Somatosensory evoked potential monitoring of peripheral nerves during external fixation for limb lengthening and correction of deformity in children

We undertook a retrospective analysis of 306 procedures on 233 patients, with a mean age of 12 years (1 to 21), in order to evaluate the use of somatosensory evoked potential (SSEP) monitoring for the early detection of nerve compromise during external fixation procedures for limb lengthening and correction of deformity. Significant SSEP changes were identified during 58 procedures (19%). In 32 instances (10.5%) the changes were transient, and resolved once the surgical cause had been removed. The remaining 26 (8.5%) were analysed in two groups, depending on whether or not corrective action had been performed in response to critical changes in the SSEP recordings. In 16 cases in which no corrective action was taken, 13 (81.2%, 4.2% overall) developed a post-operative neurological deficit, six of which were permanent and seven temporary, persisting for five to 18 months. In the ten procedures in which corrective action was taken, four patients (40%, 1.3% overall) had a temporary (one to eight months) post-operative neuropathy and six had no deficit. After appropriate intervention in response to SSEP changes, the incidence and severity of neurological deficits were significantly reduced, with no cases of permanent neuropathy. SSEP monitoring showed 100% sensitivity and 91% specificity for the detection of nerve injury during external fixation. It is an excellent diagnostic technique for identifying nerve lesions when they are still highly reversible.

TGIF Mutations in Human Holoprosencephaly: Correlation between Genotype and Phenotype

Holoprosencephaly (HPE), which results from failed or incomplete midline forebrain division early in gestation, is the most common forebrain malformation. The etiology of HPE is complex and multifactorial. To date, at least 12 HPE-associated genes have been identified, including TGIF (transforming growth factor beta-induced factor), located on chromosome 18p11.3. TGIF encodes a transcriptional repressor of retinoid responses involved in TGF-β signaling regulation, including Nodal signaling. TGIF mutations are reported in approximately 1-2% of patients with non-syndromic, non-chromosomal HPE. We combined data from our comprehensive studies of HPE with a literature search for all individuals with HPE and evidence of mutations affecting TGIF in order to establish the genotypic and phenotypic range. We describe 2 groups of patients: 34 with intragenic mutations and 21 with deletions of TGIF. These individuals, which were ascertained from our research group, in collaboration with other centers, and through a literature search, include 38 probands and 17 mutation-positive relatives. The majority of intragenic mutations occur in the TGIF homeodomain. Patients with mutations affecting TGIFrecapitulate the entire phenotypic spectrum observed in non-chromosomal, non-syndromic HPE. We identified a statistically significant difference between the 2 groups with respect to inheritance, as TGIF deletions were more likely to be de novo in comparison to TGIF mutations (χ(2) ((2)) = 6.97, p(permutated) = 0.0356). In addition, patients with TGIF deletions were also found to more commonly present with manifestations beyond the craniofacial and neuroanatomical features associated with HPE (p = 0.0030). These findings highlight differences in patients with intragenic mutations versus deletions affecting TGIF, and draw attention to the homeodomain region, which appears to be particularly relevant to HPE. These results may be useful for genetic counseling of affected patients.

Peripheral nerve repair through multi-luminal biosynthetic implants

Peripheral nerve damage is routinely repaired by autogenic nerve grafting, often leading to less than optimal functional recovery at the expense of healthy donor nerves. Alternative repair strategies use tubular scaffolds to guide the regeneration of damaged nerves, but despite the progress made on improved structural materials for the nerve tubes, functional recovery remains incomplete. We developed a biosynthetic nerve implant (BNI) consisting of a hydrogel-based transparent multichannel scaffold with luminar collagen matrix as a 3-D substrate for nerve repair. Using a rat sciatic nerve injury model we showed axonal regeneration through the BNI to be histologically comparable to the autologous nerve repair. At 10 weeks post-injury, nerve defects repaired with collagen-filled, single lumen tubes formed single nerve cables, while animals that received the multi-luminal BNIs showed multiple nerve cables and the formation of a perineurial-like layer within the available microchannels. Total numbers of myelinated and unmyelinated axons in the BNI were increased 3-fold and 30%, respectively, compared to collagen tubes. The recovery of reflexive movement confirmed the functional regeneration of both motor and sensory neurons. This study supports the use of multi-luminal BNIs as a viable alternative to autografts in the repair of nerve gap injuries.

Fear of losing money? Aversive conditioning with secondary reinforcers

Money is a secondary reinforcer that acquires its value through social communication and interaction. In everyday human behavior and laboratory studies, money has been shown to influence appetitive or reward learning. It is unclear, however, if money has a similar impact on aversive learning. The goal of this study was to investigate the efficacy of money in aversive learning, comparing it with primary reinforcers that are traditionally used in fear conditioning paradigms. A series of experiments were conducted in which participants initially played a gambling game that led to a monetary gain. They were then presented with an aversive conditioning paradigm, with either shock (primary reinforcer) or loss of money (secondary reinforcer) as the unconditioned stimulus. Skin conductance responses and subjective ratings indicated that potential monetary loss modulated the conditioned response. Depending on the presentation context, the secondary reinforcer was as effective as the primary reinforcer during aversive conditioning. These results suggest that stimuli that acquire reinforcing properties through social communication and interaction, such as money, can effectively influence aversive learning.

Practice parameter: pharmacologic treatment of spasticity in children and adolescents with cerebral palsy (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology and the Practice Committee of the Child Neurology Society

OBJECTIVE

To evaluate published evidence of efficacy and safety of pharmacologic treatments for childhood spasticity due to cerebral palsy.

METHODS

A multidisciplinary panel systematically reviewed relevant literature from 1966 to July 2008.

RESULTS

For localized/segmental spasticity, botulinum toxin type A is established as an effective treatment to reduce spasticity in the upper and lower extremities. There is conflicting evidence regarding functional improvement. Botulinum toxin type A was found to be generally safe in children with cerebral palsy; however, the Food and Drug Administration is presently investigating isolated cases of generalized weakness resulting in poor outcomes. No studies that met criteria are available on the use of phenol, alcohol, or botulinum toxin type B injections. For generalized spasticity, diazepam is probably effective in reducing spasticity, but there are insufficient data on its effect on motor function and its side-effect profile. Tizanidine is possibly effective, but there are insufficient data on its effect on function and its side-effect profile. There were insufficient data on the use of dantrolene, oral baclofen, and intrathecal baclofen, and toxicity was frequently reported.

RECOMMENDATIONS

For localized/segmental spasticity that warrants treatment, botulinum toxin type A should be offered as an effective and generally safe treatment (Level A). There are insufficient data to support or refute the use of phenol, alcohol, or botulinum toxin type B (Level U). For generalized spasticity that warrants treatment, diazepam should be considered for short-term treatment, with caution regarding toxicity (Level B), and tizanidine may be considered (Level C). There are insufficient data to support or refute use of dantrolene, oral baclofen, or continuous intrathecal baclofen (Level U).

Clinical spectrum of SIX3-associated mutations in holoprosencephaly: correlation between genotype, phenotype and function

BACKGROUND

Holoprosencephaly (HPE) is the most common structural malformation of the human forebrain. There are several important HPE mutational target genes, including the transcription factor SIX3, which encodes an early regulator of Shh, Wnt, Bmp and Nodal signalling expressed in the developing forebrain and eyes of all vertebrates.

OBJECTIVE

To characterise genetic and clinical findings in patients with SIX3 mutations.

METHODS

Patients with HPE and their family members were tested for mutations in HPE-associated genes and the genetic and clinical findings, including those for additional cases found in the literature, were analysed. The results were correlated with a mutation-specific functional assay in zebrafish.

RESULTS

In a cohort of patients (n = 800) with HPE, SIX3 mutations were found in 4.7% of probands and additional cases were found through testing of relatives. In total, 138 cases of HPE were identified, 59 of whom had not previously been clinically presented. Mutations in SIX3 result in more severe HPE than in other cases of non-chromosomal, non-syndromic HPE. An over-representation of severe HPE was found in patients whose mutations confer greater loss of function, as measured by the functional zebrafish assay. The gender ratio in this combined set of patients was 1.5:1 (F:M) and maternal inheritance was almost twice as common as paternal. About 14% of SIX3 mutations in probands occur de novo. There is a wide intrafamilial clinical range of features and classical penetrance is estimated to be at least 62%.

CONCLUSIONS

Our data suggest that SIX3 mutations result in relatively severe HPE and that there is a genotype-phenotype correlation, as shown by functional studies using animal models.

Computational and FTIR spectroscopic studies on carbon monoxide and dinitrogen adsorption on a high-silica H-FER zeolite

Adsorption (at a low temperature) of carbon monoxide and dinitrogen on a high-silica ferrierite-type zeolite (H-FER, Si : Al = 27.5 : 1) was investigated by means of variable temperature infrared spectroscopy and theoretical calculations at the periodic DFT level. This combined experimental and computational approach led to detailed characterization of several types of hydrogen-bonded OHCO and OHN(2) complexes, formed by interaction between the adsorbed molecules and the Brønsted acid OH groups of the zeolite. CO or N(2), forming linear complexes with OH groups pointing towards a sufficiently ample void space, show the largest adsorption enthalpy which was found to be in the (approximate) range of -25 to -29 kJ mol(-1) for CO and -15 to -19 kJ mol(-1) for N(2). Less stable OHCO or OHN(2) complexes can be formed when either the Brønsted acid OH group is involved in intra-zeolite hydrogen bonding or when the free space available is too small to allow formation of linear complexes without previous re-location of the proton of the OH group involved. The details of experimental IR spectra in the O-H, C-O, and N-N stretching regions could be interpreted on the basis of good agreement between experimental and calculated results.

Extending animal models of fear conditioning to humans

A goal of fear and anxiety research is to understand how to treat the potentially devastating effects of anxiety disorders in humans. Much of this research utilizes classical fear conditioning, a simple paradigm that has been extensively investigated in animals, helping outline a brain circuitry thought to be responsible for the acquisition, expression and extinction of fear. The findings from non-human animal research have more recently been substantiated and extended in humans, using neuropsychological and neuroimaging methodologies. Research across species concur that the neural correlates of fear conditioning include involvement of the amygdala during all stages of fear learning, and prefrontal areas during the extinction phase. This manuscript reviews how animal models of fear are translated to human behavior, and how some fears are more easily acquired in humans (i.e., social-cultural). Finally, using the knowledge provided by a rich animal literature, we attempt to extend these findings to human models targeted to helping facilitate extinction or abolishment of fears, a trademark of anxiety disorders, by discussing efficacy in modulating the brain circuitry involved in fear conditioning via pharmacological treatments or emotion regulation cognitive strategies.

Perceptions of moral character modulate the neural systems of reward during the trust game

Studies of reward learning have implicated the striatum as part of a neural circuit that guides and adjusts future behavior on the basis of reward feedback. Here we investigate whether prior social and moral information about potential trading partners affects this neural circuitry. Participants made risky choices about whether to trust hypothetical trading partners after having read vivid descriptions of life events indicating praiseworthy, neutral or suspect moral character. Despite equivalent reinforcement rates for all partners, participants were persistently more likely to make risky choices with the 'good' partner. As expected from previous studies, activation of the caudate nucleus differentiated between positive and negative feedback, but only for the 'neutral' partner. Notably, it did not do so for the 'good' partner and did so only weakly for the 'bad' partner, suggesting that prior social and moral perceptions can diminish reliance on feedback mechanisms in the neural circuitry of trial-and-error reward learning.

An fMRI study of reward-related probability learning

The human striatum has been implicated in processing reward-related information. More recently, activity in the striatum, particularly the caudate nucleus, has been observed when a contingency between behavior and reward exists, suggesting a role for the caudate in reinforcement-based learning. Using a gambling paradigm, in which affective feedback (reward and punishment) followed simple, random guesses on a trial by trial basis, we sought to investigate the role of the caudate nucleus as reward-related learning progressed. Participants were instructed to make a guess regarding the value of a presented card (if the value of the card was higher or lower than 5). They were told that five different cues would be presented prior to making a guess, and that each cue indicated the probability that the card would be high or low. The goal was to learn the contingencies and maximize the reward attained. Accuracy, as measured by participant's choices, improved throughout the experiment for cues that strongly predicted reward, while no change was observed for unpredictable cues. Event-related fMRI revealed that activity in the caudate nucleus was more robust during the early phases of learning, irrespective of contingencies, suggesting involvement of this region during the initial stages of trial and error learning. Further, the reward feedback signal in the caudate nucleus for well-learned cues decreased as learning progressed, suggesting an evolving adaptation of reward feedback expectancy as a behavior-outcome contingency becomes more predictable.

Motivation-dependent responses in the human caudate nucleus

Motivation is a complex process that leads to completion or avoidance of a behavior. Past research strongly implicates the basal ganglia in a circuit integral for the control of motivation. Specifically, the human striatum has been shown to process reward information, differentiating between monetary rewards and punishments in recent neuroimaging experiments. It is unclear, however, how the dorsal striatum, particularly the caudate nucleus, responds to changes in the motivational context of a task. Using an event-related design, where participants were given positive and negative feedback upon guessing the value of an unknown card, we manipulated the motivational context of the task by dividing trials into periods of high incentive (where visual feedback indicated monetary rewards and punishments) and low incentive (where visual feedback indicated only accuracy). We found that activity in the caudate nucleus was strongly influenced by the different incentive periods. The hemodynamic response was characterized by a larger rise at the onset of trials and larger differences between positive and negative feedback during periods of high incentive. These results suggest that changes in motivation are capable of modulating basal ganglia activity, and further support an important role for the caudate nucleus in affective processing.

Dorsal striatum responses to reward and punishment: effects of valence and magnitude manipulations

The goal of this research was to further our understanding of how the striatum responds to the delivery of affective feedback. Previously, we had found that the striatum showed a pattern of sustained activation after presentation of a monetary reward, in contrast to a decrease in the hemodynamic response after a punishment. In this study, we tested whether the activity of the striatum could be modulated by parametric variations in the amount of financial reward or punishment. We used an event-related fMRI design in which participants received large or small monetary rewards or punishments after performance in a gambling task. A parametric ordering of conditions was observed in the dorsal striatum according to both magnitude and valence. In addition, an early response to the presentation of feedback was observed and replicated in a second experiment with increased temporal resolution. This study further implicates the dorsal striatum as an integral component of a reward circuitry responsible for the control of motivated behavior, serving to code for such feedback properties as valence and magnitude.

Middle interhemispheric variant of holoprosencephaly: a distinct cliniconeuroradiologic subtype

BACKGROUND

The middle interhemispheric variant (MIH) is a subtype of holoprosencephaly (HPE) in which the posterior frontal and parietal areas lack midline separation, whereas more polar areas of the cerebrum are fully cleaved. While the neuroradiologic features of this subtype have been recently detailed, the clinical features are largely unknown.

OBJECTIVE

To present the clinical manifestations of MIH and to compare them with classic subtypes (alobar, semilobar, and lobar) of HPE.

METHODS

The authors evaluated 15 patients with MIH in a multicenter study. Neuroimaging and clinical data were collected and correlated. They compared the data with those of 68 patients who had classic HPE.

RESULTS

The frequency of endocrinopathy in MIH (0%) was lower compared with the classic subtypes (72%) (p < 0.0001). This correlated with the lack of hypothalamic abnormalities. The percentage of patients with seizures (40%) did not significantly differ from classic HPE. Spasticity was the most common motor abnormality, seen in 86% of MIH patients, similar to other subtypes. The frequency of choreoathetosis in MIH (0%) was lower than that for semilobar HPE (41%) (p < 0.0039). This correlated with the lack of caudate and lentiform nuclei abnormalities. Developmental functions, including mobility, upper-extremity function, and language, of the MIH group were similar to the least severe classic type, lobar HPE.

CONCLUSION

MIH is a recognizable variant of HPE with differing clinical prognosis. Similar to the lobar subtype by functional measures, MIH differs from classic HPE by the absence of endocrine dysfunction and choreoathetosis.

Neuroanatomy of holoprosencephaly as predictor of function: beyond the face predicting the brain

BACKGROUND

Despite advances in neuroimaging and molecular genetics of holoprosencephaly (HPE), the clinical spectrum of HPE has remained inadequately described.

OBJECTIVE

To better characterize the clinical features of HPE and identify specific neuroanatomic abnormalities that may be useful predictors of neurodevelopmental function.

METHODS

The authors evaluated 68 children with HPE in a multicenter, prospective study. Neuroimaging studies were assessed for the grade of HPE (lobar, semilobar, and alobar), the degree of nonseparation of the deep gray nuclei, and presence of dorsal cyst or cortical malformation.

RESULTS

In general, the severity of clinical problems and neurologic dysfunctions correlated with the degree of hemispheric nonseparation (grade of HPE). Nearly three-quarters of the patients had endocrinopathies, with all having at least diabetes insipidus. The severity of endocrine abnormalities correlated with the degree of hypothalamic nonseparation (p = 0.029). Seizures occurred in approximately half of the children with HPE. The presence of cortical malformations was associated with difficult-to-control seizures. The presence and degree of dystonia correlated with the degree of nonseparation of the caudate and lentiform nuclei and the grade of HPE (p < 0.05). Hypotonia correlated with the grade of HPE (p < 0.05). Mobility, upper extremity function, and language correlated with the degree of nonseparation of the caudate, lentiform and thalamic nuclei, and grade of HPE (p < 0.01).

CONCLUSIONS

Patients with HPE manifest a wide spectrum of clinical problems and neurologic dysfunction. The nature and severity of many of these problems can be predicted by specific neuroanatomic abnormalities found in HPE.

Use of botulinum toxin type A in pediatric patients with cerebral palsy: a three-center retrospective chart review

Over the last several years, botulinum toxin type A has gained widespread use for the management of focal spasticity in children with cerebral palsy. To assess the current patterns of botulinum toxin type A use in the clinical setting, the dose, muscles injected, age at injection, and interval between injections of botulinum toxin type A treatments were examined in a retrospective chart review of children with cerebral palsy (N = 270) over a 2-year period at three major treatment centers. The average dose of botulinum toxin type A across the three centers ranged from 7.7 to 10.8 U/kg body weight, and the average total amount of botulinum toxin type A injected at a single visit ranged from 154 to 205 U. The majority of botulinum toxin type A injections were to the muscles to the lower limbs. The average age at first injection was 6.2 years, and the average interval between injections ranged from 134 to 199 days.

Tracking the hemodynamic responses to reward and punishment in the striatum

Research suggests that the basal ganglia complex is a major component of the neural circuitry that mediates reward-related processing. However, human studies have not yet characterized the response of the basal ganglia to an isolated reward, as has been done in animals. We developed an event-related functional magnetic resonance imaging paradigm to identify brain areas that are activated after presentation of a reward. Subjects guessed whether the value of a card was higher or lower than the number 5, with monetary rewards as an incentive for correct guesses. They received reward, punishment, or neutral feedback on different trials. Regions in the dorsal and ventral striatum were activated by the paradigm, showing differential responses to reward and punishment. Activation was sustained following a reward feedback, but decreased below baseline following a punishment feedback.

Abnormal sudomotor function in the hypomelanotic macules of tuberous sclerosis complex

To investigate the integrity of sympathetic innervation in the hypomelanotic macules of tuberous sclerosis complex, we studied sudomotor function in nine patients with tuberous sclerosis complex. Postganglionic sudomotor function was assessed using the Silastic imprint test in nine patients with tuberous sclerosis complex who have at least one hypomelanotic macule greater than 2 cm in diameter. Sweating was induced by iontophoresis with 0.5% pilocarpine nitrate and sweat droplets were counted under a microscope using a 1 x 1 cm grid. Silastic imprint testing of an analogous skin area contralateral to the hypomelanotic macule was measured as a control. Sweat volume quantitation using sweat collectors was performed in five of the subjects. The sweat volume collected from the hypomelanotic macule was reduced compared to the control skin in four of the five subjects. Sweat droplet counts from the hypomelanotic macule were significantly reduced in only one of nine subjects. These data suggest that, although there is no difference in the number of functioning sweat glands in most hypomelanotic macules, the sweat glands produce less sweat (ie, decreased sweat volume) than in normal skin. We hypothesize that focal abnormalities of sympathetic innervation might be responsible for the hypomelanotic macules of tuberous sclerosis complex.

A preliminary report of the use of botulinum toxin type A in infants with clubfoot: four case studies

This report describes the use of botulinum toxin type A (BTX-A) in four infants with very severe clubfoot deformity. The gastrocnemius and posterior tibial muscles were injected with BTX-A after the patients reached a treatment plateau in physical therapy. Significant improvement in foot dorsiflexion and foot flexibility was seen in two patients, and surgery was not required. Surgical intervention was necessary in the remaining two patients, both of whom were ultimately diagnosed with a demyelinating neuropathy. The use of botulinum toxin as an adjunct to conservative care in infants with clubfoot is discussed.

Working memory for letters, shapes, and locations: fMRI evidence against stimulus-based regional organization in human prefrontal cortex

Investigations of working memory (WM) systems in the frontal cortex have revealed two stimulus dimensions along which frontal cortical representations may be functionally organized. One hypothesized dimension dissociates verbal from nonverbal WM processes, dividing left from right frontal regions. The second hypothesized dimension dissociates spatial from nonspatial WM, dividing dorsal from ventral frontal regions. Here we used functional magnetic resonance imaging to probe WM processes associated with three different types of stimuli: letters (verbal and nonspatial), abstract shapes (nonverbal and nonspatial), and locations (nonverbal and spatial). In a series of three experiments using the "n-back" WM paradigm, direct statistical comparisons were made between activation patterns in each pairwise combination of the three stimulus types. Across the experiments, no regions that demonstrated responses to WM manipulations were discovered to be unique to any of the three stimulus types. Therefore, no evidence was found to support either a left/right verbal/nonverbal dissociation or a dorsal/ventral spatial/nonspatial dissociation. While this could reflect a limitation of the present behavioral and imaging techniques, other factors that could account for the data are considered, including subjects' strategy selection, encoding of information into WM, and the nature of representational schemes in prefrontal cortex.

Recommendations for the use of botulinum toxin type A in the management of cerebral palsy

Botulinum toxin type A (BTX-A) is increasingly being used for the treatment of childhood spasticity, particularly cerebral palsy. However, until very recently, all such use in this indication has been unapproved with no generally accepted treatment protocols, resulting in considerable uncertainty and variation in its use as a therapeutic agent. In view of the increasing awareness of, and interest in, this approach to the treatment of spasticity, and also the recent licensing in a number of countries of a BTX-A preparation for treating equinus deformity in children, it would seem timely to establish a framework of guidelines for the safe and efficacious use of BTX-A for treating spasticity in children. This paper represents an attempt, by a group of 15 experienced clinicians and scientists from a variety of disciplines, to arrive at a consensus and produce detailed recommendations as to appropriate patient selection and assessment, dosage, injection technique and outcome measurement. The importance of adjunctive physiotherapy, orthoses and casting is also stressed.

Predicting the probability of meningioma recurrence based on the quantity of peritumoral brain edema on computerized tomography scanning

OBJECT

The goal of this study was to determine whether the quantity of peritumoral brain edema displayed on computerized tomography (CT) scanning could be correlated with brain invasion and subsequent recurrence of meningiomas.

METHODS

One hundred thirty-five patients who underwent resection of intracranial meningiomas at the Ottawa Civic Hospital were followed during the period 1980 to 1998. A complete resection was defined as one in which tumor, invaded bone, and involved dura were removed. Tumors were examined microscopically for evidence of brain invasion. The mean follow-up period was 9 +/- 4 years (standard deviation [SD]) and the mean time to recurrence was 5 +/- 4 years (SD). The authors used a simple grading system based on the average thickness (in centimeters) of edema seen on an axial CT slice showing the most tumor. Edema grade was linearly related to edema volume determined by digitizing the scans (r = 0.96; 29 cases). The chance of brain invasion increased by 20% for each centimeter of edema (r(s) = 1, p < 0.0001; 124 cases). The presence of brain invasion was predictive of recurrence after complete resection with an accuracy of 83%, a sensitivity of 89%, and a specificity of 82%. The chance of recurrence within 10 years after complete resection was given by the equation: percentage chance of recurrence = (centimeter of edema)3 x 0.7, which can be used to predict the chance of recurrence based on findings on CT scans (r(s) = 1, p < 0.0001; 86 patients). Statistical significance was confirmed using Kaplan-Meier and univariate and multivariate analyses. Completeness of resection was the most powerful predictor of recurrence (p < 0.00001, r = 0.6), followed by edema grade and brain invasion (both p = 0.02, r = 0.1). Patient age and gender and tumor location, size, and histological subtype were nonsignificant factors.

CONCLUSIONS

Brain invasion causes peritumoral edema. Invaded brain tissue is also the source of residual cells in cases of tumor recurrence after gross-total resection.

Therapeutic drug concentration monitoring using saliva samples. Focus on anticonvulsants

In the last 30 years there has been great interest in the use of saliva in therapeutic drug monitoring. Numerous investigators have suggested that saliva be used as an alternative body fluid for the therapeutic drug monitoring of anticonvulsant drugs. Not only can saliva be obtained easily on multiple occasions with minimal discomfort to the patient but, more importantly, useful relationships exist between the saliva and blood concentrations of the most commonly used anticonvulsant drugs. The measurement of anticonvulsant drug concentrations in saliva has been applied to pharmacokinetic and pharmacodynamic studies, and for therapeutic drug monitoring in a variety of seizure disorders. However, this simple and non-invasive method is not widely accepted in clinical practice. Several recent developments in sample collection and analytical methods, and the growing interest in free drug concentrations, provide a renewed impetus for saliva sampling for therapeutic drug monitoring of anticonvulsant drugs. Salivary flow rates vary significantly both between individuals and under different conditions. The use of stimulated saliva has several advantages over resting saliva. The salivary flow rate and pH, sampling conditions, contamination and many other pathophysiological factors may influence the concentrations of the medication in saliva. However, under standardised and well-controlled sampling condition, therapeutic drug monitoring of anticonvulsant drugs in saliva can be useful for determining compliance with medication in paediatric patients, for analysing the concentration of free drug and in situations where repeated sampling is necessary. Saliva is an alternative matrix for the therapeutic drug monitoring of carbamazepine, phenytoin, primidone and ethosuximide because the concentrations of these medications in saliva reflect the concentrations of the drug in serum. This is not the case for valproic acid (valproate sodium) and some controversy exists for phenobarbital. Further studies are required to assess the clinical value of monitoring anticonvulsant drugs and their metabolites in saliva, to examine the influence of pathophysiological factors on salivary drug concentrations, to improve the design of special devices to reproducibly and conveniently collect saliva samples, and to develop and use new analytical methods to achieve more sensitive and accurate results.

Renal lesion growth in children with tuberous sclerosis complex

PURPOSE

Renal lesions, including angiomyolipoma, renal cysts (simple and polycystic kidney disease) and renal cell carcinoma, develop in patients with tuberous sclerosis complex. While there is limited information that these lesions may grow in adults with tuberous sclerosis complex, the incidence, characterization and growth rate in children have not been reported. Also, the age at which these lesions first appear, thus providing insight into their natural history, is unknown. We present our data from a longitudinal renal surveillance study of children with tuberous sclerosis complex.

MATERIALS AND METHODS

Since 1985 children with tuberous sclerosis complex at our hospital have undergone periodic renal imaging by ultrasonography or computerized tomography to monitor renal lesions. A total of 35 girls and 25 boys 1 to 18 years old have undergone at least 2 or more annual renal ultrasounds.

RESULTS

On initial evaluation 33 of 60 children (55%) (mean age 6.9 years) had an identifiable renal lesion, which increased to 48 of 60 (80%) at followup (mean age 10.5 years). Angiomyolipoma was the most frequent lesion (75%) followed by simple renal cysts (17%). Angiomyolipomas increased in size and/or number in 10 of 18 boys (56%) and 18 of 27 girls (66%). The largest growth rate in 1 year was from 0 to 4 cm. and from 5 to 9 cm. in diameter. The youngest patient demonstrated lesions at age 2 years. The average age at which a normal ultrasound became abnormal was 7.2 years. While a total of 27 patients had a normal ultrasound on entering the study, lesions had developed in 15 at followup (11 with angiomyolipomas, 4 with cysts). Five patients had cysts that had disappeared at followup. A 7-year-old boy had a 9 cm. renal cell carcinoma removed. One patient has renal lesions characteristic of autosomal dominant polycystic kidney disease.

CONCLUSIONS

Renal involvement in patients with tuberous sclerosis complex begins in infancy, and angiomyolipoma is the most common lesion (75%). Angiomyolipomas are more likely to grow than remain stable, although the rate of growth varies. Simple renal cysts may appear or disappear with time but angiomyolipomas do not disappear. An initially normal renal ultrasound does not rule out future development of lesions. Periodic surveillance is indicated in children with tuberous sclerosis complex.

Early diagnosis of subependymal giant cell astrocytoma in patients with tuberous sclerosis

We present 19 patients with tuberous sclerosis complex and subependymal giant cell astrocytoma. The mean age at the time of tumor diagnosis was 9.4 years (range, 1.5 to 21 years). Computed cranial tomography (CT) or cranial magnetic resonance imaging (MRI) identified the lesion which was resected in all cases. Seven patients had hydrocephalus and there was an interval increase in the tumor size or a large tumor without hydrocephalus in 12 patients. Surgical criteria included: (1) presence of hydrocephalus; (2) interval increase in tumor size; (3) new focal neurologic deficit attributable to the tumor; and/or (4) symptoms of increased intracranial pressure. Eight patients were identified through a surveillance program involving annual computed cranial tomography. All of these eight patients had their tumor removed prior to the development of symptoms, none had neurologic deficits which persisted after surgery, and none has so far developed recurrent subependymal giant cell astrocytoma. In contrast, of the 11 patients from the non-surveillance group 7 were symptomatic at tumor diagnosis, 1 had a complicated postoperative course, 2 developed recurrent giant cell astrocytoma, and 1 had an extensive lesion that could not be completely excised. Periodic cranial imaging may help to identify subependymal giant cell astrocytomas in tuberous sclerosis patients before they become symptomatic. Earlier diagnosis and treatment could reduce surgical morbidity and the risk of tumor recurrence.

Germ-line mutational analysis of the TSC2 gene in 90 tuberous-sclerosis patients

Ninety patients with tuberous-sclerosis complex (TSC) were tested for subtle mutations in the TSC2 gene, by means of single-strand conformational analysis (SSCA) of genomic DNA. Patients included 56 sporadic cases and 34 familial probands. For all patients, SSCA was performed for each of the 41 exons of the TSC2 gene. We identified 32 SSCA changes, 22 disease-causing mutations, and 10 polymorphic variants. Interestingly, we detected mutations at a much higher frequency in the sporadic cases (32%) than in the multiplex families (9%). Among the eight families for which linkage to the TSC2 region had been determined, only one mutation was found. Mutations were distributed equally across the gene; they included 5 deletions, 3 insertions, 10 missense mutations, 2 nonsense mutations, and 2 tandem duplications. We did not detect an increase in mutations either in the GTPase-activating protein (GAP)-related domains of TSC2 or in the activating domains that have been identified in rat tuberin. We did not detect any mutations in the exons (25 and 31) that are spliced out in the isoforms. There was no evidence for correspondence between variability of phenotype and type of mutation (missense versus early termination). Diagnostic testing will be difficult because of the genetic heterogeneity of TSC (which has at least two causative genes: TSC1 and TSC2), the large size of the TSC2 gene, and the variety of mutations. More than half of the mutations that we identified (missense, small in-frame deletion, and tandem duplication) are not amenable to the mutation-detection methods, such as protein-truncation testing, that are commonly employed for genes that encode proteins with tumor-suppressor function.

Monitoring peripheral nerve function during external fixation of upper extremities

Limb lengthening of the upper extremity using external fixation devices is associated with a high risk of neurovascular impairment. To aid early detection of nerve injury, intraoperative monitoring of neural function was performed in five patients undergoing Ilizarov-type circular external-fixator application. The apparatus was applied to the humerus in two cases and to the forearm in the other three cases. The function of ulnar, median, and radial nerves was assessed continuously throughout the surgery by using sensory-evoked potential (SEP) monitoring technique. The responses were elicited by stimulation of these nerves in the distal forearm with recording at Erb's point and over the anterior cervical spine. During apparatus application, radial-response attenuation was identified in two instances. No corrective actions were performed in one case, and the patient had symptoms of radial nerve deficit postoperatively. In the other case, prompt removal of the offending half-pin after the detection of electrophysiologic abnormalities resulted in subsequent response restoration and the avoidance of postoperative nerve dysfunction. Sensory-evoked potential monitoring proved to be a reliable indicator of nerve compromise during external fixation of upper extremities and may be considered a valuable surgical adjunct.

Schizencephaly: correlations of clinical and radiologic features

Schizencephaly is an uncommon congenital disorder of cerebral cortical development. Although a well-recognized cause of seizures and developmental deficits in children, previous reports describe the range of neurodevelopmental outcome in only 47 patients. We report the clinical and cranial imaging features of 47 children with unilateral open-lip (17), unilateral closed-lip (12), bilateral open-lip (12), and bilateral closed-lip (6) schizencephaly, as defined radiologically. The schizencephalic cleft occurred more often in the anterior than in the posterior neocortex. Children with closed-lip schizencephaly presented with hemiparesis or motor delay whereas patients with open-lip schizencephaly presented with hydrocephalus or seizures. Forty-three patients (91%) had associated cerebral developmental anomalies, most commonly absence of the septum pellucidum (45%) and focal cortical dysplasia (40%). There was a history of seizures in 57% of cases, a third of which were classified as difficult to control. Neurodevelopmental outcome was generally poor, with 51% of patients (24/47) having severe deficits, 32% of patients (15/47) having moderate impairment, and 17% of patients (8/47) having mild or no problems. Patients with closed-lip schizencephaly were more likely to have a mild to moderate outcome than those with open-lip type (78% versus 31%; p < 0.05). Children with unilateral schizencephaly had a mild or moderate outcome more frequently than those with bilateral lesions (62% versus 28%; p < 0.05). Children who had involvement of a single lobe accounted for 88% of those with mild outcomes and 53% of those with moderate outcomes. Unilateral closed-lip schizencephaly was associated with the best neurodevelopmental outcome; in contrast, 11 of 12 children with bilateral open-lip clefts had severe disabilities. Language development was significantly more likely to be normal in those children with unilateral schizencephaly than in those with bilateral clefts (48% versus 6%; p < 0.002). Thus, the presentation and outcome of children with schizencephaly are quite variable but are related to the extent of cortex involved in the schizencephalic defect.

Mutations and polymorphisms in the tuberous sclerosis complex gene on chromosome 16

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder of benign tumor formation, hamartomata, and hamartias. TSC has been shown to be genetically heterogeneous, with one causative gene mapping to chromosome 9q (denoted TSC1) and at least one other gene on chromosome 16p (denoted TSC2). The TSC2 gene was recently cloned. We have tested 88 TSC probands with the TSC2 cDNA by Southern blotting searching for gross deletions/rearrangements/insertions. We detected two deletions and a rare intragenic polymorphic variant. This is a similar rate of mutation detection (2/88; 2.3%) to that in the original report (10/260/; 3.8%). The rare polymorphic variant was initially detected in the proband of a chromosome 9-linked multiplex TSC family. The polymorphism segregated with previously tested markers on chromosome 16 independently of the disease gene, verifying that the variation was unrelated to TSC status. We have also begun searching for subtle mutations by SSCA and direct sequencing. After screening three exons, we found two intragenic polymorphic variants. Both polymorphisms are common, making them useful for linkage studies in known affected families.

Effects of external fixation and limb lengthening on peripheral nerve function

To identify factors affecting peripheral nerve function during limb lengthening, serial somatosensory evoked potentials studies were performed in 18 goats and correlated with gross appearance of the soft tissues at necropsy. In 15 goats, a 20% or 30% tibial lengthening was done using the Ilizarov apparatus at a rate of 0.75 mm per day and rhythm of 1, 4, or 720 times per day. Three animals served as frame/corticotomy controls. Seven lengthened and 2 control animals maintained normal somatosensory evoked potentials throughout the study. At necropsy, the peroneal and tibial nerves appeared grossly normal. In one control animal with irreversible loss of evoked potentials documented intraoperatively, peroneal nerve impalement by a transfixion wire was identified at necropsy. Eight lengthened animals experienced significant changes of peroneal nerve conduction. In 6 of these 8 animals, transfixion wires were found to be disrupting the nerve in some way. In the remaining 2 animals, no offending wires were identified, but there was extensive diffuse soft tissue fibrosis within the extremity. The rhythm of distraction did not have an important influence on evoked potential changes during the course of distraction. Although there was a correlation between the amount of lengthening performed and the degree of evoked potentials deterioration, the anatomic relationship between the wires and nerves was a more important factor in the development of these abnormalities.

Intraoperative SSEP monitoring during external fixation procedures in the lower extremities

The efficacy of somatosensory evoked potentials (SSEPs) to detect acute peripheral nerve injury during external-fixator application in the lower extremities was evaluated in 40 children with 42 Ilizarov surgical procedures. The study included patients who were either clinically normal or who had preexisting neuropathy but consistent and reliable SSEP responses preoperatively. SSEPs were recorded from the popliteal fossa and lumbar regions after alternating stimulation of the peroneal and posterior tibial nerves at the ankle. SSEP changes due to anesthesia, Ilizarov apparatus application, and other intraoperative variables are described. Significant deterioration or total loss of SSEP response during surgery occurred in four cases. Two of these patients were normal preoperatively and had symptoms of neurologic deficit postoperatively; the other two had exacerbations of pre-existing neuropathy. In general, the peroneal nerve was at greater risk for injury during surgery. SSEP monitoring proved to be technically feasible in external-fixation procedures on the lower extremities and may be a practical tool for detection of intraoperative nerve compromise.

Discontinuation of antiepileptic drug treatment after two seizure-free years in children with cerebral palsy

OBJECTIVE

The risk of seizure relapse after antiepileptic drug (AED) discontinuation in children has been reported to vary between 6% and 40%. It has been suggested that neurologic deficit and mental retardation are poor prognostic factors for seizure relapse after AED discontinuation. Because epileptic children with cerebral palsy (CP) have neurologic deficits, and many have mental retardation, it is important to know their risk for seizure relapse.

METHODS

AED treatment was discontinued in 65 children with CP and histories of epilepsy after 2 seizure-free years. All of the patients were followed until they had seizure relapses or for at least 2 years without seizures after AEDs were stopped. Multiple factors were analyzed for possible association with seizure relapse.

RESULTS

Twenty-seven patients (41.5%) had seizure relapses. Patients with spastic hemiparesis had the highest relapse rate (61.5%), and those with spastic diplegia had the lowest rate (14.3%). No other factor correlated significantly with the risk of seizure relapse.

CONCLUSIONS

Discontinuation of AEDs in children with CP can, and should, be practiced when possible after patients have been seizure-free for at least 2 years. AED discontinuation in patients with spastic hemiparesis is significantly more likely to lead to seizure relapse than in patients with other CP types, but no other factor is yet known to increase the chance of relapse.

Identification and molecular confirmation of a small chromosome 10q duplication [dir dup(10)(q24.2-->q24.3)] inherited from a mother mosaic for the abnormality

We describe a family in which two siblings exhibited developmental delay, reduced muscle tone and mild muscle weakness. Cytogenetic evaluation demonstrated that both children had a tandem duplication of a small portion of the long arm of chromosome 10 [46,XX or XY,dir dup(10)(q24.2-->q24.3)], inherited from their clinically normal mother, who was found to be mosaic for the duplicated chromosome 10. Fluorescence in situ hybridization approaches, including total chromosome painting and the use of regional specific cosmid probes, were used to confirm the chromosome 10q origin of the duplicated material. This is the smallest confirmed duplication of this portion of chromosome 10 reported to date.

Interactions of phenobarbital and phenytoin with carbamazepine and its metabolites' concentrations, concentration ratios, and level/dose ratios in epileptic children

The effects of phenytoin (PHT) or phenobarbital (PB) comedication on the concentrations, concentration ratios, and level/dose ratios of carbamazepine (CBZ) and its metabolites were investigated. The hetero-induction effects of CBZ metabolism by PHT or PB were clearly demonstrated. Serum CBZ level/dose ratios in patients with CBZ polytherapy were decreased while CBZ-10,11-epoxide (CBZ-E) and trans-10,11-dihydroxy-10,11-dihydro-CBZ (CBZ-H) concentrations were increased as compared with those of patients receiving CBZ alone. The concentration ratios of CBZ-H/CBZ and CBZ-E/CBZ were also greater in patients receiving CBZ+PHT or CBZ+PB than in patients receiving CBZ alone. In addition, positive correlations between serum PHT concentration and CBZ-H/CBZ or CBZ-E/CBZ concentration ratios were observed. There were no significant differences in CBZ-H/CBZ-E concentration ratios, the free fractions of CBZ and its metabolites, and CBZ-E or CBZ-H level/dose ratios among the three groups of patients. Because this approach investigates the in vivo relation between the substrates and products of the enzymes involved in CBZ biotransformation, more detailed information about the drug interactions was obtained. The results suggest that the PHT has a potent induction effect on CBZ epoxidase, whereas PB is a moderate inducer.

Interactions of valproic acid with carbamazepine and its metabolites' concentrations, concentrations ratios, and level/dose ratios in epileptic children

In two groups of epileptic children receiving carbamazepine (CBZ) therapy with or without valproic acid (VPA) comedication, we investigate the drug interactions of VPA on serum CBZ and its metabolites' concentrations, concentration ratios, and level/dose ratios. Serum total and free CBZ-10, 11-epoxide (CBZ-E) concentrations are significantly increased in patients taking CBZ plus VPA, together with higher CBZ-E/CBZ concentration ratios and CBZ-E level/dose ratios. These results reflect the accumulation of CBZ-E. The decreased concentration ratios of trans-10, 11-dihydroxy-10, 11-dihydro-CBZ (CBZ-H)/CBZ-E observed in patients taking CBZ plus VPA suggest an inhibition in the biotransformation from CBZ-E to CBZ-H. Significant negative correlations are found between serum VPA level and CBZ-H/CBZ-E concentration ratios, indicating that the inhibition of CBZ-E hydrolysis by VPA may depend on the concentration of VPA (total or free CBZ-H/CBZ-E concentration ratio = [formula: see text], respectively). VPA concentration also shows significant positive correlations with CBZ-E and CBZ level/dose ratios. Patients taking CBZ plus VPA have significant higher free fractions of CBZ and CBZ-E than do patients on CBZ alone, suggesting a protein-binding displacement by VPA.

Tuberous sclerosis

Tuberous sclerosis complex is a disorder of cellular differentiation and proliferation that is inherited as an autosomal dominant trait with variable penetrance and a high spontaneous mutation rate. Lesions occur in the brain, skin, kidneys, heart, and other organs. Recent studies suggest genetic heterogeneity, with at least two gene loci on chromosomes 9, 16, and perhaps 11.

Somatosensory evoked potential evaluation of acute nerve injury associated with external fixation procedures

The effects of different mechanisms of acute nerve injury on peripheral nerve function during K wire application and 1 stage limb lengthening were evaluated prospectively in 24 goats using somatosensory evoked potentials. Stable somatosensory evoked potential recordings throughout 3-day experiments were obtained in animals with wires placed at a distance from or directly adjacent to a nerve but without producing any tension or pressure. Complete loss of the peroneal nerve somatosensory evoked potentials occurred if this nerve was perforated by wire, underwent excessive pressure by wire, or had been over-stretched due to acute 10% limb lengthening. Acute distraction resulted only in peroneal nerve dysfunction, while the tibial nerve was relatively unaffected. Although somatosensory evoked potential changes were not specific for the type of injury produced and the time of waveform disappearance varied, significant somatosensory evoked potential changes (> 50% amplitude reduction, > 10% latency delay or both) were seen within the first 15 minutes after injury in 90% of the cases. The somatosensory evoked potential changes did not reverse if the offending wire or distraction was left in place for the full duration of the experiment. Variable nerve conduction recovery was observed in all animals who had the insult removed immediately after the somatosensory evoked potentials disappearance. The greatest improvement occurred after discontinuation of nerve distraction. The worst somatosensory evoked potential waveform recovery was noted in animals with nerve perforation. Intraoperative somatosensory evoked potential monitoring proved to be a reliable and useful technique for earlier detection of acute nerve injury during external fixation procedures.

A comprehensive study of the relation between serum concentrations, concentration ratios, and level/dose ratios of carbamazepine and its metabolites with age, weight, dose, and clearances in epileptic children

We made a comprehensive study of the relation between age, weight, carbamazepine (CBZ) dose, total clearance (TC), and intrinsic clearance (IC) and concentrations, concentration ratios, and level/dose ratios of CBZ, carbamazepine-10,11-epoxide (CBZ-E) and trans-10,11-dihydroxy-10,11- dihydro-carbamazepine (CBZ-H) in a group of epileptic children receiving CBZ monotherapy. Body weight and age showed negative correlations with TC, IC, CBZ dose, and CBZ-E/CBZ and CBZ-H/CBZ concentration ratios, and had positive relation with CBZ, CBZ-E, and CBZ-H level/dose ratios. These results indicate decreased CBZ metabolism with patient maturity. Correlations between CBZ dose with TC, IC, and the concentration ratios of CBZ-E/CBZ, CBZ-H/CBZ-E, and CBZ-H/CBZ were positive. CBZ dose also had negative associations with CBZ and CBZ-E level/dose ratios, indicating dose-dependent autoinduction of CBZ metabolism. Our data suggest that weight, age, and CBZ dose have less influence on epoxide-hydrolase activities than on epoxidase activities. The CBZ-E/CBZ concentration ratio can be used as an indicator of the degree of autoinduction of CBZ metabolism, even in patients receiving CBZ monotherapy.

Influence of sex, age, weight, and carbamazepine dose on serum concentrations, concentration ratios, and level/dose ratios of carbamazepine and its metabolites

We have conducted a comprehensive study in a group of epileptic children (25 boys and 30 girls) receiving carbamazepine (CBZ) monotherapy. The influence of sex, age, weight, and CBZ daily dose on serum CBZ, carbamazepine-10,11-epoxide (CBZ-E), and trans-10,11-dihydroxy-10,11-dihydro-carbamazepine (CBZ-H) concentrations, concentration ratios, and level/dose ratios were investigated. Compared with girls, boys required significantly larger CBZ dose and showed higher CBZ apparent clearances and lower level/dose ratios of CBZ and its metabolites. There were no significant differences between boys and girls in serum concentrations, concentration ratios, and free fractions of CBZ and its metabolites, although there were trends that boys had slightly higher concentration ratios. The relationship analysis suggested that there was a dose-dependent autoinduction of CBZ metabolism, and CBZ metabolism was decreased as patients mature, as measured by weight and age. Age showed a significant positive relationship with the free fractions of CBZ and its metabolites, indicating decreased protein binding of CBZ and its metabolites with the increase of age. Serum CBZ concentration is not a reliable index of CBZ dose, as there is only a weak correlation between them. Serum CBZ-H concentration showed strong positive correlations with CBZ dose and might be a valuable index in assessing patient compliance. The influence of sex, body weight, age, and CBZ dose on CBZ and its metabolites should be taken into consideration in further clinical studies.

Thrombocytopenia secondary to high valproate levels in children with epilepsy

We reviewed the frequency of valproate-induced thrombocytopenia in children with epilepsy in our institution. Sixty-four (21%) of 306 children taking valproate developed thrombocytopenia. Thirty-two of these 64 patients had at least one platelet count lower than 100 x 10(3)/mm3. Eight patients developed signs of bleeding. Low platelet levels were typically noted in patients with serum valproate levels of over 140 micrograms/mL, and reduction of the medication dose usually resulted in a prompt increase in the number of platelets. Only one patient developed thrombocytopenia unrelated to high serum drug levels, and her platelet count did not improve until the drug was discontinued. Neither the age of the patient nor the use of additional antiepileptic medication correlated with the platelet count. However, duration of valproate use was related. These data suggest that, although valproate may cause thrombocytopenia via more than one mechanism, by far the most common factor is the presence of high valproate levels. Thus, the medication can be safely lowered in most patients with thrombocytopenia rather than discontinued altogether. Platelet counts should probably be monitored more carefully in patients known to have higher drug levels.

Improved therapeutic monitoring of drug interactions in epileptic children using carbamazepine polytherapy

Drug interactions in epileptic children with carbamazepine (CBZ) polytherapy were investigated by analysis of total and free CBZ and its metabolites simultaneously. Heteroinduction effects of CBZ metabolism by other antiepileptic drugs (AEDs), including phenytoin (PHT), phenobarbital (PB), or primidone (PRM), were clearly demonstrated. Serum CBZ level/dose ratios in patients taking CBZ plus other AEDs were decreased while CBZ-10,11-epoxide (CBZ-E) and trans-10,11-dihydroxy-10,11-dihydro-CBZ (CBZ-H) concentrations were significantly increased compared to patients with CBZ alone. Concentration ratios of CBZ-H/CBZ and CBZ-E/CBZ were also significantly higher in patients taking CBZ plus other AEDs. Interactions between CBZ and valproic acid (VPA) involved both protein binding displacement and metabolic inhibition. Patients taking CBZ plus VPA showed significantly increased free fractions of CBZ and CBZ-E and substantially increased serum CBZ-E concentrations and CBZ-E level/dose ratios, while CBZ-H/CBZ-E concentration ratios were decreased compared with patients on CBZ alone. Since this approach investigates the in vivo relationship between substrates and products of the enzymes involved in CBZ biotransformation (the ratios between CBZ and its metabolites), detailed information about the activities of the enzymes may be obtained. This approach appears to be a practical way to improve the monitoring of CBZ metabolism influenced by various physiological or pathological conditions and achieve a better understanding of the drug interactions under different drug regimens (coadministered inhibitor or inducer). This principle may also be adopted for other drugs with similar metabolic characteristics.

The influence of polytherapy on the relationships between serum carbamazepine and its metabolites in epileptic children

The influence of polytherapy on the relationships between the age, weight, carbamazepine (CBZ) dose, total clearance, and intrinsic clearance, with concentrations, concentration ratios, and level/dose ratios of CBZ, carbamazepine-10,11-epoxide (CBZ-E) and trans-10,11-dihydroxy-10,11-dihydro-carbamazepine (CBZ-H) are investigated. Three groups of patients with CBZ monotherapy, or receiving CBZ polytherapy by taking CBZ and valproic acid (VPA) or CBZ plus other antiepileptic drugs (AEDs) were studied. The significant correlations between serum CBZ concentrations and CBZ dose in patients taking CBZ alone were no longer significant in patients with polytherapy, and the positive associations between serum CBZ-E concentrations and CBZ dose were lost in patients with CBZ + VPA. Only the concentrations of CBZ-H had significant correlations with CBZ dose in all three groups of patients. Results from this relationship study indicate a heteroinduction effect of other AEDs on CBZ metabolism, and a relatively weak influence on CBZ-E elimination. Data also suggest that there is a block in the biotransformation from CBZ-E to CBZ-H in patients taking CBZ + VPA, presumably caused by the inhibition effect of VPA on epoxide hydrolase. Therapeutic drug monitoring of CBZ will benefit from the knowledge obtained from the relationship study.