Nerve fibre and sensory end organ density in the epidermis and papillary dermis of the human hand

Age related changes in skin sensitivity assessed with smartphone vibration testing

The capacity to perceive tactile input at the fingertips, referred to as tactile sensitivity, is known to diminish with age due to regressive changes to mechanoreceptor density and morphology. Sensitivity is measured as perceptual responses to stimuli of varying intensity. Contrary to traditional sensitivity monitoring instruments, smartphones are uniquely suited for remote assessment and have shown to deliver highly calibrated stimuli along a broad spectrum of intensity, which may improve test reliability. The aim of this study was to evaluate a vibration-emitting smartphone application, the Vibratus App, as a mode of estimating tactile sensory thresholds in the aging adult. The peripheral nerve function of 40 neurologically healthy volunteers (ages 18-71) was measured using monofilaments, a 128-Hz tuning fork, the Vibratus App, and nerve conduction studies (NCS). Between group differences were analyzed to determine each measurement's sensitivity to age. Spearman correlation coefficients depicted the associative strength between hand-held measurements and sensory nerve action potential (SNAP) amplitude. Inter-rater reliability of traditional instruments and the software-operated smartphone were assessed by intraclass correlation coefficient (ICC2,k). Measurements taken with Vibratus App were significantly different between age groups (p < 0.001). The inter-rater reliability of monofilament, smartphone vibration, and tuning fork testing was moderate to good (ICC2,k = 0.65, 0.69, and 0.79, respectively). The findings of this study support further investigation of smartphones as sensitivity monitoring devices for at home monitoring of skin sensitivity.

Comparison of the effectiveness of local anesthesia for the digital block between single-volar subcutaneous and double-dorsal finger injections: a systematic review and meta-analysis of randomized control trials

Local anesthesia is an effective method to perform digital nerve blocks. In this study, we compare the effectiveness of single-volar subcutaneous and double-dorsal injection through a systematic review and meta-analysis of randomized controlled trials (RCTs). A systematic search of PubMed, Embase, and the Cochrane Library from inception to 7 April 2021 was performed. RCTs with the effects of single-volar subcutaneous and double-dorsal injection were eligible. Meta-analysis was performed using random effect models with pooled standardized mean differences (SMDs) and 95% confidence intervals (CI). RoB 2.0 and GRADE of Recommendation Assessment, Development, and Evaluation criteria were applied for evaluating the bias. A total of 2484 studies were initially identified, with 11 eligible RCTs finally included in the meta-analysis (1363 patients). The pooled data of nine studies showed single-volar injection had a statistically significantly lower pain score (pooled SMD: 0.20, 95% CI, 0.01 to 0.39, p = 0.041, I2 = 58%, N = 1187) and higher patient preference but invalid anesthesia at the dorsal proximal digit. No significant differences were observed in the onset of anesthesia, adjacent digit invalid numbness, distal phalanx invalid anesthesia, additional injection rate, and adverse effects. In conclusion, this meta-analysis of RCTs showed that the single-volar injection was associated with a lower pain sensation during injection and higher patient satisfaction with a reduced anesthetic effect over the proximal dorsal phalanx. Further high-quality RCTs with a higher number of cases are needed to validate our results.

Study of event-related potentials by withdrawal friction on the fingertip

OBJECTIVES

The lack of understanding about the brain's reaction processes in perceiving touch and separation between skin and object surfaces is a barrier to the development of existing brain-computer interface technologies and virtual haptics. These technologies are limited in their ability to advance. It leaves prosthesis users with a limited amount of tactile information that they can feel. This study aims to determine whether distinct surface aspects of various items trigger different reactions from the brain when friction is removed from the surface.

METHODS

When friction is suddenly removed from the surface of an item, a technique called event-related potential, (ERP) is used to study the features of people's EEGs. It is done after the subject has actively explored the object's surface. A 64-channels EEG collecting system was utilized to acquire EEG data from the individuals. [Corrections added on 5 December 2022, after first online publication: The preceding sentence has been updated.] The event-related potentials for friction removal were generated using the Oddball paradigm, and the samples consisted of sandpaper with three distinct degrees of roughness. We utilized a total of 20 participants, 10 of whom were male, and 10 of whom were female, with a mean age of 21 years.

RESULTS

It was discovered that the P3 component of event-related potentials, which is essential for cognition, was noticeably absent in the friction withdrawal response for various roughnesses. It was the case regardless of whether the surface was smooth or rough. Moreover, there was no statistically significant difference between the P1 andP2 components, which suggests that the brain could not recognize the surface properties of objects with varying roughness as the friction withdrawal was being performed.

CONCLUSIONS

It has been demonstrated that tactile recognition does not occur after friction withdrawal. The findings of this paper could have significant repercussions for future research involving the study of haptic perception and brain-computer interaction in prosthetic hands. It is a step toward future research on the mechanisms underlying human tactile perception, so think of it as preparation.

Reverse Neurocutaneous Flap Based on the Dorsal Branch of the Ulnar Artery for Palm Coverage in Children: Long-Term Results

PURPOSE

Although the palm is spared mostly in severe burn injuries, it often is affected in children and requires radical excision of contracting scar tissue to allow normal hand development. Since alternatives are limited for palmar coverage, we primarily use a reverse-perfused, neurocutaneous dorsal ulnar artery flap. We report here our long-term follow-up results.

METHODS

We reviewed the long-term results of 10 postburn palmar contracture release and flap coverage procedures in 10 children. The applied flap was based distally on the dorsal branch of the ulnar artery and harvested along the ulnar aspect of the hand and wrist. The pivot point of the flap was located dorsally, close to the 4th and 5th metacarpal base. Patients were followed for a median period of 6 years (range, 4-20 years).

RESULTS

Flap size ranged from 60-130 mm in length and 20-35 mm in width. This variation in flap dimensions resulted from different hand sizes, because of the various patient ages at surgery. All flaps survived, donor site healing was uneventful, and marginal flap necrosis occurred only once. Satisfactory restoration of range of motion without secondary contractures was observed. Moreover, we detected adequate progressive growth, adaptability and sensory recovery in all flaps. Over time, the flaps mostly become hairless and progressively flattened without debulking.

CONCLUSIONS

The importance of this flap lies in the potential for considerable tissue mobilization to cover palmar defects without sacrificing any major vascular axis. The adequate progressive growth of the flap facilitates functional hand development in children. The predictable vascular anatomy, wide range, and durable, thin, and pliable skin make the reverse neurocutaneous dorsal ulnar artery flap an appealing option for soft tissue reconstruction of the palm in children.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic V.

Outcomes of Flexor Tendon Repair in Patients With Concurrent Neurovascular Injuries of Multiple Digits in Zone 1

PURPOSE

We treated several patients with multiple flexor (flexor digitorum profundus; FDP) injuries accompanied by injuries to the digital nerve or vessels around the distal interphalangeal crease (zone 1). Here, we retrospectively report the outcomes and review the literature.

MATERIALS AND METHODS

Between January 2010 and December 2018, 16 patients who met the study inclusion criteria were investigated. Tendons were repaired using the cross-locked cruciate (Adelaide) technique (6-strand) or modified Becker method (4-strand). The neurovascular structures were repaired under a microscope.

RESULTS

Sixteen patients (47 digits) were treated. According to the criteria of Moiemen and Elliot, the lacerated areas were in zones IA and IB in 7 and 40 digits, respectively. The mean ranges of motion were 149.27 ± 7.78 and 66.43 ± 2.04 degrees according to the Strickland and modified Strickland assessments, respectively. The mean 2-point discrimination was 5.00 ± 0.63 mm. Four patients (group 1) presented with injuries to 2 digits, and 9 (group 2) and 3 (group 3) patients had 3 and 4 injured digits, respectively. The outcomes were satisfactory in terms of the mean range of motion; 2-point discrimination; cold tolerance; visual analog scale pain score; Disabilities of the Arm, Shoulder, and Hand score; and grip strength. There were no differences among the groups.

CONCLUSIONS

Open multiple-finger injuries involving flexor digitorum profundus rupture with concurrent neurovascular injuries on one or both sides occasionally occur in industrial environments. Fortunately, each digit exhibits a consistent injury type in a particular anatomical location; appropriate repair yields satisfactory outcomes despite the presence of multiple injuries.

Daylight-PDT: everything under the sun

5-Aminolevulinic acid-based photodynamic therapy (ALA-PDT) was first implemented over three decades ago and has since been mainly part of clinical practice for the management of pre-cancerous and cancerous skin lesions. Photodynamic therapy relies on the combination of a photosensitizer, light and oxygen to cause photo-oxidative damage of cellular components. 5-Aminolevulinic acid (ALA) is a natural precursor of the heme biosynthetic pathway, which when exogenously administered leads to the accumulation of the photoactivatable protoporphyrin IX. Although, effective and providing excellent cosmetic outcomes, its use has been restricted by the burning, stinging, and prickling sensation associated with treatment, as well as cutaneous adverse reactions that may be induced. Despite intense research in the realm of drug delivery, pain moderation, and light delivery, a novel protocol design using sunlight has led to some of the best results in terms of treatment response and patient satisfaction. Daylight PDT is the protocol of choice for the management of treatment of multiple or confluent actinic keratoses (AK) skin lesions. This review aims to revisit the photophysical, physicochemical and biological characteristics of ALA-PDT, and the underlying mechanisms resulting in daylight PDT efficiency and limitations.

Characteristics of Pruritus in Various Clinical Variants of Psoriasis: Results of the Multinational, Multicenter, Cross-Sectional Study

Psoriasis is a chronic, inflammatory skin disease present in about 3% of the world’s population. The clinical symptoms manifest diversely, therefore one can distinguish several subtypes of psoriasis. The majority of patients with psoriasis experience pruritus, which is an unpleasant sensation that decreases patients’ quality of life. The knowledge on pruritus in different subtypes of psoriasis is limited. We have performed a cross-sectional, prospective, and multicenter study to evaluate the relationship between clinical subtypes of psoriasis (large-plaque, nummular, guttate, palmoplantar, inverse, erythrodermic, palmoplantar pustular, generalized pustular psoriasis, and psoriasis of the scalp) and the prevalence, intensity, and clinical manifestation of itch. We introduced a questionnaire assessing various aspects of pruritus to a total of 254 patients. Out of these, 42 were excluded. Pruritus was present in 92.9% of the remaining patients and its prevalence did not depend on the clinical subtype. A correlation between the severity of psoriasis and the intensity of itch was explicitly noticeable in palmoplantar pustular psoriasis and scalp psoriasis (p < 0.05). The itch sensation was individual and differed among subtypes of psoriasis. In conclusion, pruritus is a frequent phenomenon, and its presentation is different in various subtypes of psoriasis.

Sensuator: A Hybrid Sensor–Actuator Approach to Soft Robotic Proprioception Using Recurrent Neural Networks

Soft robotic actuators are now being used in practical applications; however, they are often limited to open-loop control that relies on the inherent compliance of the actuator. Achieving human-like manipulation and grasping with soft robotic actuators requires at least some form of sensing, which often comes at the cost of complex fabrication and purposefully built sensor structures. In this paper, we utilize the actuating fluid itself as a sensing medium to achieve high-fidelity proprioception in a soft actuator. As our sensors are somewhat unstructured, their readings are difficult to interpret using linear models. We therefore present a proof of concept of a method for deriving the pose of the soft actuator using recurrent neural networks. We present the experimental setup and our learned state estimator to show that our method is viable for achieving proprioception and is also robust to common sensor failures.

Teaching children with autism to tact private events based on public accompaniments

We evaluated a method for teaching children with autism spectrum disorder to respond to tactile stimulation of multiple body parts. Various objects (e.g., hairbrush) produced the sensations (e.g., prickly). In a multiple baseline design across participants, participants learned 9 sensation body part tacts and the evaluation concluded with tests of generalization to 3 novel body parts, 6 novel objects, and 3 novel sensations. Participants demonstrated generalization to novel objects, and to a lesser extent, novel body parts, but did not generalize tacts to novel sensations. These findings are discussed in terms of implications for teaching children with autism to tact sensations.

Re-evaluation of the distribution of Meissner's corpuscles in human skin

Meissner’s corpuscles are generally considered to be located in the dermal papilla of hairless skin on the fingers, toes, palms, soles, lips, eyelids, nipples, and genital organs. We used hematoxylin and eosin staining to examine the distribution of Meissner’s corpuscles in skin tissues of the fingertips, palms, lips, nipples, and labia majora and minora obtained from cadavers. Many Meissner’s corpuscles were observed in the dermal papilla of the fingertips, whereas the palms had only 20% as many. Meissner’s corpuscles were rare in the lips, nipples, and external genital organs, which have relatively high two-point discrimination. Because Meissner’s corpuscles are rapidly adapting mechanoreceptors, they may quickly detect changes in tactile sensation, including two-point discrimination, in the movable glabrous skin. In conclusion, Meissner’s corpuscles might be rare in non-movable glabrous skin compared to the fingertips and palms.

Outcomes of surgical repair of a single digital nerve in adults

Current standard management of a cut digital nerve is end-to-end microsurgical nerve coaptation where possible. A recent systematic review of adult digital nerve injuries that were either repaired or left unrepaired showed that the evidence for good nerve recovery or improved function following nerve repair is poor. In the 30 studies included, only 24% of repaired nerves regained sensory recovery close to or equivalent to estimated pre-injury levels. Neuroma rates were the same in those nerves repaired (4.6%) and those not repaired (5%). Questions under debate include proper assessment methods of outcomes, decision making for repair or no repair to different fingers or the thumb, levels of injury, age, and hand dominance. This review summarizes the major evidence available and debates the surgical dogma that surrounds this injury.

Spinal cord injury transiently alters Meissner's corpuscle density in the digit pads of macaque monkeys

Meissner's corpuscles (MCs) are cutaneous mechanoreceptors found in glabrous skin and are exquisitely sensitive to light touch. Along with other receptors, they provide continuous sensory feedback that informs the execution of fine manual behaviors. Following cervical spinal deafferentation injuries, hand use can be initially severely impaired, but substantial recovery occurs over many weeks, even when ~95% of the original input is permanently lost. While most SCI research focuses on central neural pathway responses, little is known about the role of peripheral receptors in facilitating recovery. We begin to address this by asking the following: (1) What is the normal pattern of MCs in the distal pads of all five digits in the macaque monkey (with hands similar to humans)? (2) What happens to these receptors 4-5 months following either a dorsal column lesion (DCL) or a combined dorsal root/dorsal column lesion (DRL/DCL), when functional recovery is largely complete? (3) What happens chronically, 12-14 months later? Our findings show that in normal monkeys, MCs are densest in the distal pads of the opposing thumb and index finger, with the greatest concentration on the thumb. This reflects a close functional relationship between receptor density and precision grip. At 4-5 months post-injury, there was a (~30%) loss of MCs on the deafferented digits of the injured hand compared with the contralateral side. However, 12-14 months after a DRL/DCL, receptor densities had returned to normal levels. Our findings indicate a complex peripheral response and highlight the importance of the periphery in shaping central changes.

Factors Affecting and Adjustments for Sex Differences in Current Perception Threshold With Transcutaneous Electrical Stimulation in Healthy Subjects

OBJECTIVE

Current perception threshold (CPT) measurement is a noninvasive, easy, and semi-objective method for determining sensory function using transcutaneous electrical stimulation. Previous studies have shown that CPT is determined by physical characteristics, such as sex, age, physical sites, and presence of neuropathy. Although the CPT reported in males is clearly higher than that in females, the reason for this difference remains unclear. This study investigates the cause of sex-based differences in CPT and suggests an adjustment method, which may suppress the sex difference in CPT.

MATERIALS AND METHODS

Electrical stimulation was applied with PainVision® via five sizes of circular surface electrodes. Seventy healthy participants were examined thrice under each electrode. The relationship among body water percentage, body fat percentage, and CPT was then analyzed.

RESULTS

CPT values are higher in males than that in females, with statistically significant sex differences with each electrode pairs (EL 1: p < 0.001; EL 2: p = 0.006; EL 3: p < 0.001; EL 4: p < 0.001; EL 5: p < 0.001). By adjusting for body fat percentage or body water percentage, the log-transformation values (CPT values) no longer exhibit sex differences with any electrode pairs (body fat: p = 0.09; body water: p = 0.08).

CONCLUSION

We conclude that sensitivity for perceiving electrical stimulation can be influenced by the subjects' characteristics, such as body fat or body water percentages.

Does Site Matter? Comparing Accuracy and Patient Comfort of Blood Glucose Samples Taken From the Finger and Palm of the Perioperative Patient

PURPOSE

This study compared two blood glucose (BG) point of care sampling methods to determine which is least painful yet accurate.

DESIGN

The two-period, two-treatment crossover trial compared the traditional fingertip sampling method to a form of alternative site testing (AST), palm of the hand.

METHODS

Subjects received both methods of BG sampling to compare comfort and accuracy. They were randomly assigned to determine which method was used first. Pain rating (0 to 10) and glucose results for both methods were documented.

FINDING

Results indicated that pain rating was significantly lower with AST (1.65) than with the standard site (2.83) (P < .001). There was no significant difference in mean glucose measurements between standard care (150 mg/dL) and AST (149 mg/dL). The numbers were closely correlated (r = 0.9815).

CONCLUSIONS

Findings support AST via the palm of the hand as an accurate and less painful method of obtaining BG results on diabetic patients.

Somatosensory organ topography across the star of the star-nosed mole (Condylura cristata)

Quantifying somatosensory receptor distribution in glabrous skin is usually difficult because of the diversity of skin receptor subtypes and their location within the dermis and epidermis. However, the glabrous noses of moles are an exception. In most species of moles, the skin on the nose is covered with domed mechanosensory units known as an Eimer's organs. Eimer's organs contain a stereotyped array of different mechanosensory neurons, meaning that the distribution of mechanosensitive nerve endings can be inferred by visual inspection of the skin surface. Here we detail the distribution of Eimer's organs on the highly derived somatosensory star on the rostrum of the star-nosed mole (Condylura cristata). The star consists of 22 fleshy appendages, or rays, that are covered in Eimer's organs. We find that the density of Eimer's organs increases from proximal to distal locations along the length of the star's rays with a ratio of 1:2.3:3.1 from the surface nearest to the nostril, to the middle part of ray, to the ray tip, respectively. This ratio is comparable to the increase in receptor unit density reported for the human hand, from the palm, to the middle of the digits, to the distal fingertips. We also note that the tactile fovea of the star-nosed mole, located on the medial ventral ray, does not have increased sensory organ density, and we describe these findings in comparison with other sensory fovea.

The normal sensibility of the hand declines with age--a proclamation for the use of delta two-point discrimination values for sensibility assessment after nerve reconstruction

The scores used to evaluate sensibility after digital nerve reconstruction do not take the patient's age into consideration, although there is evidence that the outcome after digital nerve reconstruction is age-dependent. However, it is not clear if the normal sensibility of the hand is also age-dependent, as the existing studies have major limitations. We evaluated the normal sensibility of the hand in 232 patients using static and moving two-point discrimination (2PD) tests and the Semmes-Weinstein-monofilament test. We found the climax of sensibility in the third decade with age-dependent deterioration afterwards in all three tests. Mean 2PD values of the radial digital nerve of the index finger (N3) showed to be significantly lower than values of the ulnar digital nerve of the small finger (N10). To overcome shortcomings of classification systems that do not consider the patient's age and inter-individual differences, we suggest using the difference of the static 2PD values of the injured to the uninjured contralateral nerve (delta 2PD) for assessment of sensibility after digital nerve reconstruction.

Microsurgeons do better--tactile training might prevent the age-dependent decline of the sensibility of the hand

Recent data demonstrate that the normal sensibility of the hand seems to be age-dependent with the best values in the third decade and a consecutive deterioration afterwards. However, it is not clear if long-term tactile training might prevent this age-dependent decline. We evaluated sensibility of the hand in 125 surgeons aged between 26 and 75 years who perform microsurgical operations, thereby undergoing regular tactile training. We examined sensibility of the radial digital nerve of the index finger (N3) and the ulnar digital nerve of the small finger (N10) using static and moving two-point discrimination (2PD) tests and compared the results to 154 age-matched individuals without specific long-term tactile training. We found significantly lower static and moving 2PD values for the sixth, seventh, and eighth decade of life in the microsurgery group compared to the control group (p < 0.05). This study demonstrates that long-term tactile training might prevent the known age-dependent decline of the sensibility of the hand.

Enhancing aesthetic outcomes of soft-tissue coverage of the hand

Hand aesthetics in general and aesthetic refinements of soft-tissue coverage of the hand in particular have been increasingly considered over the past few years. Advancements of microsurgery together with the traditional methods of tissue transfer have expanded the number of techniques available to the reconstructive surgeon, thus shifting the reconstructive paradigm from simply "filling the defect" to reconstructive refinement to provide the best functional and aesthetic results. However, drawing the boundary between what does and what does not constitute "aesthetic" reconstruction of the hand is not straightforward. The selection among the vast amount of currently available reconstructive methods and the difficulties in objectively measuring or quantifying aesthetics have made this task complex and rather arbitrary. In this article, the authors divide the hand into several units and subunits to simplify the understanding of the basic functional and aesthetic requirements of these regions that may ultimately bring order to complexity.

Dermatological and immunological conditions due to nerve lesions

Some syndromes are of interest to both neurologists and dermatologists, because cutaneous involvement may harbinger symptoms of a neurological disease. The aim of this review is to clarify this aspect. The skin, because of its relationships with the peripheral sensory nervous system, autonomic nervous system and central nervous system, constitutes a neuroimmunoendocrine organ. The skin contains numerous neuropeptides released from sensory nerves. Neuropeptides play a precise role in cutaneous physiology and pathophysiology, and in certain skin diseases. A complex dysregulation of neuropeptides is a feature of some diseases of both dermatological and neurological interest (e.g. cutaneous and nerve lesions following herpes zoster infection, cutaneous manifestations of carpal tunnel syndrome, trigeminal trophic syndrome). Dermatologists need to know when a patient should be referred to a neurologist and should consider this option in those presenting with syndromes of unclear etiology.

Cutaneous lesions sensory impairment recovery and nerve regeneration in leprosy patients

It is important to understand the mechanisms that enable peripheral neurons to regenerate after nerve injury in order to identify methods of improving this regeneration. Therefore, we studied nerve regeneration and sensory impairment recovery in the cutaneous lesions of leprosy patients (LPs) before and after treatment with multidrug therapy (MDT). The skin lesion sensory test results were compared to the histopathological and immunohistochemical protein gene product (PGP) 9.5 and the p75 nerve growth factor receptors (NGFr) findings. The cutaneous neural occupation ratio (CNOR) was evaluated for both neural markers. Thermal and pain sensations were the most frequently affected functions at the first visit and the most frequently recovered functions after MDT. The presence of a high cutaneous nerve damage index did not prevent the recovery of any type of sensory function. The CNOR was calculated for each biopsy, according to the presence of PGP and NGFr-immunostained fibres and it was not significantly different before or after the MDT. We observed a variable influence of MDT in the recovery from sensory impairment in the cutaneous lesions of LPs. Nociception and cold thermosensation were the most recovered sensations. The recovery of sensation in the skin lesions appeared to be associated with subsiding inflammation rather than with the regenerative activity of nerve fibres.

Fine-grained nociceptive maps in primary somatosensory cortex

Topographic maps of the receptive surface are a fundamental feature of neural organization in many sensory systems. While touch is finely mapped in the cerebral cortex, it remains controversial how precise any cortical nociceptive map may be. Given that nociceptive innervation density is relatively low on distal skin regions such as the digits, one might conclude that the nociceptive system lacks fine representation of these regions. Indeed, only gross spatial organization of nociceptive maps has been reported so far. However, here we reveal the existence of fine-grained somatotopy for nociceptive inputs to the digits in human primary somatosensory cortex (SI). Using painful nociceptive-selective laser stimuli to the hand, and phase-encoded functional magnetic resonance imaging analysis methods, we observed somatotopic maps of the digits in contralateral SI. These nociceptive maps were highly aligned with maps of non-painful tactile stimuli, suggesting comparable cortical representations for, and possible interactions between, mechanoreceptive and nociceptive signals. Our findings may also be valuable for future studies tracking the time course and the spatial pattern of plastic changes in cortical organization involved in chronic pain.

Evaluating dermal myelinated nerve fibers in skin biopsy

Although there has been extensive research on small, unmyelinated fibers in the skin, little research has investigated dermal myelinated fibers in comparison. Glabrous, nonhairy skin contains mechanoreceptors that afford a vantage point for observation of myelinated fibers that have previously been seen only with invasively obtained nerve biopsies. This review discusses current morphometric and molecular expression data of normative and pathogenic glabrous skin obtained by various processing and analysis methods for cutaneous myelinated fibers. Recent publications have shed light on the role of glabrous skin biopsy in identifying signs of peripheral neuropathy and as a potential biomarker of distal myelin and mechanoreceptor integrity. The clinical relevance of a better understanding of the role of dermal myelinated nerve terminations in peripheral neuropathy will be addressed in light of recent publications in the growing field of skin biopsy.

Spatiotemporal dynamics of re-innervation and hyperinnervation patterns by uninjured CGRP fibers in the rat foot sole epidermis after nerve injury

The epidermis is innervated by fine nerve endings that are important in mediating nociceptive stimuli. However, their precise role in neuropathic pain is still controversial. Here, we have studied the role of epidermal peptidergic nociceptive fibers that are located adjacent to injured fibers in a rat model of neuropathic pain. Using the Spared Nerve Injury (SNI) model, which involves complete transections of the tibial and common peroneal nerve while sparing the sural and saphenous branches, mechanical hypersensitivity was induced of the uninjured lateral (sural) and medial (saphenous) area of the foot sole. At different time points, a complete foot sole biopsy was taken from the injured paw and processed for Calcitonin Gene-Related Peptide (CGRP) immunohistochemistry. Subsequently, a novel 2D-reconstruction model depicting the density of CGRP fibers was made to evaluate the course of denervation and re-innervation by uninjured CGRP fibers. The results show an increased density of uninjured CGRP-IR epidermal fibers on the lateral and medial side after a SNI procedure at 5 and 10 weeks. Furthermore, although in control animals the density of epidermal CGRP-IR fibers in the footpads was lower compared to the surrounding skin of the foot, 10 weeks after the SNI procedure, the initially denervated footpads displayed a hyper-innervation. These data support the idea that uninjured fibers may play a considerable role in development and maintenance of neuropathic pain and that it is important to take larger biopsies to test the relationship between innervation of injured and uninjured nerve areas.

On the development of neurocutaneous units--implications for the histogenesis of congenital, acquired, and dysplastic nevi

This study of spontaneous abortions and fetal deaths in utero used immunostains to evaluate the structure of developing cutaneous nerves. Melan-A immunostains were also used to screen 25 cases of grossly normal fetal skin for occult fetal nevi. Discrete portions of epidermis were generally supplied by branches emanating from regularly spaced deep cutaneous nerves, producing a wedge shape, interpreted as neurocutaneous units (NCU). Deeper nerves embraced broader portions of epidermis. Some nerves ran parallel to epidermis, especially near the superficial vascular plexus at the junction of superficial and deep dermis. Nerve sheath stem cells in each NCU may supply the melanocytes needed by the corresponding portion of epidermis. Transformed nerve sheath stem cells may lead to formation of occult prenatal nevi, whose histology and histogenesis may best be understood in terms of NCUs. In particular, the size and shape of a nevus may be largely determined by its NCU of origin. Six fetal nevi were detected, and 3 occult lumbosacral Mongolian spots; all in deep dermis, no later than the middle of the second trimester, mainly with a pattern of singly dispersed deep dermal melanocytes. These findings suggest that congenital (prenatal) nevi begin as intradermal nevi. In addition to explaining congenital nevi, these findings have implications for the histogenesis of acquired (postnatal) nevi and dysplastic nevi.

Rodents rely on Merkel cells for texture discrimination tasks

The cutaneous somatosensory system contains multiple types of mechanoreceptors that detect different mechanical stimuli (Johnson, 2001). These stimuli, either alone or in combination, are ultimately interpreted by the brain as different aspects of the sense of touch. Psychophysical and electrophysiological experiments in humans and other mammals implicate one of these mechanoreceptors, the Merkel cell/neurite complex, in two-point discrimination and the detection of curvature, shape, and texture (Johnson and Lamb, 1981; Johnson et al., 2000; Johnson, 2001). However, whether Merkel cell/neurite complex function is required for the detection of these stimuli is unknown. We genetically engineered mice that lack Merkel cells (Maricich et al., 2009; Morrison et al., 2009) to directly test the hypothesis that Merkel cell/neurite complexes are necessary to perform these types of sensory discrimination tasks. We found that mice devoid of Merkel cells could not detect textured surfaces with their feet while other measures of motor and sensory function were unaffected. Interestingly, these mice retained the ability to discriminate both texture and shape using their whiskers, suggesting that other somatosensory afferents can functionally substitute for Merkel cell/neurite complexes in this sensory organ. These findings suggest that Merkel cell/neurite complexes are essential for texture discrimination tasks involving glabrous skin but not whiskers.

The nerve injury and the dying neurons: diagnosis and prevention

Following distal nerve injury significant sensory neuronal cell death occurs in the dorsal root ganglia, while after a more proximal injury, such as brachial plexus injury, a sizeable proportion of spinal motoneurons also undergo cell death. This phenomenon has been undervalued for a long time, but it has a significant role in the lack of functional recuperation, as neuronal cells cannot divide and be replaced, hence the resulting nerve regeneration is usually suboptimal. It is now accepted that this cell death is due to apoptosis, as indicated by analysis of specific genes involved in the apoptotic signalling cascade. Immediate nerve repair, either by direct suturing or nerve grafting, gives a degree of neuroprotection, but this approach does not fully prevent neuronal cell death and importantly it is not always possible. Our work has shown that pharmacological intervention using either acetyl-L-carnitine (ALCAR) or N-acetyl-cysteine (NAC) give complete neuroprotection in different types of peripheral nerve injury. Both compounds are clinically safe and experimental work has defined the best dose, timing after injury and duration of administration. The efficacy of neuroprotection of ALCAR and NAC can be monitored non-invasively using MRI, as demonstrated experimentally and more recently by clinical studies of the volume of dorsal root ganglia. Translation to patients of this pharmacological intervention requires further work, but the available results indicate that this approach will help to secure a better functional outcome following peripheral nerve injury and repair.

Sensory innervation of the female human umbilical skin: morphological studies

BACKGROUND

Sensory stimuli are conducted by several cutaneous sensory nerves and tactile corpuscles. The latter are specialized sensory organs that represent the starting point of many afferent sensory pathways. To date, our knowledge about the distribution of the sensory innervation in the umbilical skin of females is incomplete.

AIM OF THE STUDY

To elucidate the morphology of the cutaneous innervation of the normal female umbilical skin.

MATERIALS AND METHODS

Biopsies of normal umbilical skin were obtained from female patients undergoing umbilical hernial repair. The specimens were processed for both immunohistological (antibodies against PGP9.5, pan-neuronal marker, and S-100 protein, marker of Schwann cells) and ultrastructural (transmission electron microscopy) examinations.

RESULTS

The authors found abundant genital end-bulb-like structures, numerous epidermal and dermal Merkel cells, Meissner and Ruffini corpuscles, intraepidermal nerve terminals, and multiple free nerve endings surrounding the ducts and acini of the sweat glands.

CONCLUSIONS

The umbilical skin of females has abundant sensory innervation similar to that of the glans penis.

Development and neuronal dependence of cutaneous sensory nerve formations: Lessons from neurotrophins

Null mutations of genes from the NGF family of NTs and their receptors (NTRs) lead to loss/reduction of specific neurons in sensory ganglia; conversely, cutaneous overexpression of NTs results in skin hyperinnervation and increase or no changes in the number of sensory neurons innervating the skin. These neuronal changes are paralleled with loss of specific types of sensory nerve formations in the skin. Therefore, mice carrying mutations in NT or NTR genes represent an ideal model to identify the neuronal dependence of each type of cutaneous sensory nerve ending from a concrete subtype of sensory neuron, since the development, maintenance, and structural integrity of sensory nerve formations depend upon sensory neurons. Results obtained from these mouse strains suggest that TrkA positive neurons are connected to intraepithelial nerve fibers and other sensory nerve formations depending from C and Adelta nerve fibers; the neurons expressing TrkB and responding to BDNF and NT-4 innervate Meissner corpuscles, a subpopulation of Merkell cells, some mechanoreceptors of the piloneural complex, and the Ruffini's corpuscles; finally, a subpopulation of neurons, which are responsive to NT-3, support postnatal survival of some intraepithelial nerve fibers and Merkel cells in addition to the muscle mechanoreceptors. On the other hand, changes in NTs and NTRs affect the structure of non-nervous structures of the skin and are at the basis of several cutaneous pathologies. This review is an update about the role of NTs and NTRs in the maintenance of normal cutaneous innervation and maintenance of skin integrity.

Intraepidermal nerve fibre density at wrist level in diabetic and non-diabetic patients

AIMS

Myelinated nerve fibre pathology has been demonstrated at wrist level in diabetic patients. We examined if quantification of intra-epidermal nerve fibre density (IENFD) in hairy and glabrous skin at wrist level could detect signs of subclinical small nerve fibre neuropathy.

METHODS

In 35 diabetic patients who were age and gender matched with 31 non-diabetic patients, punch biopsies were obtained in conjunction with surgical carpal tunnel release. Biopsies were immunostained with anti-protein gene product (PGP) 9.5. The IENFD was quantified using manual counting by light microscopy.

RESULTS

We could not demonstrate significant differences in IENFD between diabetic or non-diabetic patients. Additionally, no differences were found between patients with Type 1 and Type 2 diabetes or in diabetic patients with and without neurophysiologic signs of mild peripheral neuropathy. However, the IENFD was significantly higher in hairy skin compared with glabrous skin. Furthermore, the IENFD was significantly higher in females than in males and correlated with age, but not with duration of diabetes or glycated haemoglobin (HbA(1c)).

CONCLUSIONS

In mild neuropathy no difference in IENFD at the wrist level could be detected between diabetic and non-diabetic patients. Independent of diabetes, we found IENFD to be higher in hairy skin compared with glabrous skin and higher in females than in males. These results must be taken into consideration when assessing small nerve fibre pathology in the upper extremity.

The Meissner and Pacinian sensory corpuscles revisited new data from the last decade

This article reviews the biochemical, physiological, and experimental data cumulated during the last decade on the Meissner and Pacinian corpuscles. It includes information about (i) the localization of molecules recently detected in sensory corpuscles; (ii) the unsolved problem of the accessory fibers in sensory corpuscles and the occurrence of myelin within them; (iii) the development of sensory corpuscles, especially their neuronal and growth factor dependency; (iv) the composition and functional significance of the extracellular matrix as an essential part of the mechanisms involved in the genesis of the stimuli generated in sensory corpuscles; (v) the molecular basis of mechanotransduction; (vi) a miscellaneous section containing sparse new data on the protein composition of sensory corpuscles, as well as in the proteins involved in live-death cell decisions; (vii) the changes in sensory corpuscles as a consequence of aging, the central, or peripheral nervous system injury; and finally, (viii) the special interest of Meissner corpuscles and Pacinian corpuscles for pathologists for the diagnosis of some peripheral neuropathies and neurodegenerative diseases.

Sensory capacity of reinnervated skin after redirection of amputated upper limb nerves to the chest

Targeted reinnervation is a new neural-machine interface that has been developed to help improve the function of new-generation prosthetic limbs. Targeted reinnervation is a surgical procedure that takes the nerves that once innervated a severed limb and redirects them to proximal muscle and skin sites. The sensory afferents of the redirected nerves reinnervate the skin overlying the transfer site. This creates a sensory expression of the missing limb in the amputee's reinnervated skin. When these individuals are touched on this reinnervated skin they feel as though they are being touched on their missing limb. Targeted reinnervation takes nerves that once served the hand, a skin region of high functional importance, and redirects them to less functionally relevant skin areas adjacent to the amputation site. In an effort to better understand the sensory capacity of the reinnervated target skin following this procedure, we examined grating orientation thresholds and point localization thresholds on two amputees who had undergone the targeted reinnervation surgery. Grating orientation thresholds and point localization thresholds were also measured on the contralateral normal skin of the targeted reinnervation amputees and on analogous sites in able-bodied controls. Grating orientation thresholds for the reinnervated skin of the targeted reinnervation amputees were found to be similar to normal ranges for both the amputees' contralateral skin and also for the control population. Point localization thresholds for these amputees were found to be lower for their reinnervated skin than for their contralateral skin. Reinnervated point localization thresholds values were also lower in comparison to homologous chest sites on the control population. Mechanisms appear to be in place to maximize re-established touch input in targeted reinnervation amputees. It seems that sound sensory function is provided to the denervated skin of the residual limb when connected to afferent pathways once serving highly functionally relevant regions of the brain. This suggests that tactile interface devices could be used to give a physiologically appropriate sense of touch to a prosthetic limb, which would likely help with better functional utilization of the prosthetic device and possibly help to more effectively integrate the device with the user's self-image.

Current considerations about Merkel cells

Since the discovery of Merkel cells by Friedrich S. Merkel in 1875, knowledge of their structure has increased with the progression of new technologies such as electron and laser microscopy, and immunohistochemical techniques. For most vertebrates, Merkel cells are located in the basal layer of the epidermis and characterized by dense-core granules that contain a variety of neuropeptides, plasma membrane spines and cytoskeletal filaments consisting of cytokeratins and desmosomes. The presence of the two latter structures would suggest that Merkel cells originate from the epidermis rather than from the neural crest, even though such a hypothesis is not unanimously accepted. The function of the Merkel cell is also very controversial. For a long time, it has been accepted that Merkel cells with associated nerve terminals act as mechanoreceptors although the transduction mechanism has not yet been elucidated. Merkel cells that do not make contact with nerve terminals have an endocrine function. The present review aims to shed new and comparative light on this field with an attempt to investigate the stimuli that Merkel cells are able to perceive.

Considerations in evaluating new treatment alternatives following peripheral nerve injuries: A prospective clinical study of methods used to investigate sensory, motor and functional recovery

The current problem finding reliable and objective methods for evaluating results after peripheral nerve repair is a challenge when introducing new clinical techniques. The aim of this study was to obtain reference material and to evaluate the applicability of different tests used for clinical assessment after peripheral nerve injuries. Fifteen patients with a history of complete median nerve transsection and repair, and 15 healthy volunteers were included. Each subject was investigated using a battery of conventional and new tests for functional, sensory and motor recovery including questionnaires, clinical evaluations, neurophysiological and physiological findings. The results were statistically analysed and comparisons were made within the patient group and between patients and healthy volunteers using a 'per protocol' and an 'intention to treat' approach. Criteria for success were stipulated in order to be able to judge the usefulness of each method. The results showed that 19 of 34 variables, representing six of 16 methods, were not able to fulfil the criteria and were thus questionable for the evaluations of nerve repair in a clinical trial setting. However, 2pd, sensory recovery according to the non-modified British Medical Research Council, sensory neurography, manual muscle test, electromyography, questionnaires (i.e. DASH and the 4 question form) and performance tests (i.e. AMPS and Sollerman's subtests 4 and 8) did fulfil the criteria defined for being useful.

Hindlimb Withdrawal Reflexes Evoked by Er:YAG Laser and Scalpel Incisions in Rats

OBJECTIVE

In this study, we assessed the magnitudes of nociceptive withdrawal reflexes evoked by skin and muscle incisions made with steel scalpel and erbium:yttrium-aluminum-garnet (Er:YAG) laser.

BACKGROUND DATA

A few studies have suggested that laser incisions would be less painful than conventional scalpel incisions.

METHODS

Twenty adult male Sprague-Dawley rats were used. Under light barbiturate anesthesia, graded incisions were made into the plantar surface of the animals' hindpaws. Electromyographic (EMG) recordings from a hamstring muscle were used to estimate the nociceptive response.

RESULTS

The mean amplitude of EMG activity was significantly higher during incisions made with steel scalpel than with any of the laser irradiation parameters. All laser irradiation parameters produced similar nociceptive responses.

CONCLUSION

Er:YAG laser incisions may be less painful, albeit considerably slower, than scalpel incisions. Laser incisional pain would be more closely related to the mechanical rather than the thermal effect of laser ablation.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.