Poroviscoelastic finite element model including continuous fiber distribution for the simulation of nanoindentation tests on articular cartilage.

Articular cartilage is a soft hydrated tissue that facilitates proper load transfer in diarthroidal joints. The mechanical properties of articular cartilage derive from its structural and hierarchical organization that, at the micrometric length scale, encompasses three main components: a network of insoluble collagen fibrils, negatively charged macromolecules and a porous extracellular matrix. In this work, a constituent-based constitutive model for the simulation of nanoindentation tests on articular cartilage is presented: it accounts for the multi-constituent, non-linear, porous, and viscous aspects of articular cartilage mechanics. In order to reproduce the articular cartilage response under different loading conditions, the model considers a continuous distribution of collagen fibril orientation, swelling, and depth-dependent mechanical properties. The model's parameters are obtained by fitting published experimental data for the time-dependent response in a stress relaxation unconfined compression test on adult bovine articular cartilage. Then, model validation is obtained by simulating three independent experimental tests: (i) the time-dependent response in a stress relaxation confined compression test, (ii) the drained response of a flat punch indentation test and (iii) the depth-dependence of effective Poisson's ratio in a unconfined compression test. Finally, the validated constitutive model has been used to simulate multiload spherical nanoindentation creep tests. Upon accounting for strain-dependent tissue permeability and intrinsic viscoelastic properties of the collagen network, the model accurately fits the drained and undrained curves and time-dependent creep response. The results show that depth-dependent tissue properties and glycosaminoglycan-induced tissue swelling should be accounted for when simulating indentation experiments.

GFAP mutations, age at onset, and clinical subtypes in Alexander disease.

OBJECTIVE: To characterize Alexander disease (AxD) phenotypes and determine correlations with age at onset (AAO) and genetic mutation. AxD is an astrogliopathy usually characterized on MRI by leukodystrophy and caused by glial fibrillary acidic protein (GFAP) mutations. METHODS: We present 30 new cases of AxD and reviewed 185 previously reported cases. We conducted Wilcoxon rank sum tests to identify variables scaling with AAO, survival analysis to identify predictors of mortality, and χ(2) tests to assess the effects of common GFAP mutations. Finally, we performed latent class analysis (LCA) to statistically define AxD subtypes. RESULTS: LCA identified 2 classes of AxD. Type I is characterized by early onset, seizures, macrocephaly, motor delay, encephalopathy, failure to thrive, paroxysmal deterioration, and typical MRI features. Type II is characterized by later onset, autonomic dysfunction, ocular movement abnormalities, bulbar symptoms, and atypical MRI features. Survival analysis predicted a nearly 2-fold increase in mortality among patients with type I AxD relative to those with type II. R79 and R239 GFAP mutations were most common (16.6% and 20.3% of all cases, respectively). These common mutations predicted distinct clinical outcomes, with R239 predicting the most aggressive course. CONCLUSIONS: AAO and the GFAP mutation site are important clinical predictors in AxD, with clear correlations to defined patterns of phenotypic expression. We propose revised AxD subtypes, type I and type II, based on analysis of statistically defined patient groups.

Mutational analysis of the RPGRIP1L gene in patients with Joubert syndrome and nephronophthisis.

Joubert syndrome (JS) is an autosomal recessive disorder, consisting of mental retardation, cerebellar vermis aplasia, an irregular breathing pattern, and retinal degeneration. Nephronophthisis (NPHP) is found in 17-27% of these patients, which was designated JS type B. Mutations in four separate genes (AHI1, NPHP1, CEP290/NPHP6, and MKS3) are linked to JS. However, missense mutations in a new ciliary gene (RPGRIP1L) were found in type B patients. We analyzed a cohort of 56 patients with JS type B who were negative for mutations in three (AHI1, NPHP1, and CEP290/NPHP6) of the four genes previously linked to the syndrome. The 26 exons encoding RPGRIP1L were analyzed by means of PCR amplification, CEL I endonuclease digestion, and subsequent sequencing. Using this approach, four different mutations in the RPGRIP1L gene in five different families were identified and three were found to be novel mutations. Additionally, we verified that missense mutations are responsible for JS type B and cluster in exon 15 of the RPGRIP1L gene. Our studies confirm that a T615P mutation represents the most common mutation in the RPGRIP1L gene causing disease in about 8-10% of JS type B patients negative for NPHP1, NPHP6, or AHI1 mutations.

Recessive missense mutations in LAMB2 expand the clinical spectrum of LAMB2-associated disorders.

Congenital nephrotic syndrome is clinically and genetically heterogeneous. The majority of cases can be attributed to mutations in the genes NPHS1, NPHS2, and WT1. By homozygosity mapping in a consanguineous family with isolated congenital nephrotic syndrome, we identified a potential candidate region on chromosome 3p. The LAMB2 gene, which was recently reported as mutated in Pierson syndrome (microcoria-congenital nephrosis syndrome; OMIM #609049), was located in the linkage interval. Sequencing of all coding exons of LAMB2 revealed a novel homozygous missense mutation (R246Q) in both affected children. A different mutation at this codon (R246W), which is highly conserved through evolution, has recently been reported as causing Pierson syndrome. Subsequent LAMB2 mutational screening in six additional families with congenital nephrotic syndrome revealed compound heterozygosity for two novel missense mutations in one family with additional nonspecific ocular anomalies. These findings demonstrate that the spectrum of LAMB2-associated disorders is broader than previously anticipated and includes congenital nephrotic syndrome without eye anomalies or with minor ocular changes different from those observed in Pierson syndrome. This phenotypic variability likely reflects specific genotypes. We conclude that mutational analysis in LAMB2 should be considered in congenital nephrotic syndrome, if no mutations are found in NPHS1, NPHS2, or WT1.

Patterns of memory performance in children with controlled epilepsy on the CVLT-C.

Decreased memory skills have been reported in children with epilepsy. However, standardized instruments to evaluate learning and memory in children have been unavailable until recently. The present study was designed to assess memory patterns in children with epilepsy based on the California Verbal Learning Test-Children's Version (CVLT-C). The test was administered to 44 children with complex partial seizures and 21 children with generalized seizures between 8 and 13 years of age. Children in the study had been treated for epilepsy for at least 6 months, had well-controlled seizures on monotherapy, and had no evidence of anticonvulsant toxicity. Children with head injuries, learning disabilities, or hyperactivity were excluded. Test results did not reflect differences in memory performance based on seizure type. Scores for the entire sample indicated intact new learning, decreased intrusions and perseverative responses, and better short-term than long-term delayed recall. Recognition skills were stronger than long-term delayed recall skills and suggested that memory performance may be improved for these children when a multiple-choice format is available in academic settings.

Altered sleeping arrangements in pediatric patients with epilepsy.

Parental fears concerning seizure occurrence may be associated with behavioral changes within the home environment. One possible change involves sleeping arrangements. Questionnaires concerning demographics, medical history, and sleeping arrangements were completed by parents of 179 children with epilepsy and by parents of 155 children with diabetes for comparison purposes. Based on parental response, 40 (22%) children with epilepsy changed to less independent sleeping arrangements. Logistic regression suggested that parental concern over seizure occurrence was highly associated with this change (p=<0.001). In contrast, 13 (8%) of the children with diabetes changed to a less independent sleep pattern. Results suggest changes in sleeping arrangements may alert the pediatrician to possible parental anxiety that may need to be addressed.

Acute mental status changes and hyperchloremic metabolic acidosis with long-term topiramate therapy.

Mental status changes and metabolic acidosis may occur with topiramate therapy. These adverse events were reported during dosage titration and with high dosages of the drug. A 20-year-old man receiving topiramate, valproic acid, and phenytoin experienced acute-onset mental status changes with hyperchloremic metabolic acidosis. He had been receiving a modest dose of topiramate for 9 months. He was weaned off topiramate over 5 days, and his mental status returned to baseline within 48 hours of discontinuing the agent. This case illustrates the need for close evaluation of patients who experience acute-onset mental status changes during topiramate therapy.

Acute management of hypersensitivity reactions and seizures.

The most crucial step in the management of an antiepileptic drug (AED) hypersensitivity reaction is the recognition of the clinical syndrome and cessation of the presumed offending agent. The severity of the developing reaction will shape the course of treatment because multiple organ systems may become affected. Management of conjunctival involvement and treatment of skin lesions dominate care, with patients whose skin lesions are extensive benefitting from treatment in a structured burn unit. Neutropenia and sepsis are common and potentially fatal complicating factors. The use of steroids remains controversial, as is the utility of immune modulation with other agents such as cyclophosphamide and i.v. immunoglobulin. Acute treatment of seizures should be addressed with i.v. benzodiazepines, given either intermittently or by continuous infusion. Choice of long-term maintenance AEDs should take into consideration the crossreactivity among AEDs that share an arene oxide metabolite.

Cognition and behavior after temporal lobectomy in pediatric patients with intractable epilepsy.

The increased use of surgical intervention for intractable epilepsy during childhood has resulted in a critical need for information concerning possible cognitive and behavioral changes in pediatric patients after surgery. In this pilot study, comprehensive neuropsychologic evaluations were completed on nine children who had a temporal lobectomy for intractable epilepsy before 16 years of age. Performances before and after surgery were compared using cognitive and behavioral measures. Repeated measures analysis of variance did not indicate differences in performance on the basis of laterality of surgery, although the number of left (n = 5) vs right (n = 4) temporal resections was small. Paired comparison t tests, which included all patients, did not suggest marked changes in cognitive functioning after surgery, although decreases in delayed verbal memory were evident. Positive effects on quality of life during the first year after surgical intervention were suggested by reduced internalizing symptoms and increased social interaction. Replication of this study is recommended with a larger number of patients and multicenter collaboration.

Does short-term antiepileptic drug treatment in children result in cognitive or behavioral changes?

PURPOSE: To determine possible cognitive and behavioral effects of antiepileptic drug (AED) therapy by assessing children with newly diagnosed epilepsy before and after initiation of treatment. A comparison group of children with diabetes mellitus (DM) was included to control for the effects of practice, maturation, and chronic illness. METHODS: Baseline neuropsychological assessments were completed for children with epilepsy (n = 37) and children with DM (n = 26) recruited through outpatient clinics at a regional children's hospital. Children were reevaluated 6 months from baseline testing. At follow-up, children with epilepsy had therapeutic AED levels and controlled seizures. Statistical analysis included a between-group repeated measures ANCOVA with pretest scores serving as the covariate. RESULTS: Significant differences between groups were not found for any cognitive or behavioral factors, including attention (p < 0.24), immediate memory (p < 0.24), delayed memory (p < 0.10), complex motor speed (p < 0.19), or behavior problems (p < 0.89). CONCLUSIONS: Changes in performance on cognitive and behavioral measures were not different for children treated with AEDs and controls. Although adverse effects may be associated with prolonged treatment, results would not suggest adverse effects from AED monotherapy during the first 6 months of therapy.

Neuropsychological patterns in pediatric epilepsy.

Results from comprehensive neuropsychological assessments of children diagnosed with epilepsy have rarely been reported. Previous research has generally focused on the measurement of overall intellectual ability and achievement skills. In the present study, neuropsychological evaluations including memory, attention, language, achievement, fine motor, executive function, visual motor integration, and behavior were completed on children (n = 79) diagnosed with epilepsy. Neurocognitive skills were within expectations for measured intelligence with the exception of verbal and visual attention skills, which were significantly below expectations based on measured ability. Behaviorally, children were rated by their parents as demonstrating clinically elevated attentional problems. Differences in cognitive and behavioral function were not found according to seizure type. Findings suggested a more diffuse effect of childhood epilepsy reflected in a pattern of decreased attention skills.

Surgical outcome in patients with epilepsy with occult vascular malformations treated with lesionectomy.

PURPOSE: This retrospective study reports the long-term surgical outcome of patients with medically refractory epilepsy and vascular malformations who were treated with lesionectomy. A detailed analysis of surgical failures had been performed in an attempt to define predictors of surgical success and failure. METHODS: Fifteen patients with medically intractable epilepsy and angiographically occult vascular malformations (AOVMs) were treated surgically with lesionectomy at Duke University Medical Center. Lesionectomy consisted of removal of the AOVM and surrounding hemosiderin-stained brain only, without the use of electrocorticography (ECoG) to guide resection. RESULTS: Eleven (73%) patients are seizure free after lesionectomy. Three showed no significant improvement, and one patient died, presumably after a seizure. Age of onset, duration of seizures, age at resection, and gender did not affect outcome. All patients with neocortical AOVMs in whom EEG findings correlated with the site of the lesion were seizure free after lesional resection. Treatment failures were associated with the presence of multiple intracranial lesions, poorly localized or diffuse EEG findings, discordant positron emission tomography (PET) imaging, or with a lesion in close proximity to the limbic system. CONCLUSIONS: Lesionectomy, with removal of surrounding hemosiderin-stained brain, can be considered the procedure of choice in carefully selected patients with epilepsy with occult vascular malformations.

Surgical correction of obstructive sleep apnea in the complicated pediatric patient documented by polysomnography.

OBJECTIVE: Evaluate the effectiveness of surgical treatment of obstructive sleep apnea in a diverse population of children. DESIGN: A retrospective case series of pre and post operative polysomnograms (PSG) of pediatric patients with obstructive sleep apnea (OSA). SETTING: Tertiary care children's hospital. PATIENTS: 48 patients in whom sleep studies were performed pre-operatively for either an unclear history and/or physical findings or complicated OSA. Thirteen patients had no complicating medical factors, 35 patients had various associated medical problems, including 20 with morbid obesity, five with Down syndrome, four with asthma, two with cerebral palsy, and four other. The average age was 7.5 years with a range of 1.5-20 years. INTERVENTIONS: Thirty-one patients had a tonsillectomy and adenoidectomy (T and A) only, 13 had T and A with uvulopalatopharyngoplasty (UPPP), and three had tonsillectomy and UPPP. MAIN OUTCOME MEASURES: Pre and postoperative PSG results including apnea/hypopnea index (AHI), percent of sleep with oxygen saturation below 90%, and percent sleep time with end-tidal pCO2 > 50. RESULTS: The mean pre-operative (AHI) was 27 +/- 4 (mean +/- S.E.M.) and post operatively was 6 +/- 1 (P < 0.001). Twenty six of 48 (54%) had a postoperative AHI of less than five. Pre-operative percent of sleep with oxygen saturation below 90% was 17.9 +/- 4.5%, post-operatively it was 1.4 +/- 0.1% (P < 0.001). Pre-operative percent sleep time with end-tidal pCO2 > 50 was 22.3 +/- 3.4%, post operatively it was 12.6 +/- 2.9% (P < 0.01). UPPP was performed more commonly in patients with Down syndrome. There was a trend toward more improvement in patients who had T and performed than those undergoing UPPP (post op AHI of 4.7 vs. 7.4 respectively). CONCLUSIONS: Tonsillectomy, adenoidectomy and UPPP are effective in the treatment of OSA in a diverse group of pediatric patients. Patients with asthma, cerebral palsy, Down syndrome, morbid obesity, and hereditary syndromes all improved significantly with surgical management.

Bromism: intoxication from a rare anticonvulsant therapy.

Bromide, the first effective therapy for epilepsy, is not commonly prescribed today but has been advocated by some pediatric neurologists for the treatment of intractable seizures in children. We report a 17-year-old female patient with intractable epilepsy who insidiously developed bromism while on treatment with triple bromide elixir. We review the clinical presentation, diagnosis, pathophysiology, and management of bromism.

Dextromethorphan in nonketotic hyperglycinaemia: metabolic variation confounds the dose-response relationship.

Nonketotic hyperglycinaemia (NKH) is an inborn error of the glycine cleavage system resulting in seizures and mental retardation. Two prior reports noted an anticonvulsant effect from high-dose dextromethorphan (DM) in this disorder, although the two reported patients demonstrated widely disparate DM requirements and drug levels. We report two children with NKH who also demonstrated disparate and variable DM metabolism which markedly influenced the dose-concentration-response relationship. Levels of DM and its primary metabolite dextrorphan (DX) were utilized to guide DM therapy and exhibited patterns reflective of the extensive and poor metabolizer phenotypes for CYP2D6, the cytochrome P450 isoform responsible for DM metabolism. In the patient who appeared to represent the extensive metabolizer (EM) phenotype, treatment with the non-specific cytochrome P450 inhibitor cimetidine was required to reduce biotransformation of DM to DX and, thus, to increase DM plasma concentrations. In the patient with the apparent poor metabolizer (PM) phenotype, a change in the DM preparation to a sustained-release form and increase in the dosing interval was required to lower DM plasma concentrations. These cases demonstrate the importance of CYP2D6 phenotype in providing safe and effective DM therapy to patients with NKH.

Broad A band disease: a new benign congenital myopathy.

We report a second child with broad A band disease. This child differs from the first in having normal vision and no electrophysiological evidence of a congenital retinal dystrophy. Neurological abnormalities at presentation included diffuse hypotonia, developmental delay, and delayed speech development. Histological and preliminary histochemical evaluation of biopsied thigh muscle showed no abnormality. However, 1-micrometer-thick plastic sections and electron microscopy showed numerous foci of broadened A bands accompanied by loss of distinct I bands. The Z lines in these areas were normal except for a fine waviness. Ultrastructurally, the thick filaments in these lesions appeared misaligned. Immunohistochemical reactions for desmin, vimentin, connectin (titin), and 2B myosin showed normal reactivity. An immunohistochemical reaction for fetal myosin showed sparse reacting fibers, which were unremarkable on adjacent sections stained with hematoxylin and eosin. These findings differ from those of other previously described congenital myopathies. Both of our patients have shown good strength and motor development by 5 years of age, suggesting that this ultrastructural abnormality is essentially benign.

Behavioral descriptors that differentiate between seizure and nonseizure events in a pediatric population.

The diagnosis and treatment of epilepsy relies heavily on descriptions of behavioral changes noted during seizure episodes. A pilot study was completed to determine the frequency of occurrence of behaviors commonly associated with seizures in a pediatric population (n = 153). Caretakers of the children (ages = 4 months to 19 years) were asked to respond to a checklist containing 40 behavioral descriptors. Thirteen descriptors were found to differentiate between seizure and nonseizure events. Twelve of these behaviors were endorsed significantly more frequently by caretakers of children with seizures including the following: does not remember what happened, moves mouth funny, drools, jerking/twitching, becomes stiff, changes in breathing, stares off, bites or chews tongue, eyes look glassy, will not respond, mumbles or slurs words, and eyes or head turn to one side. One behavior, fidgets in seat, was significantly more associated with nonseizure episodes. The behavioral descriptors may be presented in a checklist format or incorporated within a clinical interview in primary care settings for initial screening of children with possible seizure disorders.

Mitochondrial encephalomyopathies presenting with features of autonomic and visceral dysfunction.

Three children are reported with mitochondrial encephalomyopathy who presented with autonomic dysfunction. Autonomic dysfunction included gastrointestinal dysmotility, apnea, cardiac arrhythmias, decreased lacrimation, supersensitivity to metacholine, altered sweating, and postural hypotension. These patients illustrate that in some mitochondrial encephalomyopathies autonomic features may be prominent and can mimic the clinical features associated with hereditary sensory and autonomic neuropathies.