Rhabdomyolysis featuring muscular dystrophies

The utility of electrodiagnostic testing in unprovoked rhabdomyolysis in the era of next-generation sequencing

INTRODUCTION/AIMS

Rhabdomyolysis is an etiologically heterogeneous, acute necrosis of myofibers characterized by transient marked creatine kinase (CK) elevation associated with myalgia, muscle edema, and/or weakness. The study aimed to determine the role of electrodiagnostic (EDX) testing relative to genetic testing and muscle biopsy in patients with unprovoked rhabdomyolysis in identifying an underlying myopathy.

METHODS

EDX database was reviewed to identify unprovoked rhabdomyolysis patients who underwent EDX testing between January 2012 and January 2022. Each patient's clinical profile, EDX findings, muscle pathology, laboratory, and genetic testing results were analyzed.

RESULTS

Of 66 patients identified, 32 had myopathic electromyography (EMG). Muscle biopsy and genetic testing were performed in 41 and 37 patients, respectively. A definitive diagnosis was achieved in 15 patients (11 myopathic EMG and 4 nonmyopathic EMG; p = .04) based on abnormal muscle biopsy (4/11 patients) or genetic testing (12/12 patients, encompassing 5 patients with normal muscle biopsy and 3 patients with nonmyopathic EMG). These included seven metabolic and eight nonmetabolic myopathies (five muscular dystrophies and three ryanodine receptor 1 [RYR1]-myopathies). Patients were more likely to have baseline weakness (p < .01), elevated baseline CK (p < .01), and nonmetabolic myopathies (p = .03) when myopathic EMG was identified.

DISCUSSION

Myopathic EMG occurred in approximately half of patients with unprovoked rhabdomyolysis, more likely in patients with weakness and elevated CK at baseline. Although patients with myopathic EMG were more likely to have nonmetabolic myopathies, nonmyopathic EMG did not exclude myopathy, and genetic testing was primarily helpful to identify an underlying myopathy. Genetic testing should likely be first-tier diagnostic testing following unprovoked rhabdomyolysis.

Anoctamin-5 related muscle disease: clinical and genetic findings in a large European cohort

Anoctamin-5 related muscle disease is caused by biallelic pathogenic variants in the anoctamin-5 gene (ANO5) and shows variable clinical phenotypes: limb-girdle muscular dystrophy type 12 (LGMD-R12), distal muscular dystrophy type 3 (MMD3), pseudometabolic myopathy or asymptomatic hyperCKaemia. In this retrospective, observational, multicentre study we gathered a large European cohort of patients with ANO5-related muscle disease to study the clinical and genetic spectrum and genotype-phenotype correlations. We included 234 patients from 212 different families, contributed by 15 centres from 11 European countries. The largest subgroup was LGMD-R12 (52.6%), followed by pseudometabolic myopathy (20.5%), asymptomatic hyperCKaemia (13.7%) and MMD3 (13.2%). In all subgroups, there was a male predominance, except for pseudometabolic myopathy. Median age at symptom onset of all patients was 33 years (range 23-45 years). The most frequent symptoms at onset were myalgia (35.3%) and exercise intolerance (34.1%), while at last clinical evaluation most frequent symptoms and signs were proximal lower limb weakness (56.9%) and atrophy (38.1%), myalgia (45.1%) and atrophy of the medial gastrocnemius muscle (38.4%). Most patients remained ambulatory (79.4%). At last evaluation, 45.9% of patients with LGMD-R12 additionally had distal weakness in the lower limbs and 48.4% of patients with MMD3 also showed proximal lower limb weakness. Age at symptom onset did not differ significantly between males and females. However, males had a higher risk of using walking aids earlier (P = 0.035). No significant association was identified between sportive versus non-sportive lifestyle before symptom onset and age at symptom onset nor any of the motor outcomes. Cardiac and respiratory involvement that would require treatment occurred very rarely. Ninety-nine different pathogenic variants were identified in ANO5 of which 25 were novel. The most frequent variants were c.191dupA (p.Asn64Lysfs*15) (57.7%) and c.2272C>T (p.Arg758Cys) (11.1%). Patients with two loss-of function variants used walking aids at a significantly earlier age (P = 0.037). Patients homozygous for the c.2272C>T variant showed a later use of walking aids compared to patients with other variants (P = 0.043). We conclude that there was no correlation of the clinical phenotype with the specific genetic variants, and that LGMD-R12 and MMD3 predominantly affect males who have a significantly worse motor outcome. Our study provides useful information for clinical follow up of the patients and for the design of clinical trials with novel therapeutic agents.

Infection-Induced Rhabdomyolysis in a Pregnant Woman with Undiagnosed Myotonic Dystrophy: A Case Report

A 34-year-old nulliparous gravid female presented with acute bilateral pyelonephritis at 29 + 5 weeks gestation. The patient was relatively well until two weeks ago when a slight increase in amniotic fluid was noted. Further investigation revealed myoglobinuria and significantly elevated levels of creatine phosphokinase. The patient was subsequently diagnosed with rhabdomyolysis. Twelve hours after admission, the patient noted reduced fetal movements. A non-stress test revealed fetal bradycardia and non-reassuring variability in fetal heart rate. An emergency cesarean section was performed, and a "floppy" female child was delivered. Genetic testing revealed congenital myotonic dystrophy, and the mother was also diagnosed with myotonic dystrophy. Rhabdomyolysis has a very low incidence in pregnancy. Herein, we report a rare case of myotonic dystrophy with rhabdomyolysis in a gravid female with no history of myotonic dystrophy. Acute pyelonephritis is a causative agent of rhabdomyolysis that results in preterm birth.

Inherited myopathy plus: Double-trouble from rare neuromuscular disorders

A rare disorder in the USA is one that affects <200,000 people, making inherited myopathies rare diseases. Increasing access to genetic testing has been instrumental for the diagnosis of inherited myopathies. Genetic findings, however, require clinical correlation due to variable phenotype, polygenic etiology of certain inherited disorders, and possible co-existing independent neuromuscular disorders. We searched the Mayo Clinic Rochester medical record (2004-2020) to identify adult patients carrying pathogenic variants or likely pathogenic variants in genes causative of myopathies and having a coexisting independent neuromuscular disorder classified as rare at https://rarediseases.info.nih.gov/. One additional patient was identified at Nationwide Children's hospital. Clinical and laboratory findings were reviewed. We identified 14 patients from 13 families fulfilling search criteria. Seven patients had a "double-trouble" inherited myopathy; two had an inherited myopathy with coexistent idiopathic myositis; three had an inherited myopathy with coexisting rare neuromuscular disorder of neurogenic type; a female DMD carrier had co-existing distal spinal muscular atrophy, which was featuring the clinical phenotype; and a patient with a MYH7 pathogenic variant had Sandhoff disease causing motor neuron disease. These cases highlight the relevance of correlating genetic findings, even when diagnostic, with clinical features, to allow precise diagnosis, optimal care, and accurate prognosis.

Using gene panels in the diagnosis of neuromuscular disorders: A mini-review

The diagnosis of inherited neuromuscular disorders is challenging due to their genetic and phenotypic variability. Traditionally, neurophysiology and histopathology were primarily used in the initial diagnostic approach to these conditions. Sanger sequencing for molecular diagnosis was less frequently utilized as its application was a time-consuming and cost-intensive process. The advent and accessibility of next-generation sequencing (NGS) has revolutionized the evaluation process of genetically heterogenous neuromuscular disorders. Current NGS diagnostic testing approaches include gene panels, whole exome sequencing (WES), and whole genome sequencing (WGS). Gene panels are often the most widely used, being more accessible due to availability and affordability. In this mini-review, we describe the benefits and risks of clinical genetic testing. We also discuss the utility, benefits, challenges, and limitations of using gene panels in the evaluation of neuromuscular disorders.

The management and diagnosis of rhabdomyolysis-induced acute kidney injury: a case study

Rhabdomyolysis is characterised by a rapid dissolution of damaged or injured skeletal muscle that can be the result of a multitude of mechanisms. It can range in severity from mild to severe, leading to multi-organ failure and death. Rhabdomyolysis causes muscular cellular breakdown, which can cause fatal electrolyte imbalances and metabolic acidosis, as myoglobin, creatine phosphokinase, lactate dehydrogenase and other electrolytes move into the circulation; acute kidney injury can follow as a severe complication. This article reflects on the case of a person who was diagnosed with rhabdomyolysis and acute kidney injury after a fall at home. Understanding the underpinning mechanism of rhabdomyolysis and the associated severity of symptoms may improve early diagnosis and treatment initiation.

Emergency Planning as Part of Healthcare Transition Preparation for Patients with Duchenne Muscular Dystrophy

BACKGROUND

Emergency care planning is an important component of healthcare transition, particularly for patients with medical complexity. Duchenne muscular dystrophy (DMD) is a complex, progressive pediatric-onset disease affecting multiple organ systems including impairment of cardiac and pulmonary function, high risk for fractures, fat embolism, adrenal crisis and malignant hyperthermia. Appropriate interdisciplinary emergency management is critical for survival for these patients. The purpose of this quality improvement project was to develop a process to reliably share an individualized emergency care plan (ECP) with patients and their families as part of a larger plan to develop an integrated transition program.

METHODS

An interdisciplinary team of nurses and clinicians used the principles of quality improvement to develop a reliable process to assure patients with DMD received an individualized, multidisciplinary ECP at routine interdisciplinary clinic visits. Additionally, the project used surveys to assess patient and family satisfaction with the letter and whether it improved their knowledge of emergency care.

RESULTS

Sixty-two patients were seen during the study timeframe. All received an ECP. Sixty-two surveys were sent and twenty-three surveys were returned. Of those that responded, the majority stated the ECP increased their knowledge of emergency care.

CONCLUSION

ECPs can be developed and disseminated to patients with DMD and their caregivers. This tool can potentially promote timely and appropriate emergency care for these patients with unique and complex medical needs.

Characteristics of pediatric rhabdomyolysis and the associated risk factors for acute kidney injury: a retrospective multicenter study in Korea

Background

The clinical features of pediatric rhabdomyolysis differ from those of the adults with rhabdomyolysis; however, multicenter studies are lacking. This study aimed to investigate the characteristics of pediatric rhabdomyolysis and reveal the risk factors for acute kidney injury (AKI) in such cases.

Methods

This retrospective study analyzed the medical records of children and adolescents diagnosed with rhabdomyolysis at 23 hospitals in South Korea between January 2007 and December 2016.

Results

Among 880 patients, those aged 3 to 5 years old composed the largest subgroup (19.4%), and all age subgroups were predominantly male. The incidence of AKI was 11.3%. Neurological disorders (53.6%) and infection (39.0%) were the most common underlying disorder and cause of rhabdomyolysis, respectively. The median age at diagnosis in the AKI subgroup was older than that in the non-AKI subgroup (12.2 years vs. 8.0 years). There were no significant differences in body mass index, myalgia, dark-colored urine, or the number of causal factors between the two AKI-status subgroups. The multivariate logistic regression model indicated that the following factors were independently associated with AKI: multiorgan failure, presence of an underlying disorder, strong positive urine occult blood, increased aspartate aminotransferase and uric acid levels, and reduced calcium levels.

Conclusions

Our study revealed characteristic clinical and laboratory features of rhabdomyolysis in a Korean pediatric population and highlighted the risk factors for AKI in these cases. Our findings will contribute to a greater understanding of pediatric rhabdomyolysis and may enable early intervention against rhabdomyolysis-induced AKI.

Guidelines for genetic testing of muscle and neuromuscular junction disorders

Despite recent advances in the understanding of inherited muscle and neuromuscular junction diseases, as well as the advent of a wide range of genetic tests, patients continue to face delays in diagnosis of sometimes treatable disorders. These guidelines outline an approach to genetic testing in such disorders. Initially, a patient's phenotype is evaluated to identify myopathies requiring directed testing, including myotonic dystrophies, facioscapulohumeral muscular dystrophy, oculopharyngeal muscular dystrophy, mitochondrial myopathies, dystrophinopathies, and oculopharyngodistal myopathy. Initial investigation in the remaining patients is generally a comprehensive gene panel by next-generation sequencing. Broad panels have a higher diagnostic yield and can be cost-effective. Due to extensive phenotypic overlap and treatment implications, genes responsible for congenital myasthenic syndromes should be included when evaluating myopathy patients. For patients whose initial genetic testing is negative or inconclusive, phenotypic re-evaluation is warranted, along with consideration of genes and variants not included initially, as well as their acquired mimickers.

Pediatric Paroxysmal Exercise-Induced Neurological Symptoms: Clinical Spectrum and Diagnostic Algorithm

Paroxysmal exercise-induced neurological symptoms (PENS) encompass a wide spectrum of clinical phenomena commonly presenting during childhood and characteristically elicited by physical exercise. Interestingly, few shared pathogenetic mechanisms have been identified beyond the well-known entity of paroxysmal exercise-induced dyskinesia, PENS could be part of more complex phenotypes including neuromuscular, neurodegenerative, and neurometabolic disease, epilepsies, and psychogenetic disorders. The wide and partially overlapping phenotypes and the genetic heterogeneity make the differential diagnosis frequently difficult and delayed; however, since some of these disorders may be treatable, a prompt diagnosis is mandatory. Therefore, an accurate characterization of these symptoms is pivotal for orienting more targeted biochemical, radiological, neurophysiological, and genetic investigations and finally treatment. In this article, we review the clinical, genetic, pathophysiologic, and therapeutic landscape of paroxysmal exercise induced neurological symptoms, focusing on phenomenology and differential diagnosis.

Risk factors and future directions for preventing and diagnosing exertional rhabdomyolysis

Exertional rhabdomyolysis may occur when an individual is subjected to strenuous physical exercise. It is occasionally associated with myoglobinuria (i.e. "cola-colored" urine) alongside muscle pain and weakness. The pathophysiology of exertional rhabdomyolysis involves striated muscle damage and the release of cellular components into extracellular fluid and bloodstream. This can cause acute renal failure, electrolyte abnormalities, arrhythmias and potentially death. Exertional rhabdomyolysis is observed in high-performance athletes who are subjected to intense, repetitive and/or prolonged exercise but is also observed in untrained individuals and highly trained or elite groups of military personnel. Several risk factors have been reported to increase the likelihood of the condition in athletes, including: viral infection, drug and alcohol abuse, exercise in intensely hot and humid environments, genetic polymorphisms (e.g. sickle cell trait and McArdle disease) and epigenetic modifications. This article reviews several of these risk factors and proposes screening protocols to identify individual susceptibility to exertional rhabdomyolysis as well as the relevance of proteomics for the evaluation of potential biomarkers of muscle damage.

The etiology of rhabdomyolysis: an interaction between genetic susceptibility and external triggers

Background and purpose

Rhabdomyolysis is a medical emergency characterized by acute skeletal muscle breakdown with a sudden rise and subsequent fall of serum creatine kinase (CK) levels. Rhabdomyolysis events are provoked by exposure to external triggers, possibly in combination with an increased genetic susceptibility. We aimed to describe comprehensively the external triggers and potentially pathogenic genetic variants possibly implicated in increased rhabdomyolysis susceptibility.

Methods

We performed a retrospective single‐center study, including a total of 1302 patients with an acute CK level exceeding 2000 IU/l.

Results

Anoxia was the most frequently reported trigger (40%). A subset of 193 patients were clinically suspected of an underlying genetic disorder (recurrent episodes, a positive family history, very high or persistently increased CK levels). In 72 of these patients, an unequivocal genetic defect was identified. A total of 22 genes with pathogenic variants were identified, including 52 different variants. Of those, 11 genes have been previously associated with rhabdomyolysis (ACADVL, ANO5, CPT2, DMD, DYSF, FKRP, HADHA, PGM1, LPIN1, PYGM, RYR1). Eleven genes are probably implicated in increased susceptibility (including AGL, CAPN3, CNBP, DMPK, MAGT1, ACADM, SCN4A, SGCA, SGCG, SMPD1, TANGO2).

Conclusion

These findings suggest that the spectrum of genetic susceptibility for rhabdomyolysis has not yet been completely clarified. With the increasing availability of next‐generation sequencing in a diagnostic setting, we expect that in more cases a genetic defect will be identified.

Anoctamin 5 (ANO5) muscular dystrophy-three different phenotypes and a new histological pattern

OBJECTIVE

Anoctamin 5 (ANO5) is a putative intracellular calcium-activated chloride channel. Recessive mutations in ANO5 may present from asymptomatic hyperCKemia and exercise-induced myalgia to proximal and/or distal muscle weakness. Here we describe the clinical, pathological, and molecular findings of three unrelated patients with ANO5-related muscular dystrophy.

METHODS

In this retrospective study, we analyzed our database which includes 1700 muscle biopsies performed for diagnostic purposes from October 2004 to February 2019. Patients were attended by two myology experts, who performed and analyzed the muscle biopsies. Muscle biopsies were frozen in cooled isopenthane, cryostat sectioned, and routinely stained and reacted (minimum 16 stainings). A custom panel, including 115 genes (Nextera Rapid Capture, Illumina) and whole-exome sequencing analysis, was used for next-generation sequencing in cases without a definite pathological diagnosis.

RESULTS

Three patients were diagnosed with ANO5-related muscular dystrophy, with all presenting the common exon 5 mutation c.191dup plus a compound heterozygous missense mutation. They showed three different phenotypes (distal myopathy, LGMD2L, and asymptomatic hyperCKemia). Curiously, all three muscle biopsies showed different patterns, but numerous ragged-red fibers with little endomysial inflammation and partial invasion cell by T lymphocytes were observed in one.

CONCLUSION

ANO5-related muscular dystrophy is a heterogeneous disease with different clinical phenotypes as well as different histological patterns, which may even mimic a mitochondrial myopathy. The results of this study provide further knowledge of the clinical, histological, and pathological features related to ANO5 mutations.

The Limb-Girdle Muscular Dystrophies

PURPOSE OF REVIEW

As a group, the limb-girdle muscular dystrophies (LGMDs) are the fourth most prevalent genetic muscle disease, yet they are still not well known or understood. This article defines and describes LGMDs, delineates a diagnostic strategy, and discusses treatment of the LGMDs.

RECENT FINDINGS

In 2018, the definition of the LGMDs was further refined, and a new nomenclature was proposed. Diagnosis of the LGMDs was long guided by the distinctive clinical characteristics of each particular subtype but now integrates use of genetics-with next-generation sequencing panels, exomes, and full genome analysis-early in the diagnostic assessment. Appreciation of the phenotypic diversity of each LGMD subtype continues to expand. This emphasizes the need for precision genetic diagnostics to better understand each subtype and formulate appropriate management for individual patients. Of significant relevance, the explosion of research into therapeutic options accentuates the need for accurate diagnosis, comprehensive disease characterization, and description of the natural histories of the LGMDs to move the field forward and to mitigate disease impact on patients with LGMD.

SUMMARY

The LGMDs are genetic muscle diseases that superficially appear similar to one another but have important differences in rates of progression and concomitant comorbidities. Definitive diagnoses are crucial to guide management and treatment now and in the future. As targeted treatments emerge, it will be important for clinicians to understand the nomenclature, diagnosis, clinical manifestations, and treatments of the LGMDs.

Comparative effects of Mancozeb and Disulfiram-induced striated muscle myopathies in Long-Evans rats

Dithiocarbamates (DTCs) like mancozeb (MZ) and disulfiram (DS) are used throughout agriculture and medicine and have been implicated in neurotoxicity. Little research has been studied on the reported myopathies caused by these compounds. Their pathogenesis and mechanism of muscle toxicity has not been fully studied. The aim of this study is to investigate if DTCs alter striated muscle tissues in vivo. Long-Evans rats were treated with either MZ or DS followed by analysis of muscle biomarkers and metal levels. DS resulted in increases in serum lactate dehydrogenase (LDH), cardiac troponin, and myoglobin levels. Creatine kinase-MB serum levels decreased. Mancozeb only showed an increase in serum LDH. Both MZ and DS-treatment resulted in altered metal levels in the myocardium but not skeletal muscle. Ultrastructural alterations included damaged mitochondria and myofibril splitting. The presence of multivesicular bodies, and alterations of the intercalated disc were also seen.

Clinical Features of Acute Rhabdomyolysis in 55 Pediatric Patients

Objective: This study was designed to compare the clinical manifestations, laboratory tests, etiology, and prognosis of children with acute rhabdomyolysis (RM) at various ages. This study was designed to analyze the risk factors for acute kidney injury (AKI) in children with RM and to identify the role of neuromuscular and autoimmune disease in children with RM. Methods: Clinical data for 55 children with RM were collected and statistically analyzed. Patients were stratified to an infant group (G1) (age <1 year), preschool group (G2) (age 1-6 year), school-age group (G3) (age 7-11 year), and an adolescent group (G4) (age 12-16 year). Results: The top three clinical manifestations were dark urine (52.7%), myalgia (38.2%), and fever (23.8%). Patients in G1 had fever (71.4%), vomiting (77.8%), and urinalysis abnormalities (14.3%), without triad clinical manifestations. Fifty percent of patients in G4 group had myalgia; 70.8% had dark urine; 75% had abnormal urine tests. The most common cause in each age group was as follows: sepsis (57.1%) in G1; hereditary neuromuscular diseases (44.4%) in G2; immune diseases (40%) in G3; strenuous exercise (50%) in G4. Logistic regression analysis shown that AKI was not corelated with age, gender, or peak creatine phosphokinase. AKI was, however, associated with presence of an electrolyte disorder. Conclusion: The clinical manifestations and laboratory findings in infants with acute RM are not typical and need to be taken seriously. The presence of an electrolyte disorder is a risk factor for AKI in children with RM. The most common pathogenesis of RM varies among age groups. Congenital hereditary metabolic disease and immune diseases should not be ignored as a cause of RM in children.

Spectrum of Neuromuscular Disorders With HyperCKemia From a Tertiary Care Pediatric Neuromuscular Center

Elevated creatine kinase is a useful screening test in the diagnostic workup of patients with neuromuscular disorders. We did a retrospective study of children with hyperCKemia (>175 IU/L) who were followed in the neuromuscular program of a tertiary care pediatric center from 2005 to 2016. Patients with hyperCKemia were divided into 2 groups: myopathic and nonmyopathic. Within the myopathic group, there were 3 arbitrary subgroups based on creatine kinase values: A (creatine kinase >10 times normal), B (creatine kinase 5-10 times normal), and C (creatine kinase 1-5 times normal). The 3 major categories of myopathies across all the subgroups were muscular dystrophies (commonest) followed by metabolic myopathies and inflammatory myopathies. Among the nonmyopathic causes of hyperCKemia, spinal muscular atrophy was the commonest. Muscular dystrophies should be considered in children with hyperCKemia, muscle weakness, or calf hypertrophy, and metabolic myopathies to be considered in children with recurrent rhabdomyolysis.

Recognizing, diagnosing, and treating rhabdomyolysis

Rhabdomyolysis is an acute and potentially fatal syndrome characterized by striated muscle breakdown and subsequent release of muscle cell contents into the systemic circulation. The sudden release of large quantities of potassium, calcium, organic acids, and myoglobin into the bloodstream can cause renal tubal toxicity, cardiac dysrhythmias, and death. Complications can be managed and minimized if predicted and treated early, but patients may not have classic symptoms of rhabdomyolysis and may even be asymptomatic on presentation. This article reviews the pathophysiology, causes, diagnosis, and treatment of acute rhabdomyolysis.

Untangling the complexity of limb-girdle muscular dystrophies

The limb-girdle muscular dystrophies (LGMDs) are a group of genetically heterogeneous, autosomal inherited muscular dystrophies with a childhood to adult onset, manifesting with hip- and shoulder-girdle muscle weakness. When the term LGMD was first conceptualized in 1954, it was thought to be a single entity. Currently, there are 8 autosomal dominant (LGMD1A-1H) and 26 autosomal recessive (LGMD2A-2Z) variants according to the Online Mendelian Inheritance in Man database. In addition, there are other genetically identified muscular dystrophies with an LGMD phenotype not yet classified as LGMD. This highlights the entanglement of LGMDs, which represents an area in continuous expansion. Herein we aim to simplify the complexity of LGMDs by subgrouping them on the basis of the underlying defective protein and impaired function. Muscle Nerve 58: 167-177, 2018.

Hyperckemia and myalgia are common presentations of anoctamin-5-related myopathy in French patients

INTRODUCTION

Patients with anoctamin-5 (ANO5) mutations may present not only with limb-girdle muscular dystrophy type 2L or adult-onset Miyoshi-type myopathy but also with asymptomatic hyperCKemia, exercise intolerance, or rhabdomyolysis.

MATERIALS AND METHODS

Data from 38 patients in France with ANO5 mutations with and without muscle weakness on first examination were compared.

RESULTS

Twenty patients presented without muscle weakness. Median age at symptom onset or discovery of hyperCKemia was 23 years. Creatine kinase levels ranged from 200 to 40,000 U/L. Electromyography showed a myopathic pattern in 5 patients, and muscle imaging showed involvement of posterior calf muscles in 10 patients. Mild cardiac involvement was observed in 2 patients. Sixteen patients remain free of weakness after a median follow-up period of 5 years.

DISCUSSION

Asymptomatic, sometimes mild hyperCKemia or exercise intolerance is a presentation of ANO5-related myopathy and may remain isolated or precede muscle weakness by many years. Muscle Nerve 56: 1096-1100, 2017.

Exertional rhabdomyolysis: physiological response or manifestation of an underlying myopathy?

Exertional rhabdomyolysis is characterised by muscle breakdown associated with strenuous exercise or normal exercise under extreme circumstances. Key features are severe muscle pain and sudden transient elevation of serum creatine kinase (CK) levels with or without associated myoglobinuria. Mild cases may remain unnoticed or undiagnosed. Exertional rhabdomyolysis is well described among athletes and military personnel, but may occur in anybody exposed to unaccustomed exercise. In contrast, exertional rhabdomyolysis may be the first manifestation of a genetic muscle disease that lowers the exercise threshold for developing muscle breakdown. Repeated episodes of exertional rhabdomyolysis should raise the suspicion of such an underlying disorder, in particular in individuals in whom the severity of the rhabdomyolysis episodes exceeds the expected response to the exercise performed. The present review aims to provide a practical guideline for the acute management and postepisode counselling of patients with exertional rhabdomyolysis, with a particular emphasis on when to suspect an underlying genetic disorder. The pathophysiology and its clinical features are reviewed, emphasising four main stepwise approaches: (1) the clinical significance of an acute episode, (2) risks of renal impairment, (3) clinical indicators of an underlying genetic disorders and (4) when and how to recommence sport activity following an acute episode of rhabdomyolysis. Genetic backgrounds that appear to be associated with both enhanced athletic performance and increased rhabdomyolysis risk are briefly reviewed.