Extraocular muscles: light microscopy and ultrastructural features

A review of the histopathological findings in myasthenia gravis: Clues to the pathogenesis of treatment-resistance in extraocular muscles

In myasthenia gravis autoantibodies target components of the neuromuscular junction causing variable degrees of weakness. In most cases, autoantibodies trigger complement-mediated endplate damage and extraocular muscles may be most susceptible. A proportion of MG cases develop treatment-resistant ophthalmoplegia. We reviewed publications spanning 65 years reporting the histopathological findings in the muscles and extraocular muscles of myasthenic patients to determine whether pathological changes in extraocular muscles differ from non-ocular muscles. As extraocular muscles represent a unique muscle allotype we also compared their histopathology in myasthenia to those in strabismus. We found that in myasthenia gravis, the non-ocular muscles frequently demonstrate neurogenic changes regardless of myasthenic serotype. Mitochondrial stress/damage was also frequent in myasthenic muscles and possibly more evident in muscle-specific kinase antibody-positive MG. Although myasthenia-associated paralysed extraocular muscles demonstrated prominent fibro-fatty replacement and mitochondrial alterations, these features appeared commonly in paralysed extraocular muscles of any cause. We postulate that extraocular muscles may be more susceptible than limb muscles to poor contractility as a consequence of myasthenia, resulting in a cascade of atrophy signaling pathways and altered mitochondrial homeostasis which contribute to the tipping point in developing treatment-resistant myasthenic ophthalmoplegia. Early strategies to improve force generation in extraocular muscles are critical.

Prognostic CT findings of diplopia after surgical repair of pure orbital blowout fracture

PURPOSE

Diplopia is a common sequela of blowout fracture even after proper surgical management. We investigated the prognostic factors of diplopia after surgery of pure blowout fracture.

MATERIALS AND METHODS

We retrospectively reviewed CT images of 181 patients with pure orbital blowout fracture who underwent at least six months of postoperative follow-up. We evaluated the following CT factors: (1) fracture site (orbital floor, medial wall of the orbit, or both), (2) fracture type (closed flap, open flap), (3) fracture size, (4) volume of herniated orbital soft tissue, (5) ratio of volume of herniated orbital soft tissue to fracture size, (6) number of points of contact between extraocular muscle (EOM) and bony edge, (7) presence of EOM thickening, (8) EOM swelling ratio, (9) presence of displacement of EOM, (10) presence of deformity of EOM, (11) presence of tenting of EOM, and (12) presence of entrapment of EOM. The associations between diplopia at six months after surgical repair and various risk factors were analyzed using logistic regression models for univariable and multivariable analyses.

RESULTS

EOM tenting and deformity and ratio of volume of herniated orbital soft tissue to fracture size were found to be statistically significant risk factors of diplopia at six months after repair on univariable analysis (all P < 0.05). Patients who showed EOM tenting or deformity on CT images had 5.22 and 10.85 times greater probability of diplopia after surgery, respectively (P-value, <0.001 and 0.026; 95% confidence interval of odds ratio, 2.071-13.174 and 1.323-88.915, respectively). On the other hand, ratio of volume of herniated orbital soft tissue to fracture size was not significant on multivariable analysis (P = 0.472).

CONCLUSION

The prognosis of patients was predicted by CT evaluation. Patients who have tenting or deformity of EOM on CT scan are more likely to have postoperative diplopia.

Differences in gene expression between strabismic and normal human extraocular muscles

PURPOSE

Strabismic extraocular muscles (EOMs) differ from normal EOMs in structural and functional properties, but the gene expression profile of these two types of EOM has not been examined. Differences in gene expression may inform about causes and effects of the strabismic condition in humans.

METHODS

EOM samples were obtained during corrective surgery from patients with horizontal strabismus and from deceased organ donors with normal EOMs. Microarrays and quantitative PCR identified significantly up- and down-regulated genes in EOM samples. Analysis was performed on probe sets with more than 3-fold differential expression between normal and strabismic samples, with an adjusted P value of ≤ 0.05.

RESULTS

Microarray analysis showed that 604 genes in these samples had significantly different expression. Expression predominantly was upregulated in genes involved in extracellular matrix structure, and down-regulated in genes related to contractility. Expression of genes associated with signaling, calcium handling, mitochondria function and biogenesis, and energy homeostasis also was significantly different between normal and strabismic EOM. Skeletal muscle PCR array identified 22 (25%) of 87 muscle-specific genes that were significantly down-regulated in strabismic EOMs; none was significantly upregulated.

CONCLUSIONS

Differences in gene expression between strabismic and normal human EOMs point to a relevant contribution of the peripheral oculomotor system to the strabismic condition. Decreases in expression of contractility genes and increases of extracellular matrix-associated genes indicate imbalances in EOM structure. We conclude that gene regulation of proteins fundamental to contractile mechanics and extracellular matrix structure is involved in pathogenesis and/or consequences of strabismus, suggesting potential novel therapeutic targets.

Ultrastructural organization of muscle fiber types and their distribution in the rat superior rectus extraocular muscle

Extraocular muscles (EOMs) are unique as they show greater variation in anatomical and physiological properties than any other skeletal muscles. To investigate the muscle fiber types and to understand better the structure-function correlation of the extraocular muscles, the present study examined the ultrastructural characteristics of the superior rectus muscle of rat. The superior rectus muscle is organized into two layers: a central global layer of mainly large-diameter fibers and an outer C-shaped orbital layer of principally small-diameter fibers. Six morphologically distinct fiber types were identified within the superior rectus muscle. Four muscle fiber types, three single innervated fibers (SIFs) and one multiple innervated fiber (MIF), were recognized in the global layer. The single innervated fibers included red, white and intermediate fibers. They differed from one another with respect to diameter, mitochondrial size and distribution, sarcoplasmic reticulum and myofibrillar size. The orbital layer contained two distinct MIFs in addition to the red and intermediate SIFs. The orbital MIFs were categorized into low oxidative and high oxidative types according to their mitochondrial content and distribution. The highly specialized function of the superior rectus extraocular muscle is reflected in the multiplicity of its fiber types, which exhibit unique structural features. The unique ultrastructural features of the extraocular muscles and their possible relation to muscle function are discussed.

Pediatric orbital floor trapdoor fractures: outcomes and CT-based morphologic assessment of the inferior rectus muscle

INTRODUCTION

Trauma to the pediatric orbit may produce a unique fracture in which entrapment of the periorbital tissue and/or inferior rectus muscle may occur due to a "trap-door" effect of the compliant orbital floor. This study was designed to assess the outcome following the surgical management of orbital trapdoor fractures in children and to examine alterations in the morphology of the inferior rectus (IR) muscle.

METHODOLOGY

Outcome assessment on patients undergoing surgery at the Hospital For Sick Children, Toronto with symptomatic orbital floor trapdoor fractures over a 10-year period and a CT-based morphometric analysis of the inferior rectus muscle were performed.

RESULTS

18 patients (5F, 13M) mean age 12.6 years (range 8.3-16.6 years) underwent surgical exploration (average time to surgery 9.7 ± 3.5 days (range 1-45 days). Follow-up was 15.4 months (range 6-36 months). All patients noted improvement in extra-ocular muscle (EOM) range of motion post-operatively: 7 patients had normal EOM with no diplopia; 9 patients had minimal diplopia on extreme secondary (upwards) gaze and 2 patients had residual significant diplopia with upward gaze. CT morphologic assessment (8 patients) demonstrated: a) zone of bony injury was posterior to the equator of the globe; b) minimal to no extra-conal fat exists to protect the IR muscle; c) a trend toward increased length in the injured IR muscle.

CONCLUSIONS

With surgical intervention, improvement of diplopia (complete or near-complete resolution) occurred in 16/18 (89%) of patients presenting with symptomatic trapdoor orbital floor fractures. CT-based assessment demonstrated the vulnerability of the inferior rectus muscle with close proximity to the orbital floor and lack of periorbital fat for protection. Alteration of the length of the IR muscle may impact the force-length relationship and play a role in the outcomes. Early surgical intervention for symptomatic trapdoor fractures is recommended.

Histochemical analysis of muscle fiber types of rat superior rectus extraocular muscle

Extraocular muscles (EOMs) represent a distinctive class among mammalian skeletal muscles in exhibiting unique anatomical and physiological properties. To gain insight into the basis for the unique structural/functional diversity of EOM fiber types and to explain their high fatigue resistance, rat superior rectus muscle (SRM) was studied using histochemical techniques. Muscle fibers were typed with regard to their oxidative and glycolytic profiles generated from succinic dehydrogenase (SDH) and phosphorylase activities in combination with their morphologic characteristics. Superior rectus muscle is organized into two layers, a central global layer (GL) of mainly large diameter fibers and an outer C-shaped orbital layer (OL) of principally small diameter fibers. Five muscle fiber types were recognized within the SRM: I, II, III, IV and V. In the global layer, four muscle fiber types were identified: type I (18.25±0.96μm; 32%) showed intermediate SDH (coarse type) and high phosphorylase activity. Type II fibers (14.45±0.82μm; 22%) exhibited high SDH (fine type) and intermediate phosphorylase activity. Low SDH (granular type) and high phosphorylase activity were demonstrated by type III fibers (22.65±1.73μm; 36%). Type IV fibers (26.24±1.32μm; 10%) were recognized by their low oxidative and glycolytic reactions. In the orbital region, only three muscle fiber types were recognized; fiber types I and II were found to compose approximately two-thirds of the layer. The third orbital fiber type (type V, 10.05±0.99μm) exhibited low SDH and low phosphorylase profiles. In this paper, the functional significance of the histochemical characteristics of the EOM fiber types is discussed.

Molecular and cellular adaptations to chronic myotendinous strain injury in mdx mice expressing a truncated dystrophin

Myotendinous strain injury is the most common injury of human skeletal muscles because the majority of muscle forces are transmitted through this region. Although the immediate response to strain injury is well characterized, the chronic response to myotendinous strain injury is less clear. Here we examined the molecular and cellular adaptations to chronic myotendinous strain injury in mdx mice expressing a microdystrophin transgene (microdystrophin(DeltaR4-R23)). We found that muscles with myotendinous strain injury had an increased expression of utrophin and alpha7-integrin together with the dramatic restructuring of peripheral myofibrils into concentric rings. The sarcolemma of the microdystrophin(DeltaR4-R23)/mdx gastrocnemius muscles was highly protected from experimental lengthening contractions, better than wild-type muscles. We also found a positive correlation between myotendinous strain injury and ringed fibers in the HSA(LR) (human skeletal actin, long repeat) mouse model of myotonic dystrophy. We suggest that changes in protein expression and the formation of rings are adaptations to myotendinous strain injury that help to prevent muscle necrosis and retain the function of necessary muscles during injury, ageing and disease.

Myosin flares and actin leptomeres as myofibril assembly/disassembly intermediates in sonic muscle fibers

The sonic muscle of type 1 male midshipman fish produces loud and enduring mating calls. Each sonic muscle fiber contains a tubular contractile apparatus with radially arranged myofibrillar plates encased in a desmin-rich cytoskeleton that is anchored to broad Z bands (approximately 1.2 micro m wide). Immunomicroscopy has revealed patches of myosin-rich "flares" emanating from the contractile tubes into the peripheral sarcoplasm along the length of the fibers. These flares contain swirls of thick filaments devoid of associated thin filaments. In other regions of the sarcoplasm at the inner surface of the sarcolemma and near Z bands, abundant ladder-like leptomeres occur with rungs every 160 nm. Leptomeres consist of dense arrays of filaments (approximately 4 nm) with a structure that resembles myofibrillar Z band structure. We propose that flares and leptomeres are distinct filamentous arrays representing site-specific processing of myofibrillar components during the assembly and disassembly of the sarcomere. Recent reports that myosin assembles into filamentous aggregates before incorporating into the A band in the skeletal muscles of vertebrates and Caenorhabditis elegans suggest that sonic fibers utilize a similar pathway. Thus, sonic muscle fibers, with their tubular design and abundant sarcoplasmic space, may provide an attractive muscle model to identify myofibrillar intermediates by structural and molecular techniques.

Muscle weakness in a mouse model of nemaline myopathy can be reversed with exercise and reveals a novel myofiber repair mechanism

Patients with the inherited muscle disease nemaline myopathy experience prolonged muscle weakness following periods of immobility. We have examined endurance exercise as a means of improving recovery following muscle inactivity in our alpha-tropomyosin(slow)(Met9Arg)-transgenic mouse model of nemaline myopathy. Physical inactivity, mimicked using a hindlimb immobilization protocol, resulted in fiber atrophy and severe muscle weakness. Following immobilization, the nemaline mice (NM) were weaker than WT mice but regained whole-body strength with exercise training. The disuse-induced weakness and the regain of strength with exercise in NM were associated with the respective formation and resolution of nemaline rods, suggesting a role for rods in muscle weakness. Muscles from NM did not show the typical features of muscle repair during chronic stretch-immobilization of the soleus muscle (regeneration occurred with relative lack of centralized nuclei). This indicates that the normal process of regeneration may be altered in nemaline myopathy and may contribute to poor recovery. In conclusion, endurance exercise can alleviate disuse-induced weakness in NM. The altered myofiber repair process in the nemaline mice may be a response to primary myofibrillar damage that occurs in nemaline myopathy and is distinct from the classical repair in muscular dystrophy resulting from plasma membrane defects.

Case Report: Exotropia Surgery in CPEO

Exotropia in a patient with CPEO was managed with bilateral medial rectus resections. Molecular genetic analysis of DNA from a skeletal muscle biopsy confirmed a deletion of the mitochondrial DNA. The resected muscle tendon was subjected to transmission electron microscopy, revealing muscle fibre variability and ragged red fibres with mitochondrial abnormalities.

Mechanisms of extraocular muscle injury in orbital fractures

The gross and microscopic events that occur after orbital blowout fractures were evaluated to assess the mechanisms of diplopia and muscle injury. Intramuscular and intraorbital pressures were evaluated in experimental animals, in cadavers, and at the time of orbital fracture explorations for repair of orbital fractures in humans. Histologic and circulatory changes, muscle pressure recordings, and operative observations were evaluated. Creation of a compartment syndrome was evaluated to include a histologic evaluation of the orbital fibrous sheath network for the extraocular muscles and the intramuscular vasculature. These experiments and observations do not support the role of a compartment syndrome in ocular motility disturbances because (1) intramuscular pressures were subcritical in both humans and animals; (2) no limiting fascial compartment could be demonstrated; and (3) microangiograms and histologic evaluations did not confirm areas of compartmental ischemic necrosis. Muscle contusion, scarring within and around the orbital fibrous sheath network, nerve contusion, and incarceration within fractures remain the probable causes of diplopia, with the most likely explanations being muscle contusion and fibrosis or incarceration involving the muscular fascial network.

Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles

Congenital fibrosis of the extraocular muscles is an autosomal dominant congenital disorder characterized by bilateral ptosis, restrictive external ophthalmoplegia with the eyes partially or completely fixed in an infraducted (downward) and strabismic position, and markedly limited and aberrant residual eye movements. It has been generally thought that these clinical abnormalities result from myopathic fibrosis of the extraocular muscles. We describe the intracranial and orbital pathology of 1 and the muscle pathology of 2 other affected members of a family with chromosome 12-linked congenital fibrosis of the extraocular muscles. There is an absence of the superior division of the oculomotor nerve and its corresponding alpha motor neurons, and abnormalities of the levator palpebrae superioris and rectus superior (the muscles innervated by the superior division of the oculomotor nerve). In addition, increased numbers of internal nuclei and central mitochondrial clumping are found in other extraocular muscles, suggesting that the muscle pathology extends beyond the muscles innervated by the superior division of cranial nerve III. This report presents evidence that congenital fibrosis of the extraocular muscles results from an abnormality in the development of the extraocular muscle lower motor neuron system.

Extraocular muscles: basic and clinical aspects of structure and function

Although extraocular muscle is perhaps the least understood component of the oculomotor system, these muscles represent the most common site of surgical intervention in the treatment of strabismus and other ocular motility disorders. This review synthesizes information derived from both basic and clinical studies in order to develop a better understanding of how these muscles may respond to surgical or pharmacological interventions and in disease states. In addition, a detailed knowledge of the structural and functional properties of extraocular muscle, that would allow some degree of prediction of the adaptive responses of these muscles, is vital as a basis to guide the development of new treatments for eye movement disorders.

Involvement of extraocular muscle in mitochondrial encephalomyopathy

We carried out a histological examination of the extraocular muscles (EOMs) in a case of myoclonus epilepsy associated with ragged-red fibers (MERRF) and two cases of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), which did not manifest external ophthalmoplegia clinically. By light microscopy, many granular and vesicular fibers were seen associated with endomysial fibrosis. Electron microscopy revealed that the fibers showed prominent accumulation of abnormal mitochondria, extensive loss of myofibrils, proliferation of free sarcoplasmic reticulum and an increased amount of lipid vacuoles. These changes were more pronounced in MELAS than in MERRF. Hirano bodies were often seen in the subsarcolemmal area of muscle fibers and also in the intramuscular myelinated nerve fibers and axon terminals. These findings suggest the presence of mitochondrial myopathy of the EOMs in cases of MELAS and MERRF.

Crystalloid bodies in skeletal muscle of hypothyroid myopathy. Ultrastructural and histochemical studies

Crystalloid bodies in skeletal muscle fibers have been described in myopathic and non-myopathic conditions. They have been interpreted as viral, glycogen, protein-glycogen complex, artifacts and of unknown nature. This report described similar crystalloid bodies in the postmortem muscle samples of two patients with hypothyroid myopathy. The crystalloid bodies were preferentially located in the I band and Z line region and in the subsarcolemmal region closely associated with lipofuscin. Some were present within basophilic bodies. They were formed by parallel filaments of 6-10 nm beaded periodically by electron-dense particles of 10-18 nm in a lattice, hexagonal or parallel-ripple pattern. Merging of filaments of crystalloid bodies into actin filaments of the I band was noted. The electron-dense particles stained strongly with periodic acid-thiocarbohydrazide-silver proteinate method for polysaccharides and were unaffected or partially digested by diastase treatment on the ultrathin sections. The filamentous component was neither stained for polysaccharides nor digested by diastase treatment. It is suggested that crystalloid bodies of muscle fibers are composed of two distinct subunits with particles of glycogen complex attached to filaments of unknown nature.

Periosteal epithelioid hemangioendothelioma with leptomeric fibrils

A case of recurrent periosteal epithelioid hemangioendothelioma of the right femur in a 66-year-old woman is reported. Microscopic examination showed epithelioid tumor cells with frequent intracytoplasmic vacuoles arranged in small nests or cords in hyalinized stroma. Immuno- and lectin-histochemical studies for factor VIII-related antigen and ulex europaeus I lectin indicated the endothelial nature of the tumor cells. Ultrastructurally, a few tumor cells contained leptomeric fibrils and crystalline filamentous aggregates in addition to showing certain features of endothelial cells. There seems to be no previous report of a vascular tumor containing leptomeric fibrils, which are often noted in normal striated muscle cells and their tumors. The bland appearance of the epithelioid tumor cells, poor vasoformative nature and prolonged clinical course differentiated this tumor from conventional angiosarcoma and so-called hemangioendothelioma of bone.

Hirano body in an inflammatory cell of leptomeningeal vessel infected by fungus Paecilomyces

An intracytoplasmic microfilamentous lattice, ultrastructurally identical to Hirano body, was found in an inflammatory cell within a leptomeningeal vessel wall infected by fungus Paecilomyces javanicus. The structure was well preserved and not associated with phagosomes. This is the first report of Hirano body found in an inflammatory cell at the site of fungal infection. The present finding suggests that the formation of Hirano body is non-specific and not restricted to the cell of the neuro-muscular system.

Mitochondrial morphometrics of histochemically identified human extraocular muscle fibers

Three fiber types--coarse, granular, and fine--were readily identified in histochemical cryostat sections of human extraocular muscle (EOM). The cryostat retrieval method was utilized to identify these three fiber types in serial electron microscopic thin sections. Using morphometric techniques, five mitochondrial variables (mitochondrial volume fraction, mitochondrial profile size, mitochondrial profile density, and clusters of two or of three or more mitochondrial profiles) were determined for a total of 162 histochemically identified fibers from two regions (orbital and global zones) from six EOMs. Coarse fibers had numerous large-sized mitochondrial profiles, often occurring in clusters. Granular fibers had fewer and smaller-sized profiles scattered across the fiber. Fine fibers had the most numerous, but smallest-sized mitochondrial profiles. Despite significant differences in group (fiber types) means for the mitochondrial variables, no single variable was sufficient for separating fiber types into distinct populations. Although a scattergram plot of two variables was sufficient to separate orbital zone fibers, a computer-generated, multivariate discriminant analysis was needed to separate the global zone fibers into distinct populations. These results will aid future studies on normal and pathological human EOM by providing a morphometric basis for identifying fiber types in the orbital and global zones.

Hirano body in extraocular muscle

Thirty-three rectus superior extraocular muscles from 23 autopsy cases, all over 60 years, were examined. Eosinophilic inclusions (Hirano bodies) were observed in all the muscles; they were stained deep red by Masson's trichrome stain and were positive for protein stain. They consisted of a collection of filamentous structures of two types: (1) a regular array of filaments 100 A in diameter which sometimes were arrayed in perpendicular planes and (2) another type in a herring bone or ladder-like pattern. Both structures were closely associated with the accumulated thin filaments 50-60 A in diameter (actin?) in the subsarcolemma. The frequent appearance in aged muscle fibers of Hirano bodies indicates that their formation is a change closely related with aging.

The ultrastructure of intramuscular nerves in amyotrophic lateral sclerosis

Muscle biopsies of 11 patients suffering from amyotrophic lateral sclerosis (ALS) were examined and the i.m. nerves found in seven of them were examined by electron microscopy. In atrophied muscles there was a marked decrease of myelinated fibers. The ultrastructure of the remaining myelinated axons showed changes in the neurofilaments, mitochondria, and vesicles. There was a decrease in the number of unmyelinated fibers as well as the myelinated fibers. Occasionally, there was an increase of unmyelinated fibers containing small fine axons. There were corpora amylacea in unmyelinated axons and banded structures in the extracellular area of the Schwann cells of the unmyelinated fibers. Some of these findings were considered as the ultrastructural features of degeneration and regeneration in i.m. nerves of motoneurons in ALS.

Möbius syndrome. Neuropathologic observations

Neuropathologic findings in an infant with congenital right facial and bilateral lateral rectus palsy (Möbius syndrome) are presented. Multiple microscopic foci of necrosis were found in the lower pontine tegmentum, involving the region of the intramedullary course of 6th and 7th cranial nerves. The significance of pathologic findings in this infant and 14 additional published cases of Möbius syndrome is discussed.

Extraocular muscle biopsy in chronic progressive external ophthalmoplegia

A quantitatives assessment of the pathological changes in extraocular muscle is presented in 8 patients with chronic progressive external ophthalmoplegia (CPEO). Serial cross-sections of extraocular muscle were stained with a battery of histochemical and immunohistochemical techniques and compared with 36 normal extraocular muscles and 1 muscle from a patient who had longstanding third nerve plasy with anomalous reinnervation. Several of the patients had a striking increase in the number of ragged-red fibers in extraocular muscle, particularly if frequent ragged-red fibers also were found on limb muscle biopsy. One patients demonstrated extrajunctional acetylcholine receptor (AChR) in a small percentage of fibers, although this finding was not present in the reinnervated muscle. Numerous darkly staining central regions were noted in the ocular muscle fibers of a patient with Stephens syndrome (CPEO, peripheral neuropathy, and cerebellar disease) and in the reinnervated muscle. A patient with myotubular myopathy had single central nuclei in both limb and ocular muscle. All patients demonstrated in their extraocular muscles variation in both the size and distribution of each of the three histochemical fiber types. Extraocular muscle biopsy proved to be a safe, reliable technique. As a similar quantitative analysis is applied to the study of further patients, a better understanding of the pathogenesis of CPEO should be possible.

Congenital hypotonia revisited

The definition of neuromuscular diseases affecting infants has depended on factors as various as the rate of progression of the illness, the clinical picture, and, recently, the morphologic peculiarities in the muscle biopsy. A review of the literature suggests that there are discrepancies in the classification of such illnesses, no matter what system is used. In some instances, a single diagnosis seems to include patients with quite separate illnesses, whereas other patients with seemingly identical diseases have been given different diagnoses.

Ultrastructural studies of extraocular muscles in ocular motility disorders. II. Morphological analysis of 38 biopsies

Thirty eight extraocular muscle biopsies obtained from thirty patients (1 normal and 29 affected with various kinds of ocular motility disorders such as strabismus, Duane's syndrome, paralysis), were studied by electron microscopy. Except for the control biopsy considered as normal, they showed: atrophy, disorganization of myofilaments, double Z-disks, rods, curving arrays of myofibrils, concentrically disposed electron-dense sarcotubules, clusters of mitochondria with numerous modifications of their cristae, and subsarcolemmal inclusions, such as dense bodies, laminated bodies, lipofuscin granules and lipid droplets. In addition, subsarcolemmal granulo-fibrillar aggregates, characterized by periodic granulated foci spaced at about 120 nm intervals, were seen in all the biopsies, even in that of the control case. The authors stress the pecularity of the granulo-fibrillar aggregates which, up to now, have never been described in skeletal muscles and the function of which in the extraocular muscles fibers is impossible to define. They point out the difficulty in determining if the motility disturbances may be related to the various changes observed in extraocular muscles of squinting eyes.

Ultrastructural comparison between skeletal muscle and cardiac rhabdomyomas

The electron microscope features of three primary cardiac rhabdomyomas and one skeletal muscle rhabdomyoma arising from the floor of the mouth are compared, along with a review of the previously reported ultrastructural features of skeletal rhabdomyomas. Cardiac rhabdomyoma filaments appear more orderly and have features suggestive of origin from both Purkinje and myocardial fibers. Zebra bodies were seen exclusively in the cardiac rhabdomyomas. In comparison, the extracardiac rhabdomyoma filaments were more disorderly and many cases had hypertrophic Z bands corresponding to the jackstraw or matchstick structures seen with the light microscope. This finding, along with the presence of satellite cells, was not seen in the cardiac rhabdomyomas.

Leptomeres in cultured human muscle

Leptomeres, the laminated structures consisting of bundles of very fine filaments separated into bands about 260 nm wide by periodic transverse dense lines 20--80 nm wide, were observed frequently in cultured muscle fibers of 8 patients with acid maltase deficiency, 4 with sporadic, adult-onset idiopathic "autophagic" vacuolar myopathy (that is not acid-maltase deficient) and one with abnormal mitochondria, but in only one of greater than 50 other cultures of normal and denervated human muscle. They were also induced abundantly in cultured normal human muscle by exposure to 0.5 mM DNP.

Structural alterations of extraocular muscle associated with Apert's syndrome

An inferior oblique muscle from a patient with Apert's syndrome was examined by light and electron microscopy. Alterations in the muscle fibres, the myoneural junctions, and intramuscular nerves were observed. These data are not compatible with the widespread notion that motility disturbances in this syndrome are solely due to mechanical limitations.

Spindle-shaped, cross-banded structures in human peripheral nerves

Fusiform, cross-banded structures (fibrous long-spacing collagen, or Luse bodies) were found in a nerve contained in the perivascular connective tissue of the short saphenous vein and in the sural nerve in man. The periodicity of cross-bandings was 140-170 nm and there was no intraperiod striation. The banded structures were found either isolated in the endoneurial spaces or contiguous with the surface of Schwann cells or fibroblasts. The nature, origin, and pathological significance of structures of this type in peripheral nerve are briefly discussed.