Evaluation of creatine kinase (CK)-MB to total CK ratio as a diagnostic biomarker for primary tumors and metastasis screening

Objective

Creatine kinase (CK) and its myocardial band isoenzyme (CK-MB) were considered important diagnostic indicators for identifying suspected acute myocardial infarction. However, the serum level of CK-MB is frequently exaggerated in some pathological states without cardiogenic damage, like cancer. Sometimes, the CK-MB level is even greater than the total CK. This study intended to investigate the association between malignancy and an abnormally high ratio of CK-MB to total CK (CK-MB/CK) and to assess the diagnostic relevance of this ratio as a biomarker for cancer.

Methods

Patients hospitalized between September 2019 and September 2022 at Shandong Provincial Qianfoshan Hospital (Jinan, Shandong, China) with serum CK-MB activity greater than total CK activity (CK-MB/CK > 1.0) were recruited as research subjects. Then the demographic and clinical characteristics of these patients were systemically analyzed. The correlation between clinical characteristics (such as cancer types, tumor locations, and tumor metastasis) and laboratory test results (such as serum CK-MB activity, total CK activity, and the CK-MB/CK ratio) was also investigated.

Results

We found that over 44% of the patients with CK-MB/CK > 1.0 were diagnosed with malignancies, and the CK-MB/CK ratio in malignancies patients was significantly higher than in non-malignancies patients. The increase of CK-MB/CK ratio was most obvious in patients with colorectal carcinoma and prostatic carcinoma. Additionally, extremely elevated CK-MB/CK ratios were observed in individuals with metastatic neoplasms, especially in those who suffered from numerous sites of metastasis.

Conclusions

The serum CK-MB/CK ratio can be utilized as a readily accessible supplement diagnostic biomarker in screening for primary and metastatic cancers.

Macro-CK type 2 in metastatic prostate cancer

The isoenzyme creatine kinase muscle/brain (CK-MB) still plays an important role for the differential diagnosis of CK elevations and the clarification of their origin from heart or skeletal muscle. Therefore, it is necessary to know the diagnostic pitfalls in interpreting CK-MB results. We demonstrate a case of macro-CK type 2 in a 75-year-old patient with metastatic castration-resistant prostate cancer and its identification by isoenzyme electrophoresis, which can be typical for cancer diseases.

Serum creatine kinase isoenzymes and macroenzymes in dogs with different neurologic diseases

BACKGROUND

Increased serum activity of CK isoenzymes and macroenzymes, and in particular of the brain isoenzyme (CK-BB) has been reported in dogs with central nervous system (CNS) disorders. However, no studies on the possible differences in serum activities of CK iso- or macroenzymes (Macro-CK1 and Macro-CK2) in different neurologic diseases are available.

OBJECTIVE

The aim of this study was to describe the electrophoretic distribution of CK iso- and macroenzymes in dogs with CNS disorders in order to assess whether this distribution depends on a specific neurologic disease.

METHODS

This study was done on sera from 45 dogs with neurologic diseases (degenerative, n = 7; idiopathic epilepsy [IE], n = 14; inflammatory, n = 16; space occupying lesions [SOL], n = 8) and from 10 clinically healthy dogs. The separation of serum CK isoenzymes and macroenzymes was performed using an automated electrophoretic method already validated in dogs.

RESULTS

Compared with healthy dogs, dogs with CNS disorders had significantly higher total CK and CK-BB activities, and a significantly lower Macro-CK2 activity (P < .001). Comparison of pathologic subgroups and healthy dogs revealed significant differences (P < .01) in dogs with IE and inflammatory disorders for total CK activity, in all the subgroups for CK-BB (P < .01), and in dogs with IE and SOL for Macro-CK2 (P < .01).

CONCLUSIONS

The results of this study suggest that CK-BB is released by neurons damaged by inflammatory or degenerative conditions or due to compressive effects of SOL. However, the neurologic diseases cannot be differentiated based on CK-BB or Macro-CK2 activities, unless further studies allow the definition of diagnostic thresholds.

Avaliação dos indicadores de lesão miocárdica em cães com leishmaniose visceral

O objetivo deste estudo foi avaliar os indicadores laboratoriais, eletrocardiográficos e histológicos de lesão cardíaca em diferentes grupos clínicos de cães com leishmaniose visceral. Foram analisados marcadores séricos, traçado eletrocardiográfico e fragmentos de tecido cardíaco de 41 cães naturalmente infectados, distribuídos em três grupos: assintomático, oligossintomático e sintomático. Todos os animais apresentaram aumento na atividade sérica da enzima creatina quinase fração MB. No traçado eletrocardiográfico, o complexo de baixa voltagem foi o distúrbio de condução mais frequente (8/10). Na análise histológica, 75,6% dos cães apresentaram reação inflamatória com predomínio de infiltrados linfo-histiocítico (13/31) de intensidade discreta a moderada e distribuição multifocal. As alterações microscópicas identificadas no miocárdio foram independentes dos achados laboratoriais, eletrocardiográficos e do quadro clínico apresentado pelos animais estudados. A ausência de associação entre alterações histopatológicas e os parâmetros investigados alerta para a dificuldade de identificação de cardiopatia em cães com leishmaniose visceral e ressalta a importância de incluir a leishmaniose visceral no diagnóstico de patologias cardíacas principalmente em regiões endêmicas para o agente.

Macro creatine kinase type 1: a cause of spuriously elevated serum creatine kinase associated with leukoencephalopathy in a child

Macro creatine kinase type 1 is a complex formed by the creatine kinase isoenzyme BB and monoclonal IgG and occurs in about 1% of patients studied. First identified as a cause of spurious elevation of the total serum creatine kinase in patients suspected of myocardial infarction, the test has been largely replaced by the measurement of troponin levels. We present a child with delayed milestones and persistently elevated total serum creatine kinase measurements (∼ 1000-4000 IU) normal electromyogram and brisk myotatic reflexes. Creatine kinase isoenzymes and brain imaging showed the presence of macro creatine kinase type 1 and extensive signal abnormality of the cerebral white matter. Macro creatine kinase type 1 has been associated with several conditions though it has not been described in association with leukoencephalopathy or in patients this young. Macro creatine kinase type 1 can be a cause of elevated total creatine kinase in patients without primary muscle disease. The significance of the relationship of the macro creatine kinase to the leukoencephalopathy in this patient is unknown.

Comparison of Mass Versus Activity of Creatine Kinase MB and Its Utility in the Early Diagnosis of Re-infarction

Currently employed markers for the detection of acute coronary syndrome are Troponin T, CK (Creatine Kinase) and CKMB activity. CKMB activity measured by immunoinhibition method can give falsely elevated results due to the presence of atypical CK and CKBB and at times lead to the mis-diagnosis of acute coronary syndrome. Hence, CKMB mass (CKMB) measured by electrochemiluminence sandwich principle was employed. In this cross-sectional study 183 samples of 61 patients were analyzed within 6 h of diagnosis of acute coronary syndrome and followed up to 72 h. The correlation coefficient between CKMB activity and CKMBM at 4-6 h was 0.744, while at 12-24 h it was 0.909 and at 48-72 h it was 0.337. Thus there was good association between the two methods at 12-24 h but, statistically for method comparison studies and for replacing one method by another, the two methods need to be in agreement with one another. In this study the two methods are not in agreement with one another and thus analytically not replaceable. Another finding was obtained that CKMBM reached cut off levels prior to CKMB enzyme activity and hence, CKMBM is clinically better than CKMB activity to detect reinfarction.

Macro CK2 accumulation in tenofovir-treated HIV patients is facilitated by CK oligomer stabilization but is not predictive for pathology

BACKGROUND

Ubiquitous mitochondrial creatine kinase (uMtCK) accumulates as macroenzyme creatine kinase type 2 (macro CK2) in the serum of HIV-infected patients under a tenofovir disoproxil fumarate (TDF)-containing antiretroviral regimen. The genesis and clinical significance of this finding is unclear.

METHODS

A prospective observational 5-year follow-up study was performed on those patients in which macro CK2 appearance was initially described ('TDF switch study' cohort). In addition, tenofovir (TFV), its prodrug TDF and its active, intracellular derivative TFV diphosphate (TDP) were tested in vitro for their effects on different key properties of uMtCK to clarify possible interactions of uMtCK with TFV compounds.

RESULTS

In just under 5 years of continuous TDF treatment, only 4/12 (33%) patients remained macro CK2-positive, whereas 8/12 (66%) originally positive patients were macro CK2-negative at the end of follow-up. Prospective clinical follow-up data indicate that macro CK2 appearance under TDF is not associated with significant cell damage or occurrence of malignancies. A trend towards grade 1 hypophosphataemia suggests subclinical proximal tubular dysfunction in macro-CK2-positive patients, although it was not associated with a significant decrease in estimated glomerular filtration rate. In vitro, TFV, TDF and TDP did not interfere with uMtCK enzyme activity as competitive inhibitors or pseudo-substrates, but TFV and TDF stabilized the native uMtCK octameric structure in dilute solutions.

CONCLUSIONS

Appearance of octameric uMtCK as macro CK2 in the serum of TDF-treated patients is suggested to result from a combination of low-level mitochondrial damage caused by subclinical renal tubular dysfunction together with possible compensatory uMtCK overexpression and a putative concomitant stabilization of uMtCK octamers by higher levels of TFV in proximal tubules.

Increased activity of serum mitochondrial isoenzyme of creatine kinase in hepatocellular carcinoma patients predominantly with recurrence

BACKGROUND & AIMS

Mitochondrial isoenzyme of creatine kinase (MtCK) is reportedly highly expressed in hepatocellular carcinoma (HCC). Clinical relevance of serum MtCK activity in patients with HCC was assessed using a novel immuno-inhibition method.

METHODS

Among patients with cirrhosis caused by hepatitis B or C virus, 147 patients with HCC (12 with the first occurrence and 135 with recurrence) and 92 patients without HCC were enrolled.

RESULTS

Serum MtCK activity was higher in cirrhotic patients with HCC than in those without HCC or healthy subjects. Elevated serum MtCK activity in HCC patients decreased after radiofrequency ablation. In case of prediction of HCC, MtCK had a sensitivity of 62.6% and a specificity of 70.7% at a cut-off point of 8.0 U/L, with an area under the receiver operating curve of 0.722 vs. 0.713 for alpha-fetoprotein (AFP) and 0.764 for des-gamma-carboxy prothrombin (DCP). Among the HCC patients, serum MtCK activity was elevated in 52.9% individuals with serum AFP level < 20 ng/ml and 63.2% individuals with serum DCP level < 40 mAu/ml. Even in patients with a single HCC ≤ 2 cm, the sensitivity of serum MtCK activity for the prediction of HCC was 64.4%, which was comparable to the overall sensitivity. This increased activity was due to an increase in ubiquitous MtCK, not sarcomeric MtCK, and the enhanced mRNA expression of ubiquitous MtCK was observed in cell lines originating from HCCs in contrast to healthy liver tissues.

CONCLUSIONS

Serum MtCK activity merits consideration as a novel marker for HCC to be further tested as for its diagnostic and prognostic power.

The use of trypsin to confirm the presence of macrocreatine kinase on isoenzyme electrophoresis

Background

Macrocreatine kinase (MCK) type 1 is a high molecular weight form of CK that is non-pathological. Identification of MCK is beneficial in preventing unnecessary investigations that may follow a persistently elevated CK of unknown origin. Currently, gel filtration chromatography can be used as a confirmatory technique, but it is laborious, time-consuming and expensive. The aim of this work, carried out as part of a larger investigation into the prevalence of MCK, was to determine whether trypsin can be used as an alternative to confirm the presence of MCK on isoenzyme electrophoresis.

Methods

Five samples found to have bands running in the MCK region on isoenzyme electrophoresis were treated with trypsin. Electrophoresis was carried out using the Helena Biosciences Sas-1 Plus system. These samples were also analysed by the confirmatory technique of gel filtration chromatography.

Results

Of the five samples treated with trypsin, three were found to be MCK-positive and two MCK-negative. These results correlated with those obtained by the reference method of gel filtration chromatography.

Conclusions

There appears to be a potential use of trypsin in confirming the presence of MCK following isoenzyme electrophoresis. If these findings were verified, this would provide a less labour-intensive, less time-consuming and more cost-effective confirmatory technique. Further study is required, which needs to be expanded to include a larger number of patients, before this method can be adopted routinely.

Increase in serum mitochondrial creatine kinase levels induced by tenofovir administration

Recently, 2 monoclonal antibodies that specifically inhibit mitochondrial creatine kinase (MtCK) activity have been developed. In this study, we measured the serum MtCK activity in HIV-1-infected individuals (n = 100) by employing a novel method using these antibodies. The mean serum MtCK activity in 44 patients treated with highly active antiretroviral therapy (HAART) including tenofovir disoproxil fumarate (TDF) was 16.0 IU/L. The MtCK activity was significantly higher in patients receiving TDF than in those receiving HAART without TDF (3.4 IU/L) or in naïve patients (6.9 IU/L) (Tukey-Kramer test, p < 0.0001 and p = 0.0029, respectively). The serum MtCK activity reached a plateau at 1 month after the initiation of TDF administration and decreased upon discontinuation. It showed no significant correlation with the trough plasma TDF concentration, serum creatinine level, or red blood cell count. The activity was elevated in 75% of the patients receiving TDF, and this elevation was specific to TDF; it was not observed with other anti-HIV drugs. In addition, our report emphasizes the careful interpretation of creatine kinase-MB (CK-MB) test results in patients receiving TDF because MtCK in serum could cause false-positive results on a conventional CK-MB test, which does not include MtCK-specific inhibitory antibodies.

Statin myopathy: a lipid clinic experience on the tolerability of statin rechallenge

INTRODUCTION

Statin myopathy is a generally encountered side effect of statin usage. Both muscle symptoms and a raised serum creatine kinase (CK) are used in case definition, but these are common manifestations of other conditions, which may not be statin related. Statin rechallenge assuming no contraindication in selected cases is an option before considering a different class of lipid-lowering agent.

AIMS

We aim to characterize retrospectively the patients referred to our Lipid Clinic with a diagnosis of statin myopathy. The tolerability of different statins was assessed to determine a strategy for rechallenging statins in such patients in the future.

RESULTS

Patients with statin myopathy constitute 10.2% of our Lipid Clinic workload. They are predominantly female (62.0%), Caucasian (63.9%), with a mean age of 58.3 years and mean body mass index (BMI) of 29.3 kg/m(2). The serum CK and erythrocyte sedimentation rate (ESR) were statistically higher compared to patients with statin intolerances with no muscular component or CK elevations. Secondary causes of statin myopathy were implicated in 2.7% of cases. Following statin myopathy to simvastatin we found no statistical difference between the tolerability rates between atorvastatin, rosuvastatin, pravastatin, and fluvastatin. Fibrates, cholestyramine, and ezetimibe were statistically better tolerated in these patients.

CONCLUSIONS

Statin rechallenge is a real treatment option in patients with statin myopathy. Detailed history and examination is required to exclude muscle diseases unrelated to statin usage. In patients developing statin myopathy on simvastatin, we did not find any statistical difference between subsequent tolerability rates to rosuvastatin, pravastatin, and fluvastatin.

Anomalous Activity Measurements of Creatine (Phospho) Kinase, CK-MB Isoenzyme in Indian Patients in the Diagnosis of Acute Coronary Syndrome

In the present study, the cause of suspected false-positive (anomalous) values for CK-MB activity, in Indian patients investigated for ACS. Total serum CK and CK-MB activity, serum Troponin I were measured and CK-MB as a percentage of the total CK activity (%CK-MB) calculated. CK-MB was also estimated using densitometry and CK-MB mass assay. Anomalous specimens were tested for the presence of CK isoenzymes. In 22 healthy subjects, 11 male and female, the %CK-MB ranged from 3.6 to 30.2. In 11 male patients, with proven ACS, the %CK-MB was from 4.0 to 17.5. The cut off for anomalous CK-MB activity values was set as >33.0%. In 35 patients with anomalies, total CK values ranged from 39 to 231 U/L, CK-MB from 30 to 161 U/L. Investigation of CK isoenzymes, showed 10 patients had a CK-BB band, 14 an intermediate band between CK-MM and CK-MB (macro-CK type 1), 7 had a cathodal band (macro-CK type 2), and 3 had a band intermediate between CK-MB and CK-BB. This later band does not seem to have been previously reported. Against the CK-MB mass assay, the activity assay showed no correlation, in 43 patients (19 M, 24 F), Pearson coefficient (R(2)) was 0.006. The CK-MB immunoinhibition assay is better described as measuring "non-CK-MM activity." A %CK-MB activity >6% as a marker of ACS is not valid in our patient population. Laboratories should not use only CK-MB activity as a biochemical marker of ACS.

Biochemical markers of muscular damage

Muscle tissue may be damaged following intense prolonged training as a consequence of both metabolic and mechanical factors. Serum levels of skeletal muscle enzymes or proteins are markers of the functional status of muscle tissue, and vary widely in both pathological and physiological conditions. Creatine kinase, lactate dehydrogenase, aldolase, myoglobin, troponin, aspartate aminotransferase, and carbonic anhydrase CAIII are the most useful serum markers of muscle injury, but apoptosis in muscle tissues subsequent to strenuous exercise may be also triggered by increased oxidative stress. Therefore, total antioxidant status can be used to evaluate the level of stress in muscle by other markers, such as thiobarbituric acid-reactive substances, malondialdehyde, sulfhydril groups, reduced glutathione, oxidized glutathione, superoxide dismutase, catalase and others. As the various markers provide a composite picture of muscle status, we recommend using more than one to provide a better estimation of muscle stress.

Electrophoretic fractionation of creatine kinase isoenzymes and macroenzymes in clinically healthy dogs and cats and preliminary evaluation in central neurologic disease

Background: Information about the electrophoretic distribution of CK‐MM, CK‐MB, and CK‐BB, serum creatine kinase (CK) isoenzymes that are indicators of skeletal muscle, cardiac muscle, and brain lesions, respectively, and CK macroenzymes (macro‐CK1 and macro‐CK2) in dogs and cats with and without central neurologic disease is scant and equivocal.

Objectives: The objectives of this study were to describe the electrophoretic distribution of CK isoenzymes and macroenzymes in healthy dogs and cats and to provide a preliminary assessment of the utility of CK enzymatic electrophoresis in dogs and cats with central neurologic disease.

Methods: Electrophoretic separation of serum CK isoenzymes and macroenzymes was performed on freeze‐thawed serum samples from 20 healthy dogs and 3 dogs with central neurologic disease and from 14 healthy cats and 6 cats with neurologic feline infectious peritonitis (FIP). Electrophoretic separation was also performed on supernatants of homogenized brain, skeletal muscle, and cardiac muscle from both species, to assess the tissue distribution of isoenyzmes in dogs and cats.

Results: CK‐MM was the predominant isoenzyme in the serum of healthy dogs and cats, followed by macro‐CK2 and CK‐BB in dogs and by both macroenzymes in cats. In dogs, CK‐MB was essentially absent from both serum and homogenized hearts. CK‐BB increased in dogs with neurologic disease. In cats, CK‐BB was essentially absent from serum, but was present in brain homogenates. Two of 6 cats with FIP had increased macro‐CK1 and increased CK‐BB activity.

Conclusions: This study identified the electophoretic distribution of CK isoenzymes and macroenzymes of dogs and cats and provided encouraging data about the possible use of CK‐BB as a biomarker for canine neurologic disorders, but not for FIP.

Macroenzyme creatine kinase in the era of modern laboratory medicine

Among the conditions in which creatine kinase (CK)-MB activity is elevated in the absence of myocardial injury or infarction, macroenzyme (macro) CK merits special attention from clinicians. We present 2 cases, 1 with macro CK type 1 and the other with macro CK type 2, to stress the common clinical situations and diagnostic dilemma that clinicians encounter when evaluating patients with macro CK. Moreover, the rare conditions associated with macro CK, and the phenomenon of spuriously high CK-MB activity out of proportion to total CK, are discussed. The biochemical characteristics, clinical significance and potential implications of macro CK are reviewed within the scope of modern laboratory medicine.

Clinical role of recurrently elevated macro creatine kinase type 1

The typical creatine kinase (CK) isoenzymes include CK-BB, CK-MB, and CK-MM. Macro CK type 1, one of the atypical CK enzymes, has been identified in human serum, but the clinical significance still remains uncertain. In our laboratory, 105 patients who expressed serum macro CK isoenzyme type 1 were identified from March 2004 to March 2007. We found that macro CK type 1 recurred after at least one month in 16 patients. Clinical diagnoses were myopathy in 14 patients, sepsis in one, and acute coronary syndrome in one. The averages of serum total CK and macro CK type 1 were 9,132 and 1,925 (U/L), respectively. The linear regression analysis between recurrent macro CK type 1 and total CK revealed a good correlation (y=3.5054x+2381.3, R(2)=0.7822, P<0.001). Three patients had critical illness, including one respiratory failure and two mortalities. Good linear correlation is documented between total CK and recurrent macro CK type 1. In conclusion, the macro CK type I isoenzyme recurred primarily in patients with myopathy.

Macroenzyme Creatine Kinase (Ck) Type 2 in HIV-Infected Patients is Significantly Associated with Tdf and Consists of Ubiquitous Mitochondrial Ck

Objective

To evaluate the prevalence and origin of macroenzyme creatine kinase type 2 (Macro CK2) in HIV-1-infected patients on antiretroviral treatment.

Design

CK, CK-MB activity and protein weight, electrophoretic behaviour, glomerular filtration rate (GFR), aspartate aminotransferase (AST), alanine aminotransferase (ALT), bone alkaline phosphatase (AP), (2-microglobulin serum levels and proteinuria were analysed in 468 HIV-infected outpatients. Sera with detectable Macro CK2 were further analysed using immunoblotting.

Results

CK-MB isoenzyme activity and mass concentration revealed the presence of Macro CK2 in 32/408 (7.8%) outpatients. Tenofovir DF (TDF) treatment was a prominent common feature in these patients. Prospective examination of sera from 41 patients collected prior to and during TDF exposure showed Macro CK2 in 20/41 (48%) TDF-treated patients and in 0/19 control sera from patients with TDF-free regimens. Macro CK2 was not present prior to TDF exposure. Patients with Macro CK2 showed a significant elevation of serum (2-microglobulin levels. GFR, AST/ALT ratio, bone AP and proteinuria remained unchanged. Electrophoresis and immunoblotting demonstrated that the Macro CK2 in TDF-treated patients consisted of the ubiquitous (uMtCK) and not the sarcomeric type (sMtCK) of mitochondrial CK (MtCK).

Conclusions

Macro CK2 consisting of uMtCK is associated with the use of TDF-containing regimens. Whether the appearance of uMtCK in these patients reflects mitochondrial damage remains to be clarified.

CK-MM autoantibodies: Prevalence, immune complexes, and effect on CK clearance

Although the blood level of creatine kinase (CK) is the most commonly used marker of muscle injury, there is marked interindividual variability in this measure. Part of this variability may be attributed to variability in the rate of CK clearance from the circulation. In this study, we assessed the possibility that CK-MM autoantibodies form immune complexes with CK following muscle injury and subsequently affect the CK clearance rate. Using an enzyme-linked immunosorbent assay, CK-MM autoantibodies were detected in all 25 human subjects studied but the levels varied greatly. Using protein A-sepharose, the percentage of the plasma CK activity found in immune complexes was determined to be correlated with the CK-MM autoantibody level at lower CK levels (<1,022 U/L). When CK-MM antibodies were administered to mice, plasma CK activity following a bolus CK injection was reduced by 11%-32%. We conclude that CK-MM autoantibodies can modulate the rate of CK clearance from the circulation. Thus, the relatively low blood CK levels seen in some individuals following injury may be attributed partly or entirely to an autoantibody-enhanced clearance of CK.

Age-associated Increase in Creatine Kinase-MB-Specific Activity in Human Serum Confounds its use as an Injury Marker

This study retrospectively examined a consecutive series of patient CKMB samples for a relationship between age (242 subjects, aged from 20 to 96 years old), serum CKMB activity and corresponding mass results analyzed for CKMB-specific activity (activity per molecule, unit/mg). Patients were categorized into six age groups. The means for specific activity of CKMB, standard error and 95% confidence intervals of each group were calculated. CKMB-specific activity in human serum increases with age regardless of gender or MI severity. As this greater propensity for increased CKMB activity may be due to alteration in part due to protein modification of post-MI release in the blood circulation, these findings add further weight for the current move to the use of troponins and other markers of myocardial injury.

[Biological markers of myocardial necrosis]

New biological markers of myocardial injury have improved the management of patients with acute coronary syndromes. Among these markers, the most relevant are the cardiac troponins (troponin I and troponin T) because of their cardiospecificity, and myoglobin because of its combination of diagnostic sensitivity and usefulness for an early diagnosis. The serial analysis and combined use of both markers fulfill all diagnostic and prognostic requirements, and are helpful in indicating therapeutic strategies for acute coronary syndromes. However, these markers also have limitations, and their concentrations should always be interpreted in the light of the patient's clinical status.

Laboratory testing in the diagnosis and management of idiopathic inflammatory myopathies

Laboratory testing commonly used to assess the idiopathic inflammatory myopathies (IIMs) can be divided into three categories: (1) measurement of serum activities or concentrations of muscle-derived factors--such as enzymes, myoglobin, and other molecules--in order to assess muscle injury; (2) immunologic tests that detect markers of the disease process, including serum autoantibodies that have been associated with myositis; and (3) general laboratory tests that are used to assess the patient's general status and medical condition. The laboratory assessment of muscle-derived factors that reflect muscle injury, and the determination of serum autoantibodies, play valuable roles in the diagnosis and management of the IIM. Enzyme elevations do not correlate with disease activity in all patients, however, and they must be interpreted within the clinical context. Autoantibodies can identify disease subsets with distinctive patterns of clinical manifestations, genetics, responses to therapy and prognosis, but disease-specific autoantibodies are present in only half of patients with IIM. Recent studies have defined additional myositis autoantibodies that may improve our capacity to diagnose and manage the IIM.

Creatine Kinase Gene Mutation in a Patient with Muscle Creatine Kinase Deficiency

Background: We describe a 56-year-old woman admitted to the hospital with a diagnosis of acute myocardial infarction without an increase of serum creatine kinase (CK) activity during her clinical course. She died on the 11th hospital day, and the diagnosis was confirmed by autopsy. The patient had had no previous muscular symptoms.

Methods: Expression of the CK-muscle (CK-M) protein in cardiac tissue was examined by immunoblotting and immunochemical staining. CK-M mRNA expression was estimated by semiquantitative reverse transcription–PCR. Gene structure of CK-M was determined by Southern blotting and direct sequencing of 2251 bp. Existence of a point mutation in the CK-M gene was examined by restriction fragment length polymorphism analysis of PCR products (PCR-RFLP) in the patient and in 108 controls.

Results: CK-M protein in the myocardial tissue of the patient was substantially lower (103 ± 7 ng/mg protein) than in control myocardial tissue (35 800 ± 2860 ng/mg protein). Immunoreactive CK-M in the patient tissue sample was 0.3% of the value for the control sample. CK-M mRNA was 53-fold less in the patient sample compared with the control. This very low expression of CK-M mRNA was considered to be the primary reason for CK-M deficiency. Direct sequencing revealed a point mutation at residue 54 in exon 2, which was specific for the patient. No other abnormalities were found in the CK-M gene of the patient.

Conclusions: This report identifies a molecular abnormality in human CK deficiency and discusses the physiologic relevance of CK-M.

A juvenile case of overlap syndrome of systemic lupus erythematosus and polymyositis, later accompanied by systemic sclerosis with the development of anti-Scl 70 and anti-Ku antibodies

We describe a 16-year-old girl with an overlap syndrome consisting of systemic lupus erythematosus (SLE) from the age of 7 and polymyositis (PM) from the age of 10, later accompanied by systemic sclerosis (SSc) from the age of 15. She was diagnosed as having SLE with exudative malar erythema, photosensitivity, and discoid rashes with positive antinuclear antibody (ANA) and anti-DNA antibody titers. The diagnosis of PM was also made in accordance with findings of a high titer of muscle enzymes and a muscle biopsy specimen demonstrating marked degeneration of the muscle fibers and perivascular infiltration of mononuclear cells. She developed Raynaud's phenomenon and pitting ulcers on her fingers with positive anti-Scl 70 and anti-Ku antibodies, leading to a diagnosis of SSc. The patient was treated with prednisolone. To our knowledge this is the youngest case of SLE-PM overlap syndrome later accompanied by SSc.

[Macro creatine kinase type 1 as a cause of increase of CF-MB isoenzyme. Apropos of 7 cases]

INTRODUCTION

The macro-creatine kinase type 1 is a complex of IgG linked to the BB fraction of the creatine kinase enzyme. Its presence in serum interferes with the immunoinhibition methods normally used in emergency room laboratories that produce false elevations of the creatine kinase MB isoenzyme, and which may cause a misunderstanding in the evaluation of patients who are suspected of having ischemic cardiopathy.

PATIENTS AND METHOD

We have studied seven patients using an immunoinhibition method. They showed high levels of creatine kinase MB isoenzyme with normal values of creatine kinase enzyme. Electrophoresis was performed on all patients to determine the presence of creatine kinase enzyme.

RESULTS

The electrophoresis showed in all the cases the presence of a macro-creatine kinase type 1 responsible for this interference. The clinical and analytical evaluation, as well as the radiological and electrocardiographical evaluation of this patients did not show any acute coronary disease.

CONCLUSIONS

The macro-creatine kinase type 1 has been related to the existence of underlying cardiovascular pathology; a fact that was confirmed in three patients. With the immunoinhibition methods, the macro-creatine kinases usually, occurs with high values of creatine kinase MB isoenzyme (normally above 50% of the total activity of the creatine kinase) with normal creatine kinase levels. This fact, although strongly suggesting its presence, creates the necessity of using more sensitive methods to prevent these interferences. Likewise, we recommend using the electrophoresis of the creatine kinase enzyme to determine the nature of these interferences.

Progress in myocardial damage detection: new biochemical markers for clinicians

New clinical requirements for triaging chest pain patients challenge the abilities of the current cardiac markers. Serial measurements of myoglobin, creatine kinase (CK) isoenzyme MB (CKMB) mass, or CK isoforms in emergency rooms help to rapidly rule out acute myocardial infarction (AMI). However, within the first 3 to 4 h from chest pain onset, their sensitivities are too low to contribute significantly to AMI diagnosis during this period. CKMB and lactate dehydrogenase (LDH) isoenzyme 1 are not heart-specific, which hampers reliable diagnosis in patients with concomitant skeletal muscle damage. By contrast, the regulatory proteins troponin I and troponin T are expressed in three different isoforms: one for slow-twitch skeletal muscle fibers, one for fast-twitch skeletal muscle fibers, and one for cardiac muscle (cTnI, cTnT); cardiac-specific cTnI and cTnT assays are already available for routine use. cTnT and cTnI are the most promising markers for risk stratification in patients with unstable angina pectoris. Recent reports on increased cTnT in patients with renal failure or myopathy without evidence of myocardial injury and undetectable cTnI suggest that cTnT could be reexpressed similar to CKMB and LDH-1 in chronically damaged human skeletal muscle. Therefore, cTnI is probably the most heart-specific marker. Among the recently proposed new markers for early AMI diagnosis: glycogen phosphorylase isoenzyme BB (GPBB), fatty acid binding protein, phosphoglyceric acid mutase isoenzyme MB, enolase isoenzyme alpha beta, S100a0, and annexin V, GPBB is the most promising because it increases as early as 1 to 4 h from chest pain onset and its early release appears to be essentially dependent on ischemic myocardial injury.

Laboratory evaluation of the inflammatory myopathies

The laboratory plays an important role in the diagnosis, evaluation, and classification of the heterogeneous group of diseases known as the IIM, which are characterized by chronic muscle inflammation. Serial measurements of the levels of muscle-derived enzymes in serum are the traditional laboratory studies used to follow the clinical course of patients with IIM, although other laboratory tests can also be useful in assessing myositis disease activity. Several markers of immune system activation, including cytokines and lymphocyte markers, show promise as possibly more sensitive measures of myositis disease activity. Discovery of a unique group of MSAs over the past decade has provided an immunologic basis for defining relatively homogeneous subsets of patients who share similar clinical features, disease courses, and responses to therapy. Future investigations of novel immunologic activation markers, as well as the cloning and expression of target autoantigens of the MSAs, should allow better diagnostic assays, enhanced prognosis, and a better understanding of the pathogenesis of these disorders.