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Skeletal muscle involvement in infantile systemic hyalinosis.

Infantile Systemic Hyalinosis is a rare autosomal recessive entity, characterised by deposition of hyaline material in skin and bone, often complicated by visceral involvement. The characteristic features are marked delay in motor milestones attributed to severe progressive flexion contractures of proximal and distal joints, and skin and mucosal hypertrophy and thickening, followed by failure to thrive. Pain secondary to osteolytic lesions is also a predominant feature. We report a patient with Infantile Systemic Hyalinosis, confirmed by the clinical findings, who also displayed clear evidence of proximal muscle weakness. Muscle biopsy revealed myopathic changes, which have not been reported previously. We suggest that skeletal muscle is involved in Infantile Systemic Hyalinosis and contributes to the characteristic poor outcome of these patients.

Alleles↗

Statin-associated myopathy.

Statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) are associated with skeletal muscle complaints, including clinically important myositis and rhabdomyolysis, mild serum creatine kinase (CK) elevations, myalgia with and without elevated CK levels, muscle weakness, muscle cramps, and persistent myalgia and CK elevations after statin withdrawal. We performed a literature review to provide a clinical summary of statin-associated myopathy and discuss possible mediating mechanisms. We also update the US Food and Drug Administration (FDA) reports on statin-associated rhabdomyolysis. Articles on statin myopathy were identified via a PubMed search through November 2002 and articles on statin clinical trials, case series, and review articles were identified via a PubMed search through January 2003. Adverse event reports of statin-associated rhabdomyolysis were also collected from the FDA MEDWATCH database. The literature review found that reports of muscle problems during statin clinical trials are extremely rare. The FDA MEDWATCH Reporting System lists 3339 cases of statin-associated rhabdomyolysis reported between January 1, 1990, and March 31, 2002. Cerivastatin was the most commonly implicated statin. Few data are available regarding the frequency of less-serious events such as muscle pain and weakness, which may affect 1% to 5% of patients. The risk of rhabdomyolysis and other adverse effects with statin use can be exacerbated by several factors, including compromised hepatic and renal function, hypothyroidism, diabetes, and concomitant medications. Medications such as the fibrate gemfibrozil alter statin metabolism and increase statin plasma concentration. How statins injure skeletal muscle is not clear, although recent evidence suggests that statins reduce the production of small regulatory proteins that are important for myocyte maintenance.

Adverse Drug Reaction Reporting Systems↗

Usefulness and reliability of neurological signs for level diagnosis in cervical myelopathy caused by soft disc herniation.

We retrospectively analyzed neurological signs of 106 patients with cervical myelopathy caused by single-level soft disc herniation. Neurological signs that were intensively analyzed were deep tendon reflexes, the uppermost level of impaired pinprick sensation, the uppermost weak muscle, and region of numbness in the hands. Characteristic signs for each intervertebral level were deduced, and sensitivity, specificity, and accuracy of these signs were calculated. Deep tendon reflexes were specific signs for each intervertebral level, although not as sensitive as the neurological signs. Muscle weakness and pinprick sensation were neither sensitive nor specific. Hand numbness was moderately sensitive and specific. On the whole, there was no neurological sign that was both highly sensitive and specific for an intervertebral level, and therefore, neurological level diagnosis in cervical myelopathy should be performed comprehensively according to more specific signs, i.e., deep tendon reflexes and hand numbness.

Adult↗

A case of vacuolar myopathy during the course of chronic hepatitis C.

Several cases of inflammatory myopathy have been reported during the chronic course of hepatitis C (HC) in recent years. It has been suggested that this muscular inflammatory involvement in HC is related to an immune-mediated mechanism caused by the hepatitis C virus (HCV), as HCV RNA has been detected in the muscle of patients with concomitant inflammatory myopathy and chronic HC. Herein, we report on a patient with a history of chronic HC, who developed a slowly progressive proximal muscle weakness; muscle biospy revealed a vacuolar myopathy. Histological, immunohistochemical and biochemical study did not disclose any known cause of vacuolar myopathy. To our knowledge, this is the first report of a vacuolar myopathy during the course of HC. We suggest that it may be opportune to include HC among the possible aetiologies of vacuolar myopathy, should other reports confirm this association.

Hepatitis C, Chronic↗

A mitochondrial myopathy in an infant with lactic acidosis.

We describe a girl with mitochondrial myopathy, who presented with general muscle weakness, muscle hypotonia and motor retardation. The level of blood lactate and pyruvate was consistently increased. Enzymatic studies showed impairment of NADH-dehydrogenase activity (complex I of the respiratory chain) in skeletal muscle. Electron-microscopy of a muscle biopsy showed abnormalities of a mitochondrial myopathy. The girl, now aged 30 months, has been treated with riboflavine (vitamin B2) since the age of 14 months, and lactate and pyruvate levels have decreased to normal. The patient still shows mild muscle hypotonia and weakness, but good motor progress and normal cognitive development.

Acidosis, Lactic↗

Respiratory muscles in COPD: regulation of trophical status.

Chronic obstructive pulmonary disease, COPD is a highly prevalent disorder of increasing medical and socio-economical importance. It is characterized by irreversible airflow obstruction. Besides airflow obstruction also other features are present. One of these is respiratory muscle weakness. Inspiratory muscle weakness is caused by hyperinflation and by generalized muscle weakness causing both respiratory and peripheral muscle dysfunction. The expiratory muscles partake in this generalized muscle weakness. Hyperinflation shortens the inspiratory muscles although in chronic hyperinflation sarcomere adaptation occurs. Generalized muscle weakness is caused by deconditioning, malnutrition, electrolyte disturbances, cardiac failure, systemic inflammation and treatment with corticosteroids causing steroid-induced myopathy. The latter disease was studied intensively both in patients and in animal models of disease. The major findings were that microscopically a myopathic pattern was present associated with generalized fiber atrophy. This is in contrast to classical belief that the atrophy would be confined to type IIx fibers. We noted severe down-regulation of the IGF-I mRNA expression, without important changes in the expression of the binding proteins. This may be responsible for the observed muscle atrophy and the myopathy. The latter is likely to be caused by a simultaneous upregulation of the ubiquitin protease pathway attacking structural proteins. Presently, we study the relationship between local and systemic cytokine expression and respiratory and peripheral muscle dysfunction in COPD patients. Respiratory and peripheral muscle dysfunction have significant consequences for COPD patients. Both respiratory and peripheral muscle dysfunction are associated with reduced exercise tolerance and reduced quality of life. Both are independent determinants of survival, in addition to the degree of airflow obstruction as measured by FEV1. Finally, also the utilization of health care resources appeared to be related to respiratory and peripheral muscle weakness. Treatment of respiratory and peripheral muscle weakness in COPD patients is possible. Respiratory and peripheral muscle training have been shown to produce beneficial effects. Nutritional intervention and anabolic steroids are only useful in combination with muscle training. Systemic administration of growth hormone and IGF-I only produces small effects. In animal models, local administration of IGF-I and transfer of the IGF-I gene transfer appear more promising for the future. Lung volume reduction surgery, LVRS, improves the force-generating capacity of the inspiratory muscles, presumably because of the geometrical alterations it causes in these muscles. It does not appear to improve intrinsic inspiratory muscle function.

Animals↗

Reconditioning aging muscles.

Weakness or stiffness of key posture muscles can cause much of the disability seen in elderly patients. Too much tension and too little exercise greatly increase the natural loss of muscular fitness with age. A systematic program of exercise, stressing relaxation and stretching of tight muscles and strenghthening of weak muscles, can improve physical fitness. The program must be tailored to the patient, starting with relaxation and gentle limbering exercises and proceeding ultimately to vigorous muscle-stretching exercises. Muscle aches and pain from tension and muscle imbalance are to be expected. Relaxation relieves tension pain, and strengthening weak muscles and stretching tight muscles will correct muscle imbalance. To prevent acute muscle spasm, the patient should avoid excessive exertion and increase exercise intensity gradually.

Aged↗

Surface electromyography assessment of back muscle intrinsic properties.

The purpose of this study was to assess (1) the reliability and (2) the sensitivity to low back pain status and gender of different EMG indices developed for the assessment of back muscle weakness, muscle fiber composition and fatigability. Healthy subjects (men and women) and chronic low back pain patients (men only) performed, in a static dynamometer, maximal and submaximal static trunk extension tasks (short and long duration) to assess weakness, fiber composition and fatigue. Surface EMG signals were recorded from four (bilateral) pairs of back muscles and three pairs of abdominal muscles. To assess reliability of the different EMG parameters, 40 male volunteers (20 controls and 20 chronic low back pain patients) were assessed on three occasions. Reliable EMG indices were achieved for both healthy and chronic low back pain subjects when specific measurement strategies were applied. The EMG parameters used to quantify weakness and fiber composition were insensitive to low back status and gender. The EMG fatigue parameters did not detect differences between genders but unexpectedly, healthy men showed higher fatigability than back pain patients. This result was attributed to the smaller absolute load that was attributed to the patients, a load that was defined relative to their maximal strength, a problematic measure with this population. An attempt was made to predict maximal back strength from anthropometric measurements but this prediction was prone to errors. The main difficulties and some potential solutions related to the assessment of back muscle intrinsic properties were discussed.

Abdominal Wall↗

[Lower motor neuron disease and signs of dysimmunity].

Twenty-two patients (12 men, 10 women, age range 16 to 60) affected with an adult-onset, sporadic, lower motor neuron disease were studied. Motor weakness was associated with a severe muscular atrophy but never in a peripheral nerve distribution. Weakness predominated in the proximal parts of the limbs in 3 cases, in distal parts in 10 cases involving predominantly the upper limbs in 10. It was diffuse in all four limbs in six cases and was monomelic in the last 2 two others. Reflexes were generally lost in weak muscles. Electrodiagnostic findings consisted of pure motor axonal features, subtle sensory involvement was present in 3 cases with an IgM monoclonal gammopathy, in only one case the neurological syndrome was associated with a lymphoproliferative disorder despite complete investigations. All patients had dysimmune biological features (MGUS or anti-GM1 antibodies). We studied SMN gene in 12 patients and found no deletion. 16 patients were treated with IVIg and five improved but in 2 cases the improvement was transcient and lasted less than six months. Intravenous cyclophosphamide (1g/m(2) repeated monthly during 6 to 9 months) was used in six patients and three improved. Among these three patients two received also plasma exchanges on two days before the infusion. In all three patients, muscle weakness gradually deteriorated in the months following the end of the treatment. Nor the weakness pattern nor the type of biological marker was predictive of a good response to treatment. Lower motor neuron diseases appear to be much less sensitive to treatment than multifocal motor neuropathy with conduction block. However, treatment with IVIg or cyclophosphamide must be considered in the most severe forms or in case of a young onset.

Adolescent↗

Presymptomatic neuromuscular disorders disclosed following statin treatment.

It is well recognized that statins affect muscular tissue adversely and that their use is associated with clinically important myositis, rhabdomyolysis, mild elevation of serum creatine kinase (CK) levels, myalgias, muscle weakness, muscle cramps, and persistent myalgias or serum CK level elevations after statin treatment is discontinued. The association between statins and the disclosure of presymptomatic metabolic myopathy is another underrated phenomenon related to statin therapy that was recently recognized in rare cases. The purpose of this report is to provide additional support for this association and to report other neuromuscular disorders that have also been seen following statin intake. The present case series illustrates that statins may act as unmasking agents in asymptomatic patients with a latent neuromuscular disorder. Thus, it may be postulated that statin intake may be a sufficient insult to precipitate neuromuscular symptoms and substantially increase muscle enzymes in presymptomatic patients with an abnormal neuromuscular substrate. In conclusion, muscular symptoms or increased serum CK levels persisting after statin treatment discontinuation should alert the clinician to pursue further diagnostic evaluations for the detection of potential underlying neuromuscular diseases.

Biopsy↗

Prenatal alcohol exposure and early postnatal changes in the developing nerve-muscle system.

BACKGROUND: Extensive research on prenatal alcohol exposure has proven the potent teratogenicity of this substance of abuse. Children born to alcoholic mothers are often diagnosed with fetal alcohol syndrome (FAS). Those afflicted with FAS often have muscle weakness, muscle wasting, and atrophy. This study assessed the effects of prenatal alcohol exposure on the developing rat neuromuscular system. METHODS: Pregnant Sprague-Dawley rats were injected intraperitoneally with 1.0 ml of 20% ethyl alcohol/100 gm body weight. Unexposed rats served as controls. The offspring were killed 2, 3, 4, and 5 weeks after birth, and their body weights were recorded. The tibialis anterior (TA) and extensor digitorum longus (EDL) muscles were recovered and weighed. The TA muscles were histochemically stained by silver cholinesterase in order to study the pattern of innervation. The EDL muscles were processed and stained by hematoxylin-eosin. The number and size of the EDL muscle fibers was quantified. The sciatic nerve was also removed and stained by Swank and Davenport's method to demonstrate the myelin pattern. RESULTS: Assessment at the neuromuscular junction showed a higher proportion of endplates polyneuronally innervated in the alcohol-exposed rats. The muscle weights, as well as the number and size of the muscle fibers, were significantly reduced in these animals. A light-microscopy examination of the nerve sections revealed alterations in the connectivity of myelin. CONCLUSIONS: The finding that a higher proportion of endplates were polyneuronally innervated in the alcohol-exposed rats indicates that the maturation process of the neuromuscular system was delayed, thus confirming the deleterious effects of alcohol on growth and maturation of the nerve-muscle system.

Animals↗

Exercise-induced myalgia in hypothyroidism.

Recurrent rhabdomyolysis is very uncommon in hypothyroid myopathy. A 30-year-old woman is reported, who presented with exercise-induced myalgias and high levels of serum creatine kinase but no muscle weakness. Muscle biopsy showed signs of a recurrent rhabdomyolysis. Hypothyroidism was diagnosed by serum hormone levels. The myopathy rapidly improved with thyroxine treatment.

Adult↗

Peripheral motor neuropathy caused by excessive intake of dapsone (Avlosulfon).

A case of selective peripheral motor polyneuropathy caused by excessive intake of dapsone is described. The condition was characterized by a peripheral muscle weakness in all limbs, normal sensitivity and present, although weak, muscle reflexes. Neurophysiologically, low amplitude muscle responses, prolonged distal latencies and reduced motor conduction velocities were found together with electromyographic signs of denervation. Sensory neurography was normal. The patient showed a complete clinical recovery and a marked neurophysiological restitution after termination of the excessive drug intake. The patient was found to acetylate dapsone at a slow rate. The case is compared with those previously reported in the literature.

Adult↗

Familial inclusion body myopathy with desmin storage.

We report two adult familial cases of inclusion body myopathy (IBM) with desmin storage in skeletal muscle. Clinically, both patients presented late-onset, progressive, symmetrical, both proximal and distal muscle weakness. Muscle biopsy findings were identical in both cases and consisted of marked variability in fiber size, increased number of central nuclei and vacuolation involving 10% of fibers. Single or multiple vacuoles were located subsarcolemmally or in the center, and were rimmed by basophilic material. At the ultrastructural level, tubulofilamentous nuclear and cytoplasmic inclusions of 16-21 nm in diameter were frequently observed. In addition, large subsarcolemmal and central deposits composed of electron-dense granular material were present in many fibers. Immunocytochemistry revealed staining for desmin, vimentin and ubiquitin within both inclusions and vacuolated fibers. Possible structural and functional associations between these two types of muscle changes remain unclear. They may either represent two coexistent disease processes or merely reflect an abnormal form of muscle fiber degradation, with unidentifiable specificity.

Adult↗

INPP5K-related muscular dystrophy caused by a novel synonymous splicing variant in a Chinese patient: a case report.

Congenital muscular dystrophies (CMDs) are a genetically heterogeneous group of disorders. Variants in the INPP5K gene, which encodes a phosphoinositide phosphatase, are a rare cause of CMD. The condition is commonly associated with muscle weakness, early-onset cataracts, and intellectual disability, and prior reports have primarily identified missense, frameshift, or deletion variants. We describe the first Chinese case of INPP5K-related muscular dystrophy in a 28-year-old male with a mild phenotype, notably lacking intellectual disability. His presentation included bilateral cataracts at age 5 and adolescent onset limb girdle weakness. Muscle magnetic resonance imaging (MRI) revealed a characteristic pattern of selective fatty infiltration, with severe involvement of gluteal and thigh muscles and striking sparing of the rectus femoris, sartorius, and gracilis. Genetic analysis identified compound heterozygous novel INPP5K variants: a missense c.274C>T, p.(Arg92Cys) and a synonymous c.261G>A, p.(Lys87=) change. Functional studies confirmed the synonymous variant causes aberrant splicing (exon 3 skipping), leading to a frameshift and premature termination p.(Leu52SerfsTer49). According to American College of Medical Genetics and Genomics guidelines, the c.274C>T and c.261G>A variants were classified as likely pathogenic and pathogenic, respectively. This first report of a Chinese patient with INPP5K-related muscular dystrophy broadens both the genetic and clinical spectrum of the disorder. We identify the first disease-causing synonymous variant (via aberrant splicing) and a novel hypomorphic missense variant p.(Arg92Cys), the combination of which explains the attenuated phenotype lacking intellectual disability. Our case highlights the critical role of RNA analysis in diagnosing non-canonical variants and confirms the universal diagnostic relevance of the characteristic muscle MRI pattern.

Adult↗

Subacute neurotoxicity following long-term exposure to carbaryl.

Carbaryl, a widely used insecticide, is reputed to have a wide safety margin. It can induce acute cholinesterase poisoning, which is rapidly reversible on discontinuation of exposure. Long-term sequelae from long-term exposure have not previously been described in humans. This report describes the experience of a 75-year-old man who had long-term excessive exposure to carbaryl and in whom a debilitating syndrome, including headaches, memory loss, proximal muscle weakness, muscle fasciculation, muscle cramps, and anorexia with marked weight loss, developed. At the time of diagnosis, serum pseudocholinesterase levels were low, and his major symptoms resolved on termination of exposure. Late clinical features were sleep apnea and progressive development of a peripheral neuropathy. The difficulty in diagnosing the cause of a group of relatively nonspecific symptoms raises the question of whether chronic carbaryl neurotoxicity might be occurring more frequently than previously suspected.

Aged↗

Muscle carnitine levels in neuromuscular disease.

The production of energy in muscle from long-chain fatty acid oxidation is dependent upon the presence of carnitine. An abnormally low level of muscle carnitine, as seen in patients with the carnitine deficiency syndrome, results in marked muscle weakness. Muscle from 83 consecutive patients undergoing diagnostic muscle biopsy was assayed for carnitine. Carnitine levels (mean +/- SEM, expressed as nmoles carnitine per mg noncollagen protein) in muscle from patients with Duchenne dystrophy (8.1 +/- 1.7) and possible Becker dystrophy (10.6 +/- 3.0) were significantly (P less than 0.001) different from histologically normal muscle (24.0 +/- 1.4). Carnitine levels in patients with limb-girdle dystrophy (16.1 +/- 3.1) and polymyositis/dermatomyositis (16.6 +/- 3.2) were also low, although not as low as in Duchenne dystrophy. Carnitine levels from patients with denervation atrophy (22.1 +/- 3.6), nonspecific fiber atrophy (21.3 +/- 1.3), and a group of miscellaneous neuromuscular diseases (20.4 +/- 1.4) were not significantly different from histologically normal muscle. The low values of carnitine seen in Duchenne dystrophy and a group of possible Becker dystrophy patients may be a nonspecific effect, related to severe muscle damage.

Carnitine↗

A new mutation of IGHMBP2 gene in spinal muscular atrophy with respiratory distress type 1.

This report presents a new mutation in the first Japanese female infant with spinal muscular atrophy with respiratory distress type 1. She manifested the characteristic clinical features, including early-onset respiratory failure due to diaphragmatic paralysis and severe distal muscle weakness. Muscle biopsy in the femoral muscle indicated massive neurogenic changes. Sural nerve biopsy disclosed a moderate reduction of myelinated fibers, predominantly reduced large fibers. She had a novel homozygous missense mutation 2685 C -->A, leading to a T879K substitution in the immunoglobulin mu-binding protein 2 gene. Both parents were heterozygous for this mutation.

DNA-Binding Proteins↗