Congenital hypothyroidism: no adverse effects of high dose thyroxine treatment on adult memory, attention, and behaviour

Neuropsychological Alterations in Patients with Congenital Hypothyroidism Treated with Levothyroxine: Linked Factors and Thyroid Hormone Hyposensitivity

Eighty-five percent of the studies of patients with congenital hypothyroidism (CH) treated with Levothyroxine (L-T₄) report neuropsychological sequelae throughout life. In neonates and infants, there is a deficit in sensorimotor skills (impaired balance). In preschool and elementary school children and adolescents, there are alterations in intellectual quotient (low scores), language (delayed phonological acquisition), memory (visual, verbal, visuospatial, visuoconstructive, autobiographical, and semantic), sensorimotor skills (impaired fine and gross motor control), and visuoconstructive–visuospatial domain (low scores in spatial location, block design, and object assembly). These neuropsychological domains are also affected in young adults, except for language (adequate verbal fluency) and visuoconstructive–visuospatial domain (no data). The onset and severity of neuropsychological sequelae in patients with treated CH depend on several factors: extrinsic, related to L-T₄ treatment and social aspects, and intrinsic, such as severity and etiology of CH, as well as structural and physiological changes in the brain. In this review, we hypothesized that thyroid hormone hyposensitivity (THH) could also contribute to neuropsychological alterations by reducing the effectiveness of L-T₄ treatment in the brain. Thus, further research could approach the THH hypothesis at basic and clinical levels to implement new endocrinological and neuropsychological therapies for CH patients.

Cognitive and White Matter Microstructure Development in Congenital Hypothyroidism and Familial Thyroid Disorders

CONTEXT

Children with congenital hypothyroidism (CH) are at risk for suboptimal neurodevelopment.

OBJECTIVES

To evaluate neurocognitive function and white matter microstructure in children with permanent or transient CH and to correlate these findings with disease severity.

DESIGN, PARTICIPANTS AND METHODS

A retrospective and prospective observational study was conducted in 39 children with permanent or transient CH, and in 39 healthy children. Cognitive function was assessed by Wechsler Intelligence Scale, Fourth Edition, and by other tests; the white matter microstructure was investigated by 3 Tesla magnetic resonance imaging.

RESULTS

Children with permanent CH have lower cognitive scores at a median age of 9.5 years than those with transient CH and controls. An IQ score between 71 and 84 was found in 28.6% of permanent CH and of <70 (P = 0.06) in 10.7%. The Processing Speed Index (PSI; P = 0.004), sustained visual attention (P = 0.02), reading speed (P = 0.0001), written calculations (P = 0.002), and numerical knowledge (P = 0.0001) were significantly lower than controls. Children born to mothers with Hashimoto's thyroiditis have significantly lower IQ values (P = 0.02), Working Memory Index (P = 0.03), and PSI (P = 0.02). Significantly lower IQ and Verbal Comprehension Index values were found in children with a family history of thyroid disorders (P = 0.004 and P = 0.009, respectively). In children with permanent CH, significant correlations between abnormalities in white matter microstructural, clinical, and cognitive measures were documented.

CONCLUSIONS

These findings indicate that children with CH are at risk of neurocognitive impairment and white matter abnormalities despite timely and adequate treatment. The association between offspring cognitive vulnerability and maternal thyroid disorders requires careful consideration.

[Formula: see text]Socioeconomic aspects are crucial to better intellectual outcome in early-treated adolescents with congenital hypothyroidism

Congenital hypothyroidism (CH) is an important cause of preventable intellectual disability. Implementation of CH neonatal screening programs leading to early treatment has improved cognitive outcome. However, more subtle cognitive impairments are still reported, and there is lack of clarity regarding factors that impact long-term cognitive outcome. Research to better understand these factors can lead to further improvements in the cognitive prognosis for these patients. The current study aimed to evaluate the cognitive performance of adolescents who were early-treated for primary permanent CH and possible associated variables. Neurocognitive evaluation was carried out in 66 adolescents, 11 to 16 years old: 34 with CH and 29 paired controls. Intellectual quotient (IQ), verbal fluency, processing speed, executive functions, and memory were investigated. CH patients and control subjects were comparable regarding sex, age, schooling, family's socioeconomic status and caregiver's educational level. Both groups presented not only similar IQ scores but also equivalent performances regarding Perceptual Reasoning, Working Memory and Processing Speed index scores. Patients presenting different CH etiologies (dysgenesis and dyshormonogenesis) showed similar cognitive performance. Socioeconomic aspects along with the initial levothyroxine dose were the main variables to positively influence the cognitive performance, the family's socioeconomic status having the strongest association with patients' cognitive skills.

Early environmental risk factors for neurodevelopmental disorders - a systematic review of twin and sibling studies

While neurodevelopmental disorders (NDDs) are highly heritable, several environmental risk factors have also been suggested. However, the role of familial confounding is unclear. To shed more light on this, we reviewed the evidence from twin and sibling studies. A systematic review was performed on case control and cohort studies including a twin or sibling within-pair comparison of neurodevelopmental outcomes, with environmental exposures until the sixth birthday. From 7,315 screened abstracts, 140 eligible articles were identified. After adjustment for familial confounding advanced paternal age, low birth weight, birth defects, and perinatal hypoxia and respiratory stress were associated with autism spectrum disorder (ASD), and low birth weight, gestational age and family income were associated with attention-deficit/hyperactivity disorder (ADHD), categorically and dimensionally. Several previously suspected factors, including pregnancy-related factors, were deemed due to familial confounding. Most studies were conducted in North America and Scandinavia, pointing to a global research bias. Moreover, most studies focused on ASD and ADHD. This genetically informed review showed evidence for a range of environmental factors of potential casual significance in NDDs, but also points to a critical need of more genetically informed studies of good quality in the quest of the environmental causes of NDDs.

Performance in motor, communicative and cognitive skills of girls with congenital hypothyroidism treated from the neonatal period

OBJECTIVE

To compare the performance in gross motor, fine motor-adaptive, language, cognitive and personal-social development skills of girls with a mean age of 36 to 71 months with Congenital Hypothyroidism treated from the neonatal period with that of their peers without thyroid alterations.

METHODS

The participants included in the study were 30 children aged between 36 and 70 months divided into two groups paired for chronological age and socioeconomic status: 15 girls diagnosed with Congenital Hypothyroidism - Experimental Group (EG) and 15 girls without thyroid changes - Control Group (CG). The following assessment instruments were used: Interview with parents, Peabody Picture Vocabulary Test - Revised (PPVT-R), and Denver Developmental Screening Test - 2nd edition (DDST-II). Psychological testing of intellectual functioning was conducted with application of the Stanford-Binet Intelligence Scale (SBIS). The descriptive statistical analysis was performed using Student's t-test and the Mann-Whitney test at a significance level of 5% (p<0.05).

RESULTS

Comparison of the PPVT-R and SBIS results showed a statistically significant difference between the EG and CG. Comparison of the DDST-II results showed a statistically significant difference between the groups for the fine motor-adaptive, language and gross motor areas.

CONCLUSION

The present study confirms that Congenital Hypothyroidism affects child development, even when children are diagnosed and treated early, leading to alterations that can impair their motor, cognitive and language development.

White matter microstructural abnormalities in children with severe congenital hypothyroidism

This study assessed white matter microstructural integrity and behavioral correlates for children with severe congenital hypothyroidism (CH) who were identified and treated early following newborn screening. Eighteen children with severe CH and 21 healthy controls underwent a battery of behavioral measures of hearing, language and communication, along with diffusion MR imaging. Tract-based spatial statistics were performed on standard diffusion parameters of fractional anisotropy and diffusivity metrics. Microscopic diffusion anisotropy mapping based on the Spherical Mean Technique was also used to evaluate biologically specific metrics. Compared with age-matched controls, children with severe CH had poorer hearing and communication skills, albeit generally within normal limits. Children with severe CH had fractional anisotropy that was significantly lower in the cerebellum, bilateral thalami and right temporal lobe, and radial diffusivity that was significantly higher in the cerebellum and bilateral thalami. Microscopic fractional anisotropy and intra-neurite volume fraction were also significantly decreased, and transverse microscopic diffusivity was significantly increased, in the CH group in areas including the cerebellum, thalamus, occipital lobe, and corpus callosum, and in the white matter adjacent to sensorimotor cortex, particularly in the left hemisphere. Significant and widespread correlations were observed between behavioral measures and measures of white matter microstructural integrity in children with CH. The results indicate that children with severe CH who are identified through newborn screening may have significant brain white matter microstructural abnormalities despite early treatment.

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Children with severe CH show reductions in white matter microstructural integrity.

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Hearing and communication abilities are impaired for some children with severe CH.

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White matter abnormalities are associated with communication abilities in CH.

Congenital Hypothyroidism: Optimal Initial Dosage and Time of Initiation of Treatment: A Systematic Review

CONTEXT

Appropriate management of neonates, tested positive for congenital hypothyroidism (CH), in particular, the initial dosage of levothyroxine and the time of initiation of treatment is a critical issue. The aim of this study was to assess all current evidence available on the subject to ascertain the optimal initial dose and optimal initiation time of treatment for children with CH.

EVIDENCE ACQUISITION

In this study, all published research related to the initiation treatment dose and the onset time of treatment in congenital hypothyroidism were reviewed. The searched electronic databases included Medline, Science direct, Scopus EMBASE, PsycINFO, Cochrane, BIOSIS and ISI Web of Knowledge. Additional searches included websites of relevant organizations, reference lists of included studies, and issues of major thyroid and pediatrics journals published within the past 35 years. Studies were included if they were written in English and investigated levothyroxine dose or timing of treatment or both, used for the treatment of children with congenital hypothyroidism.

RESULTS

Two thousand three hundred and seventy-four articles (excluding duplicates) were retrieved from the primary search. After reviewing the titles, abstracts and full-texts of studies, eventually, 22 studies were found that met our inclusion criteria. Amongst these, 17 and 12 evaluated outcomes of different treatment doses and treatment timing, respectively. Overall, the majority of these studies emphasized the initial high dose of levothyroxine and early treatment of newborns with hypothyroidism. There were, however, some studies that disagreed with increasing levothyroxine dose at initiation of treatment.

CONCLUSIONS

Considering the results of this review, apparently there is no difference in opinion regarding the early initiation of treatment, whereas determining the optimal dose of levothyroxine for start of treatment in CH patients still remains a controversial issue, demonstrating the need for further studies, despite the fact that use of high doses can lead to rapid normalization of biochemical indices, although this may cause complications.

How well does the capillary thyroid-stimulating hormone test for newborn thyroid screening predict the venous free thyroxine level?

OBJECTIVES

To determine, in newborn infants referred with elevated capillary thyroid-stimulating hormone (TSH), a threshold below which a frankly subnormal venous free thyroxine (fT4) level of <10 pmol/L is unlikely, so that treatment with levo-thyroxine (L-T4) might be deferred until venous thyroid function tests (TFTs) become available.

SUBJECTS AND METHODS

All infants referred in Scotland since 1979 with capillary TSH elevation were studied, with particular focus on infants screened using the AutoDELFIA assay between 2002 and 2013.

RESULTS

Of the 321 infants referred with capillary TSH elevation using AutoDELFIA, 35 were excluded (fT4/TSH unavailable (12), venous sample either preceding or >10 days after capillary sampling (13, 10)), leaving 286 eligible for analysis (208 definite/probable hypothyroidism, 61 transient TSH elevation, 17 of uncertain thyroid status). Capillary TSH and venous T4 were strongly correlated (Spearman's rank correlation coefficient -0.707355). The optimal capillary TSH threshold for predicting a venous fT4 of <10 pmol/L was found to be >40 mU/L (90.3% sensitivity and 65.9% specificity compared with 90.25% and 59.1% for >35 mU/L and 88.3% and 68.2% for >45 mU/L). 93 infants (32.5%) had capillary TSH ≤40 mU/L at referral of whom 15 (9.7%) had venous fT4 <10 pmol/L, comprising seven with true congenital hypothyroidism, five with transient TSH elevation and three with uncertain status, two of whom died.

CONCLUSION

For infants in whom capillary TSH is ≤40 mU/L, it is reasonable to defer L-T4 treatment until venous TFT results are known provided that the latter become available quickly.

Neurobehavioral deficits, diseases, and associated costs of exposure to endocrine-disrupting chemicals in the European Union

CONTEXT

Epidemiological studies and animal models demonstrate that endocrine-disrupting chemicals (EDCs) contribute to cognitive deficits and neurodevelopmental disabilities.

OBJECTIVE

The objective was to estimate neurodevelopmental disability and associated costs that can be reasonably attributed to EDC exposure in the European Union.

DESIGN

An expert panel applied a weight-of-evidence characterization adapted from the Intergovernmental Panel on Climate Change. Exposure-response relationships and reference levels were evaluated for relevant EDCs, and biomarker data were organized from peer-reviewed studies to represent European exposure and approximate burden of disease. Cost estimation as of 2010 utilized lifetime economic productivity estimates, lifetime cost estimates for autism spectrum disorder, and annual costs for attention-deficit hyperactivity disorder. Setting, Patients and Participants, and Intervention: Cost estimation was carried out from a societal perspective, ie, including direct costs (eg, treatment costs) and indirect costs such as productivity loss.

RESULTS

The panel identified a 70-100% probability that polybrominated diphenyl ether and organophosphate exposures contribute to IQ loss in the European population. Polybrominated diphenyl ether exposures were associated with 873,000 (sensitivity analysis, 148,000 to 2.02 million) lost IQ points and 3290 (sensitivity analysis, 3290 to 8080) cases of intellectual disability, at costs of €9.59 billion (sensitivity analysis, €1.58 billion to €22.4 billion). Organophosphate exposures were associated with 13.0 million (sensitivity analysis, 4.24 million to 17.1 million) lost IQ points and 59 300 (sensitivity analysis, 16,500 to 84,400) cases of intellectual disability, at costs of €146 billion (sensitivity analysis, €46.8 billion to €194 billion). Autism spectrum disorder causation by multiple EDCs was assigned a 20-39% probability, with 316 (sensitivity analysis, 126-631) attributable cases at a cost of €199 million (sensitivity analysis, €79.7 million to €399 million). Attention-deficit hyperactivity disorder causation by multiple EDCs was assigned a 20-69% probability, with 19 300 to 31 200 attributable cases at a cost of €1.21 billion to €2.86 billion.

CONCLUSIONS

EDC exposures in Europe contribute substantially to neurobehavioral deficits and disease, with a high probability of >€150 billion costs/year. These results emphasize the advantages of controlling EDC exposure.

Thyroid-related neurological disorders and complications in children

BACKGROUND

Thyroid hormones exert critical roles throughout the body and play an important and permissive role in neuroendocrine, neurological, and neuromuscular function.

METHODS

We performed a PubMed search through June 2014 with search terms including "hypothyroidism," "hyperthyroidism," "neurological complications," "neuropathy," "myopathy," "congenital hypothyroidism," and "encephalopathy." Relevant publications reviewed included case series, individual case reports, systematic reviews, retrospective analyses, and randomized controlled trials. The neurological outcomes of congenital hypothyroidism were reviewed, along with the clinical features of associated neuromuscular syndromes of both hypothyroidism and hyperthyroidism, including other autoimmune conditions. Evidence for, and pathophysiological controversies surrounding, Hashimoto encephalopathy was also reviewed.

RESULTS

The establishment of widespread newborn screening programs has been highly successful in attenuating or preventing early and irreversible neurological harm resulting from congenital thyroid hormone deficiency, but some children continue to display neuromuscular, sensory, and cognitive defects in later life. Acquired disorders of thyroid function such as Hashimoto thyroiditis and Graves' disease are associated with a spectrum of central nervous system and/or neuromuscular dysfunction. However, considerable variation in clinical phenotype is described, and much of our knowledge of the role of thyroid disease in childhood neurological disorders is derived from adult case series.

CONCLUSIONS

Early and aggressive normalization of thyroxine levels in newborn infants with congenital hypothyroidism is important in minimizing neurological sequelae, but maternal thyroid hormone sources are also critically important to the early developing brain. A spectrum of neurological disorders has been reported in older children with acquired thyroid disease, but the frequency with which these occur remains poorly defined in the literature, and much must be extrapolated from adult data. A high index of suspicion for acquired thyroid disease is paramount in the investigation of many neurological disorders of youth, as many reported sequelae of hypothyroidism and hyperthyroidism are reversible with appropriate endocrine management.

Congenital hypothyroidism: a clinical update of long-term outcome in young adults

Congenital hypothyroidism (CH) is the most common congenital endocrine disorder. The early treatment of CH patients has successfully improved the prognosis and management of this disorder. Optimal treatment and management throughout the patient's life, beginning in the neonatal period, are required to ensure long-term health. Affected patients should be offered assessments of associated medical conditions and provided with accurate information about their condition throughout their lives, but particularly during the transition from pediatric to adult services. This review provides a summary of current knowledge about the long-term outcomes of these patients and appropriate management into early adulthood. We carried out a systematic search of the Medline database to identify relevant articles. Despite major improvements in prognosis, the impact of CH is clearly not uniform, and management should take into account a broader range of relevant indicators, including CH severity, associated comorbid conditions and the adequacy of treatment during childhood and adulthood. The early diagnosis and management of associated medical conditions, and better educational strategies to improve compliance with treatment, should improve the long-term prognosis. Further studies are required to explore changes with aging.

Effects of early thyroid hormone deficiency on children's autobiographical memory performance

Memory deficits and hippocampal abnormalities have been described in individuals with thyroid hormone (TH) insufficiencies; however, no study has yet examined their autobiographical memory (AM) abilities, which are known to be compromised by hippocampal damage. Investigations in adults have shown that AM consists of both episodic and semantic components and that the hippocampus is preferentially involved in episodic AM. The present study used the Children's Autobiographical Interview (CAI) to study episodic and semantic AM in 79 children aged 9 to 14 years, including 26 with early-treated congenital hypothyroidism (CH), 23 born to women with inadequately treated hypothyroidism during pregnancy (HYPO), and 30 typically developing controls. Results showed that relative to controls, CH and HYPO groups both exhibited weaknesses in episodic AM, but not semantic AM. In particular, CH and HYPO groups showed difficulty in recalling event details (i.e., the main happenings) and visual details from past experiences. Overall, this study highlights the importance of TH for early neurodevelopment and provides critical new insight into the effects of early treated TH deficiency on long-term memory performance. Furthermore, the present study indicates that the CAI is an effective tool for investigating episodic AM impairment in clinical pediatric populations.

Optimising outcome in congenital hypothyroidism; current opinions on best practice in initial assessment and subsequent management

Congenital hypothyroidism (CH), usually of the primary and permanent variety, is an eminently preventable cause of growth retardation and mental handicap whose outlook has been transformed by newborn screening, usually involving the measurement of capillary thyroid stimulating hormone (TSH). Severe primary CH, due for example to athyreosis, may result in subtle cognitive, behavioural and sensori-motor deficits, but the extent to which these can be offset by optimal postnatal diagnosis and management remains uncertain. This is because the available adult follow-up data reflect the outcome of previous management in the 1970's and 1980's, and also because the accurate neuro-psychological assessment of children is difficult, particularly in the preschool population. There is an urgent need to develop new consensus guidelines and to ensure that the children managed according to such guidelines are systematically and prospectively assessed so that good quality outcome data become available. In this review, key recommendations in the management of CH include: screening at day 3 so that severely affected infants can begin treatment within the first 10 days of life; setting the TSH referral cut-off at 8-10 mU/L; adopting a disciplined diagnostic algorithm to evaluate referred cases, with measurement of venous free thyroxine (T4), TSH and thyroglobulin combined with dual ultrasound and radioisotope imaging; initial treatment with a T4 dose of 50 μg daily in infants weighing ≥ 2.5 kg and 15 μg/kg/day in infants weighing < 2.5 kg followed by weekly review until thyroid function is normalised; and maintenance of free T4 levels between 15-26 pmol/L and TSH between 0.5-5 mU/L thereafter to avoid both under- and overtreatment.

Visuospatial associative memory and hippocampal functioning in congenital hypothyroidism

Congenital hypothyroidism is a pediatric endocrine disorder caused by insufficient endogenous thyroid hormone production. Children with congenital hypothyroidism have difficulties with episodic memory and abnormalities in hippocampal structure, suggesting deficient hippocampal functioning. To assess hippocampal activation in adolescents with congenital hypothyroidism (N = 14; age range, 11.5-14.7 years) compared with controls (N = 15; age range, 11.2-15.5 years), a functional magnetic resonance imaging visuospatial memory task was used. In this task, participants had to decide if object pairings were novel or were previously studied or if object pairs were in the same location as they were at study or had switched locations. Despite no group differences in task performance, adolescents with congenital hypothyroidism showed both increased magnitude of hippocampal activation relative to controls and bilateral hippocampal activation when only the left was observed in controls. Furthermore, the increased activation in the congenital hypothyroidism group was correlated with the severity of the hypothyroidism experienced early in life. These results suggest that perinatal deprivation of thyroid hormone has longstanding effects on hippocampal function and may account for memory problems experienced by adolescents with congenital hypothyroidism.

[Development skills in children with congenital hypothyroidism: focus on communication]

BACKGROUND

congenital hypothyroidism may cause alterations in the child's global development.

AIM

to outline the development profile in children with congenital hypothyroidism, focusing on communication, and to verify the influence of clinical history on the outlined profile.

METHOD

35 children, with ages between 2 to 36 months, with congenital hypothyroidism detected by neonatal screening, and who were in treatment for at least one month using hormonal replacement were assessed using the Early Language Milestone Scale (ELM) and the Portage Operation Inventory (POI). The clinical history was obtained in an interview with the family and from the analysis of medical records.

RESULTS

in the ELM, eleven children presented a poor performance in the expressive auditory function, two in the visual function and one in the receptive auditory function. In the POI, seven children presented a poor performance in the language section, five in cognitive section, four in the motor and social sections and three in the self-care section. There was no correlation between the results obtained in the assessments and the clinical history.

CONCLUSION

most of the children presented adequate performances in the evaluated skills. For the children with altered performance, larger deficits were observed in the language section, for the expressive aspects, and in the cognitive section. The influence of clinical history on the development profile was not confirmed. However, a tendency for an adequate performance was observed in those children who underwent neonatal screening, received an early diagnosis and treatment for the congenital hypothyroidism and who received higher doses of thyroxine at the beginning of treatment. The importance of a speech-language follow-up for communication development in this population is highlighted.

Importância do fonoaudiólogo no acompanhamento de indivíduos com hipotireoidismo congênito

TEMA: o hipotireoidismo congênito é uma alteração metabólica que traz conseqüência graves para indivíduos não tratados e mesmo as crianças que realizam o tratamento podem apresentar distúrbios do desenvolvimento. O Programa Nacional de Triagem Neonatal, instituído pelo Ministério da Saúde, prevê o acompanhamento longitudinal de indivíduos com equipe multidisciplinar. Entretanto, a Fonoaudiologia não é incluída nesta equipe. Deste modo, considerando a ocorrência de distúrbios da comunicação nestes indivíduos, realizou-se levantamento bibliográfico nas bases de dados Lilacs, MedLine e PubMed, no período de 1987 a 2007, referente às alterações em habilidades do desenvolvimento decorrentes do hipotireoidismo congênito. OBJETIVO: verificar, na literatura científica, presença de alterações do desenvolvimento em indivíduos com hipotireoidismo congênito e refletir sobre a importância da atuação fonoaudiológica, em conjunto com equipe multidisciplinar especializada, no acompanhamento dos mesmos. CONCLUSÃO: a literatura relata alterações nas habilidades do desenvolvimento (motoras, cognitivas, lingüísticas e de autocuidados) e destaca que crianças com hipotireoidismo congênito são de risco para alterações no desenvolvimento lingüístico e, portanto, necessitam do acompanhamento longitudinal do desenvolvimento comunicativo. Torna-se evidente a importância da atuação do fonoaudiólogo nos Programas de Triagem Neonatal credenciados pelo Ministério da Saúde. Ressalta-se ainda a necessidade de investigações referentes às outras alterações metabólicas contempladas nestes programas, nas quais o fonoaudiólogo pode atuar de modo a prevenir, habilitar e reabilitar os distúrbios da comunicação, contribuindo para o trabalho em equipe, promovendo saúde nesta população.

Longitudinal Assessment of Levo-Thyroxine Therapy for Congenital Hypothyroidism: Relationship with Aetiology, Bone Maturation and Biochemical Features

AIMS

To evaluate therapy and dose adjustments in patients with congenital hypothyroidism (CH), longitudinally followed up until 16 years old, according to aetiology, Beclard's nuclei presence, and thyroxine (T4) level at diagnosis.

METHODS

L-T4/kg/day and dose change ratio (CR) were assessed in 74 CH patients.

RESULTS

The dose was statistically larger in athyreosis than in dyshormonogenesis (1-10 and beyond 14 years) and in ectopy (2, 15, 16 years). The ectopic children required statistically larger L-T4/kg than the dyshormonogenetic ones (3-7 years). The L-T4/kg/day was increased, not statistically, in patients or with T4 <30 nmol/l or without Beclard's nuclei at diagnosis. The CR progressively dropped after the 6th month at each attendance, without any difference in terms of aetiology, T4 level at diagnosis, or Beclard's nuclei. The total CR was greater (significantly) in patients without Beclard's nuclei, and (not significantly) in those with T4 <30 nmol/l at diagnosis or with agenesia.

CONCLUSION

The L-T4 dose in CH is highly affected by the aetiology. The CR is higher in patients with delayed bone maturation at diagnosis. We suggest that these latter patients need blood tests more frequently to obtain a proper titration of the therapy.

Young adults with severe congenital hypothyroidism: Cognitive event related potentials (ERPs) and the significance of an early start of thyroxine treatment

Congenital hypothyroidism (CH) has devastating effects upon brain development if left untreated. Despite early start of thyroxine treatment, patients still show subtle cognitive deficits compared to controls. We aimed to study auditory event related potentials (ERPs) in young CH adults (N = 12) to verify previous reports of normal attention functions measured by P3 in CH children. We also include ERP components (P1, N1, P2) allowing assessment of a wider range of auditory processing functions. No significant change in P3 latency or amplitude was found in the CH group, but a more subtle change in amplitude topography. A later start of thyroxine treatment was related to increased P3 latency and reduced amplitude. Group differences were found in early ERP components tapping sensory processing, sensory gating and selective attention. The results suggest persisting abnormalities in auditory processing and selective attention that may have influenced cognitive development.

Mental development of infants with congenital hypothyroidism: a longitudinal study

The purpose of this study was to assess the relationship between the clinical findings before starting treatment and the development quotient in children treated for congenital hypothyroidism. Patients with congenital hypothyroidism (n = 129) were divided into favorable and unfavorable groups according to intellectual performance. Children with congenital hypothyroidism generally have a similar intellectual outcome to that of healthy children. However, a low birth weight, the presence of complications, and a high serum thyroid-stimulating hormone value are the risk factors for unfavorable cases, who consistently have a development quotient score of less than 100.

Dorsal hippocampal administration of triiodothyronine enhances long-term memory for trace cued and delay contextual fear conditioning in rats

Thyroid hormones play critical roles in brain maturation and cognitive functions. The present study investigated the role of thyroid hormone in emotional learning and memory using trace and delay contextual and cued fear conditioning tasks, respectively. Rats were administered triiodothyronine (T3) into the dorsal hippocampal area 10 min before training or immediately after training, and were scored for freezing behaviour in the same context and in a novel context with and without an auditory cue that had been paired previously with an aversive stimulus, a foot shock. Rats administered T3 before and after training both exhibited significantly increased long-term fear memory in the trace cued and the delay contextual fear conditioning procedures compared to their control groups. The T3-administered rats were not significantly different from their respective controls on the acquisition and short-term fear memory in the trace and delay fear conditioning tasks. No significant difference on long-term trace contextual and delay cued fear memory, respectively, was found. These results indicate that the observed T3-induced enhancement of long-term contextual and cued fear memory was specific to the hippocampus-dependent conditioning tasks. These findings are the first to demonstrate that infusion of T3 into the dorsal hippocampus can improve performance on an emotional memory task.

Effects of early high-dose levothyroxine treatment on auditory brain event-related potentials at school entry in children with congenital hypothyroidism

AIMS

We tested whether brain event-related potentials (ERPs) are normal in children with congenital hypothyroidism (CH) after early high-dose levothyroxine treatment.

METHODS

Auditory ERPs were recorded in 33 normal controls and in 15 children with CH at 5 years 9/12. Based on bone maturation at diagnosis, the CH group was divided into severe (n = 8) and moderate (n = 7) subgroups. CH patients were treated at a median age of 14 days with a mean initial dose of levothyroxine of 11.6 microg/kgxday. Two ERP components (N100 and N200) were measured and clinical follow-up variables collected.

RESULTS

The functional anatomical and cognitive organisation of the auditory system, as revealed by the analyses of ERP measures, did not differ between CH and controls, or between severe and moderate CH subjects. However, N200 latency was globally longer in the CH than in the control group (p = 0.01) and was positively correlated with the over-treatment index (r = 0.61; p < 0.05) and verbal IQ. N200 amplitude was negatively correlated with initial dose (r = -0.74; p < 0.005).

CONCLUSION

These data suggest that sensitive tools such as ERPs can reveal differences between CH and controls and relate these differences to the adequacy of treatment of CH.