Comparison of 3 instruments to measure muscle strength in children: A prospective study.

AIM: To establish which instrument is the most valid and reliable measure of muscle strength in children aged 4-11 years and can improve the diagnostic procedure in children with suspected myopathy to spare more of them from muscle biopsy. METHODS: In a prospective study over a 2 year period, 22 patients aged 4-11 years were recruited. They had all been referred to our specialist centre on the suspicion of myopathy. Hand-held dynamometry, the Jamar dynamometer and a new Motor Performance Test were administered before muscle biopsy. Validity was assessed by the power to discriminate between patients with and without myopathy using logistic regression analysis and receiver operating characteristic (ROC) analysis. The area under the ROC curve (AUC) was calculated as a measure of the diagnostic power. RESULTS: Comparison of the three instruments showed that the Motor Performance Test had the highest validity. Hand-held dynamometry generally had lower validity and showed wide variation in the 11 muscle groups. The Jamar dynamometer had very low validity in early stage myopathy. CONCLUSION: The Motor Performance Test was the most valid and reliable instrument to indicate the presence of myopathy in children. This objective, non-invasive and child-friendly instrument can improve the diagnostic procedure and exclude more children without myopathy from muscle biopsy.

Changes in cerebral oxygenation and hemodynamics during cranial ultrasound in preterm infants.

OBJECTIVES: To evaluate whether application of a transducer on the anterior fontanelle during cranial ultrasound (US) examination effects cerebral hemodynamics and oxygenation in preterm infants. STUDY DESIGN*: During cranial US examination, changes in cerebral blood oxygenation (cHbD) and cerebral blood volume (CBV) were assessed using near infrared spectrophotometry (NIRS) in 76 infants (GA 30.7 (4.1)wk, BW 1423 (717)g) within two days after birth. Ten of these infants (GA 29.1 (1.6)wk, BW 1092 (455)g) were studied again at a postnatal age of one week. RESULTS*: We obtained stable and consistent NIRS registrations in 54 infants within the first two days after birth. Twenty-eight of these infants showed a decrease in cHbD (0.59 (0.54) micromol/100g) during the scanning procedure while CBV did not change. Twenty-four infants showed no changes in NIRS and 2 infants showed an atypical NIRS response during cranial US examination. At the postnatal age of one week, stable and consistent NIRS registrations were obtained in 7 infants. None of these infants showed changes in NIRS variables during cranial US examination. CONCLUSIONS: Application of an US transducer on the anterior fontanelle causes changes in cerebral oxygenation and hemodynamics in a substantial number of preterm infants. ( *values are expressed as median (interquartile range)).

Pericardial and abdominal fluid accumulation in congenital disorder of glycosylation type Ia.

The association of fetal hydrops with Congenital Disorders of Glycosylation (CDG) has been reported previously. Pericardial fluid accumulation and ascites were also observed in a few young patients with CDG type Ia. Here we describe the clinical and biochemical features in three children developing life-threatening extravascular fluid accumulation. All patients carried severe PMM2 mutations comparable to the earlier reported patients with fetal hydrops. One patient was successfully treated with a pericardial-pleural shunt placement. Pericardial fluid accumulation and generalized oedema resolved temporarily in the other two children on regular albumin infusions and the use of diuretics. Sequential abdominal punctures were unsuccessful in the treatment of the extensive ascites production. The use of non-steroid anti-inflammatory agents and the application of high dose steroids had no clinical effect. Severe extravascular fluid accumulation progressed to decompensation and death. Biochemical investigations of the abdominal fluid and pericardial fluid demonstrated a high extracellular protein concentration, increased cytokine concentrations and an abnormal transferrin isoelectric focusing pattern characteristic of CDG type I. Our results are consistent with a local activation of the cytokine pathways and subsequent protein transport through the endothelial surface to the extravascular space. Normal glycosylation of cell surface proteins is essential for the normal fluid balance and protein transport through the pericardial and peritoneal membrane. Future therapeutic efforts should be directed to inhibit the abnormal immune response and excessive protein transport in this life-threatening complication of CDG syndrome.

Muscle 3243A-->G mutation load and capacity of the mitochondrial energy-generating system.

OBJECTIVE: The mitochondrial energy-generating system (MEGS) encompasses the mitochondrial enzymatic reactions from oxidation of pyruvate to the export of adenosine triphosphate. It is investigated in intact muscle mitochondria by measuring the pyruvate oxidation and adenosine triphosphate production rates, which we refer to as the "MEGS capacity." Currently, little is known about MEGS pathology in patients with mutations in the mitochondrial DNA. Because MEGS capacity is an indicator for the overall mitochondrial function related to energy production, we searched for a correlation between MEGS capacity and 3243A-->G mutation load in muscle of patients with the MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes) syndrome. METHODS: In muscle tissue of 24 patients with the 3243A-->G mutation, we investigated the MEGS capacity, the respiratory chain enzymatic activities, and the 3243A-->G mutation load. To exclude coinciding mutations, we sequenced all 22 mitochondrial transfer RNA genes in the patients, if possible. RESULTS: We found highly significant differences between patients and control subjects with respect to the MEGS capacity and complex I, III, and IV activities. MEGS-related measurements correlated considerably better with the mutation load than respiratory chain enzyme activities. We found no additional mutations in the mitochondrial transfer RNA genes of the patients. INTERPRETATION: The results show that MEGS capacity has a greater sensitivity than respiratory chain enzymatic activities for detection of subtle mitochondrial dysfunction. This is important in the workup of patients with rare or new mitochondrial DNA mutations, and with low mutation loads. In these cases we suggest to determine the MEGS capacity.

Cerebral hemodynamics and oxygenation after serial CSF drainage in infants with PHVD.

The aim of our study was to assess consecutive changes in cerebral oxygenation and hemodynamics after serial cerebrospinal fluid (CSF) drainage from a subcutaneous ventricular catheter reservoir (SVCR) in infants with PHVD. Infants with PHVD were studied during CSF drainage from a SVCR on the day of SVCR placement, half a week and one week after SVCR placement. Changes in cHbD and CBV were assessed using near infrared spectrophotometry. Time averaged peak flow velocity (TAPFV), end diastolic flow velocity (EDFV), peak systolic flow velocity (PSFV) and pulsatility index (PI) were measured before (baseline) and after CSF drainage using Doppler ultrasound. Longitudinal data analysis was performed using linear mixed models. Seven patients (GA 26.7-40.4 weeks, BW 800-4575 g) were studied. CSF drainage resulted in a statistically significant increase in CBV during each measurement. The change in CBV was maximal on the day of SVCR placement. A significant increase in cHbD and EDFV, and decrease in PI was observed after CSF drainage only on the day of SVCR placement. Baseline values of all Doppler variables improved consecutively after serial CSF removal in the first week after SVCR placement. Frequent CSF drainage results in consecutive improvement of cerebral perfusion and oxygenation in infants with PHVD.

Spectrophotometric assay for complex I of the respiratory chain in tissue samples and cultured fibroblasts.

BACKGROUND: A reliable and sensitive complex I assay is an essential tool for the diagnosis of mitochondrial disorders, but current spectrophotometric assays suffer from low sensitivity, low specificity, or both. This deficiency is mainly due to the poor solubility of coenzyme-Q analogs and reaction mixture turbidity caused by the relatively high concentrations of tissue extract that are often required to measure complex I. METHODS: We developed a new spectrophotometric assay to measure complex I in mitochondrial fractions and applied it to muscle and cultured fibroblasts. The method is based on measuring 2,6-dichloroindophenol reduction by electrons accepted from decylubiquinol, reduced after oxidation of NADH by complex I. The assay thus is designed to avoid nonspecific NADH oxidation because electrons produced in these reactions are not accepted by decylubiquinone, resulting in high rotenone sensitivity. RESULTS: The assay was linear with time and amount of mitochondria. The K(m) values for NADH and 2,6-dichloroindophenol in muscle mitochondria were 0.04 and 0.017 mmol/L, respectively. The highest complex I activities were measured with 0.07 mmol/L decylubiquinone and 3.5 g/L bovine serum albumin. The latter was an essential component of the reaction mixture, increasing the solubility of decylubiquinone and rotenone. In patients with previously diagnosed complex I deficiencies, the new assay detected the complex I deficiencies in both muscle and fibroblasts. CONCLUSIONS: This spectrophotometric assay is reproducible, sensitive, and specific for complex I activity because of its high rotenone sensitivity, and it can be applied successfully to the diagnosis of complex I deficiencies.

Validity and reproducibility of the Jamar dynamometer in children aged 4-11 years.

PURPOSE: Validity and reproducibility of the Jamar dynamometer were evaluated in children aged 4-11 years. METHOD: Hand grip strength was measured on the dominant side and non-dominant side in 67 patients who had been referred to our specialist centre in the past 3 years because of suspected myopathy. All the patients had had muscle biopsy. Sixteen out of the 67 patients proved to have myopathy, while 51 had no myopathy. The investigator was blinded against the true diagnosis and clinical course of the patients at the time of testing. Validity was assessed by the power to discriminate between patients with and without myopathy, using logistic regression analysis and receiver operating characteristic (ROC) analysis. The area under the ROC curve (AUC) was calculated as a measure of the discriminative power. Sensitivity (Se) and specificity (Sp) were assessed at a specifically chosen cut-off point. Reproducibility was assessed by evaluating the test-retest reliability in a stratified random sample of 40 patients who returned for remeasurements, using the intraclass correlation coefficient (ICC). RESULTS: AUCs ranged from 0.78 - 0.82. At an Se = 81% cut-off point, Sp varied from 67-73%. ICCs ranged from 0.91-0.93. CONCLUSIONS: The Jamar dynamometer had discriminative power in children with suspected myopathy. Reproducibility was high. The Jamar dynamometer was a good, but not completely accurate, test for myopathy.

A new motor performance test in a prospective study on children with suspected myopathy.

In the development of a new diagnostic motor performance test to spare more children from painful muscle biopsy, seven functional items were used to measure muscle strength and muscle endurance in a prospective study on new patients. Over a 2-year period, 22 patients (12 males, 10 females; mean age 8y 1mo [SD 2y 6mo], range 4-11y) were recruited for the study. They had all been referred with suspected myopathy. The motor performance test was administered before muscle biopsy. Validity of the seven items was assessed using logistic regression analysis and receiver operating characteristic (ROC) analysis. Two items were withdrawn from the test because they were not suitable for children aged 4 to 5 years. The five remaining items were: Heels, Circuit, Stairs, Jump, and Gowers. A full logistic regression model including these five items was fitted to the total population of 90 patients suspected of having myopathy (from this study and our previous study) to make the best prediction of whether myopathy was present. The ROC area under the curve of the diagnostic prediction model was 0.92 (95% confidence interval [CI] 0.87-0.98) and 0.89 (95% CI 0.87-0.92) after bootstrap correction. This indicated the high diagnostic power that can be expected for future, similar patients. This non-invasive and child-friendly motor performance test can improve diagnostic procedure and, therefore, spare more children from unnecessary muscle biopsy.

Measurement of the energy-generating capacity of human muscle mitochondria: diagnostic procedure and application to human pathology.

BACKGROUND: Diagnosis of mitochondrial disorders usually requires a muscle biopsy to examine mitochondrial function. We describe our diagnostic procedure and results for 29 patients with mitochondrial disorders. METHODS: Muscle biopsies were from 43 healthy individuals and 29 patients with defects in one of the oxidative phosphorylation (OXPHOS) complexes, the pyruvate dehydrogenase complex (PDHc), or the adenine nucleotide translocator (ANT). Homogenized muscle samples were used to determine the oxidation rates of radiolabeled pyruvate, malate, and succinate in the absence or presence of various acetyl Co-A donors and acceptors, as well as specific inhibitors of tricarboxylic acid cycle or OXPHOS enzymes. We determined the rate of ATP production from oxidation of pyruvate. RESULTS: Each defect in the energy-generating system produced a specific combination of substrate oxidation impairments. PDHc deficiencies decreased substrate oxidation reactions containing pyruvate. Defects in complexes I, III, and IV decreased oxidation of pyruvate plus malate, with normal to mildly diminished oxidation of pyruvate plus carnitine. In complex V defects, pyruvate oxidation improved by addition of carbonyl cyanide 3-chlorophenyl hydrazone, whereas other oxidation rates were decreased. In most patients, ATP production was decreased. CONCLUSION: The proposed method can be successfully applied to the diagnosis of defects in PDHc, OXPHOS complexes, and ANT.

Validity and reproducibility of hand-held dynamometry in children aged 4-11 years.

OBJECTIVE: To evaluate validity and reproducibility of hand-held dynamometry in 11 different muscle groups in children. DESIGN AND PATIENTS: Maximum isometric muscle strength was measured with a calibrated hand-held dynamometer in 61 patients aged 4-11 years who had been referred to our specialist centre in the past 3 years because of suspected myopathy. All the patients had had muscle biopsy. METHODS: Validity was assessed by the power to discriminate between patients with and without myopathy, using logistic regression analysis and receiver operating characteristic analysis and sensitivity and specificity at a specifically chosen cut-off point. Reproducibility was evaluated by test-retest reliability in a stratified random sample of 40 patients who returned for re-measurements, using the intraclass correlation coefficient and the standard error of measurement. RESULTS: In the patients, areas under the receiver operating characteristic curve ranged from 0.66 to 0.88. At a specifically chosen cut-off point, sensitivity varied from 73% to 87%, while specificity varied from 54% to 80%. Intraclass correlation coefficients ranged from 0.73 to 0.91. The standard error of measurement ranged from 3.3 N to 12.2 N. CONCLUSION: Performance of hand-held dynamometry varied widely in the 11 muscle groups. Highest performance was observed in the elbow flexors. Test-retest reliability of the mean value of 2 efforts was generally higher than the maximum value.

Validity and reproducibility of a new diagnostic motor performance test in children with suspected myopathy.

To spare more children from painful muscle biopsy, a new non-invasive diagnostic motor performance test is undergoing development. Fifteen functional items were used to measure muscle strength and muscle endurance in 68 patients (47 males, 21 females; mean age 7y 8mo, SD 2y 2mo; range 4 to 11y), who had been referred to our specialist centre in the past 3 years on suspicion of myopathy. All the patients had undergone muscle biopsy. To correct the patients' outcomes for age, sex, and body size, regression prediction equations were obtained from a stratified random sample of 64 normally developing primary-school children aged 4 to 11 years (32 males, 32 females; mean age 8y 1mo, SD 2y 4mo). Feasibility was evaluated on the basis of five criteria. Validity was assessed using logistic regression analysis, receiver operating characteristic analysis, and sensitivity and specificity at a specifically chosen cut-off point. Reproducibility was evaluated by test-retest reliability in a stratified random sample of 40 patients who returned for re-measurements using the intraclass correlation coefficient. Seven items satisfied all five feasibility criteria, had high diagnostic power, and high test-retest reliability. The motor performance test can improve diagnostic procedure in children suspected of having myopathy.

Ductus arteriosus with left-to-right shunt during venoarterial extracorporeal membrane oxygenation: effects on cerebral oxygenation and hemodynamics.

OBJECTIVE: To investigate the effect on cerebral oxygenation and hemodynamics of a patent ductus arteriosus with left-to-right shunt during venoarterial extracorporeal membrane oxygenation in a lamb model. DESIGN: Prospective intervention study in animals. SETTING: Animal research laboratory of a university medical center. SUBJECTS: Six anesthetized newborn lambs with patent ductus arteriosus and left-to-right shunt, installed on venoarterial extracorporeal membrane oxygenation. INTERVENTIONS: Six lambs of 140 days gestational age were prepared to keep the ductus arteriosus open by infiltration of the vessel wall with formaline 10%. The animals were installed on standard venoarterial extracorporeal membrane oxygenation. With a mechanical occluder, the ductus was closed. MEASUREMENTS AND MAIN RESULTS: Changes of mean arterial blood pressure and carotid artery blood flow were measured simultaneously. Using near infrared spectrophotometry, we calculated changes in cerebral concentration of oxyhemoglobin and deoxyhemoglobin (reflecting changes in cerebral oxygen supply) and total hemoglobin (reflecting changes in cerebral blood volume). Also, cerebral oxygen delivery before and after ductus closure was calculated. Before ductus closure there was a left-to-right shunt with a mean +/- SEM of 41 +/- 20% of total body blood flow. Closure of the ductus resulted in an immediate increase in mean arterial blood pressure and carotid artery blood flow. The concentration of oxyhemoglobin increased and the concentration of deoxyhemoglobin decreased, representing increased cerebral oxygen supply. The concentration of total hemoglobin was unchanged, representing unchanged cerebral blood volume. There was an increase in cerebral oxygen delivery. CONCLUSIONS: In this lamb model, a considerable left-to-right shunt over the ductus during venoarterial extracorporeal membrane oxygenation reduced cerebral circulation and oxygenation.

Congenital conductive hearing loss in dyschondrosteosis.

Conductive hearing loss was detected in a boy with a previous diagnosis of dyschondrosteosis. Dyschondrosteosis is a rare inherited condition characterized by mesomelic dwarfism and Madelung's deformity. The syndrome can be caused by mutations in the SHOX gene, and in that case, the pattern of inheritance is pseudoautosomal dominant. Indeed, SHOX mutation analysis in our patient revealed a deletion. The combination of dyschondrosteosis and conductive hearing loss has been reported in 2 previous cases. In our patient, exploratory tympanotomy revealed ankylosis of the stapes and a malformed incus. A substantial gain in hearing threshold was obtained by a stapedectomy in combination with a malleovestibulopexy.

Adenine nucleotide translocator 1 deficiency associated with Sengers syndrome.

Sengers syndrome is characterized by congenital cataracts, hypertrophic cardiomyopathy, mitochondrial myopathy, and lactic acidosis, but no abnormalities have been found with routine mitochondrial biochemical diagnostics (the determination of pyruvate oxidation rates and enzyme measurements). In immunoblot analysis, the protein content of the mitochondrial adenine nucleotide translocator 1 (ANT1) was found to be strongly reduced in the muscle tissues of two unrelated patients with Sengers syndrome. In addition, low residual adenine nucleotide translocator activity was detected upon the reconstitution of detergent-solubilized mitochondrial extracts from the patients' skeletal or heart muscle into liposomes. Sequence analysis and linkage analysis showed that ANT1 was not the primary genetic cause of Sengers syndrome. We propose that transcriptional, translational, or posttranslational events are responsible for the ANT1 deficiency associated with the syndrome.