Afterdischarges in myotonic dystrophy type 1

OBJECTIVE

Electrodiagnostic testing is an important screening test for myotonic dystrophy type 1 (DM1). Although myotonic discharges are observed on electromyography in cases of DM1, it is difficult to distinguish DM1 from other myotonic disorders clinically. In the present study, afterdischarges, another type of pathological potential revealed by electrodiagnostic testing, were analyzed, and their role in distinguishing DM1 from other myotonic disorders was explored.

METHODS

Data from 33 patients with myotonic discharges on electromyography were analyzed retrospectively. According to gene testing, the patients were divided into DM1 (n = 20) and non-DM1 myotonia (n = 13) groups. Afterdischarges were investigated by retrospectively evaluating the electrodiagnostic findings of motor nerve conduction studies, F-waves, and repetitive nerve stimulations.

RESULTS

Afterdischarges were observed in 17 of the 20 patients with DM1, with an occurrence rate of approximately 85%. However, afterdischarges were absent in all patients with non-DM1 myotonia. There were significant differences in the occurrence rate between the two groups (P < 0.01).

CONCLUSION

Afterdischarges may serve as a suggestive role in clinical diagnosis of DM1. The discovery that DM1 can present with afterdischarges may pave a new way to study the pathogenesis of DM1.

Expert Insights from a Delphi-driven Neurologists' Panel: Real-world Mexiletine use in Patients with Myotonic Disorders in Italy

Background

Myotonic disorders, such as non-dystrophic myotonias (NDMs) and myotonic dystrophies (DMs) are characterized by a delay in muscle relaxation after a contraction stimulus. There is general consensus that protocols to treat myotonia need to be implemented.

Objective

Mexiletine is the only pharmacological agent approved for the symptomatic treatment of myotonia in adult patients with NDM and is considered to be the first-line treatment for DMs; however, its production in Italy was halted in 2022 making its availability to patients problematic.

Methods

A panel of 8 Italian neurologists took part in a two-round Delphi panel between June and October 2022, analyzing the current use of mexiletine in Italian clinical practice.

Results

The panelists assist 1126 patients (69% DM type1, 18% NDM and 13% DM type2). Adult NDM patients receive, on average, 400-600 mg of mexiletine hydrochloride (HCl) while adult DM patients receive 100-600 mg, per day in the long-term. The severity of symptoms is considered the main reason to start mexiletine treatment for both NDM and DM patients. Mexiletine is reckoned to have a clinical impact for both NDM and DM patients, but currently drug access is problematic.

Conclusions

Mexiletine treatment is recognized to have a role in the reduction of the symptomatic burden for NDM and DM patients. Patient management could be improved by facilitating access to therapy and developing new drug formulations.

Idiopathic Inflammatory Myopathy with Delayed Finger Opening Resembling Grip Myotonia

Grip myotonia can be a clue for the diagnosis of myotonic disorders. However, several clinical conditions cause delayed finger opening mimicking grip myotonia. We herein report a 44-year-old man with idiopathic inflammatory myopathy who presented with delayed finger opening resembling grip myotonia. The delayed finger opening differed from grip myotonia given the absence of the warm-up phenomenon and percussion myotonia, relative sparing of the thumb extension, and pronounced weakness of the extensor digitorum. Focusing on the extension of the thumb and other fingers may aid in the differentiation between delayed finger opening and true grip myotonia.

Diagnostics in skeletal muscle channelopathies

INTRODUCTION

Skeletal muscle channelopathies (SMCs) are a heterogenous group of disorders, caused by mutations in skeletal ion channels leading to abnormal muscle excitability, resulting in either delayed muscle relaxation (myotonia) which characterizes non-dystrophic myotonias (NDMs), or membrane transient inactivation, causing episodic weakness, typical of periodic paralyses (PPs).

AREAS COVERED

SMCs include myotonia congenita, paramyotonia congenita, and sodium-channel myotonia among NDMs, and hyper-normokalemic, hypokalemic, or late-onset periodic paralyses among PPs. When suspecting an SMC, a structured diagnostic approach is required. Detailed personal and family history and clinical examination are essential, while neurophysiological tests should confirm myotonia and rule out alternative diagnosis. Moreover, specific electrodiagnostic studies are important to further define the phenotype of de novo cases and drive molecular analyses together with clinical data. Definite diagnosis is achieved through genetic testing, either with Sanger sequencing or multigene next-generation sequencing panel. In still unsolved patients, more advanced techniques, as exome-variant sequencing or whole-genome sequencing, may be considered in expert centers.

EXPERT OPINION

The diagnostic approach to SMC is still mainly based on clinical data; moreover, definite diagnosis is sometimes complicated by the difficulty to establish a proper genotype-phenotype correlation. Lastly, further studies are needed to allow the genetic characterization of unsolved patients.

Muscle Channelopathies

PURPOSE OF REVIEW

This article describes the clinical features, diagnosis, pathophysiology, and management of nondystrophic myotonia and periodic paralysis.

RECENT FINDINGS

An increasing awareness exists about the genotype-phenotype overlap in skeletal muscle channelopathies, and thus genetic testing is needed to make a definitive diagnosis. Electrodiagnostic testing in channelopathies is highly specialized with significant overlap in various mutation subtypes. Randomized clinical trials have now been conducted in these disorders with expanded treatment options for patients with muscle channelopathies.

SUMMARY

Skeletal muscle channelopathies are rare heterogeneous conditions characterized by lifelong symptoms that require a comprehensive management plan that includes pharmacologic and nonpharmacologic interventions. The significant variability in biophysical features of various mutations, coupled with the difficulties of performing clinical trials in rare diseases, makes it challenging to design and implement treatment trials for muscle channelopathies.

Sequence CLCN1 and SCN4A genes in patients with nondystrophic myotonia in Chinese people

BACKGROUND

This study aimed to characterize the genetic, pathological, and clinical alterations of 17 patients in China presenting with nondystrophic myotonia (NDM) and to analyze the relationship between genotype and clinical phenotype.

METHODS

CLCN1 and SCN4A genes in patients with clinical features and muscle pathology indicative of NDM were sequenced. Furthermore, KCNE3 and CACNA1S genes were assessed in patients with wild-type CLCN1 and SCN4A.

RESULTS

Patients may have accompanying atypical myopathy as well as muscle hypertrophy, secondary dystonia, and joint contracture as determined by needle electromyography. All the study participants were administered mexiletine in combination with carbamazepine and showed significant improvements in myotonia symptoms in response to this therapy. CLCN1 gene mutation was detected in 8 cases diagnosed with myotonia congenital using gene screening. The detected mutations included 5 missense, 2 nonsense, 1 deletion, and 2 insertions. Further gene analysis showed 4 mutations in the SCN4A gene in patients diagnosed with paramyotonia congenita.

CONCLUSIONS

Myotonia congenita and paramyotonia congenita are the predominant forms of NDM in China. NDM may be best diagnosed using genetic analysis in associated with clinical features.

A Myotonic Dystrophy Type I patient with Predominant Proximal Muscle Weakness without Action Myotonia- A Case Report and Review of Pathology

PURPOSE

Early distal muscle weakness and myotonia are typical clinical presentations in type I myotonic dystrophy (DM1). We present a DM1 case with unusual predominant proximal weakness without action myotonia.

CASE REPORT

The chief complaint of this 48-year-old female was difficulty in raising her arms and frequent falling in recent years. On neurological examination, proximal muscle weakness was more pronounced than the distal muscle groups, in addition to facial involvement. Although she did not experience any action myotonia throughout her life, hand and tongue myotonia were readily inducible by percussion during neurological examination. The diagnosis of DM1 was later supported by electromyography and neuropathological studies, and confirmed by molecular testing. The pathological findings in this patient and the characteristic features in typical DM1 patients were briefly reviewed.

CONCLUSION

The unusual presentation of this DM1 patient suggests the importance of comprehensive neurological examination including percussion of thenar and tongue muscles, even in a patient with atypical distribution of muscle weakness and without a clear personal and family history of myotonia. In addition to molecular testing, muscle biopsy remains supportive in making the diagnosis.

Myotonic Muscular Dystrophy Type 2 in CT, USA: A Single-Center Experience With 50 Patients

ABSTRACT

Myotonic dystrophy type 2 (DM2) is an autosomal dominant disorder due to a (CCTG)n repeat expansion in intron 1 of the CNBP gene. In this article, we report the clinicopathologic findings in 50 patients seen at a single site over a 27 year period. DM2 was the fifth most common type of muscular dystrophy seen at our center with a 5-fold lower frequency as compared to DM1. Age of symptom onset ranged from 15 to 72 years, and the mean duration between symptom onset and diagnosis was 7.4 years. Weakness referable to the proximal lower extremities was the presenting symptom in 62% of patients. The degree of generalized weakness varied from severe in 30% to no weakness in 20% of patients. Clinical myotonia was noted in 18% and myotonic discharges on electromyography in 97% of patients. Pain symptoms were uncommon in our cohort. A significant correlation was noted between limb weakness and degree of muscle pathologic changes. There was no correlation between CCTG repeat size and other clinicopathologic findings. Six patients (12%) had cardiac abnormalities including one who developed progressive nonischemic dilated cardiomyopathy ultimately leading to cardiac transplantation. In 21 patients followed for 2 or more years, we noted a mean rate of decline in total Medical Research Council score of about 1% per year.

Episodic Muscle Disorders

PURPOSE OF REVIEW

This article reviews the episodic muscle disorders, including benign cramp-fasciculation syndrome, the periodic paralyses, and the nondystrophic myotonias. The core diagnostic criteria for a diagnosis of primary periodic paralysis, including clues to distinguish between the hypokalemic and hyperkalemic forms, and the distinctive elements that characterize Andersen-Tawil syndrome are discussed. Management of patients with these disorders is also discussed.

RECENT FINDINGS

Childhood presentations of periodic paralysis have recently been described, including atypical findings. Carbonic anhydrase inhibitors, such as dichlorphenamide, have recently been approved by the US Food and Drug Administration (FDA) for the treatment of both hypokalemic and hyperkalemic forms of periodic paralysis. Muscle MRI may be a useful outcome measure in pharmacologic trials in periodic paralysis. Genetic research continues to identify additional gene mutations responsible for periodic paralysis.

SUMMARY

This article will help neurologists diagnose and manage episodic muscle disorders and, in particular, the periodic paralyses and the nondystrophic myotonias.

The Dystrophic and Nondystrophic Myotonias

PURPOSE OF REVIEW

This article describes clinical and electrical myotonia and provides an update on the classification, diagnosis, and management of myotonic disorders.

RECENT FINDINGS

In the myotonic dystrophies, antisense oligonucleotides provide a general strategy to correct RNA gain of function and modulate the expression of CTG expanded repeats; they are currently being tested in a phase 1-2 randomized controlled trial in patients with adult-onset myotonic dystrophy type 1. New genetic mutations are continuously being identified in the nondystrophic myotonias involving sodium and chloride channels. This contributes to the difficulty in describing genotype-phenotype correlations as the same mutations can give rise to different phenotypes, and the same phenotypes can arise from different mutations. Pharmacologic therapy is moving toward mutation-targeted treatments.

SUMMARY

This article describes the clinical and diagnostic characteristics and management of the myotonic dystrophies and the nondystrophic myotonias. Clinical features of the congenital, juvenile, and classic adult forms of myotonic dystrophy type 1 are reviewed, and for the adult form, reference is made to the main diagnostic and follow-up tests for which general consensus exists. The different clinical presentations of myotonic dystrophy type 2 and its main differential diagnostic options are also discussed. The clinical spectrum of the sodium and chloride channelopathies is described, and clinical diagnostic clues to differentiate between these two groups are provided. Therapeutic options for patients with nondystrophic myotonias are also presented with reference to literature review and the author's personal experience.

Muscle channelopathies and related diseases

Muscle channelopathies and related disorders are neuromuscular disorders predominantly of genetic origin which are caused by mutations in ion channels or genes that play a role in muscle excitability. They include different forms of periodic paralysis which are characterized by acute and reversible attacks of muscle weakness concomitant to changes in blood potassium levels. These disorders may also present as distinguishable myotonic syndromes (slowed muscle relaxation) which have in common lack of involvement of dystrophic changes of the muscle, in contrast to dystrophia myotonica. Recent advances have been made in the diagnosis of these different disorders, which require, in addition to a careful clinical evaluation, detailed EMG and molecular study. Although these diseases are rare, they deserve attention since patients may benefit from drugs which can dramatically improve their condition. Patients may have atypical presentations, sometimes life-threatening, which may delay a proper diagnosis, mostly in the first months of life. The creation of specialized reference centers in the Western world has greatly benefited the proper recognition of these neuromuscular diseases.

[Pseudo abducens palsy]

In this study, we present two cases of different eye movement disorders with variable case histories but with the same end stage; abduction paresis of one of the eyes, which ceased when the other eye was covered. Our differential diagnosis is that either the ocular form of myasthenia gravis, convergence spasm or ocular myotonia could explain the symptoms. However, we hypothesize that the clinical picture corresponds to pseudo abducens palsy or focal dystonia of the extraocular muscle, which in turn could be the result of impaired inhibition of the tonic resting activity of the antagonistic medial rectus muscle. We offer an explanation for the patomechanism of pseudoabducens palsy and the variants of internuclear ophthalmoplegia.

Thyroiditis of Hashimoto and myotonia

Hypothyroidism is frequently associated with different neuromuscular disorders. However, myotonia is rarely a revealing feature. We report a case of hypothyroidism secondary to Hashimoto's thyroiditis and myotonia. The patient is a 45-year-old woman who consulted for a progressive myotonia. Blood and thyroid assessments revealed peripheral hypothyroidism with low free thyroxine, high thyroid-stimulating hormone levels and high titers of anti-thyroperoxidase antibodies. Outcome was favorable with thyroid hormone substitution. Hashimoto's thyroiditis is a common cause of hypothyroidism. The frequency of myopathy during hypothyroidism ranges from 30-80%. The main symptoms related are weakness, muscular cramps, and myalgia. Myotonia may reveal hypothyroidism. The pathogenic mechanism of this myotonia is still unknown. Good outcome of hypothyroid manifestations with thyroid hormone substitution requires systematic thyroid hormone screening in patients presenting with neuromuscular manifestations.

Diagnostics and therapy of muscle channelopathies--Guidelines of the Ulm Muscle Centre

This article is dedicated to our teacher, Prof. Erich Kuhn, Heidelberg, on the occasion of his 88th birthday on 23rd November 2008. In contrast to muscular dystrophies, the muscle channelopathies, a group of diseases characterised by impaired muscle excitation or excitation-contraction coupling, can fairly well be treated with a whole series of pharmacological drugs. However, for a proper treatment proper diagnostics are essential. This article lists state-of-the-art diagnostics and therapies for the two types of myotonic dystrophies, for recessive and dominant myotonia congenita, for the sodium channel myotonias, for the primary dyskalemic periodic paralyses, for central core disease and for malignant hyperthermia susceptibility in detail. In addition, for each disorder a short summary of aetiology, symptomatology, and pathogenesis is provided.

Computerized hand grip myometry reliably measures myotonia and muscle strength in myotonic dystrophy (DM1)

The aim of this study was to develop a reliable, sensitive, quantitative measure of grip myotonia and strength and to determine whether CTG repeat length is correlated with grip myotonia and with muscle strength in myotonic dystrophy type 1 (DM1). Three maximum voluntary isometric contractions (MVICs) of the finger flexors (i.e., handgrip) were recorded on 2 successive days using a computerized handgrip myometer in 29 genetically confirmed DM1 patients and 17 normals. An automated computer program calculated MVIC peak force (PF) and relaxation times (RTs) along the declining (relaxation) phase of the force recordings at 90%, 75%, 50%, 10%, and 5% of PF. Patients also underwent quantitative strength testing (QST) manual muscle testing (MMT). The patients had longer grip RTs and lower PFs than normals. RT (90% to 5%) was above the normal mean +2.5 SD in 25 (86%) patients. In DM1, prolongation of RT was mainly in the terminal (50% to 5%), rather than the initial (90% to 50%) phase of relaxation. PFs and RTs for each patient were reproducible on consecutive days. RTs were positively correlated with leukocyte CTG repeat length, whereas measures of muscle strength, such as PF, QST, and MMT, were negatively correlated with repeat length. We conclude that computerized handgrip myometry provides a sensitive, reliable measure of myotonia and strength in DM1 and offers a method to assess natural history and response to treatment.

Congenital myotonic dystrophy: prenatal ultrasound findings and pregnancy outcome

OBJECTIVE

The objective of this study was to assess the maternal and prenatal ultrasound findings and outcome in pregnancies complicated by congenital myotonic dystrophy Type 1 (DM1).

METHODS

A retrospective chart review of all patients with a diagnosis of DM1 and pregnancy presenting to the Oxford Radcliffe Hospital between 1990 and 2004 was undertaken. Obstetric case notes were reviewed and details of all pregnancies obtained. This included data on prenatal diagnostic tests and obstetric ultrasound scans performed as well as pregnancy complications and pregnancy outcome. Maternal and fetal CTG expansion size was also recorded where available. Maternal genetic case notes were reviewed for details of maternal grip myotonia.

RESULTS

Sixty pregnancies among 26 couples in which one of the parents was a carrier of DM1 were identified during the study period. These resulted in 36 (60%) pregnancies affected by congenital DM1 and 19 (31.7%) unaffected pregnancies. There were four miscarriages and one termination of pregnancy for non-medical reasons. Nineteen of the 36 affected pregnancies ended in termination following the antenatal diagnosis of congenital DM1 by either chorionic villus sampling (CVS) or amniocentesis. In the remaining 17 affected pregnancies (16 singleton and one twin) there was one miscarriage of an affected fetus with co-existing Down syndrome and eight perinatal deaths. The principal cause of perinatal death was respiratory failure in the early neonatal period. Antenatally noted clinical/sonographic abnormalities in these pregnancies included polyhydramnios (100%), talipes (26.6%) and borderline ventriculomegaly (13.3%). Uni- or bilateral talipes was noted at delivery in 10 of 16 (62.5%) neonates. Maternal grip myotonia was present in all but one of these cases.

CONCLUSION

The antenatal findings of polyhydramnios and talipes should prompt a search for maternal grip myotonia. If present, definitive testing for congenital DM1 should be considered.

[A girl with hereditary myotonia due to an exceptional sodium channel mutation]

A 22-month-old girl had cramps and stiffness of her muscles. After medical history, physical examination and an EMG, a short differential diagnosis based on the symptoms of myotonia was made. Initially, the symptoms were incorrectly assumed to be due to Becker's myotonia, an autosomal recessive condition caused by a mutation in the chloride channel. Molecular analysis did not show a defect in the chloride channel, but instead a defect in the sodium channel of the muscle fibre. Since defects in the sodium channel are responsible for several myotonic diseases, further analysis was necessary. Based on knowledge of the structure and mechanism of the sodium channel and study of literature on cases involving the identical mutation, the diagnosis 'potassium-aggravated myotonia' (PAM) was made. Re-evaluation of the patient showed that her symptoms fitted the diagnosis 'myotonia permanens', the severest form of PAM. She was treated with mexiletine. In myotonia several features can give direction to the diagnosis, including sensitivity to temperature and exercise, and family history. However, it is often necessary to use molecular analysis to be able to diagnose the disease correctly, make a prognosis and predict the risk of recurrence as well as to formulate a treatment plan.

Cold extends electromyography distinction between ion channel mutations causing myotonia

OBJECTIVE

Myotonias are inherited disorders of the skeletal muscle excitability. Nondystrophic forms are caused by mutations in genes coding for the muscle chloride or sodium channel. Myotonia is either relieved or worsened by repeated exercise and can merge into flaccid weakness during exposure to cold, according to causal mutations. We designed an easy electromyography (EMG) protocol combining repeated short exercise and cold as provocative tests to discriminate groups of mutations.

METHODS

Surface-recorded compound muscle action potential was used to monitor muscle electrical activity. The protocol was applied on 31 unaffected control subjects and on a large population of 54 patients with chloride or sodium channel mutations known to cause the different forms of myotonia.

RESULTS

In patients, repeated short exercise test at room temperature disclosed three distinct abnormal patterns of compound muscle action potential changes (I-III), which matched the clinical symptoms. Combining repeated exercise with cold exposure clarified the EMG patterns in a way that enabled a clear correlation between the electrophysiological and genetic defects.

INTERPRETATION

We hypothesize that segregation of mutations into the different EMG patterns depended on the underlying pathophysiological mechanisms. Results allow us to suggest EMG guidelines for the molecular diagnosis, which can be used in clinical practice.

Intra- and interrater reliabilities of the Myotonometer when assessing the spastic condition of children with cerebral palsy

The purposes of this study were to assess intra- and interrater reliabilities by novice users of the Myotonometer (Neurogenic Technologies, Inc., Missoula, MT), a portable electronic device that quantifies muscle tone (stiffness) and paresis, in assessing children with cerebral palsy. Two raters used the Myotonometer to assess the biceps brachii and medial gastrocnemius muscles of 10 children with spastic-type cerebral palsy. Muscles were measured in a relaxed state and during a voluntary isometric contraction. Intraclass correlation coefficients and repeatability coefficients were calculated for each muscle and for each condition (relaxed and contracted). Intrarater reliabilities ranged from 0.82 to 0.99 (biceps brachii muscles) and 0.88 to 0.99 (medial gastrocnemius muscles). Interrater reliabilities ranged from 0.74 to 0.99 (biceps brachii muscles) and 0.84 to 0.99 (medial gastrocnemius muscles). Repeatability coefficients indicated a 98% level of agreement between raters across all conditions. Novice users of the Myotonometer, with few exceptions, had high to very high intra- and interrater reliabilities for measurements of the biceps brachii and medial gastrocnemius muscles of children with spastic-type cerebral palsy.

Adult-onset acquired oculomotor nerve paresis with cyclic spasms: relationship to ocular neuromyotonia

PURPOSE

To describe the characteristics and significance of acquired oculomotor nerve paresis with cyclic spasm.

METHOD

Retrospective case series of two patients with a history of previous skull base irradiation for intracranial tumor who developed double vision and were found to have oculomotor nerve paresis with cyclic spasm. Both patients underwent a complete neuroophthalmologic assessment, including testing of eyelid position, pupillary size and reactivity, and ocular motility and alignment during both the paretic and spastic phases of the condition.

RESULTS

Both patients developed unilateral lid retraction and ipsilateral esotropia with limitation of abduction during the spastic phase of the cycle, with ipsilateral ptosis, exotropia, and variable limitation of adduction during the paretic phase. The cycles were continuous and were not induced or altered by eccentric gaze.

CONCLUSIONS

Cyclic oculomotor nerve paresis with spasms may occur years after irradiation of the skull base. This condition is different from the more common ocular motor disturbance that occurs in this setting-ocular neuromyotonia. However, in view of the similarity between these two disorders, it seems likely that they are caused by a similar peripheral mechanism.

Myotonia and disorders of altered muscle cell membrane excitability

Altered excitability of the skeletal muscle membrane (sarcolemma) can result in clinical signs of muscle dysfunction. Hyperexcitability of the sarcolemma results in myotonia, and hypoexcitability results in paresis or paralysis. Our understanding of the physiologic and molecular bases of disorders of sarcolemmal excitability is rapidly increasing as techniques for evaluation are improved. This article reviews muscle excitability disorders in dogs and cats and their pathogenesis.

Quantitative myotonia assessment: an experimental protocol

Severe clinical myotonia can be physically disabling and socially impairing but as yet there is no standardized treatment regimen. The aim of our study is to present a protocol to measure myotonia using quantitative muscle assessment measures. The proposed protocol addresses two main issues. Muscle strength is assessed in 8 muscles on the right and on the left using a myometer (QMA, quantitative muscle assessment) and by testing strength manually using the 5-point MRC scale (5 = normal) in 15 muscles on the right and on the left. Grip myotonia is assessed by: (a) measuring 1/2 and 3/4 relaxation times (RT) after maximum voluntary contraction (MVC) using QMA apparatus; (b) functional tests (time to open a fist 10 times, time to open and squeeze the eyes 10 times, time to climb 10 steps starting from a seated position, time to protrude the tongue 10 times, time to step onto a chair 10 times; (c) subjective measures of the severity of myotonia using an arbitrary 4-point scale (0 = absent, 4 = severe); and (d) electromyography (EMG) relaxation times after MVC. Although QMA seems to be a reliable tool to measure myotonia, there are still a number of unsolved issues. Further studies are needed to ensure the ability of QMA to quantify myotonia and to guarantee the reliability of the results for clinical research purposes.

Myotonic dystrophy and proximal myotonic myophathy

Myotonic dystrophy (DM) is a well-known multisystem disorder with dominant inheritance. Proximal myotonic myopathy (PROMM) has been defined only recently, it is rather similar to but distinct from DM. Molecular genetic testing of the CTG trinucleotide repeat expansion is a reliable diagnostic method in DM. In PROMM these CTG repeats are normal, and no genetic test is so far available. Comparing the phenotypes of DM and PROMM, an important point seems to be that PROMM is a more benign disorder. There are almost no obvious mental changes in PROMM patients; premature death is extremely rare; anticipation appears to be present but to a milder degree; a severe congenital type of PROMM apparently is very rare if it occurs at all. On the other hand, at least in the German population, the frequency of PROMM may be almost equal to that of DM.

Mutual interference of myotonia and muscular dystrophy in the mouse: a study on ADR-MDX double mutants

For Duchenne muscular dystrophy (DMD, dystrophin deficiency) and Thomsen/Becker myotonia (muscular chloride channel deficiency) genetically homologous mouse models are available, the dystrophin-deficient MDX mouse and the myotonic ADR mouse. Whereas the latter shows more severe symptoms than human myotonia patients, the MDX mouse, in contrast to DMD patients, is only mildly affected. We have introduced, by appropriate breeding, the defect leading to myotonia (Clc1 null mutation, adr allele) into MDX mice, thus creating ADR-MDX double mutants. The expectation was that, due to mechanical stress during myotonic cramps, the ADR status should symptomatically aggravate the muscle fibre necrosis caused by the dystrophin deficiency. The overall symptoms of the double mutants were dominated by myotonia. Weight reduction and premature death rate were higher in ADR-MDX than in ADR mice. Sarcolemmal ruptures as indicated by influx into muscle fibres of serum globulins and injected Evans blue were found with great inter-individual variation in MDX and in ADR-MDX muscles. Affected fibres were found mainly in large groups in MDX but single or in small clusters in ADR-MDX leg muscles. The symptoms of myotonia (aftercontractions, shift towards oxidative fibres) were less pronounced in ADR-MDX than in ADR muscles. Conversely, numbers of damaged fibres as well as the percentage of central nuclei (an indicator of fibre regeneration) were significantly lower in ADR-MDX than in MDX skeletal muscles. Thus it appears that, at the level of the muscle fibre, myotonia and muscular dystrophy attenuate each other.

Acquired neuromyotonia in a patient with spinal epidural abscess

We report a case of acquired neuromyotonia in a patient with Staphylococcus aureus septicemia and a spinal epidural abscess. Autoantibodies to voltage-gated potassium channels, which are associated with acquired neuromyotonia, were present during the patient's acute illness but became undetectable on clinical recovery. The spinal epidural abscess may have triggered the production of these specific autoantibodies, resulting in clinically and electromyographically detectable neuromyotonia.

Ocular neuromyotonia: three case reports with eye movement recordings

The objective of this article was to evaluate the etiologies, findings, and treatment of ocular neuromyotonia (ONM) in three case reports. The etiologies of ONM were determined by the histories, neuroradiologic tests, or biopsies. Clinical observations, videotaping, and electronic eye movement recordings documented the eye movement abnormalities. Intermittent diplopia developed several years after myelography with thorium dioxide (Thorotrast), radiation treatment for a pituitary tumor, and radiotherapy for medulloblastoma of the posterior fossa. All of the patients had intermittent, variable tropias that occurred spontaneously or were induced by eccentric gaze. One patient had a partial third nerve palsy, and another had a unilateral internuclear ophthalmoplegia (INO). ONM involved the paretic third nerve, extraocular muscles, and ipsilateral lateral rectus muscle in one patient, the paretic medial rectus muscle (INO) in one patient, a lateral rectus muscle (INO) in one patient, and a lateral rectus muscle in the last patient. Eye movement recordings were consistent with spasms of the involved muscles. Carbamazepine (Tegretol) abolished the ONM in two patients. The other patient had been taking carbamazepine for seizures and developed ONM when the dose was decreased. Increasing the dose abolished the ONM. ONM is an unusual cause of intermittent diplopia and strabismus, but its distinctive history and signs identify it easily. Damage to the peripheral cranial nerves might produce segmental demyelination, axonal hyperexcitability, and a self-perpetuating, reverberating circuit that causes spasms of the extraocular muscles.

Proximal myotonic myopathy. Analysis of 3 Swedish cases

Three Swedish patients with proximal muscle weakness, myotonia and lack of CTG expansion on genetical analysis are presented. Clinical neurological and neurophysiological examination and muscle biopsy were performed. There was an indication of autosomal dominant inheritance in 2 of the 3 patients. The main symptoms and clinical findings in the 3 patients were weakness of the proximal muscles, myotonia, muscle stiffness, muscle pain and muscle atrophy. Neurophysiological examination showed myotonic bursts and muscle biopsy showed a variation of fibre sizes, an increased number of muscle fibres with centralized nuclei and scattered atrophic muscle fibres. Laboratory data showed elevated CK, GT and LD in 1 patient. Before genetical analysis was performed, all 3 patients had been diagnosed as atypical cases of myotonic dystrophy. However, the symptoms, clinical signs, laboratory data, electrophysiological and muscle biopsy findings were compatible with proximal myotonic myopathy (PROMM).

[Proximal myotonic myopathy (PROMM). Clinical variability within a family]

Proximal myotonic myopathy (PROMM) is a newly described autosomal dominant inherited disorder characterized by predominant proximal weakness of the legs, mild clinical myotonia or myotonia on electromyograms (EMG), cataracts and slight elevation of liver enzymes. The trinucleotide (cytosine, thymine, and guanine) repeat size of the myotonic dystrophy (DM) gene is normal. Magnetic resonance imaging of the brain may reveal a peculiar pattern of white matter abnormalities. We describe seven patients in a new family with PROMM. The only symptoms may be subclinical myotonic changes in the EMG or cataracts, but symptoms may also include severe proximal weakness of the legs and painful paraesthesia. PROMM is an important differential diagnosis of myotonic dystrophy; and because of the proximal weakness it is also a differential diagnosis of other muscle diseases such as limb girdle dystrophy, metabolic and endocrine myopathies, and myositis. Because of the variability of the symptoms, for the definite diagnosis of PROMM it may require the examination of other family members.

Unusual causes of stiffness in two hockey players

PURPOSE

To describe two cases of competitive hockey players whose performance was impaired by generalized painless muscle stiffness. They were each found to have a separate type of myotonia.

CASE SUMMARY

The first hockey player experienced stiffness only when initiating activity after a period of inactivity. He had a family history of muscle stiffness, grip myotonia clinically, and electrophysiologic findings of myotonic discharges. He had myotonia congenita. The stiffness in the second case was episodic and occurred during bouts of intense physical activity. The legs, arms, and neck were affected. Myotonia fluctuans was the probable diagnosis. Both cases responded well to Mexiletine.

DISCUSSION

The etiology, classification, and clinical presentation of myotonia are discussed.

RELEVANCE

Because of the musculoskeletal nature of our practice, sport medicine clinicians should be aware of myotonic disorders so they can be recognized and appropriately treated.

The spectrum of arthrogryposis in 33 chinese children

The clinical profile of 33 children (19 boys, 14 girls) with multiple congenital contractures has been studied. The majority (54%) belong to arthrogryposis multiplex congenita with a static clinical course. Children were classified into three groups: group I (limb involvement only; n = 21) having arthrogryposis multiplex congenita (n = 18), distal arthrogryposis syndrome (n = 2) and Streeter syndrome (n = 1); group II (limb involvement with other malformation or anomalies; n = 7) having congenital contractural arachnodactyly (n = 3), Larsen syndrome (n = 1), multiple pterygium syndrome (n = 1), craniocarpotarsal dystrophy (n = 1), and Schwartz Jampel syndrome (n = 1); and group III (limb involvement with central nervous system dysfunction or mental retardation; n = 5) having myotonia dystrophica (n = 2), congenital muscular dystrophy (n = 1), foetal alcohol syndrome (n = 1) and Pena-Shokeir syndrome (n = 1). Three children died, one each of arthrogryposis multiplex congenita, congenital contractural arachnodactyly and myotonia dystrophica. The majority had a good prognosis with independent function and mobility.

Carrell-Krusen Symposium Invited Lecture-1997. Myotonic disorders in childhood: diagnosis and treatment

The recent discoveries that mutations in the genes for the skeletal muscle sodium and chloride channels are responsible, respectively, for paramyotonia/hyperkalemic periodic paralysis and for myotonia congenita of Thomsen have made the classification, diagnosis, and treatment of these disorders much easier. The discovery that myotonic dystrophy results from an unstable [CTG]n trinucleotide expansion has permitted the accurate diagnosis of both symptomatic and asymptomatic individuals, and has led to major advances in preventive treatment, including prenatal and genetic counseling. Diseases that resemble the inherited myotonic disorders are now easier to identify, and as a result of genetic testing a new clinical disorder that is similar to but distinct from myotonic dystrophy has emerged. This new disorder, proximal myotonic myopathy, does not appear to be linked to the genes for the sodium or chloride channels, and has cataracts, myotonia, weakness, and no abnormal expansion of the [CTG]n repeat in the gene for myotonic dystrophy. This review discusses the diagnosis and treatment of these myotonic disorders.

Proximal myotonic myopathy with MRI white matter abnormalities of the brain

Proximal myotonic myopathy (PROMM) is an autosomal dominantly inherited multisystemic disorder characterized by myotonia, proximal muscle weakness, and cataracts. This disorder is not linked to the gene locus of myotonic dystrophy (DM). We describe three new families with PROMM. In all patients, CTG repeats of the DM gene in DNA from blood leukocytes were normal. MRI of the brain revealed a consistent pattern of marked white matter hyperintensity on T2-weighted images in four patients; two additional patients had similar but mild to moderate MRI abnormalities. The morphology of these abnormalities is unknown. Clinical symptoms of brain disease were not consistent and included mental changes with hypersomnia, parkinsonian features, stroke-like episodes, and seizures. The causative relationship of these clinical features with the MRI white matter abnormalities remains to be established. Our observations suggest that PROMM may involve the brain.

Neonatal diagnosis of Schwartz-Jampel syndrome with dramatic response to carbamazepine

We report a female infant, born at 30 weeks of gestation, who exhibited generalized myotonia, facial dysmorphism, blepharophimosis, and short stature at birth. These clinical findings, along with abnormal electromyogram and muscle biopsy, are consistent with Schwartz-Jampel syndrome. Our patient, diagnosed at 4 weeks of life, lacks the major skeletal anomalies, such as pectus carinatum, congenital hip dysplasia, and bowing of the long bones usually associated with this syndrome. Treatment with carbamazepine, initiated at age 7 months (corrected age of 5 months) has produced marked and continued resolution of myotonia, lessened malformation of her bell-shaped chest, and developmental progress. We suggest that the relaxation of myotonia due to early diagnosis and treatment may prevent development of the classic skeletal dysplasia of Schwartz-Jampel syndrome.

Channelopathies: the nondystrophic myotonias and periodic paralyses

The term channelopathy does not indicate a new group of neuromuscular conditions, but a re-orientation of well- and long-known muscular conditions, the congenital myotonias, and the periodic paralyses. Although, in the past, they have overlapped clinically here and there, both groups were classified differently, as myotonias and as metabolic myopathies, respectively. The discovery of mutations in several ion channels has rewritten nosography of these disorders and procured a new term, the channelopathy-clinical, electrophysiological, and molecular genetic details of which are discussed in this chapter.

Ocular neuromyotonia

AIMS/BACKGROUND

Ocular neuromyotonia is characterised by spontaneous spasm of extraocular muscles and has been described in only 14 patients. Three further cases, two with unique features, are described, and the underlying mechanism reviewed in the light of recent experimental evidence implicating extracellular potassium concentration in causing spontaneous firing in normal and demyelinated axons.

METHODS

Two patients had third nerve neuromyotonia, one due to compression by an internal carotid artery aneurysm, which has not been reported previously, while the other followed irradiation of a pituitary tumour, a common association in the published reports. Selective activation occurred in both, where neuromyotonic activity was triggered by prolonged voluntary activation of specific extraocular muscles with or without spread of activity to other third nerve muscles. The other patient had fourth nerve involvement, where spasms of the superior oblique muscle were induced only by alcohol, a phenomenon which has not been described.

RESULTS

The two patients with third nerve involvement responded to carbamazepine and in one, an improvement in a chronic partial third nerve paresis occurred. The other has not required treatment and remains asymptomatic by refraining from alcohol.

CONCLUSIONS

A careful examination, including the effects of prolonged voluntary muscle action is required to initiate episodes and to demonstrate selective activation. Imaging is mandatory to exclude compressive intracranial lesions, particularly where there is no history of pituitary fossa irradiation. A trial of anticonvulsants should be considered in all patients. Extracellular potassium may play a role in spontaneous firing and ephatic transmission in ocular neuromyotonia.

Acquired blepharoptosis

A review is given of the aetiology and possible treatment of acquired (non-congenital), blepharoptosis, which is a common but not specific sign of neurological disease. The diagnostic categories of upper eyelid drooping are scheduled as (a) pseudo-ptosis due to a local process or overactivity of eye closure, including blepharospasm, and (b) true ptosis due to a paresis of the eyelid levators (m. tarsalis superior or m. levator palpebrae) or to a disinsertion of the m. levator palpebrae (aponeurotic ptosis). A paresis of the m. tarsalis is due to a lesion in the central, intermediate or peripheral neuron of the sympathetic chain and constitutes one of the components of Horner's syndrome. A paresis of the m. levator palpebrae may be due to a failure in central innervation, in oculomotor (n.III) function, in neuromuscular transmission or to a lesion in the muscle itself.

[Syringomyelia in orthopedic practice]

Three females with syringomyelia and atrophic shoulder arthropathy, in one patient associated also with hypertrophic elbow arthropathy and Morvan syndrome have been presented. Despite long duration and apparent symptoms the condition has been diagnosed only during hospitalization.

Intermittent diplopia and strabismus caused by ocular neuromyotonia

PURPOSE

Two cases illustrate the symptoms, signs, etiologies, and treatment of ocular neuromyotonia (ONM).

METHODS

The histories, neuroradiologic tests, and/or biopsy revealed the etiologies of ONM in both patients. Clinical observations, videotaping, and electronic eye movement recordings documented the eye movements.

RESULTS

A 72-year-old man with chronic arachnoiditis following myelography with thorium dioxide (Thorotrast) developed intermittent diplopia and a partial right third nerve palsy. Left gaze induced spasm of the right medial rectus. Right gaze produced right lateral rectus spasm. A 66-year-old woman, who had radiation treatment for a pituitary tumor and acromegaly, had intermittent spasm of the left medial rectus muscle and left esotropia. The episodes occurred spontaneously and were induced by right gaze. A left internuclear ophthalmoplegia was also found. Carbamazepine (Tegretol) abolished the ONM in both patients.

CONCLUSIONS

Although ONM is an unusual cause of intermittent diplopia and strabismus, its distinctive clinical features identify it. Injury to the peripheral cranial nerves probably leads to segmental demyelination, axonal hyperexcitability, and a self-perpetuating, reverberating circuit, which causes spasms of the extraocular muscles.