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Background and purpose Quantification of intraepidermal nerve fibers (IENFs) in skin biopsies is now the tool of choice to diagnose small fiber neuropathies. An adequate normative dataset, necessary to assess normality cutoffs, is available for brightfield microscopy but not for immunofluorescence. Methods Intraepidermal nerve fiber density data in distal leg skin samples processed with immunofluorescence were collected from 528 healthy individuals from four experienced laboratories worldwide. In all laboratories skin samples were collected, processed and analyzed according to standard procedures. Quantile regression analysis was employed to tailor the fit of the 5° percentile as the normal cutoff value and to test and measure the effect of age, gender, body mass index, race, biopsy site (lateral distal lower leg or medial posterior mid-calf) and participating laboratory as possible influential variables. Results Age, gender and biopsy site showed an independent linear correlation with IENF density. For each decade the 5° quantile IENF cutoff showed a 0.54 fibers/mm decrease, whilst females exhibited a 1.0 fiber/mm cutoff greater than males. Compared to the lateral distal lower leg, biopsies from the calf showed a 3.4 fibers/mm lower 5° percentile cutoff, documenting a variation linked by site. Conclusions An age- and gender-adjusted normative dataset for IENF density at the lateral distal lower leg obtained with indirect immunofluorescence is presented for the first time by sharing data from four experienced laboratories worldwide. This dataset can be used as reference for laboratories processing skin biopsies with this technique.

Aim: Small fibre neuropathy (SFN) diagnosis represents a challenge for neurologists. The diagnostic gold standard is intraepidermal nerve fibre (IENF) density, but in about 10–20% of patients with symptoms/signs and abnormalities on functional tests, it remains within normal range. We propose an adjunctive parameter to improve the efficiency of skin biopsy diagnosis. Methods: We recruited 31 patients with SFN symptoms/signs, normal nerve conduction study, abnormal quantitative sensory testing and normal IENF density. We also included 31 healthy controls and 31 SFN patients with reduced IENF density as control groups. Results: We measured the distance between consecutive IENFs in the three groups. Mean inter-fibre distances did not differ between patients with normal counts and healthy controls (66.7 ± 14.5 μm vs. 76.7 ± 13.4 μm; P = 0.052), while the relative standard deviation was significantly (P

In the last three decades the study of cutaneous innervation through 3 mm-punch-biopsy has provided an important contribution to the knowledge of small fiber somatic and autonomic neuropathies but also of large fiber neuropathies. Skin biopsy is a minimally invasive technique with the advantage, compared to sural nerve biopsy, of being suitable to be applied to any site in our body, of being repeatable over time, of allowing the identification of each population of nerve fiber through its target. In patients with symptoms and signs of small fiber neuropathy the assessment of IntraEpidermal Nerve Fiber density is the gold standard to confirm the diagnosis while the quantification of sudomotor, pilomotor, and vasomotor nerve fibers allows to evaluate and characterize the autonomic involvement. All these parameters can be re-evaluated over time to monitor the disease process and to evaluate the effectiveness of the treatments. Myelinated fibers and their receptors can also be evaluated to detect a “dying back” neuropathy early when nerve conduction study is still normal. Furthermore, the morphometry of dermal myelinated fibers has provided new insight into pathophysiological mechanisms of different types of inherited and acquired large fibers neuropathies. In genetic neuropathies skin biopsy has become a surrogate for sural nerve biopsy, no longer necessary in the diagnostic process, to study genotype–phenotype correlations.

Objective To describe morphological changes associated with degeneration and regeneration of large fibers in the skin using a model of chronic compression of the median nerve. Methods We studied cutaneous innervation in 30 patients with chronic compression of the median nerve at the wrist. Before surgery, we assessed the symptom severity and performed neurography, quantitative sensory testing, and analysis of nerve morphology and morphometry in skin biopsies from the third digit fingertip. Fifteen patients repeated all tests 12 months after the surgery. Thirty age- and sex-matched healthy subjects were included in the study. Results Clinical and neurophysiological basal assessment showed a moderate involvement of the median nerve. Quantitative sensory testing showed abnormal findings. The density of intraepidermal nerve fibers and intrapapillary myelinated endings was reduced. Myelinated fibers showed caliber reduction and nodal elongation. Meissner corpuscles had normal density but were located deeper in the dermis and their capsule appeared partially empty. During follow-up, patients exhibited a positive clinical and neurophysiological outcome. Quantitative sensory testing improved. Intraepidermal nerve fibers and intrapapillary myelinated endings remained unchanged, but the caliber of intrapapillary myelinated endings was increased. The neural component of the Meissner corpuscle filled the capsule of the mechanoreceptors that remained deeper in the dermis. The position of vasoactive intestinal peptide-immunoreactive fibers was more superficial compared to the basal assessment and controls. Interpretation We recognized and quantified the pathological changes associated with nerve degeneration and regeneration in skin and proposed new parameters that may increase the diagnostic yield of skin biopsy in clinical practice. Ann Neurol 2020;87:456-465.

To assess the involvement of small nerve fibers in Charcot-Marie-Tooth type 1A (CMT1A).We used indirect immunofluorescence and confocal microscopy on punch biopsies from glabrous (fingertip) and hairy (thigh and leg) skin of 20 unrelated patients with CMT1A to quantify somatic and autonomic nerve fibers. In particular, we quantified epidermal nerve fibers (ENF), Meissner corpuscles (MC), intrapapillary myelinated endings (IME), and sudomotor nerves. We correlated morphologic data with findings from quantitative sensory testing, sudomotor output, sympathetic skin response, and cardiovascular reflexes. A control population of healthy age- and sex-matched controls was included with a matching ratio of 1:2.We found a length-dependent loss of ENFs that worsened with aging. We also observed a loss of MCs, IMEs, and sudomotor nerves. The loss of ENF at distal leg correlated with the increase in heat-pain thresholds (p0.05) and with tactile thresholds (p0.05). Sudomotor nerve fiber loss correlated with ENF density (p0.05) and sweating output (p0.001).We demonstrated through morphologic, physical, and psychophysical testing that small somatic and autonomic fibers are abnormal and cause symptoms in patients with CMT1A. Awareness of such symptoms by the clinician could lead to better treatment.

The V.O2 slow component (V.O2sc) that develops during high-intensity aerobic exercise is thought to be strongly associated with locomotor muscle fatigue. We sought to experimentally test this hypothesis by pre-fatiguing the locomotor muscles used during subsequent high-intensity cycling exercise. Over two separate visits, eight healthy male participants were asked to either perform a non-metabolically stressful 100 intermittent drop-jumps protocol (pre-fatigue condition) or rest for 33 min (control condition) according to a random and counterbalanced order. Locomotor muscle fatigue was quantified with 6-s maximal sprints at a fixed pedaling cadence of 90 rev·min-1. Oxygen kinetics and other responses (heart rate, capillary blood lactate concentration and rating of perceived exertion, RPE) were measured during two subsequent bouts of 6 min cycling exercise at 50% of the delta between the lactate threshold and V.O2max determined during a preliminary incremental exercise test. All tests were performed on the same cycle ergometer. Despite significant locomotor muscle fatigue (P = 0.03), the V.O2sc was not significantly different between the pre-fatigue (464 ± 301 mL·min-1) and the control (556 ± 223 mL·min-1) condition (P = 0.50). Blood lactate response was not significantly different between conditions (P = 0.48) but RPE was significantly higher following the pre-fatiguing exercise protocol compared with the control condition (P < 0.01) suggesting higher muscle recruitment. These results demonstrate experimentally that locomotor muscle fatigue does not significantly alter the V.O2 kinetic response to high intensity aerobic exercise, and challenge the hypothesis that the V.O2sc is strongly associated with locomotor muscle fatigue. © 2016 Hopker, Caporaso, Azzalin, Carpenter and Marcora.

To assess cutaneous sensory and autonomic nerves and the vascular bed in amyotrophic lateral sclerosis (ALS).We enrolled 41 patients (M = 20, aged 63.5 ± 11.8 years), and 41 age- and gender-matched healthy volunteers (M = 20, aged 63.5 ± 11.8 years). Disease severity and sensory and autonomic symptoms were scored using dedicated rating scales. Skin biopsies obtained from thigh, leg and fingertip were processed using indirect immunofluorescence. Intraepidermal nerve fibres, Meissner corpuscles (MCs), intrapapillary myelinated endings, cholinergic and noradrenergic pilomotor nerves and dermal vessels were quantified on confocal images. Intraepidermal nerve fibres, pilomotor nerves and vessels were also assessed on distal leg skin samples of 10 spinal cord injury patients to compare our findings with those of a chronic hypomobility condition.Compared to healthy controls skin biopsies showed: (i) non-length-dependent loss of intraepidermal nerve fibres (P0.01) and loss of MCs (P0.01); (ii) reduced (P0.01) density of pilomotor nerves involving cholinergic and noradrenergic fibres and (iii) a reduced (P0.01) vascular bed. Autonomic nerve and dermal vessel densities were higher in patients with higher disease progression rate (P0.01). Moreover, we observed signs of nerve regeneration coexisting with nerve degeneration and increased complexity of the dermal vessels. In patients with posttraumatic spinal cord injury, the density of intraepidermal nerve fibres, pilomotor nerves and of the vascular bed did not differ from controls (P0.05).We demonstrated a cutaneous sensory and autonomic denervation in ALS and a previously undescribed relationship between autonomic and vascular involvement that appeared to be linked to the disease progression rate.

We used immunohistochemical techniques and confocal microscopy to study the morphometry of myelinated nerve endings in glabrous and hairy skin. A total of 30 healthy volunteers took part in this study designed to assess the possibility of obtaining reliable information on myelinated fibers using samples of hairy skin and to determine whether differences exist between myelinated terminations from different sites. We obtained consistent information on cutaneous myelinated terminations using hairy as well as glabrous skin samples. Myelinated endings from hairy and glabrous skin differ in density and distribution. However, from a comparison of our findings with data from nerve biopsy studies, we conclude that all cutaneous myelinated terminations are thinner terminal branches of large myelinated A beta fibers, whereas cutaneous terminations of small myelinated A delta fibers lose their myelin before entering the dermis and become indistinguishable from C-fiber terminations. The classic criteria, based on fiber size, used to distinguish myelinated fiber subgroups in sensory nerves are therefore not suitable for identifying myelinated terminations in the skin.

To evaluate postganglionic autonomic involvement in multiple system atrophy (MSA).We quantified sudomotor innervation in skin biopsy of 29 patients with MSA (19 male and 10 female; age 60.0 ± 7.7 years) and 29 age- and sex-matched healthy subjects. Samples were obtained from thigh and leg and, in 20 out of the 29 cases, also from fingertip. Dysautonomic complaints were evaluated by SCOPA-AUT, a self-administered questionnaire. Sudomotor function was evaluated in a subgroup of patients by the silastic imprint test. Skin samples were processed by indirect immunofluorescence using pan-neuronal and selective cholinergic markers. Total length of sudomotor nerves was measured on digital confocal images using a semiautomated morphometric approach.Measurements of sudomotor nerve density (total length of nerve per volume of glandular tissue) favorably correlated to values obtained using a stereologic unbiased method. Sudomotor nerve density was lower in patients compared to controls in all the examined sites (0.9 ± 0.2 vs 1.9 ± 0.4 nm/μm(3), p0.001, in fingertip; 0.7 ± 0.2 vs 1.9 ± 0.5 nm/µm(3), p0.001, in thigh; 0.6 ± 0.2 vs 1.8 ± 0.4 nm/µm(3), p0.001, in leg).Our data support the hypothesis that postganglionic impairment occurs in MSA and may contribute with the coexisting degeneration of central structures to the development of dysautonomic disorders in this condition.

Objectives: Quantification of the complex, autonomic networks in the skin is difficult. Although sporadic attempts focusing mainly on sudomotor plexus have been reported, an easy and reliable method of quantification has not yet been made available. We developed a method to quantify pilomotor nerve fibers (PNFs), which, compared to sudomotor nerves, have a less complex pattern. We used this procedure on a population of normal and diabetic subjects, and propose it as a new tool to study cutaneous autonomic nerves. Methods: Skin biopsies were performed from thigh and distal leg in 20 diabetic patients and 20 age- and sex-matched controls. Samples were processed applying indirect immunofluorescence and using pan-neuronal and selective markers for cholinergic and noradrenergic fibers. Pilomotor nerve fiber density was blindly calculated on single 2-μm optical sections selected from confocal z-stacks. Interobserver and intraobserver reliability was evaluated. Results were compared with values obtained by 2 other methods that explored PNFs more extensively. Pilomotor nerve fibers density was compared to epidermal nerve fiber (ENF) density, to pilocarpine-activated sweat gland density, and to the severity of neuropathy as assessed by the modified total neuropathy score. Results: A significant loss of PNFs was found in diabetic subjects9 thigh and leg. PNFs density did not correlate with ENF density, disease duration, or total neuropathy score. Noradrenergic PNFs correlated instead with sweating impairment. Conclusions: A reliable assessment of PNF density is possible. When studying cutaneous innervation, PNF quantification should be done to gain information on autonomic nerves in addition to somatic nerves.

The study of sudomotor function represents a useful tool to evaluate autonomic disorders. Currently available tests allow either the measurement of sweat output from the whole body or selected small skin locations over time, or quantification of the number and size of sweat drops at a fixed time after stimulation. We devised a dynamic sweat test (DST) that measures at the same time sweat gland density, distribution of active glands, and sweat rate, and applied it to the evaluation of sudomotor function in diabetes.The DST was used to evaluate sweating in the forearm of 14 asymptomatic diabetic subjects and 14 age- and sex-matched healthy controls. Distal leg was also tested in 7 patients and 7 controls. The formation of the imprint of pilocarpine-induced sweating was recorded by a digital video camera through a cornstarch-powdered transparent tape used as a contrast-enhancing device. Mean sweat output per gland and per skin area and sweat gland density per cm(2) were evaluated.We observed a significant reduction of sweating in diabetic subjects as compared to controls; sweat gland density per cm(2) (59.7 +/- 18.6 vs 83.7 +/- 17.3; p0.05) and mean sweat output (nL/min) per gland (4.7 +/- 0.7 vs 8.3 +/- 2.7; p = 0.01) and per skin area (261 +/- 100 vs 645 +/- 296; p = 0.01) were reduced in the lower limb. Values for the forearm were not significantly different from controls.Dynamic sweat test is an easy-to-perform, informative method to study sudomotor function. It provides the ability to detect subtle functional changes occurring in the early stages of diabetic neuropathy.