. Quality control of the procedure at all levels is mandatory (Good Practice Point). Procedures to quantify subepidermal nerve fibers and autonomic innervated structures, including erector pili muscles, and skin vessels, are under development but need to be confirmed by further studies. Sweat gland innervation can be examined using an unbiased stereologic technique recently proposed (Recommendation Level B). A reduced IENF density is associated with the risk of developing neuropathic pain (Recommendation Level B), but it does not correlate with its intensity. Serial skin biopsies might be useful for detecting early changes of IENF density, which predict the progression of neuropathy, and to assess degeneration and regeneration of IENF (Recommendation Level C). However, further studies are warranted to confirm its potential usefulness as an outcome measure in clinical practice and research. Skin biopsy has not so far been useful for identifying the etiology of SFN. Finally, we emphasize that 3-mm skin biopsy at the ankle is a safe procedure based on the experience of 10 laboratories reporting absence of serious side effects in approximately 35,000 biopsies and a mere 0.19% incidence of non-serious side effects in about 15 years of practice (Good Practice Point).

Analysis of nerve and neuropeptide patterns in vacuum-assisted closure-treated diabetic murine wounds

BACKGROUND

Reestablishment of the peripheral nervous system occurs in parallel with wound healing. With accelerated wound healing seen with the vacuum-assisted closure device, the authors studied its effects on nerve fiber regeneration, nerve sprouting, and the stimulation of neuropeptides and neurotrophins.

METHODS

A vacuum-assisted closure device was applied to a full-thickness diabetic mouse wound using continuous or cyclical modes and compared with foam dressing or occlusive dressing controls, using 10 mice per group. Nerve fibers, substance P, calcitonin gene-related peptide, and nerve growth factor were analyzed using two-dimensional immunohistochemistry and real-time reverse-transcriptase polymerase chain reaction.

RESULTS

A significant increase in dermal and epidermal nerve fiber densities and in substance P, calcitonin gene-related peptide, and nerve growth factor expression was seen in vacuum-assisted closure-treated wounds. Cyclical treatment mode correlated with the largest increase in granulation tissue production, wound surface microdeformations, and a slightly faster wound closure rate.

CONCLUSIONS

This study suggests that vacuum-assisted closure therapy can modulate nerve fiber and neuropeptide production in the wound. Optimized kinetics of vacuum-assisted closure application may provide an opportunity for clinicians to further improve wound healing in denervated wounds such as pressure sores and diabetic foot ulcerations.

Evaluation of the pathophysiology of classical trigeminal neuralgia by blink reflex study and current perception threshold testing

We recruited 49 patients with classical trigeminal neuralgia (TN) according to the latest guidelines of the International Classification of Headache Disorders, and divided them into an acute (≤30 days onset; 13 patients) and a chronic (>30 days onset; 36 patients) group. We used blink reflex study and current perception threshold (CPT) testing to evaluate the painful facial areas and contralateral non-painful areas of patients with classical TN. CPT 5 Hz examinations, which correlate with unmyelinated fiber function, showed significantly decreased CPTs in the acute stage (11.62 ± 6.99 vs. 18.69 ± 9.66, P = 0.025), but significantly increased CPTs in the chronic stage (26.67 ± 18.65 vs. 19.69 ± 13.70, P = 0.010) on the painful side when compared with the contralateral non-painful side. However, CPTs at 250 Hz (Aδ) and 2000 Hz (Aβ) examinations did not show significant differences between the painful and non-painful sides. In contrast, only three (3/49) patients showed an abnormal trigeminal nerve stimulation on the ipsilateral painful side by blink reflex study. The findings suggest that classical TN is not a simple large-myelinated nerve fiber dysfunction but a more complex process with a main dysfunction of unmyelinated nerve fibers.

Pharmacogenetics of nucleoside reverse-transcriptase inhibitor-associated peripheral neuropathy

Peripheral neuropathy is an important complication of antiretroviral therapy. Nucleoside reverse-transcriptase inhibitor (NRTI)-associated mitochondrial dysfunction, inflammation and nutritional factors are implicated in its pathogenesis. Pharmacogenetic and genomic studies investigating NRTI neurotoxicity have only recently become possible via the linkage of HIV clinical studies to large DNA repositories. Preliminary case-control studies using these resources suggest that host mitochondrial DNA haplogroup polymorphisms in the hemochromatosis gene and proinflammatory cytokine genes may influence the risk of peripheral neuropathy during antiretroviral therapy. These putative risk factors await confirmation in other HIV-infected populations but they have strong biological plausibility. Work to identify underlying mechanisms for these associations is ongoing. Large-scale studies incorporating clearly defined and validated methods of neuropathy assessment and the use of novel laboratory models of NRTI-associated neuropathy to clarify its pathophysiology are now needed. Such investigations may facilitate the development of more effective strategies to predict, prevent and ameliorate this debilitating treatment toxicity in diverse clinical settings.

NeuroAIDS: an evolving epidemic

Over 60,000 Canadians are infected with human immunodeficiency virus (HIV). Greater than 50% of these individuals will develop a neurological disorder despite the availability of highly active antiretroviral therapy. HIV causes nervous system disease at all stages of infection with adverse effects on quality of life, adherence to medications, employment and survival. These disorders include opportunistic infections in addition to distinct HIV-associated neurological syndromes and undesirable treatment-related effects. The latter two groups of disorders are often undiagnosed and untreated in both adolescents and adults. Direct HIV infection of central nervous system causes HIV-associated dementia, which is a progressive subcortical dementia. HIV infection of the peripheral nervous system produces a painful sensory neuropathy termed distal sensory polyneuropathy, which may be exacerbated by several antiretroviral drugs. Other important HIV-induced neurological disorders include vacuolar myelopathy and an increased risk of seizures. Future issues that will confound the presentation and treatment of HIV-induced nervous system disorders include the increasing prevalence of drug-resistant HIV strains, increasing age of HIV-infected patients, hepatitis C virus co-infection and the Immune Reconstitution Inflammatory Syndrome. Herein, we review the clinical presentations, underlying pathogenesis and treatments of this burgeoning group of neurological disorders.

Altered cutaneous nerve regeneration in a simian immunodeficiency virus / macaque intracutaneous axotomy model

To characterize the regenerative pattern of cutaneous nerves in simian immunodeficiency virus (SIV)-infected and uninfected macaques, excisional axotomies were performed in nonglabrous skin at 14-day intervals. Samples were examined after immunostaining for the pan-axonal marker PGP 9.5 and the Schwann cell marker p75 nerve growth factor receptor. Collateral sprouting of axons from adjacent uninjured superficial dermal nerve bundles was the initial response to axotomy. Both horizontal collateral sprouts and dense vertical regeneration of axons from the deeper dermis led to complete, rapid reinnervation of the epidermis at the axotomy site. In contrast to the slower, incomplete reinnervation previously noted in humans after this technique, in both SIV-infected and uninfected macaques epidermal reinnervation was rapid and completed by 56 days postaxotomy. p75 was densely expressed on the Schwann cells of uninjured nerve bundles along the excision line and on epidermal Schwann cell processes. In both SIV-infected and uninfected macaques, Schwann cell process density was highest at the earliest timepoints postaxotomy and then declined at a similar rate. However, SIV-infection delayed epidermal nerve fiber regeneration and remodeling of new sprouts at every timepoint postaxotomy, and SIV-infected animals consistently had lower mean epidermal Schwann cell densities, suggesting that Schwann cell guidance and support of epidermal nerve fiber regeneration may account for altered nerve regeneration. The relatively rapid regeneration time and the completeness of epidermal reinnervation in this macaque model provides a useful platform for assessing the efficacy of neurotrophic or regenerative drugs for sensory neuropathies including those caused by HIV, diabetes mellitus, medications, and toxins.

Skin biopsy for the diagnosis of peripheral neuropathy

Skin biopsy has become an accepted tool for investigating small nerve fibres, which are invisible to conventional neurophysiological tests even though they are affected early on in peripheral neuropathies of varying aetiology. Morphometric analysis of epidermal and dermal nerves has proved to be reliable, reproducible and unaffected by the severity of neuropathy, making skin biopsy useful for diagnosing small fibre neuropathy (SFN) in clinical practice. The possibility of obtaining skin biopsy specimens from different sites of the body, to repeat them within the area of the same sensory nerve, to distinguish between somatic and autonomic nerves and to investigate the expression of nerve-related proteins has widened the potential applications of this technique to clinical research. Skin biopsy performed using a minimally invasive disposable punch is a safe and painless procedure. Using specific antibodies with bright-field immunohistochemistry or immunofluorescence technique, it is possible to investigate unmyelinated fibres innervating the epidermis of hairy and glabrous skin, large myelinated fibres supplying specialized corpuscles in glabrous skin, and autonomic fibres innervating sweat glands, blood vessels and arrector pilorum muscles. This review discusses the features of skin innervation in hairy and glabrous skin, the functional properties of skin nerve fibres and their changes in peripheral neuropathies.

The diagnostic criteria for small fibre neuropathy: from symptoms to neuropathology

Small fibre neuropathy (SFN), a condition dominated by neuropathic pain, is frequently encountered in clinical practise either as prevalent manifestation of more diffuse neuropathy or distinct nosologic entity. Aetiology of SFN includes pre-diabetes status and immune-mediated diseases, though it remains frequently unknown. Due to their physiologic characteristics, small nerve fibres cannot be investigated by routine electrophysiological tests, making the diagnosis particularly difficult. Quantitative sensory testing (QST) to assess the psychophysical thresholds for cold and warm sensations and skin biopsy with quantification of somatic intraepidermal nerve fibres (IENF) have been used to determine the damage to small nerve fibres. Nevertheless, the diagnostic criteria for SFN have not been defined yet and a 'gold standard' for clinical practise and research is not available. We screened 486 patients referred to our institutions and collected 124 patients with sensory neuropathy. Among them, we identified 67 patients with pure SFN using a new diagnostic 'gold standard', based on the presence of at least two abnormal results at clinical, QST and skin biopsy examination. The diagnosis of SFN was achieved by abnormal clinical and skin biopsy findings in 43.3% of patients, abnormal skin biopsy and QST findings in 37.3% of patients, abnormal clinical and QST findings in 11.9% of patients, whereas 7.5% patients had abnormal results at all the examinations. Skin biopsy showed a diagnostic efficiency of 88.4%, clinical examination of 54.6% and QST of 46.9%. Receiver operating characteristic curve analysis confirmed the significantly higher performance of skin biopsy comparing with QST. However, we found a significant inverse correlation between IENF density and both cold and warm thresholds at the leg. Clinical examination revealed pinprick and thermal hypoesthesia in about 50% patients, and signs of peripheral vascular autonomic dysfunction in about 70% of patients. Spontaneous pain dominated the clinical picture in most SFN patients. Neuropathic pain intensity was more severe in patients with SFN than in patients with large or mixed fibre neuropathy, but there was no significant correlation with IENF density. The aetiology of SFN was initially unknown in 41.8% of patients and at 2-year follow-up a potential cause could be determined in 25% of them. Over the same period, 13% of SFN patients showed the involvement of large nerve fibres, whereas in 45.6% of them the clinical picture did not change. Spontaneous remission of neuropathic pain occurred in 10.9% of SFN patients, while it worsened in 30.4% of them.

Neuromuscular complications of human immunodeficiency virus infection

Neurologic complications of HIV infection are common, and are a significant source of morbidity. The chronic nature of HIV today, the complexity of highly active antiretroviral therapy regimens, and the multiple and diffuse effects of HIV on the nervous system present an exciting diagnostic challenge, in which a systematic, comprehensive approach to diagnosis and treatment is necessary.

Skin biopsy as a diagnostic tool in peripheral neuropathy

Skin biopsy is a safe, minimally invasive, painless and cheap tool for providing diagnostic information on small nerve fibers, which are invisible to routine neurophysiological tests. Biopsy can be performed in hairy skin to investigate unmyelinated and thinly myelinated fibers and in glabrous skin to examine large myelinated fibers. Morphometric analysis of skin nerves is readily accomplished through the use of immunohistochemical techniques, and has proved to be reliable, reproducible and unaffected by the severity of neuropathy. One further advantage of skin biopsy over conventional nerve biopsy is that it allows somatic nerve fibers to be distinguished from autonomic nerve fibers. Morphological changes, axonal degeneration and abnormal regeneration occur in cutaneous nerves very early in the course of peripheral neuropathies, making skin biopsy a promising tool for investigating the progression of neuropathy and the effect of neuroprotective treatments in clinical practice and trials. This article reviews the techniques that are used to investigate the innervation of human skin, the possible uses of skin biopsy in diagnosing and monitoring peripheral neuropathies, and correlations between skin biopsy findings and those of other diagnostic methods.

Distal sensory polyneuropathy in the context of HIV/AIDS

Peripheral neuropathy, or distal sensory polyneuropathy (DSPN), is the most common neurological problem in HIV disease. DSPN also represents a complex symptom that occurs because of peripheral nerve damage related to advanced HIV disease and in association with the use of antiretroviral therapy-particularly in individuals treated with dideoxynucleosides. Although DSPN is a frequent symptom, the specific pathophysiology is not well understood. The HIV-related neuropathies are commonly categorized as distal sensory polyneuropathies, although antiretroviral toxic neuropathies are described in the literature. Recently, mitochondrial toxicity has been identified as a possible etiology of DSPN. As individuals with HIV/AIDS survive longer, often living for decades with the disease, chronic symptoms like DSPN must be addressed. Pharmacologic approaches, complementary therapies, and self-care behaviors that may improve quality of life and limit symptoms of DSPN are important interventions for clinicians and those living with HIV/AIDS to consider in the management of peripheral neuropathy.

Skin biopsy in the management of peripheral neuropathy

Skin biopsy has been widely used in recent years for the investigation of small-calibre sensory nerves, including somatic unmyelinated intraepidermal nerve fibres, dermal myelinated nerve fibres, and autonomic nerve fibres in peripheral neuropathies, with different techniques for tissue processing and nerve fibre assessment. Here, we review the techniques for skin biopsy, the processing and assessment of the biopsy sample, their possible uses in different types of peripheral neuropathy, and their use in the follow-up of patients and in clinical trials. We also review the association between morphological measures of skin innervation and function and the limits of this method in the aetiological classification of peripheral neuropathies.

Recent advances in HIV neuropathy

PURPOSE OF REVIEW

To describe recent advances in HIV neuropathy.

RECENT FINDINGS

Epidemiologic studies since highly active antiretroviral therapy was introduced have shown that the incidence of HIV-associated distal sensory polyneuropathy is reduced. Studies have also shown the relationship between distal sensory polyneuropathy and the use of neurotoxic antiretroviral drugs. Skin punch biopsy for assessment of epidermal nerve fiber density is valuable both for diagnosis of distal sensory polyneuropathy and as a predictor of the condition occurring in the future. An in-vitro model of antiretroviral toxic neuropathy showed that dideoxynucleoside analogues that cause neuropathy exert direct mitochondrial toxicity that is not mediated indirectly through the inhibition of DNA polymerase-gamma. HIV envelope protein gp120 exerts axonal toxicity directly or indirectly via perineuronal Schwann cells. A feline model of HIV, infection of neonatal cats with the feline immunodeficiency virus, showed development of peripheral neuropathy characterized by loss of epidermal innervation.

SUMMARY

While epidemiological studies of HIV-associated peripheral neuropathy continue to provide useful information, pathogenic studies are moving forward. Animal models of the disease will allow researchers to 'manipulate' the system. It is hoped that these types of studies will translate to an improved understanding of the pathogenesis of HIV-associated neuropathies leading to better treatments.