The normal sural nerve in man. I. Ultrastructure and numbers of fibres and cells

Unmyelinated fibers in human greater auricular and sural nerves: a comparative morphometric study

Since normal structural details of human greater auricular nerve (GAN) have not as yet been studied with modern techniques, light and electron microscopic findings of seven presumably normal GANs, obtained from five patients during radical neck dissection, were compared with those of normal sural nerves (SNs). In GANs there was a tendency to higher densities per mm2 and a larger number of small-diameter fibers in myelinated fibers (MFs) and unmyelinated fibers (UFs) without obvious signs of de- or regeneration. UF histograms were unimodal in both groups, with mean UF diameters being somewhat smaller in GANS than in SNs. Schwann cell complexes containing several or even numerous UFs were more frequent in GANs than in SNs. In GANs, UF often occurred focally in great numbers within large Schwann cell complexes (polyaxonal complexes), not commonly seen in normal SNs. It is concluded that these structural peculiarities in GANs reflect natural conditions in short sensory nerves irrespective of any specific function.

Sensory neuropathy in hereditary spastic paraplegia

A large kinship is reported with dominantly inherited spastic paraplegia starting in the first decade of life; its clinical evolution was indistinguishable from that of "pure" hereditary spastic paraplegia (HSP). However, all patients studied had electrophysiological evidence of a predominantly sensory polyneuropathy, which was confirmed on nerve biopsy in three. The histological findings indicated virtually complete loss of large diameter fibres with relative preservation of small myelinated and non-myelinated fibres. The neuropathy was largely asymptomatic and there were no trophic ulcers. This family represents a distinct entity which differs from other reported cases of HSP with neuropathy by virtue of the clinical predominance of the pyramidal syndrome, the greater impairment of large fibre sensory modalities than of pain or temperature modalities, and the consequent absence of mutilation.

Sensory neuropathy in infantile onset spinocerebellar ataxia (IOSCA)

Infantile onset spinocerebellar ataxia with sensory neuropathy is a new, inherited multisystem disorder discovered in 19 Finnish patients. In order to define the neuropathy of the disease, we measured sensory nerve action potentials and nerve conduction velocities in 18 patients, and recorded somatosensory evoked potentials (SEP) in 10 patients and performed a sural nerve biopsy in 13 patients. The fixed and teased nerve fascicles were examined by light and electron microscopy, and the whole transverse section of a nerve fascicle was photographed and enlarged for morphometric measurements. Our investigation revealed an early onset, rapidly progressive axonal neuropathy: the sensory action potentials were decreased after the age of 2 and a severe loss of mainly large myelinated fibers was found.

Infantile onset spinocerebellar ataxia with sensory neuropathy: a new inherited disease

We report the clinical findings in 19 Finnish patients, including six pairs of siblings, with a new, early onset spinocerebellar ataxia. The slowly progressive clinical symptoms manifested between one and two years of age in previously healthy infants. The first manifestation of children at that age was clumsiness and loss of ability to walk. Ataxia, athetosis and muscle hypotonia with loss of deep tendon reflexes were discovered on clinical examination. By school age ophthalmoplegia and hearing loss were diagnosed, while sensory neuropathy developed by adolescence. In addition, an acute crisis with status epilepticus was a late manifestation. We found a marked decrease in sensory nerve condition velocities, a progressive loss of myelinated fibers in sural nerve specimen, and abnormal background activity in EEG with advancing age. The main finding in neuroradiological investigations was cerebellar atrophy. The occurrence of the disease in siblings and lack of manifestations in parents indicate recessive inheritance.

Anti-NKH-1 antibody specifically stains unmyelinated fibres and non-myelinating Schwann cell columns in humans

Anti-NKH-1 antibody recognizes an isoform of the neural cell adhesion molecule (N-CAM) that is involved in cell-cell interactions during embryonic stages and has been detected in skin autonomic nerves. The specificity of anti-NKH-1 antibody for human unmyelinated fibres (UF) and the distribution of the antigens recognized by this antibody at the ultrastructural level, were evaluated by immunohistochemistry and immunoelectron microscopy on nerve biopsy samples from patients with normal nerve biopsies and a variety of peripheral neuropathies. The anti-NKH-1 antibody strongly stained all unmyelinated fibres while no myelinated fibre was stained. Autonomic nerve fibres were visualized at the periphery of blood vessels. Immunoelectron microscopy showed that the antigen recognized by the antibody was located at Schwann cell-axon interfaces and in portions of joined Schwannian surfaces, i.e. along mesaxons of non-myelinating Schwann cells. Expression of NKH-1 was basically similar in normal and diseased nerves as expression of NKH-1 was similar at the level of apposed plate-like Schwann cell processes than along normal mesaxons. The extent of labelling of diseased nerves by the anti-NKH-1 antibody likely depended on the number of residual Schwann cell columns observed by light microscopy.

Age-related changes of motor evoked potentials in healthy humans: non-invasive evaluation of central and peripheral motor tracts excitability and conductivity

A comparative analysis of the corticospinal tract nervous propagation and excitability threshold was carried out in young (25 subjects, age range 16-35 years) and in elderly (40 subjects, 51-86 years) populations of healthy volunteers. Motor evoked potentials (MEPs) were recorded from the hand and foot muscles following transcranial magnetic stimulation (TCS) during complete relaxation and active contraction of the target muscles. Threshold intensities corresponded to the stimulator's output eliciting liminal MEPs in about 50% of stimuli during relaxation. It was found that threshold values of magnetic TCS were significantly higher in the elderly (44 +/- 6.4% vs 39 +/- 3.5% for the hand; 66 +/- 10.1% vs 56 +/- 6.7% for the foot; P < 0.001) than in the young subjects. Moreover, this index progressively increased with age (P < 0.001), whilst the propagation time along the central motor tracts did not parallel such an age-related trend.

[Electrophysiological aspects of peripheral nervous system development]

Different aspects of the maturation of the peripheral nervous system have been studied in infants, essentially during the first year of postnatal life. Absolute refractory periods which enable indirect estimation of excitability have been measured in both nerve and muscle fibers. It appears that already at birth, the absolute refractory period is characteristic for a given group of nerve fibres. In each group of nerve fibres, the absolute refractory period is not correlated to conduction velocity (ie fibre diameter) and remains rather constant during development. However, the absolute refractory period of the most excitable fibres is smaller than the absolute refractory period of motor fibres independent of the subject's age. On the other hand, the absolute refractory period of muscle fibres is slightly higher in premature in comparison with full-term neonates and adults. The diameter growth of different categories of nerve, fibers (motor--IA--non nociceptive cutaneous) is assessed by measurement of conduction velocities. At each age the IA fibre conduction velocities are the highest. The marked difference which exists between length development and postnatal increase of the fibre diameter explains the particular evolution of conduction times.

Case report: autonomic postganglionic denervation--sural nerve and saphenous vein biopsy

The authors describe a 31-year-old woman of British Isle ancestry who developed a syndrome resembling familial dysautonomia in her early teenage years. Predominant manifestations included achalasia, severe orthostatic hypotension, and abnormal sweating. The study included resting and stimulated fractional catecholamines, which were almost nonexistent in both situations, and urinary catecholamines, demonstrating an increase in dopamine degradation products. Immunohistochemistry of saphenous vein was negative for dopamine beta-hydroxylase (DBH), serotonin (5-HT) and several vasoactive neuropeptides. The only neuropeptide detected at levels thought to be physiologically relevant was calcitonin gene-related peptide (CGRP), a vasodilator. This was in contrast to control veins, all of which had DBH and neuropeptide Y immunoreactive fibers but few CGRP fibers. Also in contrast to controls, electron microscopy of the saphenous vein indicated a close to total absence of terminals with norepinephrine containing vesicles. Sural nerve biopsy showed, on electron microscopy, a considerable reduction in the number of myelinated fibers, while unmyelinated fibers appeared to be in the normal range. The authors suggest, from the above findings, that the autonomic fibers were undergoing some form of distal axonal degeneration. Their findings differ from most biopsies performed in dysautonomic children, and they believe their patient has a different neurologic entity.

Topography of unmyelinated axons in regenerated soleus nerves of the rat

The topography of unmyelinated axons on cross sections of normal and regenerated soleus nerves of rat was studied by electron microscopy. The experimental nerves were crushed and assessed after 1-19 weeks. Unmyelinated axons in normal nerves were arranged in few groups. Nerve crush did not alter the arrangement of unmyelinated axons in the proximal nerve. Distal to the crush lesion, however, the unmyelinated axons became scattered throughout the entire cross section. The grouping of unmyelinated axons within the cross section was quantitated by means of a "clustering factor", defined as the percentage of unmyelinated axons in those 10% of the cross-sectional area which had the highest density of unmyelinated axons. The results indicate that unmyelinated axons during regeneration do not follow their original pathways.

Mechanically insensitive afferents (MIAs) in cutaneous nerves of monkey

A problem in the study of nociceptors is that intense stimuli are used to locate the receptive field (RF), and thus the receptor may be damaged before the first responses are recorded. In addition, some nociceptors do not respond to the mechanical stimuli often used to search for the RF. To overcome these problems, an electrical search technique was developed to locate the RF of cutaneous nociceptors. In the hairy skin of anesthetized monkey, we used this technique to locate the RF of 63 A delta-fibers and 22 C-fibers that had extremely high thresholds or were unresponsive to mechanical stimuli. We refer to these afferents as mechanically insensitive afferents (MIAs). Ten A delta-fiber MIAs had a short latency response to stepped heat stimuli and could be responsible for first pain sensation. Five A delta-fiber MIAs and one C-fiber MIA did not respond to mechanical or heat stimuli but did respond to injection into the electrical RF of an artificial inflammatory soup containing histamine, bradykinin, prostaglandin E1, and serotonin. These chemoreceptors might be responsible for the pain and itch sensations that result from chemical stimuli. Some MIAs became more responsive to mechanical stimuli after injection into the RF of the inflammatory soup and, thus, may contribute to the hyperalgesia to mechanical stimuli associated with cutaneous injury. A large proportion of the A delta-fiber (48%) and C-fiber (30%) afferents in this study were insensitive to mechanical stimuli. The role of these MIAs in sensation needs to be studied further. The electrical search technique enables a systematic study of these afferents to be performed. This technique may also be of use to identify and characterize dorsal horn neurons that have inputs from MIAs.

Subclinical peripheral nerve involvement in AIDS: an electrophysiological and pathological study

Thirty patients with AIDS without symptoms or signs of peripheral neuropathy were compared electrophysiologically with 23 age and sex matched healthy controls. The patients had a mean reduction in the amplitude of common peroneal compound muscle action potentials of 37% (95% CI 11-70%) and of sural sensory action potentials of 34% (CI 18-49%). Mean conduction velocity of both motor and sensory nerves was reduced by between 1 and 7 m/s, with a prolongation of F waves corrected for height of 5% in the arms and 13% in the legs. The distal motor latencies were unchanged. These changes did not correlate with the duration of AIDS, degree of immunosuppression (CD4 count), Body Mass Index, albumin or vitamin B12 level. Four patients had subclinical mononeuropathies. Sural nerve taken at necropsy from five asymptomatic AIDS patients had evidence of axonal degeneration without inflammation or demyelination. There was a mean reduction in myelinated fibre density of 30.5% (CI 10-51%) compared with eight age matched sudden death controls (p = 0.01). This loss principally affected the larger fibres. The pathological and electrophysiological changes indicate axonal degeneration and are similar to those seen in other chronic disorders and in normal ageing. It is concluded that this axonal degeneration is not specific to HIV.

Progress in peripheral nerve reconstruction

The development of peripheral nerve surgery over the past 15 years has been fascinating to watch. Significant improvements have been achieved by the wide application of techniques which were developed before this period. New approaches may revolutionize the tactics of nerve repair in the near future.

New method to identify nociceptor units innervating glabrous skin of the human hand

A new technique is described for detecting nociceptor activity in microelectrode recordings from cutaneous fascicles of the human median nerve. The search strategy involves combined intraneural microstimulation and microneurographic recording in intrafascicular sites, where a critically low electrical stimulus amplitude evokes a threshold sensation of pain. From the subject's projection of pain to a small area of skin, the experimenter is guided to receptive fields of recordable nociceptor units. This technique has allowed, for the first time, to identify and study receptive properties of very high threshold nociceptors with A and C fibers in the glabrous skin of the human hand.

Light and electron microscopy studies of the ulnar, saphenous, and caudal cutaneous sural nerves of the dog

Transverse sections of the ulnar, saphenous, and sural nerves taken at specific levels in normal, young-adult beagle dogs were examined qualitatively and quantitatively at both the light and electron microscopic levels. The aim of this investigation was to provide baseline information for future studies of peripheral nerve disease in this species. A systematic sampling technique was used for the determination of nerve components (i.e., unmyelinated axons and Schwann cell and fibroblast nuclei). In all nerves sampled, the average size distribution for unmyelinated axons was unimodal, and most of the axons were 0.4-1.1 micron in diameter. Within this range, there were slight individual and nerve-to-nerve variations in the location of the largest diameter peak. The mean densities of Schwann cell nuclei (numbers/mm2) ranged from 841/mm2 in the palmar branch of the ulnar nerve, to 1,223/mm2 in the caudal cutaneous sural nerve, being nearly four times the average density or fibroblast nuclei. In every animal and in almost every nerve, a few abnormalities were found; and these should be kept in mind when assessing peripheral nerves in the dog.

Effects of ethanol on rat Schwann cell proliferation and myelination in culture

It is possible to treat dissociated embryonic rat dorsal root ganglia in culture to inhibit proliferation of all nonneuronal cells except Schwann cells. Neurons have been shown to produce a mitogenic stimulus for Schwann cells under these conditions. Additionally, myelin-competent neurons induce Schwann cells to elaborate myelin sheaths. Groups of sibling cultures were exposed to various nonlethal concentrations of ethanol (0, 43, 86, or 172 mM) for 4 wk. Cultures were assessed weekly by light microscopy in a blind fashion for evidence of Schwann cell proliferation and myelin formation. Ethanol adversely affected both Schwann cell proliferation and myelin formation in culture. No obvious differences in neuronal morphology were observed among the various groups of cultures by light or electron microscopy. These observations suggest that ethanol might interfere with Schwann cell proliferation and myelin formation in culture by one or both of the following means: a) inhibit neuronal production of signals for Schwann cell proliferation and myelination or b) impede Schwann cell responses to neuronal signals. Investigation of these possibilities in culture may provide insight into neuropathologic mechanisms operative in the fetal alcohol syndrome or alcohol-associated peripheral neuropathy in humans.

Quantitative techniques in neuropathology

In the future, quantitative techniques will probably be used in industry as part of Tier II studies for the evaluation of chemicals and drugs for their neurotoxic potential. Movement towards quantifying some structures or neuropathological changes will be made possible by advances in tissue preparation and computer technology. Emphasis will need to be placed on standardized techniques, good quality samples and sampling techniques in order to produce good quantitative data in a reasonable time. In this paper, different sampling techniques are evaluated using a cross section of rat sural nerve as the tissue for quantitative investigation.

POEMS syndrome: ultrastructural observations on the sural nerve

POEMS is an acronym that stands for a multisystem disorder that includes progressive sensorimotor Polyneuropathy, Organomegaly, Endocrinopathy, an M component in blood and/or concentrated urine, and Skin changes. The morphology of the peripheral nerves was mentioned in some of these cases and ranged from normal to those with segmental demyelination and/or degeneration of myelinated axons. We analyzed quantitatively the sural nerves of two cases of POEMS syndrome. Both nerves showed a severe loss of myelinated fibers, with a minor degree of regeneration. Degeneration of unmyelinated axons was observed, but to a lesser degree. There was marked collagen deposition in the endoneurium. The pathogenesis of the changes in the peripheral nerves and other organs in POEMS syndrome is still to be elucidated.

Are there motor fibers in the sural nerve?

A case of anomalous innervation of the abductor digiti quinti of the foot (ADQ) via the sural nerve is described. A muscle action potential from the ADQ could be elicited by stimulation of both the sural and the posterior tibial nerves.

Computer-assisted morphometry of the peripheral nervous system. A diagnostic tool

A formal systematization of the set of procedures required in peripheral nerve morphometry has been implemented in a computer program, in an attempt to provide an easy-to-handle diagnostic tool in current neuropathological practice. The hardware is composed of an IBM-PC compatible computer and a graphic tablet. Programs are written in BASIC and run in computers compatible with the MS-DOS operating system. The flow of operative steps involved in the morphometric study is controlled by the software. Sequential measurements are also tested for congruence. Nerve fibre measurements are stored in pluri-dimensional matrices for subsequent statistical calculations, i.e. evaluation of size-frequency distribution of nerve fibres and correlation analysis between nerve fibre subcomponents. Stereological estimates of the parenchymal components are also derived. The increase in accuracy achieved using area instead of diameter measurements is stressed. Compared to "dedicated" machines such personal computer-assisted systems exhibit substantial advantages in terms of low cost and flexibility.

Fine structure of A: autonomic nerve fibers and terminals in human myocardium; and B: myocardial changes in congenital heart disease

In a histological and fine structural study of right atrial biopsy specimens from 31 patients with rheumatic heart disease (RHD), aged 7 to 46 years, and 11 patients with congenital heart disease (CHD), aged 3 to 36 years, nerve fibers or endings were seen by electron microscopy in 11 specimens. There was concurrence of ordinary axons along with terminals bearing pale cholinergic or dark adrenergic synaptic vesicles. Smaller and denser cholinergic vesicles suggested proliferation followed by exhaustion of such nerve endings. The closest proximity of nerve terminal to muscle fiber was about 100 nm. In one RHD specimen a "specific terminal cell" was present between a nerve ending and muscle fiber; in another a possible neuromuscular contact was developing at the surface of a regenerating small muscle fiber with a few myofilaments. Unmyelinated axons amidst increased subendocardial and subepicardial collagen, with prominent fibroblasts and depleted muscle fibers, were seen more frequently in specimens of CHD. Loss of myofibrils and accumulation of mitochondria, with infrequent formation of lipofuscin bodies, characterized degenerating muscle fibers in CHD also, although to a lesser degree than in RHD (reported earlier, 1985). The myocardial blood vessels in CHD tended to have pale swollen endothelial cells and narrowed lumen. The most severely affected cases of CHD were those with (1) a very wide atrial septal defect (ASD), (2) ventricular septal defect (VSD) with vegetations near the defect, (3) infundibular pulmonary stenosis, and (4) Fallot's tetralogy.

Age-related changes in the fibre composition of equine peripheral nerve

Transverse sections of the lateral palmar nerve from a group of horses free from neuromuscular disease were assessed quantitatively, with emphasis on differences in the fibre population related to age. Morphometric analysis of the population of myelinated and unmyelinated fibres was performed. Changes were identified, there being a loss of larger myelinated fibres in older horses. The relationship of myelin thickness to axon diameter and the unmyelinated fibre population did not alter with age. The lateral palmar nerve is suitable for biopsy and electrophysiological study in the horse, but age related changes must be appreciated in the interpretation of results.

Hereditary distal muscular atrophy with vocal cord paralysis and sensorineural hearing loss: a dominant form of spinal muscular atrophy?

In 1980 Young and Harper described a family with an unusual form of distal spinal muscular atrophy associated with vocal cord paralysis. We report a family with three similarly affected subjects. Progressive sensorineural hearing loss was an additional feature in our patients. Electrophysiological and histological investigations did not exclude an involvement of sensory neurones. Whether the classification of this dominant disorder with the spinal muscular atrophies is justified will depend on additional studies in further families.

Changes in the histograms of nerves resulting from growth and various modalities of damage. A computer simulation

A computer program simulates the changes in a nerve's histogram during normal growth and from various neuropathies. The program shows how a nerve's histogram will change from various percentages of fiber damage or from preferential damage to either thick or thin fibers, or from various degrees of fiber restitution, or from single-event or repetitive damage. In single-event damage, the main alteration is a preponderance of thin (regenerating) fibers. Patterns of selective fiber vulnerability are difficult to deduce from the shape of the histogram. Repetitive damage remodels the histogram to a broad unimodal fiber distribution at reduced mean caliber. Comparison of simulated changes with data from an experimental isoniazid neuropathy yielded a close match between observed changes and simulation.

The conduction velocities of peripheral nerve fibres conveying sensations of warming and cooling

With the current practice of measuring thresholds for warming and cooling separately, the question of the exact nature of afferents subserving these sensations assumes new importance. Experiments to measure reaction times to warming and cooling stimuli at two sites on the lower limb are described. The conduction velocity for each sensation was estimated from the conduction distance and conduction time in the limb. The estimated mean conduction velocity for warming was 0.5, SD 0.2 m/s and cooling 2.1, SD 0.8 m/s. These figures confirm that the sensation of warming is conveyed in unmyelinated and cooling in small myelinated peripheral nerve fibres.

Peripheral neuropathy in myotonic dystrophy: a nerve biopsy study

Sural nerve biopsies from 13 unselected myotonic dystrophy patients and 6 normal controls were studied morphometrically. The myelinated fiber density was reduced in 11 of the 13 myotonic dystrophy patients, with preferential loss of large myelinated fibers. Unmyelinated fiber densities and diameters were normal. Teased fiber studies commonly revealed focal areas of remyelination and abnormal wrinkling of the myelin sheath. Measurement of internodal length disclosed features of both axonal regeneration and focal demyelination-remyelination. These findings are consistent with a chronic axonopathy of moderate severity, possibly due to axonal atrophy.

Expression of nerve growth factor receptor during human peripheral nerve development

The expression of NGF receptors on human Schwann cells during development and myelination and in culture was analyzed using a murine monoclonal antibody to human NGF receptor. Nonmyelinated femoral nerves from 13- to 14-week fetuses stained strongly for NGF receptor, whereas tissues from later stages of development showed a decrease in the staining intensity. These changes correlated with the initiation of myelination (17-19 weeks), as observed by phase-contrast and electron microscopy, and the reactivity with monoclonal antibody 4C5, a marker of mature Schwann cells. In adult nerves, only the perineurium and few endoneurial cells were stained with anti-NGF receptor antibody. Cultured human fetal Schwann cells were positive for NGF receptor by immunofluorescence irregardless of donor age or length of time in culture. The decreased staining of NGF receptor with nerve maturation may reflect a dependence of antigen expression on Schwann cell differentiation and/or neuron-Schwann cell interaction.

Long-lasting neuronal activity in rat dorsal horn evoked by impulses in cutaneous C fibres during noxious mechanical stimulation

The responses of 44 nociceptive neurones in the lumbar dorsal horn evoked by controlled mechanical stimulation of the skin, with or without conduction block in myelinated afferent fibres, were studied in the halothane-anaesthetized rat, in order to evaluate the effects of impulses in cutaneous nociceptive C fibres on dorsal horn neurones. Continuous non-noxious pinch of the skin evoked a short-latency discharge (mean latency 15 ms) in all the 13 class 2 neurones (i.e. neurones responding to both non-noxious and noxious stimulation of the skin) tested. The short-latency discharge was followed by weak prolonged activity in 6 neurones. Following noxious pinch of the skin a prominent late discharge (peak latency 150 ms-2 s) was evoked, which in all but two class 2 neurones outlasted the stimulation period (5-10 s). The discharge evoked by noxious pinch in class 3 neurones (i.e. neurones responding to noxious stimulation only) did not usually outlast the stimulation period. In all but two nociceptive neurones tested (n = 26) the late activity evoked by noxious pinch remained, albeit at a lower frequency in some neurones, during a conduction block in A fibres2,3. Hence this late discharge is probably mainly generated by impulses in nociceptive C fibers. It is concluded that nociceptive C fibres have an important role in sustaining long-lasting activation of class 2 neurones during noxious stimulation of the skin and that long-lasting discharges in these neurones indicates tissue damage to their receptive fields.

A portable system for measuring cutaneous thresholds for warming and cooling

Measurement of cutaneous thermal thresholds is a valuable technique for detecting small fibre neuropathy. A robust and portable microcomputer controlled system, which separately measures thresholds for warming and cooling, is described. Thresholds at three sites have been measured; the cheek, the dorsum of the hand and the sole of the foot. Regional variability and a correlation with age have been found, indicating the sensitivity of this system.

The neurophysiologic investigation of small fiber neuropathies

We have applied our technique for the measurement of thermal thresholds to 25 patients referred with symptoms and signs of small fiber peripheral neuropathy in whom conventional electrophysiological indices were individually within the range of normal values for our laboratory. Vibration threshold determinations were also within normal range. Significant abnormalities of thermal thresholds were noted in all patients. The results indicate that the technique provides an accurate, easily performed and reproducible index of function in small A delta and C groups of nerve fibers.

The leakage of serum proteins across the blood-nerve barrier in hereditary and inflammatory neuropathies. An immunohistochemical and morphometric study

The leakage of eight different serum proteins and immunoglobulins across the blood-nerve barrier (BNB) was studied by means of the peroxidase-antiperoxidase method in hereditary and inflammatory neuropathies and graded semiquantitatively with respect to endoneurial staining intensity and distribution. These data were compared with the degree of alterations of the myelinated nerve fibre population evaluated by morphometric analysis. Our series of 18 human sural nerve biopsies included seven hereditary neuropathies (three HMSN I, two HMSN II, two tomaculous neuropathies), nine inflammatory neuropathies (seven polyneuritis, two hypertrophic neuritis) and two normal controls. In HMSN II and in tomaculous neuropathy there was no enhanced endoneurial staining for serum proteins despite of a severe nerve fibre loss, whereas in HMSN I a rise of serum proteins of small and moderate molecular size like albumin and IgG was demonstrated in the endoneurial space indicating an impaired BNB function. Qualitative changes of the BNB with leakage also of high molecular weight proteins were observed in polyneuritis and hypertrophic neuritis, irrespective of the degree of nerve fibre changes. Our results show that fibre loss and alteration of the BNB are not correlated. The unselective leakage of serum proteins through the BNB appears to be a characteristic change in inflammatory neuropathies leading to proteinous edema. With regard to the subperineurial accentuation of the endoneurial edema it will be discussed that the vascular diffusion barrier is more fragile than the perineurial diffusion barrier.

A morphometric study of human fetal sural nerve

A morphometric study was performed on sural nerves from human fetuses at 15 to 36 weeks postovulation. There were no myelinated fibres at 15 and 16 weeks, but by 21 weeks there were 5,000/mm2, rising to 25,000/mm2 at 36 weeks. During the fetal period, the mean myelin lamellar count trebled and the g ratio (axon diameter: total fibre diameter) decreased from 0.90 to 0.75, although the axon diameter of myelinated fibres did not increase. The smallest myelinated axon diameter was 0.63 micron, whereas the largest unmyelinated axon in a 1:1 relationship with a Schwann cell was 2.83 micron, suggesting that axon size is unlikely to be the only stimulus for myelination. The density of unmyelinated axons that were the sole occupants of a Schwann cell fell considerably between 23 and 33 weeks, while the ratio of total unmyelinated axons to myelinated fibres decreased from 82:1 at 21 weeks to 6:1 at 36 weeks. Data for Schwann cell nuclear density and percentages of fibres cut through the nucleus are also presented.

Porphyric neuropathy: a clinical, neurophysiological and morphological study

A case of neuropathy in the course of an attack of acute intermittent porphyria was studied from the neurophysiological and morphological points of view. The neurophysiological findings (acute neuropathy with almost complete denervation despite normal or slightly reduced conduction velocity) and the morphological findings (no segmental demyelination after teasing, conservation of the linear fiber diameter/internodal distance ratio, mainly axonal damage on ultrastructural study) seem to indicate that the disease process is chiefly an axonal neuropathy.

The density of myelinated fibres is related to the fascicle diameter in human superficial peroneal nerve. Statistical study of 41 normal samples

The density of myelinated fibres in the superficial peroneal nerve was studied in 41 samples from 24 control human subjects. Photographic montages of the whole nerve fascicle were made from semithin and ultrathin transverse sections and used for a statistical analysis of sampling procedures, range of variations and relations between density and other variables. The results indicate that the spatial distribution of myelinated fibres within a nerve is often non-uniform. Therefore, it was not possible to define a statistically valid sampling system. The study of relations between variables shows the lack of any correlation between density and age and a considerable variation in the density. In contrast, there is a strong positive linear correlation between the surface area of the nerve fascicle and its content of myelinated fibres. That is, the fibre density of a given normal nerve is related to its diameter and can be predicted within a narrow range of error. We propose the term "derived density" for this value, and its application as a tool in the diagnosis of peripheral neuropathies is now being studied.

Severe polyneuropathy in Tangier disease mimicking syringomyelia or leprosy. Clinical, biochemical, electrophysiological, and morphological evaluation, including electron microscopy of nerve, muscle, and skin biopsies

Polyneuropathy in Tangier disease can be divided into three clinical types. The most severe form (type III) with a syringomyelia-like syndrome has been described in three cases only. Here, a fourth case of this type is presented. Because of unusual trophic disturbances even leprosy was suspected. Electrodiagnostic findings, including evoked cerebral potentials in this case, were suggestive of a generalized neuropathy with some degree of primary or secondary demyelination and implied possible impairment of central structures. Sural nerve biopsy, including electron microscopy and quantitative analysis, revealed a predominant reduction of smaller myelinated and unmyelinated fibres. The main morphological feature was the abundance of abnormal non-membrane-bound vacuoles in Schwann cells, mostly of the unmyelinated type, and in some endoneurial fibroblasts, macrophages and perineurial cells. There was no inverse relationship between lipid vacuoles and axons in Schwann cell complexes as suspected by others. An excess of endoneurial collagen as well as an increased fascicular area were obvious. In five skin biopsy specimens of different regions typical vacuoles were noted in Schwann cells, histiocytes, nevus cells, and rarely in perineurial cells.

Morphometric studies of normal sural nerves in children

Quantitative histologic studies of biopsies of normal sural nerves were performed on nine children aged 4 days to 17 years. Stereologic computerized procedures were used to determine total endoneurial area, size distribution and number of myelinated, unmyelinated fibers and Schwann cell nuclei per nerve and per square millimeter, and the ratio of myelin thickness to axonal diameter. There was an inverse linear relationship between the number of myelinated fibers per square millimeter and increasing age. A stronger correlation was found between the number of Schwann cell nuclei per nerve (P less than 0.01) and per square millimeter (P less than 0.001) and the logarithm of age. The slope of myelin thickness/axon diameter regression lines (P less than 0.001) changed with age in linear relationship (correlation coefficient: P less than 0.001). There were no age-dependent changes in the number and density of unmyelinated fibers, but the number of unmyelinated axons per Schwann cell subunit decreased with age. Size distribution histograms for myelinated fibers showed a unimodal profile in the newborn. A second peak at 6-7 micron appeared at age 3 months, shifting progressively to 9-11 micron at 14 years. The distribution of unmyelinated fibers was unimodal, with a peak around 0.8 micron, irrespective of age. There were marked individual variations in endoneurial area.

Ethylene oxide polyneuropathy: clinical follow-up study with morphometric and electron microscopic findings in a sural nerve biopsy

A case is reported of ethylene oxide polyneuropathy after 5 months of exposure. There was symmetrical distal weakness of both lower extremities and transitory reduced nerve conduction velocities with increased latencies. Sural nerve biopsy revealed nerve fibre degeneration of the Wallerian type, associated with reduction of axonal cross-sectional areas and some degree of nerve fibre regeneration that could be confirmed morphometrically. In addition, there was conspicuous paranodal vesicular disintegration of individual myelin lamellae. Unusual cisternae with introverted hemidesmosomes were noted in endoneurial fibroblasts.

Motor neuron disease and adult hexosaminidase A deficiency in two families: evidence for multisystem degeneration

We studied three patients from two unrelated families with adult hexosaminidase A deficiency. A 30-year-old, non-Jewish proband in the first family had juvenile amyotrophic lateral sclerosis that evolved to mild dementia, ataxia, and axonal (neuronal) motor-sensory peripheral neuropathy. A 36-year-old Jewish proband in the second family had "pure" spinal muscular atrophy. One supposedly healthy brother of the first proband was found to have borderline IQ, mild spasticity, and ataxia but no evidence of motor neuron disease. Marked cerebellar atrophy was detected by head scans in all three patients. In both probands electromyograms were characterized by prominent, complex repetitive discharges in many muscles. Hexosaminidase A activities against the artificial substrate were similar to those reported in infantile Tay-Sachs disease; however, the hexosaminidase A level against GM2 substrates was higher than that found in infantile Tay-Sachs disease. The hexosaminidase A levels of the parents were in the heterozygous range. Motor neuron disease in our patients and in those previously described appears to be part of a multisystem degeneration of the nervous system.

Morphometric analysis of intramuscular nerves

Intramuscular nerves were obtained at autopsy from five adult controls and were morphometrically analyzed. The number of myelinated fibers was directly proportional to the diameter of the fascicles. The fascicles were grouped into six sizes according to diameter. For each group, the normal range of distribution of the number of myelinated fibers could be estimated. Fiber size distribution and myelinated fiber density were also calculated. A unimodal fiber size distribution was observed for the small fascicles (less than 50 microns in diameter), and a bimodal pattern was observed for the large fascicles. Total myelinated fiber density was high in the small fascicles, and it decreased as the fascicles became larger in size, approaching the values observed in the large peripheral nerves. This study will be helpful in objectively evaluating morphological changes of intramuscular nerves in adult neuromuscular disorders.

Hereditary motor and sensory neuropathy of demyelinating and remyelinating type in children. Ultrastructural and morphometric studies on sural nerve biopsy specimens from ten sporadic cases

Ten autosomal recessive/sporadic cases of hereditary motor and sensory neuropathy type I (HMSN I), nine of which originated from the northern part of Sweden, were included in the study. Parents were free from neurologic symptoms. Motor and sensory conduction velocity was normal when recorded, i.e., in 19 and 17 parents, respectively. Sural nerve biopsies from the ten cases revealed a varying degree of onion bulb formation. In eight of the cases the onion bulbs consisted of abundant basement membranes, whereas the Schwann cells were few and sometimes lacking. There were in some cases considerable differences between separate fascicles as to the loss of myelinated nerve fibers. In the six biopsies in which teasing was performed signs of present and previous demyelination were noticed. Numerous internodal segments were abnormally thin with reference to their length. In many such segments there were marked local thickenings of the nerve fiber. In cross sections the probable counterparts to these thickenings were nerve fibers with unduly thick myelin sheaths and complex folding of the myelin. Ultrastructural axonal changes were seen in the majority of the cases. The pathogenetic and diagnostic implications of the present findings are discussed.

Peripheral projections of nerve fibres in the human median nerve

Elementary sensations of definable quality were evoked by intraneural electrical stimulation of sensory units through tungsten microelectrodes inserted in the median nerve of awake human subjects. The most commonly reported sensations were tapping, pressure, dull pain and sharp pain, which correlated with recording from RA units, SA I units, C nociceptors and A delta nociceptors, respectively. All sensations were projected more often to the fingertips than to the palm. The multifocal projections of sensations recruited by excitation of small groups of neighbouring nerve fibres were significantly more scattered in space than anticipated if these fibres had preserved an orderly intraneural map, implying lack of somatotopy in the nerve. Mean projected field sizes were 3.4 mm2 for sharp pain, 9.2 mm2 for tapping/vibration, 29.3 mm2 for pressure and 35.4 mm2 for dull pain, and in addition the latter two showed a rising size gradient from fingertip to palm. Consideration of projected field size as a variable in discriminative touch suggests that input from RA units and A delta nociceptors may be of importance in stimulus localization, while SA I units may play an additional role in two point discrimination.

Peroneal muscular atrophy. Part 2. Nerve biopsy studies

The present study used the nerve pathology, studied by quantitative light microscopy, as the sole basis for classification of peroneal muscular atrophy (PMA). The findings in biopsies of superficial peroneal nerves of 20 patients were compared with normal values obtained from 8 controls. Three homogeneous groups comprising 17 out of 20 patients were clearly identified. The hypertrophic type (7 cases) was characterized by (1) many multilamellated onion bulb formations; (2) extensive loss of MF with both involvement of the largest and smallest fibers; (3) lack of significant cluster formation. The neuronal sensori-motor type (5 cases) was characterized by (1) absence of any OB; (2) elective loss of large MF; (3) abundance of clusters with significant increase of the small MF population. The neuronal motor type (5 cases) showed a virtually normal sensory nerve except for fairly numerous clusters in some cases. Comparing this classification based on histomorphometric grounds, with the electrophysiological data it appears that 14 patients out of 17 would be correctly classified as hypertrophic or neuronal with respect to the motor nerve conduction velocity of the median nerve alone. Three cases were not classified in the previous groups since they differed notably in one or more parameters from the typical cases. A possible intermediate group is discussed.

Sural nerve biopsies from workers with a history of chronic exposure to organic solvents and from normal control cases. Morphometric and ultrastructural studies

An ultrastructural and morphometric study was performed on sural nerve biopsies of four industrial spray painters (35-59 years) and 11 controls (6-64 years). No difference could be shown in spray painters and age-matched controls as to the number of myelinated nerve fibres per area, their size distribution, variation of internodal length along single nerve fibres or the ratio between the number of myelin lamellae and the axon circumference. There was marked scattering of the two latter parameters in older exposed and and control individuals. The distribution of NADH2-tetrazolium reductase activity was similar in exposed and control cases. The general ultrastructural appearance of nodal-paranodal regions in controls conformed with that noted in experimental animals. The overall ultrastructural organization and age-related changes of nerves of exposed cases were similar to those of control cases except for a presence of paranodal axonal mitochondria which contained glycogen-like particles in exposed cases. In one exposed case abundant dispersed or clustered glycogen-like particles were seen in the paranodal axoplasm. These findings are suggested to be an effect of chronic exposure to organic solvent vapours. Ageing seems, however, to have a much greater impact on the morphology of the sural nerve fibre than occupational exposure to organic solvent.

The peripheral neuropathy in De Sanctis-Cacchione syndrome. Histological, ultrastructural, and morphometric studies

Histological, ultrastructural, and morphometric studies were performed on nerve and muscle biopsies from three patients with de Sanctis-Cacchione syndrome. Sural nerves showed marked loss of the myelinated fibers, in proportion to decrease in nerve conduction velocities and in inverse proportion to the severity of the clinical symptoms, which were related to the survival length. The larger fibers were involved earlier and more markedly than the smaller. The unmyelinated fibers were also decreased in number. Electron-microscopic studies showed the presence of primary degeneration of myelin sheaths or Schwann cells. Muscle biopsies showed grouping of type I and type II fibers in all three patients. Therefore, peripheral nerve involvement in de Sanctis-Cacchione syndrome was suggested to result from chronic degeneration of the neuronal cells and Schwann cells.

Selective loss of small myelinated and unmyelinated fibers in Shy-Drager syndrome

The number and sizes of myelinated and unmyelinated fibers in biopsied sural nerves in cases with Shy-Drager syndrome were studied in comparison with cases with olivopontocerebellar degeneration not having autonomic dysfunction. In Shy-Drager syndrome there was a tendency for both small myelinated and unmyelinated fiber densities to be reduced in comparison with cases with olivopontocerebellar degeneration. Unmyelinated fibers more than 0.5 micrometers in diameter were significantly reduced in Shy-Drager syndrome, a fact suggesting myelinated fiber degeneration. Multilamellated Schwann cell processes, isolated Schwann cell processes, and collagen pockets were more numerous and conspicuous in cases with Shy-Drager syndrome. It was concluded that unmyelinated fibers and small myelinated fibers in the peripheral nerves were involved selectively in Shy-Drager syndrome. The significance of the findings was discussed in terms of autonomic dysfunction observed clinically.