Quantitative changes of sural nerves in various neurological diseases

Summary Quantitative histological studies were made on sural nerve biopsies from 123 patients with various neurological disorders. The myelinated fibre density, nuclear density, and the thickness of the perineurium were measured and compared with the average and standard deviation of control material in different age groups.Specimens from chronic polyneuritis and heredodegenerative neuropathy showed a reduction of myelinated fibres and an increase of nuclei, the decrease of large myelinated fibres being greater than that of small myelinated fibres.In acute polyneuritis the large and small myelinated fibres decreased equally in number. In the sensory type of SMON, small myelinated fibres decreased more than large myelinated fibres, while in the sensorimotor type of SMON, the change was the reverse. Nuclear population remained unchanged in these diseases.In spinocerebellar degeneration there was a close correlation between the decrease in myelinated fibres and the clinical findings such as sensory disturbance and diminished tendon reflexes, suggesting the presence of peripheral nerve involvement.Myelinated fibres were reduced in cases of neurological diseases hitherto considered to be free of pathological changes in sensory nerves, including motor neurone disease, myopathy, tumours or vascular diseases of the brain and spinal cord. In motor neurone disease and myopathy the large fibres were decreased more than small fibres, and nuclear population was increased. In tumours or vascular disease of the central nervous system, the large and small fibres were decreased equally in number, and the nuclear population was within normal range.     

Licht- und elektronenmikroskopische sowie cytometrische Untersuchungen an peripheren Nerven beim Morbus Tangier

Summary A sural nerve biopsy was performed in a 55-year-old male patient with Tangier disease (familiallipoprotein deficiency). Light-microscopy showed an increase in the endoneural connective tissue and a loss of nerve fibers indicating a chronic peripheral neuropathy. Electron-microscopy revealed an accumulation of lipid droplets within Schwann cells of myelinated and unmyelinated nerve fibers. When compared with age-matched controls the myelinated fiber density was reduced with a relative preponderance of small myelinated fibers. In addition, distributional cytometric studies of nerve vibers in relation to the perineurium and endoneurial capillaries showed: Contrary to 4.6–7.5 m thick nerve fibers, which accumulated in the center of the nerve fascicle, small (0.5–4.5 m) and large (7.6–10.0 m) fibers lay nearby the perineurium. The measured increase in small myelinated nerve fibers around endoneurial capillaries may be explained as a sign of regeneration.

     

A morphometric study of human fetal sural nerve

Summary 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 m, whereas the largest unmyelinated axon in a 1:1 relationship with a Schwann cell was 2.83 m, 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.Supported by the Friedreich's Ataxia Group, and by grants from Ciba-Geigy Ltd., Basel and the London University Central Equipment Fund for the purchase of image analysis equipment     

Accuracy of sampling methods in morphometric studies of human sural nerves.

The aim of this study was to ascertain the minimum sample required to accurately measure the total number of myelinated fibres, mean myelinated fibre density (MFD), myelinated fibre diameter (Ds) and axonal diameter (Da) in morphometric studies of sural nerve biopsies. Measurements were obtained by sampling a single fascicle or systematic sampling of up to 50% of the total transverse fascicular area of two control and eighteen pathological sural nerves showing varying degrees of demyelination and axonal degeneration. MFD and fibre size were heterogeneous between fascicles in both control and pathological sural nerves, and morphometric results from one fascicle and systematic sampling of up to 50% of the total transverse fascicular area did not accurately represent the whole myelinated fibre population in the sural nerve. For accurate morphometric data it is necessary to quantitate all the myelinated fibres in the sural nerve.     

Quantitative changes with age in normal sural nerves

Summary Quantitative changes with age of the myelinated fibre density, nuclear density, the thickness of the perineurium, and the vasa nervorum were studied histologically in the human sural nerve. Materials were obtained from 79 necropsies of acute death without any accompanying peripheral nerve diseases, ranging from 1 week to 88 years of age.The average small myelinated fibre density decreased rapidly from the age of 1 week (26300/mm²) to the second decade (9560/mm²), and continued to decrease gradually with age, reaching an average of 9730/mm² for the eighth decade, 74% of that for the second decade.Large myelinated fibres appeared first in a 3-month-old infant. The average large myelinated fibre density increased rapidly, attaining the level of a young adult at 3 years. The average was maximum at the third decade (6480/mm²) and thereafter decreased with age, reaching an average of 3480/mm² for the ninth decade, 54% of that of the third decade.Nuclear density decreased rapidly from 1 week of age (9800/mm²) to the second decade (3750/mm²). Subsequently, it increased gradually with age up to the eighth decade (6090/mm²), at which time it measured 163% of the average of the second decade.The decrease of large myelinated fibres could not be related to changes of vasa nervorum due to aging before 60 years, while after 60 years there was a greater reduction of large myelinated fibres when the stenosis of vasa nervorum was more pronounced.A linear relationship was found between the thickness of the perineurium and the diameter of the fascicle. The perincurial index (the thickness of perineurium/diameter of a fascicle×100) showed wide variation among individuals though it showed a tendency to increase with age.     

Ephaptic interactions between myelinated nerve fibres of rodent peripheral nerves

We report evidence that ephaptic interactions may occur between intact mammalian myelinated nerve fibres and not only between demyelinated or damaged mammalian nerve fibres or nerve cells as analysed in previous studies. The ephaptic interactions were investigated between nerve fibres traversing the lumbar dorsal roots and between bundles of fibres in the sciatic nerve in anaesthetized rats in vivo. The interactions were estimated by comparing the excitability of nerve fibres originating from one of the hindlimb nerves (peroneal or sural) under control conditions and when the stimulation of these fibres was combined with stimulation of another nerve (tibial). An increase in nerve volleys recorded from group I muscle afferents in the peroneal nerve and of the fastest skin afferents in the sural nerve was used as a measure of the increase in the excitability. The excitability of these fibres was increased during a fraction of a millisecond, coinciding with the period of passage of nerve impulses evoked by the conditioning stimulation of the tibial nerve. The degree of the increase was comparable to the increases in the excitability evoked by 1–2 min lasting fibre polarization. Ephaptic interactions were found to be more potent and with longer lasting after‐effects within the dorsal roots than within the sciatic nerve. We postulate that ephaptic interactions may result in the synchronization of information forwarded via neighbouring afferent nerve fibres prior to their entry into the spinal cord and thereby securing the propagation of nerve impulses across branching points within the spinal grey matter.     

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

Summary 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 m in diameter were significantly reduced in Shy-Drager syndrome, a fact suggesting unmyelinated 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.     

Quantitative studies of the abnormal axon-Schwann cell relationship in the peripheral motor and sensory nerves of the dystrophic mouse

The nature and extent of abnormal axon-Schwann cell relationships in peripheral portions of dystrophic motor and sensory nerves were quantitatively evaluated between 1 and 9 months of age using teased fibres and electron micrographs.The results show that in the dystrophic (dy/dy) common peroneal (CPN) and tibial nerves (TN), and less in the dy/dy sural nerve (SN): (1) the number of Schwann cell nuclei associated with myelinated axons is increased with respect to normal; (2) the average internodal length is correspondingly reduced; (3) the average dystrophic internode elongates roughly in parallel with the average normal internode, and with the dystrophic limb; the longitudinal growth of the dystrophic limb is normal; (4) the variation of internodal length is greater than normal; it does not increase with age; (5) the incidence of the nodes of Ranvier which are wider than the normal 3 μm limit does not increase with age; and (6) the number of myelinated axons is reduced in the dy/dy CPN and TN but not in the dy/dy SN; it shows no change with age.These data indicate that: (1) in the dy/dy peripheral nerves (PNS) the abnormal axon-Schwann cell relationships and the reduced number of myelinated axons have been established prior to 1 month of age, thereafter progressive degenerative processes do not appear to take place, and (2) the dy/dy sensory nerve are less affected than the motor ones.     

Sensory action potentials and biopsy of the sural nerve in neuropathy.

In 167 consecutive patients with various types of neuropathy, the amplitude of the sensory potential and the maximum conduction velocity along the sural nerve were compared with conduction in other sensory nerves, and were related to structural changes revealed by nerve biopsy. Electrophysiological findings in the sural nerve were similar to those in the superficial peroneal and the median nerve, though the distal segment of the median nerve was normal in 20 per cent of the patients when it was abnormal in the sural nerve. Quantitation of histological findings was a more sensitive method than the electrophysiological study in that two-thirds of 33 patients with normal electrophysiology in the sural nerve showed mild loss of fibres or signs of remyelination in teased fibres. The amplitude of the sensory potential was grossly related to the number of large myelinated fibres (more than 7 micrometer in diameter). Considering the 95 nerves from which teased fibres were obtained, maximum conduction velocity was abnormal in half. In 18 of these nerves, slowing in conduction was due to axonal degeneration: the velocity was as to be expected from the diameter of the largest fibres in the biopsy ("proportionate slowing"). In 9 nerves slowing was severe and more marked than to be expected from loss of the largest fibres ("disproportionate slowing"); these nerves showed paranodal or segmental demyelination in more than 30 per cent of the fibres. In 16 nerves from patients with neuropathy of different aetiology neither loss of fibres nor demyelination could explain the moderate slowing. The cause of slowing in these nerves is unknown; other conditions are referred to in which slowing in conduction cannot be attributed to morphological changes. Finally, electrophysiological and histological findings are reported in some patients with neuropathy associated with malignant neoplasm, with rheumatoid arthritis, with polyarteritis nodosa, with acute intermittent porphyria and with cirrhosis of the liver.     

Effects of sciatic nerve regeneration on axonal populations in tributary nerves

The present study tests 2 hypotheses: (1) that the numbers of axons that regenerate into a tributary nerve are in part dependent on the type of lesion used to transect the axons in the parent nerve; and (2) that the numbers of axons that regenerate will be different in different tributary nerves. Axons were counted in the sural nerve and the nerve to the medial gastrocnemius muscle 8 weeks following crush, simple transection, transection with removal of 4 mm and transection with removal of 8 mm of the sciatic nerve in the rat. The counts of myelinated and unmyelinated axons are presented in the text. If axon numbers in the 2 nerves are normalized, the proportion of regenerated to normal myelinated axon numbers are approximately the same in the 2 nerves, with more regenerated axons than normal following crush, simple transection, or 4 mm gap transection and fewer following 8 mm gap transection. The unmyelinated axons behave differently. In the nerve to the medial gastrocnemius muscle, the numbers of unmyelinated axons are greater than or equal to the normal numbers following our various surgical paradigms whereas in the sural nerve there are always fewer unmyelinated axons than normal. These findings indicate that the above hypotheses are correct for the nerves tested in the rat.     

Recessive hereditary sensory neuropathy.

Clinical features in 2 cases of a recessive form of hereditary sensory neuropathy and the light and electron microscopy of sural nerve biopsy in 1 of them are described. The patients showed symptoms typical of this form of the disease; it should be stressed however that the loss of cutaneous sensation appeared to be limited to the distal parts of the lower extremities and involved all modalities of cutaneous sensation. Histological examination of sural nerve revealed a marked reduction in the number of myelinated fibres due to Wallerian-like axonal degeneration, of which various stages were represented. In addition, segmental demyelination, probably secondary to axonal changes, was seen. The unmyelinated fibres were also involved but to a lesser degree than the myelinated fibres. The observations indicate a progressive nature of the pathological process.     

Quantitative and qualitative study of sural nerve biopsies in Krabbe's disease

Summary Sural nerve biopsies from two infants with Krabbe's disease were examined morphologically, and quantitatively analyzed to obtain the density and size distribution of myelinated and unmyelinated nerve fibers as well as the variation in internodal lengths along the course of teased nerve fibers. When compared with age-matched control material, these sural nerves revealed a 50% reduction in density of myelinated fibers with a relative preponderance of small myelinated fibers. It was estimated that each nerve contained about 15% of the large (7–10) nerve fiber population found in control nerve. No reduction in the density of unmyelinated fibers was detected.Studies of teased preparations revealed an intermittent shortening of myelin internodes with resulting increased disparity of internodal lengths along individual fibers. These changes were indicative of widespread and severe demyelination and remyelination involving peripheral myelinated nerve fibers of all sizes in Krabbe's disease. No evidence of axonal or Wallerian degeneration was detected.Lipid accumulations were seen within endoneurial macrophage and within Schwann cells of myelinated fibers in both sural nerves and in the sympathetic chain removed at autopsy in case 2. The Schwann cell deposits were osmiophilic and appeared as focal collections of paranodal granules along myclinated fibers of teased preparations.Supported by U. S. P. H. S. Grants No. NB 08620 and NS 08054, and grants from the Allen P. and Josephine B. Green Foundation, Mexico, Missouri.     

Electron microscopical study of a nerve biopsy from a case in the chronic state of “Subacute Myelo-Optico-Neuropathy”

Summary N. suralis, taken from a patient in the chronic state of Subacute Myelo-Optico-Neuropathy (SMON) was examined by electron microscopy. The nerve showed a depletion of myelinated nerve fibres. Vacuoles or degenerated mitochondria were observed in the axis cylinders of myelinated and unmyelinated nerve fibres. Schwann cells were increased in number and many of them were atrophic. Onion-bulb formations were seen diffusely; regeneration of myelinated nerve fibres was sparse.     

Polyneuropathy with osmiophilic membrane-bound, cytoplasmic inclusions in Schwann cells (POMCIS)

In the cytoplasm of Schwann cells of a sural nerve biopsy from a 21-year-old female patient with chronic neuropathy we noted numerous unique, usually double membrane-bound, osmiophilic, granular or globular inclusions, approximately 30–600 μm in diameter. Some of these membrane-bound vesicular or tubular structures contained less dense or no osmiophilic inclusions. Morphometry revealed a reduction of the myelin area per endoneural area to approximately 13% (normal value: 20– 30%) and of the density of myelinated nerve fibers to 5,412/mm² (normal value at this age: 6,000–9,000/mm²). Large myelinated nerve fibers were predominantly reduced in number, and no myelinated nerve fibers with diameters larger than 4.5 μm were seen. Numerous, usually small onion bulb formations indicated a predominantly demyelinating type of neuropathy. This is to the best of our knowledge the first case of a chronic demyelinating neuropathy in which this kind of presumably pathognostic deposits in the cytoplasm of Schwann cells was detected. Received: 5 January 1999 / Revised, accepted: 3 March 1999     

The role of Schmidt-Lanterman incisures in Wallerian degeneration

Summary It is conventionally accepted that during the early stages of Wallerian degeneration of myelinated peripheral nerve fibres Schmidt-Lanterman incisures represent the sites at which the myelin sheath, together with enclosed axoplasm, is segmented into myelin ovoids. This mechanism is considered by some authors to be facilitated by the progressive intercalation of additional incisures in order to allow the later division of primary ovoids. We have demonstrated that this reported increase in the number of incisures is a misinterpretation of the changes occurring. By 36 h after crush of the rat sural nerve most myelinated fibres showed segmentation at incisures to form myelin ovoids. At 12 h and 24 h after crush, however, no ovoids were apparent and the number of incisures present was determined from teased fibres by light microscopy using oil immersion. There was no increase in the number of incisures either internodally or paranodally at 12 h and 24 h compared with a normal control population of fibres. However at 12 h, and to a greater extent at 24h, incisures were more readily apparent than in normal fibres. It is likely, therefore, that previous reports have confused an increase in the number of incisures with an increase in their perceptibility resulting from their progressive dilatation.     

Comparative morphometric evaluation of peripheral nerves and muscle fibers in myotonic dystrophy

We compared peripheral nerve fibers and muscle fibers in myotonic dystrophy (MD) using a computer-assisted device for morphometry. In the 17 cases with MD studied, the sural nerves of 14 cases (82%) showed various degrees of reduction of the myelin sheath area (MSA) per endoneurial area. Of these, 8 cases (47%) presented with a mild reduction of the MSA, 5 cases (29.4%) with moderate reduction, and one case (6%) with severe reduction. The number of myelinated nerve fibers was not significantly reduced in MD when compared with control nerves, due to clusters of small regenerated nerve fibers. The mean diameter of the muscle fibers in 6 of the 17 cases was less than 40 microm. Of these 6 severely affected cases, 5 revealed a considerable reduction of the MSA. Other cases, which appeared to be normal in respect to the diameter of muscle fibers, showed various degrees of reduction of the MSA. Thus, there is usually, but not always a morphometric correlation of the severity of changes between peripheral nerves and muscle. The severity of the peripheral neuropathy appears to depend largely on the patient's age, the stage of the disorder, and the time of progression. Electron microscopic examination of sural nerves showed significant, though non-specific pathological changes.     

Axonal degeneration in large and small nerve fibres. An electron-microscopic and morphometric study

Using computer-aided morphometric methods, axonal degeneration following nerve crush was analysed to reassess whether small fibres degenerate before large fibres or vice versa, or simultaneously. Axonal microtubule density was used as the criterion for determining the extent of fibre degeneration. Axonal areas and axonal microtubule numbers were recorded from a large sample of myelinated fibres in the right unoperated rat sural nerve and distal to crush in the left sural nerve. Both samples were divided into small and large fibre groups, according to axonal areas. Statistical analysis of the data confirmed a significant loss of microtubules from the left crushed nerve fibres but no significant difference in the relative loss of microtubules from small and large fibres. It is concluded, therefore, that in Wallerian degeneration, axonal breakdown, as assessed by microtubule loss, occurs simultaneously in small and large fibres. The findings are related to the electrophysiological changes which occur in Wallerian degeneration.     

Tomaculous neuropathy. A histopathological study and electroclinical correlates in 10 cases

Among 980 sural nerve biopsies, the nerves of 10 patients showed a great number of focal sausage-shaped thickenings of the myelin sheaths and were investigated by light and electron microscopy, teasing and quantitative studies. Single teased nerve fibres revealed myelin thickening in more than 25 p. 100 of internodes. This condition defined the tomaculous neuropathy and differed from other degenerative or toxic neuropathies which displayed a small number of internodes with myelin thickenings, in less than 5 p. 100. Segmental demyelination and remyelination were found in 12 p. 100 to 65 p. 100 of myelinated fibres. Tomaculous swellings were observed in the internodes of these fibres. Except axonal constriction within the sausage-shaped thickenings, no fibers with axonal degeneration was observed. The density of myelinated and unmyelinated fibres was normal. The loss of large myelinated fibres was interpreted as resulting from the myelinic changes. Clinical and electrophysiological data were similar in the ten cases of tomaculous neuropathies and in hereditary neuropathy with liability to pressure palsies, i.e.: autosomal dominant inheritance, higher incidence in males, recurrent nerve trunck and/or brachial plexus involvement related to compression, slowing of nerve conduction velocities in clinically affected and unaffected nerves more pronounced in anatomical narrow sites and increased F wave latencies. One patient (case 10) showed a mixed sensory motor progressive neuropathy but signs of widespread neuropathy were noted in more advanced cases. A great number of tomaculous swellings of myelin sheaths is considered as a specific but non constant change of hereditary neuropathy with liability to pressure palsies.     

A pathological study of a peripheral nerve in a case of neonatal adrenoleukodystrophy

Summary The pathological findings for a sural nerve biopsy specimen in a case of neonatal adrenoleukodystrophy are described. The density and total number of myelinated fibers in the patient showed no significant changes compared with controls. On electric microscopy, however, thickness of the myelin was smaller in the patient than in controls. Some linear or trilamellar inclusion bodies were found in Schwann cells and fibroblasts, similar to those found in X-linked adrenoleukodystrophy. Büngner's bands were also seen on electron microscopy, and myelin ovoids and balls were seen in teased fibers. These results show that a sural nerve biopsy is useful for the diagnosis of neonatal adrenoleukodystrophy. We suspect that axonal or neuronal degeneration occurs with changes in myelin in neonatal adrenoleukodystrophy.