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

[Clinical application of pain-related evoked potentials]

Pain-related evoked potentials (PREPs) represent a novel method for the evaluation of peripheral and central nociceptive pathways, e.g. in the diagnosis of small fiber neuropathy (SFN) or after therapeutic interventions for headache. Compared to contact heat-evoked and laser-evoked potentials, recording of PREPs is less stressful for the subjects and technically less demanding. The clinical usefulness of PREPs has been described for SFN associated with diabetes, HIV and hepatitis C infections as well as in headache and facial pain disorders. They have also been evaluated after interventional methods, such as direct current stimulation (tDCS). The article reviews and discusses the advantages and pitfalls of this technique in the context of recent clinical studies as compared to other paradigms of peripheral electrical stimulation and delineates perspectives and possible indications.

Gain-of-function Nav1.8 mutations in painful neuropathy

Painful peripheral neuropathy often occurs without apparent underlying cause. Gain-of-function variants of sodium channel Na(v)1.7 have recently been found in ∼30% of cases of idiopathic painful small-fiber neuropathy. Here, we describe mutations in Na(v)1.8, another sodium channel that is specifically expressed in dorsal root ganglion (DRG) neurons and peripheral nerve axons, in patients with painful neuropathy. Seven Na(v)1.8 mutations were identified in 9 subjects within a series of 104 patients with painful predominantly small-fiber neuropathy. Three mutations met criteria for potential pathogenicity based on predictive algorithms and were assessed by voltage and current clamp. Functional profiling showed that two of these three Na(v)1.8 mutations enhance the channel's response to depolarization and produce hyperexcitability in DRG neurons. These observations suggest that mutations of Na(v)1.8 contribute to painful peripheral neuropathy.

Cutaneous innervation of the human face as assessed by skin biopsy

The morphology of cutaneous sensory and autonomic innervation in human trigeminal territory is still unknown. The aim of this study is to describe facial cutaneous innervation using skin biopsy. This new tool could be useful in understanding the mechanisms underlying several facial pain conditions. In 30 healthy subjects, we quantified epidermal nerve fibers (ENFs) and dermal myelinated fibers (MFs) in V1, V2 and V3, using indirect immunofluorescence and confocal microscopy applied to 2-mm punch skin biopsies from areas adjacent to the eyebrow, upper and lower lip. Using selective markers, we also evaluated the distribution of peptidergic, cholinergic and noradrenergic fibers. Facial skin appeared abundantly innervated and rich in annexes. The ENF density decreased and the MF density increased, moving from the supraorbital to the perioral skin. Noradrenergic sudomotor fibers were particularly and constantly expressed compared with other body sites. Distribution of vasoactive intestinal peptide-immunoreactive (VIP-ir) fibers appeared peculiar for their constant presence in the subepidermal neural plexus - in close contact, but without colocalization with calcitonin gene related peptide (CGRP) and substance P (Sub-P)-ir fibers. Finally, in perioral skin samples, we observed striated muscle fibers with their motor nerves and motor endplates. Our work provides the first morphological study of human facial cutaneous innervation, highlighting some unique features of this territory. Quantification of unmyelinated and myelinated fibers on 2-mm punch biopsies appeared to be feasible and reliable. Facial skin biopsy may be a new approach with which to study and to better characterize facial pain syndromes.

HIV-associated sensory neuropathy: still a problem in the post-stavudine era?

Sensory neuropathy (SN) is a common and difficult to manage cause of chronic pain in HIV. Recent recommendations for earlier HIV treatment and avoidance of neurotoxic antiretroviral drugs (such as stavudine) have led to optimism that HIV-SN rates may decline. We present several reasons as to why HIV-SN is likely to remain prevalent, despite improvements in HIV management, together with clinical evidence confirming high HIV-SN rates in cohorts never exposed to neurotoxic medications. A combination of epidemiologic studies, laboratory work and clinical trials are needed to understand the problem of HIV-SN in the post-stavudine era. Improved HIV-SN prevention and management strategies are needed if the morbidity associated with HIV infection is to improve along with life expectancy.

Evaluation of proxy tests for SFSN: evidence for mixed small and large fiber dysfunction

Background

Though intra-epidermal nerve fiber density (IENFD) is considered the gold standard for diagnosis of small fiber sensory neuropathy (SFSN), we aimed to determine if novel threshold values derived from standard tests of small or large fiber function could serve as diagnostic alternatives.

Methods

Seventy-four consecutive patients with painful polyneuropathy and normal nerve conduction studies (NCS) were defined as SFSN cases or controls by distal IENFD <5.4 and ≥5.4 fibers/mm, respectively. Diagnostic performance of small fiber [cooling (CDT) and heat perception (HP) thresholds, axon reflex-mediated neurogenic vasodilatation] and large fiber function tests [vibration perception thresholds (VPT) and sural nerve conduction parameters] were determined by receiver operating-characteristic (ROC) curve analyses.

Results

The 26(35%) SFSN cases had mean IENFD 3.3±1.7 fibers/mm and the 48(65%) controls 9.9±2.9 fibers/mm. Male gender (p = 0.02) and older age (p = 0.02) were associated with SFSN cases compared to controls. VPT were higher and CDT lower in SFSN cases, but the largest magnitude of differences was observed for sural nerve amplitude. It had the greatest area under the ROC curve (0.75) compared to all other tests (p<0.001 for all comparisons) and the optimal threshold value of ≤12 µV defined SFSN cases with 80% sensitivity and 72% specificity.

Conclusion

In patients presenting with polyneuropathy manifestations and normal NCS, though small fiber function tests were intuitively considered the best alternative measures to predict reduced IENFD, their diagnostic performance was poor. Instead, novel threshold values within the normal range for large fiber tests should be considered as an alternative strategy to select subjects for skin biopsy in diagnostic protocols for SFSN.

Polyneuropathy induced by HIV disease and antiretroviral therapy

OBJECTIVE

To investigate the underlying mechanisms of polyneuropathy induced by HIV infection or antiretroviral drugs.

METHODS

We tested 100 HIV patients (59 with AIDS). Ninety-three patients received antiretroviral drugs. Forty-four were treated with neurotoxic compounds (ddI, ddC, d4T). Nerve conduction velocities and the sympathetic skin response (SSR) in palms and soles were measured in all patients. In skin biopsies (ankle and thigh), the intraepidermal nerve fiber density (IENFD) and the number of epidermal fibers without contact to the basal membrane (fragments) were quantified using PGP9.5 staining.

RESULTS

Severity of the disease (CD4 +count) correlated to conduction velocities of peroneal (p < 0.01, Spearmans rank correlation), sural (p < 0.01) and median nerves (p < 0.05/p < 0.001, sensory/motor). In contrast, the duration of neurotoxic treatment did not impair conduction velocities (p > 0.3) but correlated to reduced IENFD in the ankle (r = -0.24, p < 0.05). Despite their reduced IENFD, patients with long neurotoxic treatment had a high number of fragments irrespective of their CD4 +count.

CONCLUSIONS

Neurotoxic treatment appears to primarily impair thin fiber conduction, whereas HIV neuropathy is linked to large fiber impairment and reduction of fragments of nerve fibers.

SIGNIFICANCE

These findings emphasize the differential pattern of polyneuropathy in HIV patients caused by the infection or induced by antiretroviral treatment.

Cutaneous innervation and trigeminal pathway function in a patient with facial pain associated with Parry-Romberg syndrome

Parry-Romberg syndrome (PRS) is a rare condition manifesting with progressive hemifacial atrophy. Although reported PRS clinical disturbances include facial pain and recent studies raised the possibility that PRS-related pain is a neuropathic pain condition due to the trigeminal nerve damage, no studies have directly investigated cutaneous innervation and trigeminal pathway function in patients with this rare condition. In a 50-year-old woman presenting with a 10-year history of slowly progressive hemifacial atrophy and facial pain, we investigated large myelinated fibres with masticatory muscle electromyography and trigeminal reflexes, and tested small myelinated and unmyelinated fibres with laser-evoked potentials. We also investigated cutaneous innervation by measuring the intraepidermal nerve fibre (IENF) density after skin biopsy of the supraorbital regions. We found that neurophysiological data and IENF density came within normal ranges, with no differences between normal and affected side. Our study showing that the standard reference techniques for assessing cutaneous innervation and trigeminal pathway function disclosed no abnormalities in this patient with PRS suggest that this rare and disabling condition is not associated with trigeminal system damage. These findings indicate that in this patient PRS-related pain is not a neuropathic pain condition, rather it probably arises from the musculoskeletal abnormalities.

Skin innervation at different depths correlates with small fibre function but not with pain in neuropathic pain patients

BACKGROUND

Neuropathy can lead not only to impaired function but also to sensory sensitization. We aimed to link reduced skin nerve fibre density in different levels to layer-specific functional impairment in neuropathic pain patients and tried to identify pain-specific functional and structural markers.

METHODS

In 12 healthy controls and 36 patients with neuropathic pain, we assessed clinical characteristics, thermal thresholds (quantitative sensory testing) and electrically induced pain and axon reflex erythema. At the most painful sites and at intra-individual control sites, skin biopsies were taken and innervation densities in the different skin layers were assessed. Moreover, neuronal calcitonin gene-related peptide staining was quantified.

RESULTS

Perception of warm, cold and heat pain and nerve fibre density were reduced in the painful areas compared with the control sites and with healthy controls. Warm and cold detection thresholds correlated best with epidermal innervation density, whereas heat and cold pain thresholds and axon reflex flare correlated best with dermal innervation density. Clinical pain ratings correlated only with epidermal nerve fibre density (r = 0.38, p < 0.05) and better preserved cold detection thresholds (r = 0.39, p < 0.05), but not with other assessed functional and structural parameters.

CONCLUSIONS

Thermal thresholds, axon reflex measurements and assessment of skin innervation density are valuable tools to characterize and quantify peripheral neuropathy and link neuronal function to different layers of the skin. The severity of small fibre neuropathy, however, did not correspond to clinical pain intensity and a specific parameter or pattern that would predict pain intensity in peripheral neuropathy could not be identified.

fMRI evidence of degeneration-induced neuropathic pain in diabetes: enhanced limbic and striatal activations

Persistent neuropathic pain due to peripheral nerve degeneration in diabetes is a stressful symptom; however, the underlying neural substrates remain elusive. This study attempted to explore neuroanatomical substrates of thermal hyperalgesia and burning pain in a diabetic cohort due to pathologically proven cutaneous nerve degeneration (the painful group). By applying noxious 44°C heat stimuli to the right foot to provoke neuropathic pain symptoms, brain activation patterns were compared with those of healthy control subjects and patients with a similar degree of cutaneous nerve degeneration but without pain (the painless group). Psychophysical results showed enhanced affective pain ratings in the painful group. After eliminating the influence of different pain intensity ratings on cerebral responses, the painful group displayed augmented responses in the limbic and striatal structures, including the perigenual anterior cingulate cortex (ACC), superior frontal gyrus, medial thalamus, anterior insular cortex, lentiform nucleus (LN), and premotor area. Among these regions, blood oxygen level-dependent (BOLD) signals in the ACC and LN were correlated with pain ratings to thermal stimulations in the painful group. Furthermore, activation maps of a simple regression analysis as well as a region of interest analysis revealed that responses in these limbic and striatal circuits paralleled the duration of neuropathic pain. However, in the painless group, BOLD signals in the primary somatosensory cortex and ACC were reduced. These results suggest that enhanced limbic and striatal activations underlie maladaptive responses after cutaneous nerve degeneration, which contributed to the development and maintenance of burning pain and thermal hyperalgesia in diabetes.

Diagnosis and treatment of pain in small-fiber neuropathy

Small-fiber neuropathy manifests in a variety of different diseases and often results in symptoms of burning pain, shooting pain, allodynia, and hyperesthesia. Diagnosis of small-fiber neuropathy is determined primarily by the history and physical exam, but functional neurophysiologic testing and skin biopsy evaluation of intraepidermal nerve-fiber density can provide diagnostic confirmation. Management of small-fiber neuropathy depends on the underlying etiology with concurrent treatment of associated neuropathic pain. A variety of recent guidelines proposes the use of antidepressants, anticonvulsants, opioids, topical therapies, and nonpharmacologic treatments as part of the overall management of neuropathic pain. Unfortunately, little data about the treatment of pain specifically in small-fiber neuropathy exist because most studies combine mixed neuropathic pain syndromes in the analysis. Additional studies targeting the treatment of pain in small-fiber neuropathy are needed to guide decision making.

Automated measurement of nerve fiber density using line intensity scan analysis

Quantification of nerve fibers in peripheral and central nervous systems is important for the understanding of neuronal function, organization and pathological changes. However, current methods to quantify nerve fibers are resource-intensive and often provide an indirect measurement of nerve fiber density. Here, we describe an automated and efficient method for nerve fiber quantification, which we developed by making use of widely available software and analytical techniques, including Hessian-based feature extraction in NIH ImageJ and line intensity scan analysis. The combined use of these analytical tools through an automated routine enables reliable detection and quantification of nerve fibers from low magnification, non-uniformly labeled epifluorescence images. This allows for time-efficient determination of nerve density and also comparative analysis in large brain structures, such as hippocampus or between various regions of neural circuitry. Using this method, we have obtained accurate measurements of cholinergic fiber density in hippocampus and a large area of cortex in mouse brain sections immunolabeled with an antibody against the vesicular acetylcholine transporter (VAChT). The density values are comparable among animals tested, showing a high degree of reproducibility. Because our method can be performed at relatively low cost and in large tissue sections where nerve fibers can be labeled by various antibodies or visualized by expression of reporter proteins, such as green fluorescent protein in transgenic mice, we expect our method to be broadly useful in both research and clinical investigation. To our knowledge, this is the first method to reliably quantify nerve fibers through a rapid and automated protocol.

Small nerve fibres, small hands and small feet: a new syndrome of pain, dysautonomia and acromesomelia in a kindred with a novel NaV1.7 mutation

The Na(V)1.7 sodium channel is preferentially expressed within dorsal root ganglion and sympathetic ganglion neurons and their small-diameter peripheral axons. Gain-of-function variants of Na(V)1.7 have recently been described in patients with painful small fibre neuropathy and no other apparent cause. Here, we describe a novel syndrome of pain, dysautonomia, small hands and small feet in a kindred carrying a novel Na(V)1.7 mutation. A 35-year-old male presented with erythema and burning pain in the hands since early childhood, later disseminating to the feet, cheeks and ears. He also experienced progressive muscle cramps, profound sweating, bowel disturbances (diarrhoea or constipation), episodic dry eyes and mouth, hot flashes, and erectile dysfunction. Neurological examination was normal. Physical examination was remarkable in revealing small hands and feet (acromesomelia). Blood examination and nerve conduction studies were unremarkable. Intra-epidermal nerve fibre density was significantly reduced compared to age- and sex-matched normative values. The patient's brother and father reported similar complaints including distal extremity redness and pain, and demonstrated comparable distal limb under-development. Quantitative sensory testing revealed impaired warmth sensation in the proband, father and brother. Genetic analysis revealed a novel missense mutation in the SCN9A gene encoding sodium channel Na(V)1.7 (G856D; c.2567G > A) in all three affected subjects, but not in unaffected family members. Functional analysis demonstrated that the mutation hyperpolarizes (-9.3 mV) channel activation, depolarizes (+6.2 mV) steady-state fast-inactivation, slows deactivation and enhances persistent current and the response to slow ramp stimuli by 10- to 11-fold compared with wild-type Na(V)1.7 channels. Current-clamp analysis of dorsal root ganglion neurons transfected with G856D mutant channels demonstrated depolarized resting potential, reduced current threshold, increased repetitive firing in response to suprathreshold stimulation and increased spontaneous firing. Our results demonstrate that the G856D mutation produces DRG neuron hyperexcitability which underlies pain in this kindred, and suggest that small peripheral nerve fibre dysfunction due to this mutation may have contributed to distal limb under-development in this novel syndrome.

Primary focal hyperhidrosis in a new family not linked to known loci

BACKGROUND

Primary focal hyperhidrosis (PFH) is a disabling disorder. A first locus has been mapped in families with only palmar involvement, raising the question whether other unknown genes are responsible for more diffuse phenotypes.

OBJECTIVE

We investigated a PFH family with a new phenotype, providing evidence that PFH is a clinically and genetically heterogeneous condition.

METHODS

Family members were examined by autonomic tests, skin biopsy and genetic analysis, and followed up for 4 years.

RESULTS

Age at onset was early, involving the axillae, palms and soles. Affected members had dysautonomic features also at onset. Cardiovascular dysautonomia was present in affected and unaffected members. Skin biopsy revealed impairment of intraepidermal nerve fibers and reduced innervation of sweat glands. There was no linkage to PFH and aquaporin-5 loci.

CONCLUSION

This pedigree may serve as a basis for identifying a novel unmapped gene. Skin biopsy and cardiovascular autonomic tests provide important additions to the characterization of PFH.

Expression of growth-associated protein 43 in the skin nerve fibers of patients with type 2 diabetes mellitus

The growth-associated protein 43 (GAP-43) is known as a marker of regenerating nerve fibers and their continuous remodeling in the adult human skin. The purpose of this pilot study was to investigate a possible role for GAP-43 in the detection of the early stages of small-fiber neuropathy in patients with type 2 diabetes mellitus (DM2) as compared with a well- established and validated parameter - intra-epidermal nerve fiber density (IENFD) of protein gene product 9.5 (PGP 9.5) immunoreactive intra-epidermal C fibers. In a group of 21 patients with DM2 within three years of diagnosis (13 men, 8 women; mean age 53.9±12.8; range 30-74) and a group of 17 healthy volunteers (8 men, 9 women; mean age 55.8±8.5; range 45-70 years), skin punch biopsies were taken from a distal calf and double immunostained with both PGP 9.5 and GAP-43. In healthy controls, 96.8% of 629 PGP 9.5 immunoreactive fibers were immunostained with GAP-43; the proportion of PGP 9.5 intra-epidermal nerve fibers immunoreactive for GAP-43 in control subjects ranged from 86.5 to 100%. In DM2 patients, IENFD was significantly lower compared to controls (median, 1.5 vs. 11.2/mm; p<0.001). The proportion of GAP-43 immunoreactive intraepidermal nerve fibers was significantly lower in DM2 patients compared to healthy controls (73.6% of 337 PGP 9.5 positive fibers; p<0.001); ranged from 0 to 98.1%. In conclusion, these results show that impaired regeneration of intra-epidermal C fibers in the early stages of type 2 diabetes mellitus, as indicated by GAP-43, might be a marker of incipient diabetic neuropathy.

[Usefulness of skin biopsy in the diagnosis of small fiber neuropathy]

Diagnosis of small fiber neuropathy may be challenging due to subtle clinical signs and to the normality of nerve conduction studies. Skin biopsy is a non invasive method which allows to quantify intraepidermal nerve fiber density after a simple immunostaining. The values measured must ideally be compared to normative data obtained on control subjects in order to determine their significance. When the diagnosis of small fiber neuropathy has been made by means of skin biopsy, possibly combined with laser evoked potentials, a diagnostic work up has to be done in order to find one of the classical causes of this disorder. To date, skin biopsy is useful to confirm the diagnosis of small fiber neuropathy but lacks utility to find its etiology.

Intra- and interfamily phenotypic diversity in pain syndromes associated with a gain-of-function variant of NaV1.7

BACKGROUND

Sodium channel NaV1.7 is preferentially expressed within dorsal root ganglia (DRG), trigeminal ganglia and sympathetic ganglion neurons and their fine-diamter axons, where it acts as a threshold channel, amplifying stimuli such as generator potentials in nociceptors. Gain-of-function mutations and variants (single amino acid substitutions) of NaV1.7 have been linked to three pain syndromes: Inherited Erythromelalgia (IEM), Paroxysmal Extreme Pain Disorder (PEPD), and Small Fiber Neuropathy (SFN). IEM is characterized clinically by burning pain and redness that is usually focused on the distal extremities, precipitated by mild warmth and relieved by cooling, and is caused by mutations that hyperpolarize activation, slow deactivation, and enhance the channel ramp response. PEPD is characterized by perirectal, periocular or perimandibular pain, often triggered by defecation or lower body stimulation, and is caused by mutations that severely impair fast-inactivation. SFN presents a clinical picture dominated by neuropathic pain and autonomic symptoms; gain-of-function variants have been reported to be present in approximately 30% of patients with biopsy-confirmed idiopathic SFN, and functional testing has shown altered fast-inactivation, slow-inactivation or resurgent current. In this paper we describe three patients who house the NaV1.7/I228M variant.

METHODS

We have used clinical assessment of patients, quantitative sensory testing and skin biopsy to study these patients, including two siblings in one family, in whom genomic screening demonstrated the I228M NaV1.7 variant. Electrophysiology (voltage-clamp and current-clamp) was used to test functional effects of the variant channel.

RESULTS

We report three different clinical presentations of the I228M NaV1.7 variant: presentation with severe facial pain, presentation with distal (feet, hands) pain, and presentation with scalp discomfort in three patients housing this NaV1.7 variant, two of which are from a single family. We also demonstrate that the NaV1.7/I228M variant impairs slow-inactivation, and produces hyperexcitability in both trigeminal ganglion and DRG neurons.

CONCLUSION

Our results demonstrate intra- and interfamily phenotypic diversity in pain syndromes produced by a gain-of-function variant of NaV1.7.

Nerve biopsy--some comments on procedures and indications

Nerve biopsy is most often a final step in the evaluation of patients with peripheral neuropathy. The procedure should always be expected to result in varying degree of sensory loss within the innervation area of the biopsied nerve and chronic pain in the area may also occur. Therefore appropriate informed consent must be obtained and a weighing of such side effects and benefits for the patient, particularly therapeutical consequences, should be seriously considered before the procedure is performed. The surgical procedure and the processing in the laboratory of the nerve material must hold a high standard at all levels. Nerve biopsy should not be performed before adequate clinical, electrophysiological and laboratory investigations have been performed. The choice of nerve is important, but in most instances the sural nerve is biopsied, although the superficial peroneal nerve is also an option and allows an easy access to muscle biopsy in the same procedure. Laboratories performing nerve biopsies should have the facilities and expertise to prepare and evaluate fixed and frozen sections (paraffin, cryostat and epoxy-sections) and teased fibers, and also to perform light and electron microscopy and immunohistochemistry. Although not routinely used, the option of morphometry should be available as well. We recommend that properly trained technicians start the processing procedures in the operating room and, if feasible, even in hospitals outside that of the hospital with nerve laboratory. We also prefer routine use of teased fiber analysis as this visualizes in an excellent way pathological processes like axonal degeneration, demyelination and remyelination as well as other features. Evaluation of small fiber neuropathy is rarely an indication for nerve biopsy and should be investigated with skin biopsy and visualization and quantification of intraepidermal nerve fibers. Investigation of inflammatory neuropathy, particularly to demonstrate nerve vasculitis, is the main indication of nerve biopsy.

Microneurographic identification of spontaneous activity in C-nociceptors in neuropathic pain states in humans and rats

C-nociceptors do not normally fire action potentials unless challenged by adequate noxious stimuli. However, in pathological states nociceptors may become hyperexcitable and may generate spontaneous ectopic discharges. The aim of this study was to compare rat neuropathic pain models and to assess their suitability to model the spontaneous C-nociceptor activity found in neuropathic pain patients. Studies were performed in normal rats (n=40), healthy human subjects (n=15), peripheral neuropathic pain patients (n=20), and in five rat neuropathic pain models: nerve crush (n=24), suture (n=14), chronic constriction injury (n=12), STZ-induced diabetic neuropathy (n=56), and ddC-induced neuropathy (n=15). Microneurographic recordings were combined with electrical stimulation to monitor activity in multiple C fibers. Stimulation at 0.25 Hz allowed spontaneous impulses to be identified by fluctuations in baseline latency. Abnormal latency fluctuations could be produced by several mechanisms, and spontaneous activity was most reliably identified by the presence of unexplained latency increases corresponding to two or more additional action potentials. Spontaneous activity was present in a proportion of mechano-insensitive C-nociceptors in the patients and all rat models. The three focal traumatic nerve injury models provided the highest proportion (59.5%), whereas the two polyneuropathy models had fewer (18.6%), and the patients had an intermediate proportion (33.3%). Spontaneously active mechano-sensitive C-nociceptors were not recorded. Microneurographic recordings of spontaneous activity in diseased C-nociceptors may be useful for both short- and long-term drug studies, both in animals and in humans.

Small fibre neuropathy: role in the diagnosis of diabetic sensorimotor polyneuropathy

Small fibres constitute 70-90% of peripheral nerve fibres and regulate several key functions such as tissue blood flow, temperature and pain perception as well as sweating, all of which are highly relevant to the clinical presentation and adverse outcomes associated with foot ulcerations in patients with diabetes. Recent studies demonstrated significant abnormalities in the small fibres in subjects with impaired glucose tolerance and diabetes, despite normal electrophysiology, suggesting that the earliest nerve fibre damage is to the small fibres. Unfortunately, guidelines and consensus statements focus on large fibres and continue to advocate electrophysiology as a diagnostic modality and as a primary end point for the assessment of therapeutic benefit. (In part, this reflects the difficulties in quantifying small fibre dysfunction and damage.) We have therefore critically assessed currently available techniques that measure small fibre dysfunction in diabetic neuropathy, using quantitative sensory and sudomotor testing. We have assessed the role of identifying structural damage by quantifying intraepidermal nerve fibre density in skin biopsies and corneal nerve morphology using corneal confocal microscopy. Finally, we propose a definition for diabetic neuropathy that incorporates small fibre damage.

The Glenn A. Fry award lecture 2010: Ophthalmic markers of diabetic neuropathy

Diabetic peripheral neuropathy (DPN) is a debilitating condition that affects about 50% of diabetic patients. The symptoms of DPN include numbness, tingling, or pain in the arms and legs. Patients with numbness may be unaware of foot trauma, which could develop into a foot ulcer. If left untreated, this may ultimately require amputation. Currently, the only method of directly examining peripheral nerves is to conduct skin punch or sural/peroneal nerve biopsies, which are uncomfortable and invasive. Indirect methods include quantitative sensory testing (assessing responses to heat, cold, and vibration) and nerve electrophysiology. Here, I describe research undertaken in my laboratory, investigating the possibility of using a range of ophthalmic markers to assess DPN. Corneal nerve structure and function can be assessed using corneal confocal microscopy and non-contact corneal esthesiometry, respectively. Retinal nerve structure and visual function can be evaluated using optical coherence tomography and perimetry, respectively. These techniques have been used to demonstrate that DPN is associated with morphological degradation of corneal nerves, reduced corneal sensitivity, retinal nerve fiber layer thinning, and peripheral visual field loss. With further validation, these ophthalmic markers could become established as rapid, painless, non-invasive, sensitive, reiterative, cost-effective, and clinically accessible means of screening for early detection, diagnosis, staging severity, and monitoring progression of DPN, as well as assessing the effectiveness of possible therapeutic interventions. Looking to the future, this research may pave the way for an expanded role for the ophthalmic professions in diabetes management.

Advances in the diagnosis, pathogenesis and treatment of CIDP

Chronic inflammatory demyelinating polyneuropathy (CIDP) is the most common chronic autoimmune neuropathy. Despite clinical challenges in diagnosis-owing in part to the existence of disease variants, and different views on how many electrophysiological abnormalities are needed to document demyelination-consensus criteria seem to have been reached for research or clinical practice. Current standard of care involves corticosteroids, intravenous immunoglobulin (IVIg) and/or plasmapheresis, which provide short-term benefits. Maintenance therapy with IVIg can induce sustained remission, increase quality of life and prevent further axonal loss, but caution is needed to avoid overtreatment. Commonly used immunosuppressive drugs offer minimal benefit, necessitating the development of new therapies for treatment-refractory patients. Advances in our understanding of the underlying immunopathology in CIDP have identified new targets for future therapeutic efforts, including T cells, B cells, and transmigration and transduction molecules. New biomarkers and scoring systems represent emerging tools with the potential to predict therapeutic responses and identify patients with active disease for enrollment into clinical trials. This Review highlights the recent advances in diagnosing CIDP, provides an update on the immunopathology including new target antigens, and discusses current treatments, ongoing challenges and future therapeutic directions.

Axonal fluorescence quantitation provides a new approach to assess cutaneous innervation

We present a novel approach to quantify skin innervation by measuring the PGP 9.5 immunoreactive (PGP-ir) fluorescence corresponding to axons within the epidermis and dermis. The skin biopsies from 35 controls and 45 small fiber neuropathy (SFN) patients were included. In 50-μm free-floating sections, we determined the intraepidermal nerve fiber density (IENFD) by direct fluorescence visualization and captured 2-μm thick individual optical sections using the same confocal microscope and magnification. We measured the fluorescence of the PGP-ir axons in both, epidermal and dermal area by using the ImageJ software. There was good interobserver and intraobserver reliability of PGP-ir measures, similar than for IENFD. The PGP-ir axons were found decreased in patients with SFN (1.1‰ and 9.0‰ respectively for epidermal and dermal area in contrast to 2.2‰ and 16.0‰, respectively to controls). The area under the ROC curve was 0.90 for the IENFD, 0.84 for epidermal PGP-ir axons and 0.70 for dermal PGP-ir axons. There was a positive correlation between the IENFD and the PGP-ir axons at epidermis (Spearman Rho=0.66, p<0.001) as well as for the dermal nerve length and the PGP-ir axons at dermis (Spearman Rho=0.45, p<0.05). This method is also particularly adequate for the quantitation of dermal nerve fibers. We conclude that quantifying the fluorescent PGP-ir axons could help to assess skin innervation (dermal and epidermal nerve fibers) in patients with SFN.

Asymptomatic small fiber neuropathy in diabetes mellitus: investigations with intraepidermal nerve fiber density, quantitative sensory testing and laser-evoked potentials

This study aimed at evaluating the performance of a battery of morphological and functional tests for the assessment of small nerve fiber loss in asymptomatic diabetic neuropathy (DNP). Patients diagnosed for ≥10 years with type 1 (n = 10) or type 2 (n = 13) diabetes mellitus (DM) without conventional symptoms or signs of DNP were recruited and compared with healthy controls (n = 18) and patients with overt DNP (n = 5). Intraepidermal nerve fiber density (IENFd) was measured with PGP9.5 immunostaining on punch skin biopsies performed at the distal leg. Functional tests consisted of quantitative sensory testing (QST) for light-touch, cool, warm and heat pain detection thresholds and brain-evoked potentials with electrical (SEPs) and CO(2) laser stimulation [laser-evoked potentials (LEPs)] of hand dorsum and distal leg using small (0.8 mm(2)) and large (20 mm(2)) beam sizes. Results confirmed a state of asymptomatic DNP in DM, but only at the distal leg. Defining a critical small fiber loss as a reduction of IENFd ≤-2 z scores of healthy controls, this state prevailed in type 2 (30%) over type 1 DM (10%) patients despite similar disease duration and current glycemic control. LEPs with the small laser beam performed best in terms of sensitivity (91%), specificity (83%) and area-under-the ROC curve (0.924). Although this performance was not statically different from that of warm and cold detection threshold, LEPs offer an advantage over QST given that they bypass the subjective report and are therefore unbiased by perceptual factors.

Tolerating diabetes: an alternative therapeutic approach for diabetic neuropathy

It is becoming apparent that a number of pathogenic mechanisms contribute to diabetic neuropathy, so that therapeutic interventions that target one particular mechanism may have limited success. A recently published preclinical study has adopted an alternative approach by using a novel small molecule to induce heat-shock protein 70. This confers upon neurons, and perhaps other cells of the nervous system, the ability to better tolerate the diverse stresses associated with diabetes rather than intervening in their production.