Anomalien des T-Systems und des sarkoplasmatischen Reticulums bei der Myotonie, Paramyotinie und Adynamie

Pathological findings in a patient with non-dystrophic myotonia with a mutation of the SCN4A gene; a case report

Background

Non-dystrophic myotonias (NDMs) are skeletal muscle disorders involving myotonia distinct from myotonic dystrophy. It has been reported that the muscle pathology is usually normal or comprises mild myopathic changes in NDMs. We describe various pathological findings mimicking those of myotonic dystrophy (DM) in biopsied muscle specimens from a patient with NDMs with a long disease duration.

Case presentation

A 66-year-old Japanease man presented eye closure myotonia, percussion myotonia and grip myotonia together with the warm-up phenomenon and cold aggravation from early childhood. On genetic analysis, a heterozygous mutation of the SCN4A gene (c.2065 C > T, p.L689F), with no mutation of the CLCN1, DMPK, or ZNF9/CNBP gene, was detected. He was diagnosed as having NDMs. A biopsy of the biceps brachii muscle showed increasing fiber size variation, internal nuclei, chained nuclei, necrotic fibers, fiber splitting, endomysial fibrosis, pyknotic nuclear clumps and disorganized intermyofibrillar networks. Sarcoplasmic masses, tubular aggregates and ragged-red fibers were absent.

Conclusion

It is noteworthy that the present study revealed various pathological findings resembling those seen in DM, although the pathology is usually normal or mild in NDMs. The pathological similarities may be due to muscular modification with long-standing myotonia or excessive muscle contraction based on abnormal channel activity.

Electronic supplementary material

The online version of this article (10.1186/s12883-019-1360-0) contains supplementary material, which is available to authorized users.

A large german kindred with cold-aggravated myotonia and a heterozygous A1481D mutation in theSCN4A gene

Muscle sodium-channel disorders cover a spectrum of rare myotonic diseases. In a German family with 17 affected individuals in four generations, we identified a heterozygous missense mutation in exon 24 A1481D (c.4442 C>A) of the voltage-gated sodium channel gene (SCN4A) alpha subunit. Phenotypes of 12 family members were characterized by a mild myotonia with cold sensitivity but without paramyotonia. The index patient presented with fluctuating cold- and exercise-induced stiffness of ocular, facial, and distal muscles. The myotonia became more severe at the age of 22 years. His father had had cold- and exercise-induced periodic weakness with fluctuating myotonia since age 10. Later he developed a more severe, purely exercise- and cold-aggravated myotonia of arms, hands, and facial muscles. The father's mother presented with cold-induced myotonia until age 65, when progressive weakness of proximal limb muscles developed. Her muscle biopsies revealed considerable myopathic changes with a variety of fine structural alterations. This study presents a family with cold-aggravated myotonia and progression of myopathic changes in the muscle biopsy with increasing age. In older patients, sodium channelopathies may mimic the phenotypic features of myotonic dystrophy type 2.

The origin of tubular aggregates in human myopathies

Tubular aggregates are morphological abnormalities characterized by the accumulation of densely packed tubules in skeletal muscle fibres. To improve knowledge of tubular aggregates, the formation and role of which are still unclear, the present study reports the electron microscopic analysis and protein characterization of tubular aggregates in six patients with 'tubular aggregate myopathy'. Three of the six patients also presented with myasthenic features. A large panel of immunochemical markers located in the sarcoplasmic reticulum, T-tubules, mitochondria, and nucleus was used. Despite differences in clinical phenotype, the composition of tubular aggregates, which contained proteins normally segregated differently along the sarcoplasmic reticulum architecture, was similar in all patients. All of these proteins, calsequestrin, RyR, triadin, SERCAs, and sarcalumenin, are involved in calcium uptake, storage, and release. The dihydropyridine receptor, DHPR, specifically located in the T-tubule, was also present in tubular aggregates in all patients. COX-2 and COX-7 mitochondrial proteins were not found in tubular aggregates, despite being observed close to them in the muscle fibre. The nuclear membrane protein emerin was found in only one case. Electron microscopy revealed vesicular budding from nuclei, and the presence of SAR-1 GTPase protein in tubular aggregates shown by immunochemistry, in all patients, suggests that tubular aggregates could arise from endoplasmic reticulum exit sites. Taken together, these results cast new light on the composition and significance of tubular aggregates.

Defective mitochondrial oxidative phosphorylation in myopathies with tubular aggregates originating from sarcoplasmic reticulum

Abnormalities of the sarcotubular system presenting as tubular aggregates (TAs) have been described in a variety of neuromuscular disorders. Here, we report on immunohistochemical and biochemical findings in 7 patients (2 familial and 5 sporadic cases) suffering from myopathies with TAs. In muscle biopsy specimens from 5 of the 7 patients, TAs were immunopositive for the ryanodine receptor (RYR 1) of the sarcoplasmic reticulum (SR), the SR Ca2+ pump (SERCA2-ATPase), and the intraluminal SR Ca2+ binding protein calsequestrin, indicating an SR origin of these aggregates. Furthermore, these 5 cases showed decreased respiratory chain enzyme activities (NADH:CoQ oxidoreductase. complex I and cytochrome c oxidase [COX], complex IV), while the remaining 2 patients exhibited normal values. Our findings indicate a functional link between mitochondrial dysfunction and the presence of TAs originating from the sarcoplasmic reticulum.

Chronic progressive external ophthalmoplegia and myalgia associated with tubular aggregates

Tubular aggregates represent a distinct myopathological feature characterized by basophilic sharply demarcated irregularly shaped subsarcolemmal zones consisting of parallel double-walled tubules of unknown subcellular origin. They are found on rare occasions in a wide spectrum of myopathies, but their significance for the development of muscular symptoms has not yet been fully established. We describe a patient with chronic progressive external ophthalmoplegia (CPEO) associated with exercise-induced myalgia and tubular aggregates in skeletal muscle. The association of CPEO with tubular aggregates has not been reported before and represents an important differential diagnosis to other syndromes associated with CPEO, especially mitochondrial encephalomyopathies.

Tubular aggregates and partial cytochrome c oxidase deficiency in skeletal muscle of patients with AIDS treated with zidovudine

We report on two patients, who had myalgias while receiving long-term zidovudine treatment for an HIV infection, in whom muscle biopsy findings included a partial cytochrome c oxidase (CCO) deficiency, a feature of zidovudine myopathy, and tubular aggregates, a finding hitherto unreported in HIV-infected patients. The CCO deficit was observed in 28% and 24% of muscle fibers, respectively. Tubular aggregates were the prominent histopathological feature in patient 1, and were detected by systematic electron microscopy in patient 2. Inflammation and myonecrosis were not detected. In patient 1, the typical mitochondrial and myofibrillar changes of zidovudine myopathy were present and 12% of fibers showed tubular aggregates. The aggregates were not stained at CCO reaction, and 96% of myofibers enclosing tubular aggregates showed a decreased CCO activity. This suggested more than a chance association between mitochondrial dysfunction and the formation of tubular aggregates. We conclude that tubular aggregates are detected in some patients treated by zidovudine, and that the finding could be related to the long-term administration of the drug.

Autosomal dominant neuromuscular disease with cylindrical spirals

Cylindrical spirals (CS) have been reported in muscle biopsies from five individual cases, as well as in two belonging to one family where there was another affected member, clinically associated with cramps, pain, stiffness and/or weakness. Here we studied muscle biopsies of a 70-yr-old mother and her 52-yr-old son, the latter with an associated neuropathy, both with late clinical onset in whose family at least 10 other members, spanning five generations, were diversely affected by muscular weakness, gait disorders, motor impairment and/or scoliosis, featuring an autosomal dominant trait with variable expression. CS as the main pathological findings were observed by light microscopy mostly in type 2 fibres, consisting of subsarcolemmal or intermyofibrillar granular and/or rod-like clusters, bluish with haematoxylin, bright red with Gomori's modified trichrome, non- or lightly reactive with PAS, faintly coloured with NADH-TR, non-reactive with SDH or ATPase, strongly stained with non-specific esterase and myoadenylate deaminase. Ultrastructurally, CS appeared as concentrically wrapped lamellae 1-2 microns in diameter. On occasion CS merged into tubular vesicular structures strongly resembling tubular aggregates (TA). Dilation of terminal cisternae (TC) in their proximity supports an origin from the sarcoplasmic reticulum (SR). Variable gene expression possibly explains both the highly diverse clinical compromise and time of onset.

Lacunar dilatations of intrafusal and extrafusal terminal cisternae, annulate lamellae, confronting cisternae and tubulofilamentous inclusions within the spectrum of muscle and nerve fiber changes in myotonic dystrophy

In 3 out of 5 muscle spindles available in skeletal muscle biopsy specimens from 30 patients with myotonic dystrophy (MD) unusually large lacunar dilatations of terminal cisternae were observed that had thus far only been reported in extrafusal muscle fibers. Cytoplasmic annulate lamellae, confronting cisternae and regularly proliferated terminal cisternae, as well as intranuclear tubulovesicular inclusions were found in extrafusal muscle fibers that in combination with concentric membranous bodies seen in perineurial cells and Schwann cells generally emphasize an involvement of the endoplasmic reticulum in the pathogenesis of MD. In addition, a nuclear inclusion body was observed composed of tubulofilamentous structures with close similarity to those thought to be rather specific for inclusion body myositis. Vesicles filled with amorphous material originating from outer spindle capsule cells were suggested to indicate matrical lipidic debris leading to "ghost bodies" and calcifying globules. Light microscopical evaluation of 8 sural nerve specimens revealed a neuropathy in only 2 patients that was predominantly axonal in type and of slight to moderate severity with a secondary demyelinating component in 1 patient. These findings add to the large spectrum of muscle and nerve fiber changes in MD underlining the phenotypic multiplicity of a well defined genetic defect.

Muscle hypertrophy in Duchenne muscular dystrophy. A pathological and morphometric study

In order to investigate the pathological basis of muscle hypertrophy in Duchenne dystrophy, 9 biopsy specimens of the lateral gastrocnemius and 7 of the vastus lateralis were compared. All patients had calf hypertrophy and normal strength in gastrocnemius-soleus, whereas the quadriceps biopsied were all atrophied and weak. The patients' ages ranged from 4 to 11 years. The pathological and histochemical changes were assessed semi-quantitatively. Comparison of the gastrocnemius and quadriceps groups showed that the number of hypercontracted fibres, the degree of endomysial fibrosis and the degree of fat infiltration were significantly higher in the quadriceps. The fibre type differentiation was better in the gastrocnemius group. The mean fibre diameter was above normal in all gastrocnemius biopsies and showed no increase with age. In the quadriceps, fibre hypertrophy was found early in the disease but had changed into fibre atrophy in the three oldest patients. When present, fibre hypertrophy involved both fibre types. The amount of fat-fibrosis per unit area was increased in both groups, but more severely so in the quadriceps. These results indicate that there is no true muscle hypertrophy in the gastrocnemius, in which the fat-fibrosis component was increased in all patients and that the dystrophic process is more active in the quadriceps. The finding of persistent fibre hypertrophy in the gastrocnemius is discussed with respect to the postural abnormalities observed in the lower limbs in Duchenne dystrophy.

The MRL +/+ mouse: a new model of tubular aggregates which are gender- and age-related

Congenic mice of the MRL +/+ substrain provide an animal model for study of tubular aggregates in skeletal muscle. Tubular aggregates appear limited only to males of the MRL +/+ strain and are not found in other strains, including MRL +/-, MRL lpr/lpr, BXSB/MpJ, BALB/c, SJL/J, AJ, or C3H HEJ. This strain-specific occurrence, and the gradually increasing abundance of tubular aggregates after 6 months of age until virtually all type II myofibers are affected by 2 years, implies that both genetic and developmental factors are necessary for the occurrence of tubular aggregates. These two factors are not sufficient, however, since hormonal alteration by male castration nearly completely prevents the expression of tubular aggregates. Parallels are drawn with how expression of tubular aggregates is limited largely to males in diverse acquired and hereditary human neuromuscular disorders.

A case of "myopathy with tubular aggregates" with increased muscle fibre sensitivity to caffeine

A 23-year-old man with "myopathy with tubular aggregates" had suffered from exercise-induced muscle cramps for 1 year. His general and neurological findings were normal. Laboratory investigations were within normal limits except for a slightly elevated serum creatine kinase level. Muscle biopsy showed some small angular fibres and scattered type 2B fibres with prominent tubular aggregates originating from the sarcoplasmic reticulum. Since the muscle fibres contracted at a lower concentration of caffeine, increased muscle fibre sensitivity to caffeine is probably related to muscle cramps in this disorder. Tubular aggregates are then secondarily formed in the muscle fibres.

Tubular aggregates in skeletal muscle of chronic alcoholic patients

The presence of tubular aggregates (TA) in type II muscle fibers in two of 20 alcoholic patients with chronic liver disease, and with no apparent neuromuscular disorder, is reported. The localization, histochemical reactions, and ultrastructural features of the TA are similar to those previously described in other conditions. In one of the two cases TA were demonstrated by E/M observations only and not by histochemistry. No correlations were found between the biochemical changes and the presence of tubular aggregates. We believe that TA are long-standing structures since the muscle biopsies were performed 12 and 13 days after the ingestion of alcohol had been discontinued. They may represent a non-specific response of the sarcoplasmic reticulum to compensate for the deficient calcium uptake reported in alcoholic patients.

The autosomal recessive (Becker) form of myotonia congenita

In the last two decades, two genetically distinct forms of myotonia congenita have been identified--an autosomal dominant and an autosomal recessive form. The purpose of this review is to describe the features that enable us to distinguish between these two forms in the absence of sufficient genetic data. Thus far, it can be concluded that the only probable difference between the two forms is in the fatty-acid pattern of muscle phospholipids. Clinical, histologic, ultrastructural, and electromyographic investigation may prove helpful, but they alone cannot provide a reliable means of identifying the genotype in an individual patient.

[Hypertrophy of the transversal tubular system in target fibres. An electron microscopic study (author's transl)]

In a muscle biopsy from a patient suffering about 2 years from an amyotrophic lateral sclerosis groups of atrophic fibres and target fibres were observed. By electron microscopic examination, amongst numerous parallel or spinal cisternae near the plasma membrane, single-membrane bound smooth tubular elements with a constant diameter of 200-300 A occur in the central and intermediary zone of some target fibres. The connexion between these tubules and the terminal cisternae (triads) of the sarcoplasmic reticulum, suggest that this phenomenon seems to be a proliferation of the transversal-tubular system due to the partial denervation. Only a mechanical displacement of the T-tubules as a result of the destruction of the muscle fibres is not plausible, because the T-system volumetrically amounts only 0.3-0.5% of the muscle fibre.

Electron microscopic study of extraocular muscles in myotonic dystrophy

The extraocular muscles of two middle-aged men with ophthalmoplegia secondary to myotonic dystrophy were studied by electron microscopy. The main change was disorganization in the arrangement of myofibrils rather than degeneration of the cells. Diseased muscle cells contained randomly distributed, short and irregular myofibrils and individual myofilaments. The cytologic appearance of these muscle cells was similar to that of developing muscle cells. The pathogenesis of the myopathy in myotonic dystrophy may be related to myofibrillogenesis and its maintenance.

Histochemistry and electron microscopy of muscle fibres in a case of congenital paramyotonia

In a case of congenital paramyotonia a muscle biopsy was performed and studied morphologically, histochemically and ultrastructurally. A clearcut pattern of changes has been observed with ATPase and oxidative enzymes. On electron microscopy special changes known as "tubular aggregates" were found. The relationship between the two findings, as well as the significance of such alterations in the range of periodic paralyses and myotonic phenomena, are discussed.

[Histological, histochemical, and ultrastructural findings in malignant hyperthermia (author's transl)]

Malignant hyperthermia is a rare but severe complication of modern anesthesia, induced by halothane and succinylcholine. The syndrome is characterized by a rapid sustained and extreme rise in body temperature associated with muscular rigidity, tachycardia, tachypnoea and cyanosis. The lethality is about 60%. The present paper describes the histological, histochemical and electron microscopical findings performed on muscle biopsies of 3 patients with malignant hyperthermia (1 patient died) and a so called risk patient. In all patients morphological findings consistent with a pre-existent myopathy were found. Histologically there were acute necrotic muscular fibers as well as in types I and II, variations in the fiber diameter and centralization of the nuclei. In two cases even fibers that had a normal aspect in HE slides, showed a pathologic pattern after phosphorylase reaction. In addition to acute rhabdomyolysis, electron-microscopic investigations revealed cystic expansion of the cisterns of the sarcoplasmic reticulum with a peculiar proliferation of the sarcolemma. In a degenerating mitochondrium, a crystalline inclusion was identified. These findings support the pathogenetic concept of Britt and coworkers of a functional defect in the calcium release or binding mechanism of sarcoplasmic reticulum. Since it is known that malignant hyperthermia has a familial predilection, it seems very important that clinical, biochemical, and morphological investigations be performed such as CPK estimations and muscular biopsies not only of the patients but also of the relatives in order to rule out this type of latent myopathy.