Quantitative sensory testing cannot differentiate simulated sensory loss from sensory neuropathy

Discontinuity third harmonic generation microscopy for label-free imaging and quantification of intraepidermal nerve fibers

Label-free imaging methodologies for nerve fibers rely on spatial signal continuity to identify fibers and fail to image free intraepidermal nerve endings (FINEs). Here, we present an imaging methodology-called discontinuity third harmonic generation (THG) microscopy (dTHGM)-that detects three-dimensional discontinuities in THG signals as the contrast. We describe the mechanism and design of dTHGM and apply it to reveal the bead-string characteristics of unmyelinated FINEs. We confirmed the label-free capability of dTHGM through a comparison study with the PGP9.5 immunohistochemical staining slides and a longitudinal spared nerve injury study. An intraepidermal nerve fiber (IENF) index based on a discontinuous-dot-connecting algorithm was developed to facilitate clinical applications of dTHGM. A preliminary clinical study confirmed that the IENF index was highly correlated with skin-biopsy-based IENF density (Pearson's correlation coefficient R = 0.98) and could achieve differential identification of small-fiber neuropathy (p = 0.0102) in patients with diabetic peripheral neuropathy.

Endoscopic visualization of the inferior alveolar nerve associated with somatosensory changes after impacted mandibular third molar extraction

The aim of this study is to assess the relationship between somatosensory functional changes and inferior alveolar nerve (IAN) exposure after impacted mandibular third molars (M3M) removal. We recruited 35 patients who underwent impacted M3M extraction near the IAN. The M3Ms were extracted by combined endoscopy, piezosurgery, and contra-angle high-speed turbine handpiece. All IAN canal perforations and exposed regions were recorded and measured by endoscopy after extraction and on cone-beam computed tomography (CBCT) images before extraction. The patients were followed up 1, 7, and 35 days after surgery. A standardized quantitative sensory testing (QST) battery was performed on the lower lip skin. All of 35 cases had exposed IAN on CBCT images, 5 of which had no exposed IAN under endoscopy. For the other 30 cases, the endoscopy-measured IAN length and width were shorter than the CBCT measurements (P < 0.001). The warm and mechanical detection thresholds (MDT) on the operation side were significantly higher than the contralateral side after surgery (P < 0.05). Thermal sensory limen, MDT, and cold pain threshold were strongly correlated with the exposed IAN length and MDT also with the exposed IAN width one day after surgery. In conclusion, it was found that not all exposed IAN in CBCT images were real exposure after surgery. The intraoperative exposed IAN endoscopic measurements were smaller than by CBCT and strongly correlated with some QST parameters.

Canadian Guidelines for Hereditary Transthyretin Amyloidosis Polyneuropathy Management

Hereditary transthyretin-mediated (hATTR) amyloidosis is a progressive disease caused by mutations in the TTR gene leading to multisystem organ dysfunction. Pathogenic TTR aggregation, misfolding, and fibrillization lead to deposition of amyloid in multiple body organs and frequently involve the peripheral nerve system and the heart. Common neurologic manifestations include: sensorimotor polyneuropathy (PN), autonomic neuropathy, small-fiber PN, and carpal tunnel syndrome. Many patients have significant progression due to diagnostic delays as hATTR PN is not considered within the differential diagnosis. Recently, two effective novel disease-modifying therapies, inotersen and patisiran, were approved by Health Canada for the treatment of hATTR PN. Early diagnosis is crucial for the timely introduction of these disease-modifying treatments that reduce impairments, improve quality of life, and extend survival. In this guideline, we aim to improve awareness and outcomes of hATTR PN by making recommendations directed to the diagnosis, monitoring, and treatment in Canada.

A Systematic Review of the Diagnostic Methods of Small Fiber Neuropathies in Rehabilitation

This systematic review describes the several methods to diagnose and measure the severity of small fiber neuropathies and aims to guide the physician to define all the diagnostic approaches for adopting the best strategies described in the current literature. The search was conducted in PubMed, EMBASE, Cochrane Library and Web of Science. Two reviewers independently reviewed and came to consensus on which articles met inclusion/exclusion criteria. The authors excluded all the duplicates, animals’ studies, and included the English articles in which the diagnostic measures were finalized to assess the effectiveness of rehabilitation and pharmacologic treatment of patients with small fiber neuropathies. The search identified a total of 975 articles with the keywords “small fiber neuropathy” AND “rehabilitation” OR “therapy” OR “treatment”. Seventy-eight selected full-text were analyzed by the reviewers. Forty-one publications met the inclusion criteria and were included in the systematic review. Despite the range of diagnostic tools for the assessment of small fiber neuropathy, other robust trials are needed. In addition, always different diagnostic approaches are used, a unique protocol could be important for the clinicians. More research is needed to build evidence for the best diagnostic methodologies and to delineate a definitive diagnostic protocol.

Scientific Advances in and Clinical Approaches to Small-Fiber Polyneuropathy: A Review

IMPORTANCE

Small-fiber polyneuropathy involves preferential damage to the thinly myelinated A-delta fibers, unmyelinated C sensory fibers, or autonomic or trophic fibers. Although this condition is common, most patients still remain undiagnosed and untreated because of lagging medical and public awareness of research advances. Chronic bilateral neuropathic pain, fatigue, and nausea are cardinal symptoms that can cause disability and dependence, including pain medication dependence.

OBSERVATIONS

Biomarker confirmation is recommended, given the nonspecificity of symptoms. The standard test involves measuring epidermal neurite density within a 3-mm protein gene product 9.5 (PGP9.5)-immunolabeled lower-leg skin biopsy. Biopsies and autonomic function testing confirm that small-fiber neuropathy not uncommonly affects otherwise healthy children and young adults, in whom it is often associated with inflammation or dysimmunity. A recent meta-analysis concluded that small-fiber neuropathy underlies 49% of illnesses labeled as fibromyalgia. Initially, patients with idiopathic small-fiber disorders should be screened by medical history and blood tests for potentially treatable causes, which are identifiable in one-third to one-half of patients. Then, secondary genetic testing is particularly important for familial and childhood cases. Treatable genetic causes include Fabry disease, transthyretin and primary systemic amyloidosis, hereditary sensory autonomic neuropathy-1, and ion-channel mutations. Immunohistopathologic evidence suggests that small-fiber dysfunction and denervation, especially of blood vessels, contributes to diverse symptoms, including postexertional malaise, postural orthostatic tachycardia, and functional gastrointestinal distress. Preliminary evidence implicates acute or chronic autoreactivity in some cases, particularly in female patients and otherwise healthy children and young adults. Different temporal patterns akin to Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy have been described; here, corticosteroids and immunoglobulins, which are often efficacious for inflammatory neuropathic conditions, are increasingly considered.

CONCLUSIONS AND RELEVANCE

Because small fibers normally grow throughout life, improving contributory conditions may permit regrowth, slow progression, and prevent permanent damage. The prognosis is often hopeful for improving quality of life and sometimes for abatement or resolution, particularly in the young and otherwise healthy individuals. Examples include diabetic, infectious, toxic, genetic, and inflammatory causes. The current standard of care requires prompt diagnosis and treatment, particularly in children and young adults, to restore life trajectory. Consensus diagnostic and tracking metrics should be established to facilitate treatment trials.

Potency of descending pain modulatory system is linked with peripheral sensory dysfunction in fibromyalgia: An exploratory study

Fibromyalgia (FM) is characterized by chronic widespread pain whose pathophysiological mechanism is related to central and peripheral nervous system dysfunction. Neuropathy of small nerve fibers has been implicated due to related pain descriptors, psychophysical pain, and neurophysiological testing, as well as skin biopsy studies. Nevertheless, this alteration alone has not been previously associated to the dysfunction in the descending pain modulatory system (DPMS) that is observed in FM. We hypothesize that they associated, thus, we conducted a cross-sectional exploratory study.To explore small fiber dysfunction using quantitative sensory testing (QST) is associated with the DPMS and other surrogates of nociceptive pathways alterations in FM.We run a cross-sectional study and recruited 41 women with FM, and 28 healthy female volunteers. We used the QST to measure the thermal heat threshold (HTT), heat pain threshold (HPT), heat pain tolerance (HPT), heat pain tolerance (HPTo), and conditional pain modulation task (CPM-task). Algometry was used to determine the pain pressure threshold (PPT). Scales to assess catastrophizing, anxiety, depression, and sleep disturbances were also applied. Serum brain-derived neurotrophic factor (BDNF) was measured as a marker of neuroplasticity. We run multivariate linear regression models by group to study their relationships.Samples differed in their psychophysical profile, where FM presented lower sensitivity and pain thresholds. In FM but not in the healthy subjects, regression models revealed that serum BDNF was related to HTT and CPM-Task (Hotelling Trace = 1.80, P < .001, power = 0.94, R = 0.64). HTT was directly related to CPM-Task (B = 0.98, P = .004, partial-η = 0.25), and to HPT (B = 1.61, P = .008, partial η = 0.21), but not to PPT. Meanwhile, BDNF relationship to CPM-Task was inverse (B = -0.04, P = .043, partial-η = 0.12), and to HPT was direct (B = -0.08, P = .03, partial-η = 0.14).These findings high spot that in FM the disinhibition of the DPMS is positively correlated with the dysfunction in peripheral sensory neurons assessed by QST and conversely with serum BDNF.

Definition and diagnosis of small fiber neuropathy: consensus from the Peripheral Neuropathy Scientific Department of the Brazilian Academy of Neurology

The aim of this study was to describe the results of a Brazilian Consensus on Small Fiber Neuropathy (SFN). Fifteen neurologists (members of the Brazilian Academy of Neurology) reviewed a preliminary draft. Eleven panelists got together in the city of Fortaleza to discuss and finish the text for the manuscript submission. Small fiber neuropathy can be defined as a subtype of neuropathy characterized by selective involvement of unmyelinated or thinly myelinated sensory fibers. Its clinical picture includes both negative and positive manifestations: sensory (pain/dysesthesias/pruritus) or combined sensory and autonomic complaints, associated with an almost entirely normal neurological examination. Standard electromyography is normal. A growing list of medical conditions is associated with SFN. The classification of SFN may also serve as a useful terminology to uncover minor discrepancies in the normal values from different neurophysiology laboratories. Several techniques may disclose sensory and/or autonomic impairment. Further studies are necessary to refine these techniques and develop specific therapies.

Characterizing human skin blood flow regulation in response to different local skin temperature perturbations

Small nerve fibers regulate local skin blood flow in response to local thermal perturbations. Small nerve fiber function is difficult to assess with classical neurophysiological tests. In this study, a vasomotor response model in combination with a heating protocol was developed to quantitatively characterize the control mechanism of small nerve fibers in regulating skin blood flow in response to local thermal perturbation. The skin of healthy subjects' hand dorsum (n=8) was heated to 42°C with an infrared lamp, and then naturally cooled down. The distance between the lamp and the hand was set to three different levels in order to change the irradiation intensity on the skin and implement three different skin temperature rise rates (0.03°C/s, 0.02°C/s and 0.01°C/s). A laser Doppler imager (LDI) and a thermographic video camera recorded the temporal profile of the skin blood flow and the skin temperature, respectively. The relationship between the skin blood flow and the skin temperature was characterized by a vasomotor response model. The model fitted the skin blood flow response well with a variance accounted for (VAF) between 78% and 99%. The model parameters suggested a similar mechanism for the skin blood flow regulation with the thermal perturbations at 0.03°C/s and 0.02°C/s. But there was an accelerated skin vasoconstriction after a slow heating (0.01°C/s) (p-value<0.05). An attenuation of the skin vasodilation was also observed in four out of the seven subjects during the slow heating (0.01°C/s). Our method provides a promising way to quantitatively assess the function of small nerve fibers non-invasively and non-contact.

Association Between Overactive Bladder and Polyneuropathy in Diabetic Patients

Purpose

Diabetes mellitus (DM) is a chronic metabolic disorder that often leads to complications. We aimed to correlate two complications of DM, polyneuropathy and hyperactive bladder syndrome, using noninvasive measures, such as screening tests.

Methods

We included 80 female and 40 male type 2 diabetic patients in this prospective study. Diabetic polyneuropathy evaluations were conducted using the Douleur Neuropathique 4 Questions (DN4), and overactive bladder (OAB) evaluations were performed using the Overactive Bladder Questionnaire (OAB-V8). The patients were also evaluated for retinopathy and nephropathy. The diabetic male and female patients with or without OAB were chosen and compared for microvascular complications (polyneuropathy, retinopathy, and nephropathy).

Results

There were no significant correlations between OAB and retinopathy as well as between OAB and nephropathy among diabetic patients (female patients, P>0.05; male patients, P>0.05). However, the patients with OAB were significantly more likely to develop polyneuropathy (female patients, P<0.05; male patients, P<0.05).

Conclusions

In diabetic patients, OAB and diabetic peripheral neuropathy are significantly correlated. These correlations were demonstrated using short, understandable, valid, and reliable disease-specific tests without invasive measures. Using these screening tests, both neurologists and urologists can easily diagnose these complications.

In Vivo Confocal Microscopy of the Human Cornea in the Assessment of Peripheral Neuropathy and Systemic Diseases

In vivo confocal microscopy (IVCM) of the living human cornea offers the ability to perform repeated imaging without tissue damage. Studies using corneal IVCM have led to significant contributions to scientific and clinical knowledge of the living cornea in health and pathological states. Recently the application of corneal IVCM beyond ophthalmology to wider clinical and research fields has been demonstrated. Abnormalities of the corneal subbasal nerve plexus have been associated with many forms of peripheral neuropathy and Langerhans cells correlate with systemic inflammatory states. There is a rapidly growing evidence base investigating the use of corneal IVCM in many systemic conditions and a well-established evidence base for IVCM imaging of the corneal subbasal plexus in diabetic peripheral neuropathy. This paper reviews the potential use of corneal IVCM in general clinical practice as a noninvasive method of assessing peripheral neuropathies, monitoring inflammatory states and clinical therapeutic response.

Vibrotactile evaluation: osseointegrated versus socket-suspended transfemoral prostheses

This study investigated detection thresholds of vibrometric stimuli in patients with transfemoral amputation supplied with osseointegrated (OI) and socket-suspended prostheses. It included 17 patients tested preoperatively with socket-suspended prostheses and after 2 yr with OI prostheses and a control group (n = 17) using socket-suspended prostheses, evaluated once. Assessments on the prosthetic and intact feet were conducted at six frequencies (8, 16, 32, 64, 125, and 250 Hz). Furthermore, measurements were conducted to investigate how vibrometric signals are transmitted through a test prosthesis. The results showed that the OI group had improved ability to detect vibrations through the prosthesis at 125 Hz (p = 0.01) at follow-up compared with the preoperative measurement. Compared with the control group, the OI group at follow-up had better ability to detect high frequency vibrations through the prosthesis (125 Hz, p = 0.02; 250 Hz, p = 0.03). The vibrometric signal transmitted through the test prosthesis was reduced at 8, 125, and 250 Hz but was amplified at 16, 32, and 64 Hz. Differences between the OI and the control groups were found in the highest frequencies in which the test prosthesis showed reduction of the vibrometric signal. The study provides insight into the mechanisms of vibration transmission between the exterior and bone-anchored as well as socket-suspended amputation prostheses.

The complex regional pain syndrome

Complex regional pain syndrome (CRPS) is the current consensus-derived name for a syndrome usually triggered by limb trauma. Required elements include prolonged, disproportionate distal-limb pain and microvascular dysregulation (e.g., edema or color changes) or altered sweating. CRPS-II (formerly "causalgia") describes patients with identified nerve injuries. CRPS-I (formerly "reflex sympathetic dystrophy") describes most patients who lack evidence of specific nerve injuries. Diagnosis is clinical and the pathophysiology involves combinations of small-fiber axonopathy, microvasculopathy, inflammation, and brain plasticity/sensitization. Females have much higher risk and workplace accidents are a well-recognized cause. Inflammation and dysimmunity, perhaps facilitated by injury to the blood-nerve barrier, may contribute. Most patients, particularly the young, recover gradually, but treatment can speed healing. Evidence of efficacy is strongest for rehabilitation therapies (e.g., graded-motor imagery), neuropathic pain medications, and electric stimulation of the spinal cord, injured nerve, or motor cortex. Investigational treatments include ketamine, botulinum toxin, immunoglobulins, and transcranial neuromodulation. Nonrecovering patients should be re-evaluated for neurosurgically treatable causal lesions (nerve entrapment, impingement, infections, or tumors) and treatable potentiating medical conditions, including polyneuropathy and circulatory insufficiency. Earlier impressions that CRPS represents malingering or psychosomatic illness have been replaced by evidence that CRPS is a rare complication of limb injury in biologically susceptible individuals.

Structural and functional assessment of skin nerve fibres in small-fibre pathology

Damage to nociceptor nerve fibres may give rise to peripheral neuropathies, some of which are pain free and some are painful. A hallmark of many peripheral neuropathies is the loss of small nerve fibres in the epidermis, a condition called small-fibre neuropathy (SFN) when it is predominantly the small nerve fibres that are damaged. Historically, SFN has been very difficult to diagnose as clinical examination and nerve conduction studies mainly detect large nerve fibres, and quantitative sensory testing is not sensitive enough to detect small changes in small nerve fibres. However, taking a 3-mm punch skin biopsy from the distal leg and quantification of the nerve fibre density has proven to be a useful method to diagnose SFN. However, the correlation between the nerve fibre loss and other test results varies greatly. Recent studies have shown that it is possible not only to extract information about the nerve fibre density from the biopsies but also to get an estimation of the nerve fibre length density using stereology, quantify sweat gland innervation and detect morphological changes such as axonal swelling, all of which may be additional parameters indicating diseased small fibres relating to symptoms reported by the patients. In this review, we focus on available tests to assess structure and function of the small nerve fibres, and summarize recent advances that have provided new possibilities to more specifically relate structural findings with symptoms and function in patients with SFN.

Chiropractic management of a 24-year-old woman with idiopathic, intermittent right-sided hemiparesthesia

OBJECTIVE

The purpose of this case report is to describe the chiropractic management of a patient with idiopathic, intermittent right-sided hemiparesthesia.

CLINICAL FEATURES

A 24-year-old woman presented with a 2-year history of intermittent idiopathic right arm paresthesia. She also had a 3-month history of intermittent idiopathic right leg/face paresthesia. These symptoms were strongest at night and caused insomnia and worsened over time. She rated her discomfort at 5/10 on a numeric scale.

INTERVENTION AND OUTCOME

Care included vibration stimulation therapy, spinal manipulation and cold laser therapy. She had a noticeable reduction in her paresthesia both subjectively and objectively. She showed improvement in paresthesia on the right side of her body after the first visit. The following week, after 2 visits she returned and stated that she was symptom free with 0/10 discomfort on a numeric scale.

CONCLUSION

This patient's symptoms of idiopathic, intermittent right-sided hemi-paresthesia seemed to improve with a short course of chiropractic care using manipulation, vibration therapy and cold laser therapy.

Rapid automated diagnosis of diabetic peripheral neuropathy with in vivo corneal confocal microscopy

PURPOSE

To assess the diagnostic validity of a fully automated image analysis algorithm of in vivo confocal microscopy images in quantifying corneal subbasal nerves to diagnose diabetic neuropathy.

METHODS

One hundred eighty-six patients with type 1 and type 2 diabetes mellitus (T1/T2DM) and 55 age-matched controls underwent assessment of neuropathy and bilateral in vivo corneal confocal microscopy (IVCCM). Corneal nerve fiber density (CNFD), branch density (CNBD), and length (CNFL) were quantified with expert, manual, and fully-automated analysis. The areas under the curve (AUC), odds ratios (OR), and optimal thresholds to rule out neuropathy were estimated for both analysis methods.

RESULTS

Neuropathy was detected in 53% of patients with diabetes. A significant reduction in manual and automated CNBD (P < 0.001) and CNFD (P < 0.0001), and CNFL (P < 0.0001) occurred with increasing neuropathic severity. Manual and automated analysis methods were highly correlated for CNFD (r = 0.9, P < 0.0001), CNFL (r = 0.89, P < 0.0001), and CNBD (r = 0.75, P < 0.0001). Manual CNFD and automated CNFL were associated with the highest AUC, sensitivity/specificity and OR to rule out neuropathy.

CONCLUSIONS

Diabetic peripheral neuropathy is associated with significant corneal nerve loss detected with IVCCM. Fully automated corneal nerve quantification provides an objective and reproducible means to detect human diabetic neuropathy.

Examination and clinical care of the patient with neuropathy

Examination of a patient with peripheral neuropathy starts with careful questioning of the patient about the history of symptoms and signs and of a possible familial disorder. Several steps are required during examination of the patient with peripheral neuropathy: first the pattern of neuropathy and site of lesions should be determined: roots, nerve trunks, focal, multifocal, length-dependent generalized polyneuropathy, the type of nerve fibers predominantly affected, the association with trophic changes and autonomic dysfunction, the course of the disease ranging from acute inflammatory polyneuritis or fulminant multifocal neuropathy to an extremely slow progression as in Charcot-Marie-Tooth syndromes. At the end of this first contact with the patient, the neurologist must decide which investigations seem necessary and their timing including electrophysiological tests, imaging, CSF examination, blood tests, nerve and muscle biopsy, DNA testing, etc. In some cases, life-threatening manifestations, including weakness of respiratory muscles or swallowing difficulty, or autonomic dysfunction, require urgent therapeutic decisions.

Objective evidence that small-fiber polyneuropathy underlies some illnesses currently labeled as fibromyalgia

Fibromyalgia is a common, disabling syndrome that includes chronic widespread pain plus diverse additional symptoms. No specific objective abnormalities have been identified, which precludes definitive testing, disease-modifying treatments, and identification of causes. In contrast, small-fiber polyneuropathy (SFPN), despite causing similar symptoms, is definitionally a disease caused by the dysfunction and degeneration of peripheral small-fiber neurons. SFPN has established causes, some diagnosable and definitively treatable, eg, diabetes. To evaluate the hypothesis that some patients labeled as having fibromyalgia have unrecognized SFPN that is causing their illness symptoms, we analyzed SFPN-associated symptoms, neurological examinations, and pathological and physiological markers in 27 patients with fibromyalgia and in 30 matched normal controls. Patients with fibromyalgia had to satisfy the 2010 American College of Rheumatology criteria plus present evidence of a physician's actual diagnosis of fibromyalgia. The study's instruments comprised the Michigan Neuropathy Screening Instrument (MNSI), the Utah Early Neuropathy Scale (UENS), distal-leg neurodiagnostic skin biopsies, plus autonomic-function testing (AFT). We found that 41% of skin biopsies from subjects with fibromyalgia vs 3% of biopsies from control subjects were diagnostic for SFPN, and MNSI and UENS scores were higher in patients with fibromyalgia than in control subjects (all P ≤ 0.001). Abnormal AFTs were equally prevalent, suggesting that fibromyalgia-associated SFPN is primarily somatic. Blood tests from subjects with fibromyalgia and SFPN-diagnostic skin biopsies provided insights into causes. All glucose tolerance tests were normal, but 8 subjects had dysimmune markers, 2 had hepatitis C serologies, and 1 family had apparent genetic causality. These findings suggest that some patients with chronic pain labeled as fibromyalgia have unrecognized SFPN, a distinct disease that can be tested for objectively and sometimes treated definitively.

Utility of skin biopsy in management of small fiber neuropathy

INTRODUCTION

We examined the role of skin biopsy in the evaluation and management of patients with suspected small fiber neuropathy (SFN).

METHODS

A retrospective chart review was performed among all patients who underwent skin biopsy for evaluation of SFN at our institution between March 2008 and March 2011. Change in management was defined as a new diagnosis or change in treatment in response to both positive and negative skin biopsies.

RESULTS

Among 69 patients who underwent skin biopsy, 25 had pathological evidence of an SFN, and 9 had evidence of borderline SFN. Change in management or diagnosis occurred in 14 of 25 patients with definite SFN, 6 of 9 patients with borderline SFN, and 16 of 35 biopsy negative patients.

CONCLUSIONS

Skin biopsy changed management or diagnosis in 52% of patients evaluated for a possible SFN and appears to play a valuable role in the workup of these patients.

Corneal confocal microscopy to assess diabetic neuropathy: an eye on the foot

Accurate detection and quantification of human diabetic peripheral neuropathy are important to define at-risk patients, anticipate deterioration, and assess new therapies. Easily performed clinical techniques such as neuro-logical examination, assessment of vibration perception or insensitivity to the 10 g monofilament only assess advanced neuropathy, i.e., the at-risk foot. Techniques that assess early neuropathy include neurophysiology (which assesses only large fibers) and quantitative sensory testing (which assesses small fibers), but they can be highly subjective while more objective techniques, such as skin biopsy for intra-epidermal nerve fiber density quantification, are invasive and not widely available. The emerging ophthalmic technique of corneal confocal microscopy allows quantification of corneal nerve morphology and enables clinicians to diagnose peripheral neuropathy in diabetes patients, quantify its severity, and potentially assess therapeutic benefit. The present review provides a detailed critique of the rationale, a practical approach to capture images, and a basis for analyzing and interpreting the images. We also critically evaluate the diagnostic ability of this new noninvasive ophthalmic test to diagnose diabetic and other peripheral neuropathies.

Neurophysiological techniques to detect early small-fiber dysfunction in transthyretin amyloid polyneuropathy

INTRODUCTION

Transthyretin familial amyloid polyneuropathy (TTR-FAP) is characterized by early selective involvement of small nerve fibers. Initial clinical diagnosis is complicated by psychosocial factors. We evaluated diagnostic accuracy of sural sensory nerve action potentials, plantar sympathetic skin response (SSR), and cortical laser-evoked potentials (LEP) to dorsal foot stimulation in the early diagnosis of TTR-FAP.

METHODS

Sixty-three subjects with TTR-FAP (Val30Met) mutation were split into 2 groups (asymptomatic carriers and early-symptomatic patients) and compared with 33 healthy controls.

RESULTS

The diagnostic accuracy of plantar SSR amplitude and LEP N2 latency was similar; all had very high specificity (94 to 97%) but low sensitivity (22 to 32%) in distinguishing controls from carriers and early-symptomatic patients. No control had abnormal results on both tests.

CONCLUSIONS

Plantar SSR and LEPs have similar diagnostic performance in detecting small-fiber dysfunction in early TTR-FAP; we propose that both tests should be used to investigate this population. Muscle Nerve 49: 181-186, 2014.

The rate of decline in small fibre function assessed using axon reflex-mediated neurogenic vasodilatation and the importance of age related centile values to improve the detection of clinical neuropathy

Background

The LDIflare technique (LDIflare) is a simple non-invasive test of small fibre function in dorsal foot skin involving skin heating and measuring the size of the resulting axon reflex-mediated vasodilator (flare) response using a laser Doppler imager (LDI). This study establishes age-related normative reference ranges for the test and determines the rate of decline in small fibre function per decade. Additionally, the potential value of using age related centiles rather than Receiver Operator Curves (ROC) was explored by comparison of the sensitivity and specificity of each analytic technique in identifying clinical neuropathy.

Methods

LDIflare areas were assessed in 94 healthy controls and 66 individuals with diabetes with (DN+, n = 31) and without clinical neuropathy (DN-, n = 35); neuropathy defined as a Neuropathy Disability Score ≥3. The age specific 5th centile values were used as the ‘cut-offs’ for the diagnosis of neuropathy from which sensitivity and specificity were calculated.

Results

There was a significant age dependant decrease in LDIflare size (r = −0.42, p<0.0001) with no significant gender differences. The LDIflare size reduced 0.56 cm² per decade which gives a percentage reduction of approximately 5.5% per decade. Using the normative 5th centiles as the cut-offs, the technique had a sensitivity of 77%, specificity of 90%, positive predictive value of 82% and negative predictive value of 87%.The ROC analysis gave a threshold of <3.66 cm² for the cut-off, resulting in a sensitivity of 75%, specificity of 85%, positive predictive value of 74% and negative predictive value of 86%.

Conclusions

There is an age dependent decrease in small fibre function in the foot of 5.5% per decade. Both analytic techniques demonstrate good sensitivity and specificity for detecting clinical neuropathy but the technique based on age centiles offers better diagnostic accuracy and is therefore proposed as the method of choice.

Uses of skin biopsy for sensory and autonomic nerve assessment

Skin biopsy is a valuable diagnostic tool for small-fiber-predominant neuropathy by the quantification of intraepidermal nerve fiber density (IENFD). It has the unique advantage of being a minimally invasive procedure with the potential for longitudinal evaluation of both sensory and autonomic fibers. Unmyelinated small fibers are not otherwise quantified objectively with such a level of sensitivity as has been reported with IENFD. Recent advances include an expansion of the skin punch biopsy technique to evaluate larger myelinated fibers and mechanoreceptors, and recent work has also focused on additional methods of quantifying dermal fibers and densely innervated autonomic structures. This review discusses current work using skin biopsy for the pathologic analysis of peripheral nerve fibers in neuropathy of various causes as well as its use in clinical trials.

Evidence of small-fiber polyneuropathy in unexplained, juvenile-onset, widespread pain syndromes

OBJECTIVE

We tested the hypothesis that acquired small-fiber polyneuropathy (SFPN), previously uncharacterized in children, contributes to unexplained pediatric widespread pain syndromes.

METHODS

Forty-one consecutive patients evaluated for unexplained widespread pain beginning before age 21 had medical records comprehensively analyzed regarding objective diagnostic testing for SFPN (neurodiagnostic skin biopsy, nerve biopsy, and autonomic function testing), plus histories, symptoms, signs, other tests, and treatments. Healthy, demographically matched volunteers provided normal controls for SFPN tests.

RESULTS

Age at illness onset averaged 12.3 ± 5.7 years; 73% among this poly-ethnic sample were female (P = .001). Sixty-eight percent were chronically disabled, and 68% had hospitalizations. Objective testing diagnosed definite SFPN in 59%, probable SFPN in 17%, and possible SFPN in 22%. Only 1 of 41 had entirely normal SFPN test results. Ninety-eight percent of patients had other somatic complaints consistent with SFPN dysautonomia (90% cardiovascular, 82% gastrointestinal, and 34% urologic), 83% reported chronic fatigue, and 63% had chronic headache. Neurologic examinations identified reduced sensation in 68% and vasomotor abnormalities in 55%, including 23% with erythromelalgia. Exhaustive investigations for SFPN causality identified only history of autoimmune illnesses in 33% and serologic markers of disordered immunity in 89%. Treatment with corticosteroids and/or intravenous immune globulin objectively and subjectively benefited 80% of patients (12/15).

CONCLUSIONS

More than half among a large series of patients with childhood-onset, unexplained chronic widespread pain met rigorous, multitest, diagnostic criteria for SFPN, which extends the age range of acquired SFPN into early childhood. Some cases appeared immune-mediated and improved with immunomodulatory therapies.

Cryptogenic sensory polyneuropathy

Chronic sensory or sensorimotor polyneuropathy is a common cause for referral to neurologists. Despite extensive diagnostic testing, up to one-third of these patients remain without a known cause, and are referred to as having cryptogenic sensory peripheral neuropathy. Symptoms progress slowly. On examination, there may be additional mild toe flexion and extension weakness. Electrophysiologic testing and histology reveals axonal neuropathy. Prognosis is usually favorable, as most patients maintain independent ambulation. Besides patient education and reassurance, management is focused on pharmacotherapy for neuropathic pain and physical therapy for balance training, and, occasionally, assistive devices.

Validation of the modified LDIFlare technique: a simple and quick method to assess C-fiber function

INTRODUCTION

In this study we validated a modified laser Doppler imager method (mLDIf) for assessing C-fiber function and compared it to the original (oLDIf). Both measure flare size in foot skin after heating, but the mLDIf uses 47°C (vs. 44°C), making it quicker and better suited for clinical use.

METHODS

To confirm that mLDIf assesses C-fiber function, 5 healthy controls (HC) were studied before and after local anesthesia (LA). Reproducibility and comparison with oLDIf was assessed in HC (n = 16). Finally, diabetes subjects with (DN(+), n = 10) and without (DN(-), n = 16) neuropathy were studied.

RESULTS

LA almost abolished the flare (9.3 ± 3.0 cm(2) vs. 1.7 ± 0.3 cm(2), P < 0.0001). mLDIf produced larger flares (9.9 ± 3.4 vs. 5.7 ± 2.3 cm(2), P < 0.0001), but correlated with oLDIf (r = 0.81, P < 0.001). mLDIf was reduced in DN(-) (6.8 ± 2.8 vs. HC, P = 0.003), markedly so in DN(+) (2.0 ± 1.1 vs. HC and DN(-), P < 0.0001).

CONCLUSION

The mLDIf is a quick, practical method for assessing C-fiber function in the clinical setting.

Small fiber neuropathy: is skin biopsy the holy grail?

Small fiber neuropathy (SFN) is characterized by negative sensory symptoms (thermal and pinprick hypoesthesia) reflecting peripheral deafferentation and positive sensory symptoms and signs (burning pain, allodynia, hyperalgesia), which often dominate the clinical picture. In patients with pure SFN, clinical and neurophysiologic investigation do not show involvement of large myelinated nerve fiber making the diagnosis of SFN challenging in clinical practice. Over the last 15 years, skin biopsy has emerged as a novel tool that readily permits morphometric and qualitative evaluation of somatic and autonomic small nerve fibers. This technique has overcome the limitations of routine neurophysiologic tests to detect the damage of small nerve fibers. The recent availability of normative reference values allowed clinicians to reliably define the diagnosis of SFN in individual patients. This paper reviews usefulness and limitations of skin biopsy and the relationship between degeneration and regeneration of small nerve fibers in patients with diabetes and metabolic syndrome.

Measures of small-fiber neuropathy in HIV infection

INTRODUCTION

Noninvasive methods are needed to detect distal sensory polyneuropathy in HIV-infected persons on antiretroviral therapy (ART).

METHODS

Quantitative sudomotor axon reflex test (QSART) and Utah Early Neuropathy Scale (UENS), small-fiber sensitive measures, were assessed in subjects with and without clinical neuropathy. Pain was assessed by visual analog scale (VAS).

RESULTS

Twenty-two subjects had symptoms and signs of neuropathy, 19 had neither, and all were receiving ART. Median sweat volume (μL) was lower at all testing sites in those with neuropathy compared to those without (p<0.01 for all). UENS and VAS (mm) were higher in neuropathy subjects (p<0.05 for each). Lower sweat volume at all sites correlated with higher pin UENS subscore, total UENS, and VAS (p<0.05 for all). In multivariable analyses adjusting for age, CD4⁺ T cells, sex, and use of "d-drug" ART, QSART and UENS remained associated (p=0.003).

CONCLUSION

QSART and UENS have not been previously studied in this patient population and may identify small-fiber neuropathy in HIV-infected, ART-treated persons.

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.

Diabetic neuropathy: a cross-sectional study of the relationships among tests of neurophysiology

OBJECTIVE

To determine the relationships among large, small, and autonomic fiber neurophysiological measures in a cross-sectional study of patients with diabetes.

RESEARCH DESIGN AND METHODS

We assessed 130 individuals: 25 healthy subjects and 105 subjects with diabetes. Subjects were classified by the presence or absence of neuropathy by physical examination. All subjects underwent autonomic testing, nerve conduction studies, quantitative sensory testing, and nerve-axon reflex vasodilation in addition to quantifiable neurological examination and symptom scores. Correlation and cluster analysis were used to determine relationships between and among different neurophysiological testing parameters.

RESULTS

Results of neurophysiological tests were abnormal in patients with clinical evidence of diabetic neuropathy compared with results in healthy control subjects and in those without neuropathy (P < 0.01, all tests). The correlations among individual tests varied widely, both within (r range <0.5->0.9, NS to <0.001) and between test groups (r range <0.2->0.5, NS to <0.01). A two-step hierarchical cluster analysis revealed that neurophysiological tests do not aggregate by typical "small," "large," or "autonomic" nerve fiber subtypes.

CONCLUSIONS

The modest correlation coefficients seen between the different testing modalities suggest that these techniques measure different neurophysiological parameters and are therefore not interchangeable. However, the data suggest that only a small number of neurophysiological tests are actually required to clinically differentiate individuals with neuropathy from those without. The natural clustering of both patients and healthy control subjects suggests that variations in the population will need to be considered in future studies of diabetic neuropathy.

Variation in quantitative sensory testing and epidermal nerve fiber density in repeated measurements

Quantitative sensory testing (QST) is commonly used to evaluate peripheral sensory function in neuropathic conditions. QST measures vary in repeated measurements of normal subjects but it is not known whether QST can reflect small changes in epidermal nerve fiber density (ENFd). This study evaluated QST measures (touch, mechanical pain, heat pain and innocuous cold sensations) for differences between genders and over time using ENFd as an objective-independent measure. QST was performed on the thighs of 36 healthy volunteers on four occasions between December and May. ENFd in skin biopsies was determined on three of those visits. Compared to men, women had a higher ENFd, a difference of 12.2 ENFs/mm. They also had lower tactile and innocuous cold thresholds, and detected mechanical pain (pinprick) at a higher frequency. Heat pain thresholds did not differ between genders. By the end of the 24-week study, men and women showed a small reduction (p<0.05) in the frequency of sharp mechanical pain evoked by pinprick whereas tactile and thermal thresholds showed no change. This coincided with a small decrease in ENFd, 4.18 ENFs/mm. Variation in measurements over time was large in a fraction of normal subjects. We conclude that most QST measures detect relatively large differences in epidermal innervation (12.2 ENFs/mm), but response to mechanical pain was the only sensory modality tested with the sensitivity to detect small changes in innervation (4.18 ENFs/mm). Since some individuals had large unsystematic variations, unexpected test results should therefore alert clinicians to test additional locations.

Diagnosis and assessment of neuropathic pain

Neuropathic pain and pain that has a predominant neuropathic component can be difficult to diagnose in primary care. Several screening questionnaires that incorporate patient symptoms and signs have been developed, and some are supplemented with simple bedside clinical tests for nerve dysfunction. These tools should enable a more rapid and confident diagnosis by the nonspecialist and the earlier start of appropriate treatment.

Reliability of quantitative sudomotor axon reflex testing and quantitative sensory testing in neuropathy of impaired glucose regulation

Reproducible neurophysiologic testing paradigms are critical for multicenter studies of neuropathy associated with impaired glucose regulation (IGR), yet the best methodologies and endpoints remain to be established. This study evaluates the reproducibility of neurophysiologic tests within a multicenter research setting. Twenty-three participants with neuropathy and IGR were recruited from two study sites. The reproducibility of quantitative sudomotor axon reflex test (QSART) and quantitative sensory test (QST) (using the CASE IV system) was determined in a subset of patients at two sessions, and it was calculated from intraclass correlation coefficients (ICCs). QST (cold detection threshold: ICC=0.80; vibration detection threshold: ICC=0.75) was more reproducible than QSART (ICC foot=0.52). The performance of multiple tests in one setting did not improve reproducibility of QST. QST reproducibility in our IGR patients was similar to reports of other studies. QSART reproducibility was significantly lower than QST. In this group of patients, the reproducibility of QSART was unacceptable for use as a secondary endpoint measure in clinical research trials.

Mechanisms of pain and itch caused by herpes zoster (shingles)

Study of humans with shingles or postherpetic neuralgia (PHN) is providing insights into pain mechanisms. Shingles pain is a combination of normal and neuropathic pain that reflects acute tissue and neural injury. PHN pain, which lasts after tissues have healed, is caused by persistent neural injuries. Spontaneous C-nociceptor activity has been documented in painful polyneuropathies and probably occurs in shingles as well, although there are no microneurographic studies of either shingles or PHN. It is uncertain if this persists in PHN since pathological examination of PHN-affected nerves and ganglia show chronic neuronal loss and quiescent scarring without inflammation. Skin-biopsy study has correlated the presence of PHN with the severity of persistent distal nociceptive axon loss, and autopsy has correlated pain persistence with segmental atrophy of the spinal cord dorsal horn, highlighting the importance of central responses to nerve injury. Pathological studies of tissues from patients with trigeminal neuralgia suggest that brief lancinating pains reflect ephaptic neurotransmission between adjacent denuded axons. The mechanisms of chronic spontaneous pain and mechanical allodynia remain uncertain despite considerable indirect evidence from animal models. Postherpetic itch is presumably caused by unprovoked firing of the peripheral and/or central neurons that mediate itch. If it occurs in neurons innervating skin left severely deafferented from shingles ("numb"), patients can give themselves painless injuries from scratching. Further human study, by electrophysiological recording, by structural and functional imaging, and by autopsy, should continue to provide much-needed insights.

PERSPECTIVE

Many patients continue to have chronic pain and/or itch after shingles that is unrelieved by current treatments. Many will gladly volunteer for clinical studies, including autopsy, to try and improve understanding of these common and disabling conditions. Their prevalence makes highly powered studies feasible. Funding and organization are the current bottlenecks.

Comparison of clinical evaluation and neurosensory testing in the early diagnosis of superimposed entrapment neuropathy in diabetic patients

Diabetic patients are more susceptible to the development of entrapment neuropathy than nondiabetics. Since these patients suffer from a slowly progressing diabetic polyneuropathy, standard neurosensory and motor tests of nerve function are not sufficient in the diagnosis of superimposed nerve compression. This is most evident in the early stages of compression when quantitative diagnosis is important for making decisions on surgical decompression. We evaluated the validity of computer-assisted pressure-specified sensory device (PSSD) testing in the early detection of superimposed entrapment in diabetic neuropathy in comparison with standard clinical tests. Twenty-five diabetic patients with complaints of peripheral nerve dysfunction were evaluated by clinical tests and PSSD. Out of those, nerve entrapment was detected in 15 patients (60%) (9 in late and 6 in early stage) by neurosensory PSSD testing. Standard clinical tests were confirmative in 33.3% of these cases (44% of late and 16.7% of early stage). Out of 144 evaluated nerves, 50 were diagnosed with entrapment (24 in late and 26 in early stage) using PSSD. Clinically, diagnosis was confirmed in 16% of entrapped nerves (20.8% of late and 11.5% of early stage). Average diabetes duration in patients with entrapment diagnosed using PSSD was significantly shorter than for those diagnosed clinically (4.14 +/- 2.04 vs. 7.2 +/- 1.3, respectively; P = 0.005). Among evaluated factors, mean age and diabetes duration were found to be significantly shorter in patients with entrapment than in those with advanced diffused changes (54.47 +/- 13.07 vs. 67.10 +/- 14.2; P = 0.019 and 5.33 +/- 3.74 vs.14.22 +/- 8.17; P = 0.006; respectively). Our results revealed higher sensitivity of PSSD in comparison with standard clinical tests in the detection of early-stage entrapment in patients with diabetes. To assess accuracy of PSSD in the proper patients' qualification for surgery, further prospective, postoperative studies are needed.

Therapy insight: neurological complications of prediabetes

Stroke and peripheral neuropathy are recognized neurological complications of diabetes. Increasing epidemiological evidence also implicates the prediabetic state of impaired glucose tolerance (IGT) as a risk factor for cerebrovascular events and peripheral neuropathy. Data linking IGT to cognitive decline or deficits, however, are less robust. IGT is one component of metabolic syndrome, together with central obesity, hypertension, hypertriglyceridemia and reduced HDL. Each component of metabolic syndrome is an independent risk factor for stroke, but hyperglycemia might be more important than other components in the pathogenesis of neuropathy. Goal-driven diet and exercise regimens, together with pharmacological treatment of hyperlipidemia and hypertension, reduce stroke risk, but the effect of these interventions on neuropathy has not been fully explored.