Familial idiopathic hyper-CK-emia: an underrecognized condition

Causes of HyperCKemia in Children: A Retrospective Cohort Study

Background and Objectives: Creatine kinase (CK) is a commonly used screening test for neuromuscular disorders (NMDs). However, hyperCKemia can result from several pathologic and physiologic causes. We analyzed neuromuscular disorders in noninfant children with hyperCKemia including those with no weakness and mild CK elevations (<5 times the upper limit of normal). We hypothesized that children with mild CK elevation and no weakness would be unlikely to have neuromuscular disorders and require additional evaluation. Methods: We retrospectively evaluated patients between 1 and 18 years of age seen at a single children's hospital over a 3-calendar-year period with initial total CK values greater than the upper limit of normal with at least 2 years of follow-up data. Final diagnoses were analyzed and associations with possible risk factors assessed. Receiver operating characteristic curves were generated to assess altering CK cutoff values. Results: Of 260 subjects with hyperCKemia, 18 had a neuromuscular disorder (6.9%, 95% confidence interval [CI] 4.2%-10.9%). Of 166 subjects with CK <5 times the upper limit of normal and no weakness, 8 had a neuromuscular disorder (4.8%, 95% CI 2.3%-9.6%). Weakness (odds ratio [OR] 32.5, 95% CI 4-385, P = .0002), and family history of neuromuscular disorders (OR not calculable, P = .0003) were associated with neuromuscular disorders. An optimal CK threshold of 777 was identified on receiver operating characteristic curve analysis (sensitivity of 72% and specificity of 64%). The most commonly identified neuromuscular disorders were muscular dystrophies, inflammatory myopathies, and metabolic myopathies. Conclusion: Most children with hyperCKemia will not be diagnosed with a neuromuscular disorder, but a significant minority even with mild hyperCKemia and without weakness may warrant additional evaluation.

A novel 1-bp deletion variant in DAG1 in Japanese familial asymptomatic hyper-CK-emia

Asymptomatic hyper-CK-emia (ASCK) is characterized by persistent elevation of creatine kinase (CK) in serum without any neurological symptoms. We ascertained a two-generation family of ASCK patients without clear neurological abnormalities except for the high levels of serum CK (810.5 ± 522.4 U/L). We identified a novel 1-bp deletion variant in the DAG1 gene shared by the patients in the family (NM_001177639: exon 3: c.930delC:p.R311Gfs*70). The variant causes premature termination of translation at codon 477, resulting in a protein product completely devoid of the essential DAG1 domain. Since ASCK has been associated with DAG1 in only one case carrying compound heterozygous missense variants, our new finding of a novel 1-bp deletion revealed the previously unknown dominant effect of DAG1 on ASCK.

Significance of Asymptomatic Hyper Creatine-Kinase Emia

OBJECTIVES

Whether asymptomatic hyper-CKemia (AHCE) should prompt a thorough work-up for muscle disease or not is controversially discussed. This review aims at summarizing and discussing recent findings concerning the cause, frequency, evolution, and work-up of conditions manifesting as AHCE and normal or abnormal electromyography (EMG) respectively muscle biopsy.

METHODS

Systematic PubMed search.

RESULTS

There are numerous primary (hereditary) and acquired myopathies that manifest with permanent, recurrent, or temporary AHCE with/without myopathic EMG or muscle biopsy. AHCE particularly occurs at onset of these conditions, which include dystrophinopathies, myotilinopathies, calpainopathy, caveolinopathy, dysferlinopathy, central core disease, multicore disease, desminopathy, MD1, MD2, hypoPP, malignant hyperthermia susceptibility, Pompe disease, McArdle disease, myoadenylate deaminase-deficiency, CPT2-deficiency, mitochondrial disorders, or myopathy with tubular aggregates. Most likely, other primary myopathies manifest with AHCE as well, without having been reported. Patients with AHCE should be taken seriously and repeated CK determination must be conducted. If hyper-CKemia is persisting or recurrent, these patients should undergo an EMG and eventually muscle biopsy. If noninformative, genetic work-up by a panel or whole exome sequencing should be initiated, irrespective of the family history. Patients with AHCE should avoid excessive exercise, require sufficient hydration, require counseling with regard to the risk of malignant hyperthermia, and should inform anesthesiologists and surgeons about their condition before elective surgery.

CONCLUSIONS

Recurrent AHCE should be taken seriously and managed with conventional work-up. If noninformative, genetic work-up should follow irrespective of the family history.

Muscle Toxicity of Drugs: When Drugs Turn Physiology into Pathophysiology

Drugs are prescribed to manage or prevent symptoms and diseases, but may sometimes cause unexpected toxicity to muscles. The symptomatology and clinical manifestations of the myotoxic reaction can vary significantly between drugs and between patients on the same drug. This poses a challenge on how to recognize and prevent the occurrence of drug-induced muscle toxicity. The key to appropriate management of myotoxicity is prompt recognition that symptoms of patients may be drug related and to be aware that inter-individual differences in susceptibility to drug-induced toxicity exist. The most prevalent and well-documented drug class with unintended myotoxicity are the statins, but even today new classes of drugs with unintended myotoxicity are being discovered. This review will start off by explaining the principles of drug-induced myotoxicity and the different terminologies used to distinguish between grades of toxicity. The main part of the review will focus on the most important pathogenic mechanisms by which drugs can cause muscle toxicity, which will be exemplified by drugs with high risk of muscle toxicity. This will be done by providing information on key clinical and laboratory aspects, muscle electromyography patterns and biopsy results, and pathological mechanism and management for a specific drug from each pathogenic classification. In addition, rather new classes of drugs with unintended myotoxicity will be highlighted. Furthermore, we will explain why it is so difficult to diagnose drug-induced myotoxicity, and which tests can be used as a diagnostic aid. Lastly, a brief description will be given of how to manage and treat drug-induced myotoxicity.

Abnormal calcium signalling and the caffeine-halothane contracture test

Background

The variable clinical presentation of malignant hyperthermia (MH), a disorder of calcium signalling, hinders its diagnosis and management. Diagnosis relies on the caffeine–halothane contracture test, measuring contraction forces upon exposure of muscle to caffeine or halothane (F_C and F_H, respectively). Patients with above-threshold F_C or F_H are diagnosed as MH susceptible. Many patients test positive to halothane only (termed ‘HH’). Our objective was to determine the characteristics of these HH patients, including their clinical symptoms and features of cytosolic Ca²⁺ signalling related to excitation–contraction coupling in myotubes.

Methods

After institutional ethics committee approval, recruited patients undergoing contracture testing at Toronto's MH centre were assigned to three groups: HH, doubly positive (HS), and negative patients (HN). A clinical index was assembled from musculoskeletal symptoms and signs. An analogous calcium index summarised four measures in cultured myotubes: resting [Ca²⁺]_cytosol, frequency of spontaneous cytosolic Ca²⁺ events, Ca²⁺ waves, and cell-wide Ca²⁺ spikes after electrical stimulation.

Results

The highest values of both indexes were found in the HH group; the differences in calcium index between HH and the other groups were statistically significant. The principal component analysis confirmed the unique cell-level features of the HH group, and identified elevated resting [Ca²⁺]_cytosol and spontaneous event frequency as the defining HH characteristics.

Conclusions

These findings suggest that HH pathogenesis stems from excess Ca²⁺ leak through sarcoplasmic reticulum channels. This identifies HH as a separate diagnostic group and opens their condition to treatment based on understanding of pathophysiological mechanisms.

Asymptomatic hyperCKemia during a two-year monitoring period: A case report and literature overview

High creatine kinase (CK) levels can be associated with many disorders, including neuromuscular, cardiac, metabolic, endocrine and traumatic. Idiopathic hyperCKemia is a diagnostic dilemma for physicians even though its long-term prognosis is usually benign. We report a case of a Caucasian 61-year-old woman who presented as completely asymptomatic to her general practitioner with a serum CK (sCK) level at 6,122 IU/l. A complete diagnostic evaluation, including physical and laboratory examinations, electromyogram and muscle biopsy were negative for any neuromuscular or other disorder. Two years later the patient remains asymptomatic, active and overall healthy but sCK levels remain elevated, ≤6,591 IU/l (>50-fold higher than normal values).

Approach to asymptomatic creatine kinase elevation

How to manage a patient who has an elevated serum creatine kinase (CK) level but no or insignificant muscle-related signs and symptoms is a clinical conundrum. The authors provide a systematic approach, including repeat testing after a period of rest, defining higher thresholds over which pursuing a diagnosis is worthwhile, and evaluating for a variety of nonneuromuscular causes. They also outline a workup for neuromuscular causes.

A CASQ1 founder mutation in three Italian families with protein aggregate myopathy and hyperCKaemia

BACKGROUND

Protein aggregate myopathies are increasingly recognised conditions characterised by a surplus of endogenous proteins. The molecular and mutational background for many protein aggregate myopathies has been clarified with the discovery of several underlying mutations. Familial idiopathic hyperCKaemia is a benign genetically heterogeneous condition with autosomal dominant features in a high proportion of cases.

METHODS

In 10 patients from three Italian families with autosomal dominant benign vacuolar myopathy and hyperCKaemia, we performed linkage analysis and exome sequencing as well as morphological and biochemical investigations.

RESULTS AND CONCLUSIONS

We show, by Sanger and exome sequencing, that the protein aggregate myopathy with benign evolution and muscle inclusions composed of excess CASQ1, affecting three Italian families, is due to the D244G heterozygous missense mutation in the CASQ1 gene. Investigation of microsatellite markers revealed a common haplotype in the three families indicating consanguinity and a founder effect. Results from immunocytochemistry, electron microscopy, biochemistry and transfected cell line investigations contribute to our understanding of pathogenetic mechanisms underlining this defect. The mutation is common to other Italian patients and is likely to share a founder effect with them. HyperCKaemia in the CASQ1-related myopathy is common and sometimes the sole overt manifestation. It is likely that CASQ1 mutations may remain undiagnosed if a muscle biopsy is not performed, and the condition could be more common than supposed.

A Neuromuscular Approach to Statin-Related Myotoxicity

Approximately 95% of statin-treated patients tolerate this form of cholesterol management without any adverse effects. However, given their efficacy in reducing low density lipoproteins and cardiovascular events large numbers of patients are selected for statin therapy. Therefore muscle complications are, in fact, quite common. Limited understanding of the underlying pathophysiology has hampered physicians' ability to identify patients at risk for developing statin myotoxicity. A growing number of published case reports/series have implicated statins in the exacerbation of both acquired and genetic myopathies. A clinical management algorithm is presented which outlines a variety of co-morbidities which can potentiate the adverse effects of statins on muscle. In addition, a rational approach to the selection of those patients most likely to benefit from skeletal muscle biopsy is discussed. Ongoing work will define the extent to which statin-intolerant patients represent carriers of recessive metabolic myopathies or pre-symptomatic acquired myopathies. The expanding importance of pharmacogenomics will undoubtedly be realized in the field of statin myopathy research within the next few years. Such critical information is needed to establish more definitive management and diagnostic strategies.

Muscle disorders: the latest investigations

Patients with muscle disorders can present a diagnostic challenge to physicians because of the different ways they can present and the large number of different underlying causes. Recognition of the 'myopathic phenotype' coupled with investigations usually including electrodiagnostic and histological investigations have been essential for diagnosing the underlying cause of a myopathy. Despite these standard investigations, some patients can remain undiagnosed. New tests including more specific antibody tests for immune-mediated myopathies and the introduction of next-generation sequencing promise to revolutionise diagnostic approaches for immune and inherited myopathies, but clinical expertise remains essential to choose the most appropriate tests and interpret the results. The aim of this review is to provide an overview of the different presentations to the neuromuscular clinic and the latest investigations that can be helpful in the diagnosis of muscle disorders.

Screening test for malignant hyperthermia in patients with persistent hyperCKemia: a pilot study

INTRODUCTION

Persistently elevated serum creatine kinase (CK) is frequently associated with predisposition to malignant hyperthermia (MH). We investigated whether a minimally invasive metabolic test is suitable to diagnose MH susceptibility among patients with hyperCKemia.

METHODS

Thirty-nine participants were included: 10 were MH susceptible (MHS); 21 MH were non-susceptible (MHN); and 8 had MHN with persistent hyperCKemia >500 U/L. Microdialysis probes were inserted into the vastus lateralis muscle, and halothane or caffeine was injected via an attached microtubing catheter. Lactate concentrations in dialysis samples were measured spectrophotometrically.

RESULTS

Baseline lactate did not differ between the groups. After local application of halothane or caffeine, a significant lactate increase was detected only in the MHS group.

CONCLUSIONS

Test results were not influenced by hyperCKemia. To avoid risks and complications of a surgical muscle biopsy this microdialysis test might be a useful screening tool for MH susceptibility among patients with persistent CK elevation.

Malignant hyperthermia

Malignant hyperthermia (MH) is an uncommon, life-threatening pharmacogenetic disorder of the skeletal muscle. It presents as a hypermetabolic response in susceptible individuals to potent volatile anesthetics with/without depolarizing muscle relaxants; in rare cases, to stress from exertion or heat stress. Susceptibility to malignant hyperthermia (MHS) is inherited as an autosomally dominant trait with variable expression and incomplete penetrance. It is known that the pathophysiology of MH is related to an uncontrolled rise of myoplasmic calcium, which activates biochemical processes resulting in hypermetabolism of the skeletal muscle. In most cases, defects in the ryanodine receptor are responsible for the functional changes of calcium regulation in MH, and more than 300 mutations have been identified in the RYR1 gene, located on chromosome 19q13.1. The classic signs of MH include increase of end-tidal carbon dioxide, tachycardia, skeletal muscle rigidity, tachycardia, hyperthermia and acidosis. Up to now, muscle contracture test is regarded as the gold standard for the diagnosis of MHS though molecular genetic test is used, on a limited basis so far to diagnose MHS. The mortality of MH is dramatically decreased from 70-80% to less than 5%, due to an introduction of dantrolene sodium for treatment of MH, early detection of MH episode using capnography, and the introduction of diagnostic testing for MHS. This review summarizes the clinically essential and important knowledge of MH, and presents new developments in the field.

Are the currently used reference intervals for creatine kinase (CK) reflecting the general population? The Tromsø Study

Laboratory reference intervals are not necessarily reflecting the range in the background population. This study compared creatine kinase (CK) reference intervals calculated from a large sample from a Norwegian population with those elaborated by the Nordic Reference Interval Project (NORIP). It also assessed the pattern of CK-normalization after standardized control analyses.

New upper reference limits (URL) CK values were calculated after exclusion of individuals with risk of hyperCKemia and including individuals with incidentally detected hyperCKemia after they had completed a standardized control analysis. After exclusion of 5924 individuals with possible causes of hyperCKemia, CK samples were analyzed in 6904 individuals participating in the 6th survey of The Tromsø Study. URL was defined as the 97.5 percentile.

New URL in women was 207 U/L. In men <50 years it was 395 U/L and in men ≥50 years 340 U/L. In individuals with elevated CK, normalization grade after control analysis was inversely correlated to the CK level (p<0.04).

URL CK values in women and in men <50 years of age were in accordance with URL CK values given by the NORIP. In men ≥50 years, a higher URL was found and the findings suggest an upward adjustment of URL in this age group.

Malignant Hyperthermia and Idiopathic HyperCKemia

Malignant hyperthermia (MH) is a rare but life-threatening condition that is more frequently encountered and discussed within the anesthesia literature. Here we through a case specifically discuss the susceptibility of individuals and/or families with asymptomatic unexplained elevations of creatine kinase (CK), also frequently referred to as hyperCKemia or idiopathic hyperCKemia (IHCK) in recent reports. The clinical implications would be to underscore the importance of this as a susceptibility to developing MH and highlight the importance of genetic susceptibility testing in such cases. Anesthesiologists and critical care intensivists as well as primary care physicians should keep this in mind when seeing patients with asymptomatic hyperCKemia and potentially inform them about the possibility of developing MH if exposed to triggering agents. Genetic susceptibility testing should be considered if available and family members should also receive nontriggering agents when undergoing anesthesia and wear Medic Alert tags.

Variation of serum creatine kinase (CK) levels and prevalence of persistent hyperCKemia in a Norwegian normal population. The Tromsø Study

In this cross-sectional study we assessed the prevalence of hyperCKemia, defined as persistent CK values ≥210 U/L in women, ≥400 U/L in men <50 years and ≥280 U/L in men ≥50 years (reference values according to the Nordic Reference Interval Project). Blood samples were obtained from 12,828 participants in the 6th survey of The Tromsø Study. We identified 686 (5.3%) individuals with incidentally elevated CK. After a standardized control test, 169 persons (1.3%) had persistent hyperCKemia, i.e. 69.9% normalization. Use of statins or other causes of hyperCKemia were detected in 78 individuals (46.2%), giving a prevalence of "idiopathic hyperCKemia" of 0.71%. CK variation was highest in younger men and in females between 60 and 69 years. This study has identified persistent hyperCKemia in 1.3% of the normal population, and demonstrates the importance of performing controlled CK analyses, also in those with identified risk factors.

Duchenne muscular dystrophy and idiopathic hyperCKemia in the same family

Familial hyperCKemia is a rare condition, and a combination with Duchenne muscular dystrophy (DMD) is extremely rare. A boy showed muscle weakness from the age of 10 months and presented typical signs of DMD at the age of 18 months. The diagnosis was supported by markedly elevated serum creatine kinase (CK) value as well as by neurophysiological and muscle biopsy findings at the age of 23 months. The diagnosis was confirmed by identification of a stop codon in exon 43 (p.2095Arg>X) of the dystrophin gene. Interestingly, the father and his near relatives had increased serum CK values without any clinical symptoms or signs, nor a defect in caveolin-3 gene. We suggest that the occurrence of familial hyperCKemia may have triggered the early onset of symptoms in our patient.