Effects of MRI abnormalities on WAIS-R performance in solvent abusers

An Open-label, Self-control, Prospective Study on Cognitive Function, Academic Performance, and Tolerability of Osmotic-release Oral System Methylphenidate in Children with Attention-deficit Hyperactivity Disorder

BACKGROUND

Attention-deficit hyperactivity disorder (ADHD) is the most common mental and behavioral disorder in school-aged children. This study evaluated the effect of osmotic-release oral system (OROS) methylphenidate (MPH) on cognitive function and academic performance of Chinese school-aged children with ADHD.

METHODS

This 12-week, prospective, multicenter, open-label, self-controlled study enrolled 153 Chinese school-aged children with ADHD and 41 non-ADHD children. Children with ADHD were treated with once-daily OROS-MPH (18 mg, 36 mg, or 54 mg). The primary endpoints were Inattention/Overactivity (I/O) with Aggression Conners Behavior Rating Scale (IOWA) and Digit Span Test at week 12 compared with baseline. Secondary endpoints included opposition/defiant (O/D) subscale of IOWA, Clinical Global Impression (CGI), Coding Test, Stroop Color-word Test, Wisconsin Card Sorting Test (WCST), academic performance on teacher-rated school examinations, and safety at week 12 compared with baseline. Both non-ADHD and ADHD children received the same frequency of cognitive operational test to avoid the possible bias caused by training.

RESULTS

A total of 128 patients were evaluated with cognitive assessments. The OROS-MPH treatment significantly improved IOWA Conners I/O subscale scores at week 12 (3.8 ± 2.3) versus baseline (10.0 ± 2.4; P < 0.0001). Digit Span Test scores improved significantly (P < 0.0001) with a high remission rate (81.1%) at week 12 versus baseline. A significant (P < 0.0001) improvement was observed in O/D subscale of IOWA, CGI, Coding Test, Stroop Color-word Test, WCST, and academic performance at week 12 versus baseline. Very few practice-related improvements were noticed in the non-ADHD group at week 12 compared with baseline. No serious adverse events and deaths were reported during the study.

CONCLUSIONS

The OROS-MPH treatment effectively controlled symptoms of ADHD and significantly improved academic performance and cognitive function of Chinese school-aged children with ADHD. The treatment was found to be safe and generally well-tolerated over 12 weeks.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01933880; http://clinicaltrials.gov/ct2/show/NCT01933880?term=CONCERTAATT4099&rank=1.

Serial neuropsychological assessment of an adolescent girl after suffering a sudden out-of-hospital-cardiac-arrest following recreational inhalant use

Sudden out-of-hospital-cardiac-arrest (OHCA) following recreational inhalant use is well documented in the literature. The present case study reports the long-term neuropsychological sequelae of a 14-year-old girl who suffered an OHCA secondary to recreational butane gas inhalation. The patient was assessed on day-13 as an inpatient, and again at 3- and 12-month outpatient follow-ups. Acutely the patient demonstrated significant impairment on tasks associated with verbal and non-verbal memory and executive functioning. Re-testing at 3-months post-acute state suggested improved executive and non-verbal functions while showing continued deficits in verbal memory. At 12-months she was cognitively performing at levels expected for her age. This case is reported for its rarity in successfully being able to track the patient's clinical course from hospital discharge to the successful reintegration back into school and community settings.

Occupation and the risk of chronic toxic leukoencephalopathy

Among the hundreds of environmental insults capable of inducing nervous system injury, a small number can produce clinically significant damage to the brain white matter. The use of magnetic resonance imaging (MRI) in affected individuals has greatly illuminated this previously obscure area of neurotoxicology. Toxic leukoencephalopathy has acute and chronic forms, in both of which cognitive dysfunction is the major clinical manifestation. Chronic toxic leukoencephalopathy (CTL) has been most thoroughly described in individuals with intense and prolonged exposure to leukotoxins, but the consequences of lesser degrees of exposure are not well understood. Rare cases of CTL have been reported in workers exposed to culpable leukotoxins, but study of this syndrome is hindered by many confounds such as uncertain level of toxin exposure, the presence of multiple toxins, vague dose-response relationship, comorbid medical or neurologic disorders, psychiatric illness, and legal issues. The risk of CTL in workers is low, although it is not possible to determine quantitative risk estimates. More knowledge can be expected with the application of advanced MRI techniques to the assessment of workers who may have been exposed to known or potential leukotoxins. Preventive measures for avoiding workplace CTL will be informed by clinical assessment involving the use of advanced neuroimaging and neuropsychologic evaluation in combination with accurate measurement of leukotoxin exposure.

Decreased thalamic volumes in adolescent inhalant users from Korea and Australia

OBJECTIVES

Research investigating the impact of inhalant misuse on brain structure suggests abnormalities in subcortical regions. We investigated the association between inhalant misuse and subcortical brain volumes in adolescents.

METHODS

Based on a collaborative dataset from South Korea (inhalant users: N = 15, mean age = 16.7, SD = 1.1; controls: N = 15, mean age = 15.4, SD = 1.2) and Australia (inhalant users: N = 7, mean age = 18.2, SD = 1.4; controls: N = 7, mean age = 18.9, SD = 2.6), the volumes of caudate nucleus, putamen, pallidum, amygdala, hippocampus, and thalamus were estimated in adolescent inhalant users and healthy adolescents using FreeSurfer.

RESULTS

The results revealed a significantly decreased right thalamic volume in adolescent inhalant users (P = 0.042), along with a trend-level decrease in left thalamic volume (P = 0.061). A negative correlation (r = -0.544; P = 0.036) between thalamic volume and severity of inhalant use (i.e., reduced volumes associated with greater use) was identified among Korean participants.

CONCLUSIONS

These findings suggest that compared with other subcortical structures, the thalamus is particularly sensitive to damage following chronic inhalant exposure during adolescence.

Neurochemistry of drug action: insights from proton magnetic resonance spectroscopic imaging and their relevance to addiction

Proton magnetic resonance spectroscopy ((1)H MRS) is a noninvasive imaging technique that permits measurement of particular compounds or metabolites within the tissue of interest. In the brain, (1)H MRS provides a snapshot of the neurochemical environment within a defined volume of interest. A search of the literature demonstrates the widespread utility of this technique for characterizing tumors, tracking the progress of neurodegenerative disease, and for understanding the neurobiological basis of psychiatric disorders. As of relatively recently, (1)H MRS has found its way into substance abuse research, and it is beginning to become recognized as a valuable complement in the brain imaging toolbox that also contains positron emission tomography, single-photon-emission computed tomography, and functional magnetic resonance imaging. Drug abuse studies using (1)H MRS have identified several biochemical changes in the brain. The most consistent alterations across drug class were reductions in N-acetylaspartate and elevations in myo-inositol, whereas changes in choline, creatine, and amino acid transmitters also were abundant. Together, the studies discussed herein provide evidence that drugs of abuse may have a profound effect on neuronal health, energy metabolism and maintenance, inflammatory processes, cell membrane turnover, and neurotransmission, and these biochemical changes may underlie the neuropathology within brain tissue that subsequently gives rise to the cognitive and behavioral impairments associated with drug addiction.

Deterioration of intelligence in methamphetamine-induced psychosis: comparison with alcohol dependence on WAIS-III

AIMS

Long-term use of methamphetamine could induce psychosis, but consequences with regards to intelligence have seldom been investigated. Long-term use of alcohol could also result in intellectual deterioration.

METHODS

The IQ of 34 methamphetamine-induced psychosis (MIP) patients (age, 28.7 +/- 6.1 years) and 34 alcohol-dependent (AD) patients (age, 40.7 +/- 7.3 years) was compared using the Chinese version of the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III).

RESULTS

The average full-scale IQ, verbal IQ, performance IQ, verbal comprehension index, working memory index, perceptual organization index, and processing speed index was 82.3 +/- 10.8, 84.3 +/- 11.9, 81.9 +/- 12.1, 85.5 +/- 11.9, 84.7 +/- 12.5, 85.4 +/- 13.6, and 78.5 +/- 12.7 in MIP patients and 90.5 +/- 12.0, 95.2 +/- 11.3, 86.0 +/- 13.7, 95.5 +/- 11.0, 87.1 +/- 14.5, 96.2 +/- 13.1, and 84.5 +/- 15.0 in AD patients, respectively. There were six MIP patients (17.6%) whose full-scale IQ was <70 and 13 (38.2%) whose full-scale IQ was <85 and >70, while one AD patient had a full-scale IQ <70 (2.9%) and 10 (22%) had full-scale IQ <85 and >70.

CONCLUSIONS

Long-term use of methamphetamine can result not only in psychosis, but also in mentality deterioration. Intelligence deterioration is more severe in clinical MIP patients than AD patients. Assessment of the mentality of MIP patients is suggested to help with the implementation of rehabilitative programs for these patients.

Smaller gray matter volumes in frontal and parietal cortices of solvent abusers correlate with cognitive deficits

BACKGROUND AND PURPOSE

Abuse of toluene-containing organic solvents by inhalation is a prevalent practice among adolescents. Long-term abuse of toluene causes cognitive deficits. The mechanism of cognitive deficits induced by long-term toluene abuse has not yet been defined. In the current study, we assessed the effects of chronic toluene abuse on cortical gray matter volume and the association between cognitive impairment and cortical gray matter volume distribution in chronic toluene abusers.

MATERIALS AND METHODS

Fifteen toluene abusers and 20 healthy control subjects matched in sex, age, education level, and handedness were investigated by structural MR imaging. The cognitive states of the subjects were assessed by using the third edition of the Wechsler Intelligence Scale for Children (WISC-III). The voxel-based comparison and correlation analyses of MR images were performed by using SPM5 software.

RESULTS

The voxel-based morphometric analysis revealed that toluene abusers had significantly lower gray matter volumes in the bilateral frontotemporal and right parietal cortices. In addition, the lower gray matter volumes in the frontal and parietal regions correlated with the duration of toluene abuse. There was a positive correlation between the WISC performance scale scores and gray matter volumes in the frontal and parietal cortices of the abusers.

CONCLUSIONS

The results of the current study demonstrate that chronic toluene abusers have smaller gray matter volumes than nonabusers in various regions of the brain. Moreover, the cognitive deficits are associated with the lower gray matter volumes in the frontal and parietal cortices of chronic toluene abusers.

Abuse pattern of toluene exposure alters mouse behavior in a waiting-for-reward operant task

Inhaling solvents for recreational purposes continues to be a world-wide public health concern. Toluene, a volatile solvent in many abused products, adversely affects the central nervous system. However, the long-term neurobehavioral effects of exposure to high-concentration, binge patterns typical of toluene abuse remain understudied. We studied the behavioral effects of repeated toluene exposure on cognitive function following binge toluene exposure on behavioral impulse control in Swiss Webster mice using a "wait-for-reward" operant task. Mice were trained on a fixed-ratio (FR) schedule using sweetened milk as a reward. Upon achieving FR15, a wait component was added which delivered free rewards in the absence of responses at increasing time intervals (2s, 4s, 6s, etc...). Mice continued to receive free rewards until they pressed a lever that reinstated the FR component (FR Reset). Once proficient in the FR-Wait task, mice were exposed to either 1000 ppm, 3600 ppm or 6000 ppm toluene, or 0ppm (air controls) for 30 min per day for 40 days. To avoid acute effects of toluene exposure, behavior was assessed approximately 22-23 h later. Repeated toluene exposure decreased response rates, the number of FR resets, and increased mean wait time, resulting in a higher response-to-reinforcer ratio than exhibited by controls. Mice receiving the higher exposure level (6000 ppm) showed a dramatic decrease in the number of rewards received, which was reversed when toluene exposure ceased. Mice receiving the lower exposure level (1000 ppm) showed little change in the number of rewards. These results indicate that repeated binge exposures to high concentrations of toluene can significantly interfere with performance as measured by a waiting-for-reward task, suggesting a significant impact on cognitive and/or psychomotor function.

Inhalant abuse among adolescents: neurobiological considerations

Experimentation with volatile substances (inhalants) is common during early adolescence, yet limited work has been conducted examining the neurobiological impact of regular binge use during this key stage of development. Human studies consistently demonstrate that chronic use is associated with significant toxic effects, including neurological and neuropsychological impairment, as well as diffuse and subtle changes in white matter. However, most preclinical research has tended to focus on acute exposure, with limited work examining the neuropharmacological or toxicological mechanisms underpinning these changes or their potential reversibility with abstinence. Nevertheless, there is growing evidence that commonly abused inhalants share common cellular mechanisms, and have similar actions to other drugs of abuse. Indeed, the majority of acute behavioural effects appear to be underpinned by changes in receptor and/or ion channel activity (for example, GABA(A), glycine and 5HT(3) receptor activation, NMDA receptor inhibition), although nonspecific interactions can also arise at high concentrations. Recent studies examining the effects of toluene exposure during the early postnatal period are suggestive of long-term alterations in the function of NMDA and GABA(A) receptors, although limited work has been conducted investigating exposure during adolescence. Given the critical role of neurotransmitter systems in cognitive, emotional and brain development, future studies will need to take account of the substantial neuromaturational changes that are known to occur in the brain during childhood and adolescence, and to specifically investigate the neuropharmacological and toxicological profile of inhalant exposure during this period of development.

Toluene misuse and long-term harms: a systematic review of the neuropsychological and neuroimaging literature

Organic solvent abuse is associated with increased risk for serious medical, neurological, and neuropsychological impairments. While animal research suggests that exposure to organic solvents (especially toluene) may be neurotoxic, much less is known about the consequences of long-term exposure in humans. We reviewed neuroimaging and neuropsychological studies examining chronic toluene misuse in humans. Thirty empirical studies fulfilled the inclusion and exclusion criteria, including case studies (n=9) as well as group studies with (n=11) and without a control group (n=10). Our review indicates that toluene preferentially affects white matter (relative to gray matter) structures and periventricular/subcortical (relative to cortical) regions. The lipid-dependent distribution and pharmacokinetic properties of toluene appears to explain the pattern of MRI abnormalities, as well as the common symptoms and signs of toluene encephalopathy. The commonly observed neuropsychological deficits such as impairments in processing speed, sustained attention, memory retrieval, executive function and language, are also consistent with white matter pathology. We discuss the implications of these findings in the context of a neurodevelopmental framework, as well as the neuropathology and pathophysiology of toluene abuse. We also propose a set of recommendations to guide future research in this area.

Understanding drug addiction: a neuropsychological perspective

The purpose of the present review is to describe the neuropsychological correlates of long-term substance abuse and to discuss the findings within the context of premorbid vulnerabilities, comorbidity and adolescent neurodevelopment. The authors critically review key findings from the neuropsychological literature related to the long-term sequelae of alcohol, cannabis, inhalant, opiates, psychostimulants and ecstasy use. Leading electronic databases such as PubMed were searched to identify relevant studies published in the past 20 years. References identified from bibliographies of pertinent articles and books in the field were also collected and selectively reviewed. Across substances, individuals with long-term abuse consistently demonstrate neuropsychological impairments of executive (inhibitory) control, working memory and decision making, together with neurobiological abnormalities involving frontotemporal and basal ganglia circuits. In some instances these deficits are dose dependent, implying that they are a direct consequence of prolonged drug exposure. However, comorbid behavioural, personality and mental health problems are common among drug-using populations and are associated with similar neuropsychological deficits. Presented herein is a neuropsychological model of addictive behaviour that highlights the complex interplay between cognition, brain maturation, psychopathology and drug exposure.

Gestational toluene exposure effects on spontaneous and amphetamine-induced locomotor behavior in rats

Gestational Toluene Exposure Effects on Spontaneous and Amphetamine-Induced Locomotor Behavior in Rats. Bowen, S.E., Mohammadi, M.H., Batis, J.C., and Hannigan, J.H. Neurotoxicology and Teratology, XX, 2006. The abuse of volatile organic solvents (inhalants) continues to be a major health concern throughout the world. Toluene, which is found in many products such as glues and household cleaners, is among the most commonly abused organic solvents. The neurobehavioral teratogenic sequelae of solvent abuse (i.e., repeated, brief inhalation exposures to very high concentrations of solvents) have not been examined thoroughly. In a preclinical model of inhalant abuse, timed-pregnant Sprague-Dawley rats were exposed to 0, 8000, or 12,000 parts per million (ppm) for 15 min twice daily from gestation day 8 (GD8) through GD20. In the first experiment, separate groups of offspring were observed individually in an open-field on postnatal day 22 (PN22), PN42 or PN63. In the second experiment, other offspring given identical prenatal toluene exposures were observed in an "open-field" following an acute i.p. injection of amphetamine (0, 0.56, 1.78 mg/kg) on PN28. Automated measurements of distance traveled and ambulatory time were recorded. Prenatal toluene exposure resulted in small alterations in spontaneous activity compared to non-exposed rats. Prenatal exposure to 12,000 ppm toluene resulted in significant hyposensitivity to the locomotor stimulatory effects of the amphetamine challenge in male but not female rats on PN28. The results demonstrate that prenatal exposure to abuse patterns of high concentrations of toluene through inhalation can alter spontaneous and amphetamine-induced locomotor behavior in rats. The expression of these effects also appears to depend upon the postnatal age of testing. These results imply that abuse of organic solvents during pregnancy in humans may also produce long-lasting effects on biobehavioral development.

Metabolic correlates of toluene abuse: decline and recovery of function in adolescent animals

RATIONALE

Children and adolescents will readily abuse household products that contain solvents such as toluene. It is likely that reinforcing exposures to toluene alter brain glucose metabolism.

OBJECTIVE

Using an animal model of drug reinforcement, we sought to identify a metabolic signature of toluene abuse in the adolescent rodent brain. Small animal PET (microPET), in combination with the glucose analog radiotracer, (18)FDG, were used to evaluate the metabolic consequences of inhaled toluene.

METHODS

The exposure protocol paralleled our previously established method for assessing the conditioned reinforcing effects of toluene (5,000 ppm) using the conditioned place preference (CPP) paradigm. Animals were scanned at baseline and 2 h after the last exposure. Follow-up (18)FDG scans occurred 1 day, 3 weeks, and 2 months later.

RESULTS

After six pairings, 38% of the animals preferred the toluene paired chamber and 25% were averse. The immediate metabolic effect in toluene-exposed animals was a 20% decline in whole brain (18)FDG uptake. Twenty-four hours following the last exposure, the whole brain decline was 40%, and 2 months later, the decline was 30% of pretoluene levels. A region-by-region analysis demonstrated significant additional decreases in the pons, cerebellum, striatum, midbrain, temporal cortex, and hippocampus. Two months after toluene cessation, regions of complete metabolic recovery were the thalamus and cerebellum; however, the temporal cortex did not recover.

CONCLUSIONS

Brain uptake of (18)FDG appears to be a useful tool for examining the metabolic impact of toluene abuse, which include a profound decline followed by region-specific recovery after cessation.

Neuroimaging in drug and substance abuse part II: opioids and solvents

The central nervous system is one of the primary targets for the detrimental effects of drugs of abuse. Diagnostic imaging, especially MRI, plays an important role in the detection of complications associated with drug abuse. We present the imaging findings associated with the abuse of opioids and other morphine derivatives, as well, as solvents. Of the morphine derivatives, heroin is the most commonly abused. Several CNS pathologic effects have been described in association with its abuse. These include neurovascular complications such as microvascular ischemic changes or ischemic stroke. A rare form of leukoencephalopathy has been described in those abusers who inhale heroin vapors. Other neurologic complications include atrophy and various infectious processes. Solvent inhalation is a common practice among adolescents and young adults secondary to its ease of access and low cost. The most important component of industrial solvents is toluene. Complications of toluene abuse may be either acute, showing no neuroradiological changes, or chronic, characterized by cerebral and cerebellar demyelination as well as atrophy.

The effects of toluene on the central nervous system

In recent decades the organic solvent toluene (methylbenzene) has emerged as one of the best-studied neurotoxins. Long-term and intense exposure to toluene vapors in humans who abuse spray paint and related substances has led to the recognition that toluene has a severe impact on central nervous system myelin. Chronic toluene abuse produces a devastating neurological disorder, of which dementia is the most disabling component. The clinical syndrome, toluene leukoencephalopathy, can be detected by a combination of characteristic symptoms and signs, detailed neurobehavioral evaluation, and brain magnetic resonance imaging. In this paper, we consider the impact of toluene abuse on our society, describe the specific neurobehavioral deficits in toluene leukoencephalopathy, review the spectrum of neuroimaging findings in patients with this disorder, summarize the teratogenic effects of toluene in both humans and animal models, and offer possible explanations for the range of neuropathological damage seen in brains of individuals who chronically abuse toluene.

Solvent abuse-related toluene leukoencephalopathy

The clinical and neuropathological features of a man with solvent vapour-abuse leukoencephalopathy due to toluene is described. The findings suggest that the clinical spectrum of toluene leukencepathalopathy includes dementia with prominent prefrontal dysfunction. In addition, there was evidence of ongoing white matter damage in the form of persistence of PAS-positive macrophages among the demyelinated fibres in the cerebrum and cerebellum, despite the absolute abstinence from toluene for years prior to death.

Occupational exposure to organic solvents and long-term nervous system damage detectable by brain imaging, neurophysiology or histopathology

The purpose of the present review is to assess the evidence published in scientific literature that industrial organic solvents as a generic group have the ability to induce long-term nervous system damage in workers that can be detected by techniques other than neuropsychological testing. The main body of evidence considered in this review was 40 studies involving the use of brain imaging, neurophysiological testing, gross autopsy or histopathology in groups of workers with long-term solvent exposure. Case reports involving both solvent abuse and occupational exposure, and experimental animal data have also been reviewed as supporting data. A number of the studies in groups of workers provide evidence of the presence of marginal atrophic abnormalities in the brain or deficits in nerve conduction velocity in solvent-exposed workers. However, there are limitations in the design of many of these studies, the strength of association between exposure and effect is not consistently strong, no dose-response relationship can be detected, the reported changes lack specificity and there is no coherence between the human and experimental animal data. Overall, it is not possible to draw reliable conclusions with respect to the presence or absence of nervous system damage related to the common properties of organic solvents.

Relationship of early inhalant use to substance use in college students

This study examined the relationship between early inhalant use and later substance use in a sample of college students. Data were taken from four campus-wide surveys that assessed changes in rates of substance use over time at a large Southwestern university. Within these surveys, a group of students (n = 187) who reported early use of inhalants (i.e., before age 18) was identified and examined in terms of their substance use behavior while in college (i.e., during the year and month prior to the survey). These students were compared to two other groups of students: those who reported early use of marijuana but no early use of inhalants (n = 1271) and students who reported no early use of either inhalants or marijuana (n = 1479). Results show that early use of either inhalants or marijuana substantially increased risk of frequent drinking, binge drinking, smoking, illicit drug use, and substance-related consequences during the college years. However, the early use of inhalants conferred the greatest risk and was associated with twice the rate of binge and frequent drinking and significantly greater rates of tobacco and drug use than early marijuana use alone. Implications of these findings for intervention and prevention with college students are discussed.

Central nervous system impairment caused by chronic solvent abuse-a review of Japanese studies on the clinical and neuroimaging aspects

Organic solvents are some of the most frequently abused substances in Japan. Abuse is especially prevalent among young people. In this article, we review Japanese studies, along with those of other countries, on central nervous system impairment caused by chronic solvent abuse. Neuroimaging studies provided valuable information on this problem. Magnetic resonance imaging revealed T2 prolonged lesions in diffuse white matter which were related to neurological symptoms and cognitive dysfunction. Clinical observations indicated that neurological symptoms and their reversibility differed among patients. Histopathological studies similarly revealed variation in severity of brain damage reflected by demyelination and neuronal damage. The basis of these variations are yet to be elucidated along with their causes such as severity of dependence, composition of solvents, individual predispositions and starting age of abuse. Cerebral perfusion analyses revealed some regional decreases in blood flow. These decreases may occur earlier than white matter changes and may relate to psychiatric symptoms such as apathy and lack of initiative.