Congenital hypothyroidism (CH) represents one of the most common preventable causes of mental retardation. Approximately 85% of cases are sporadic, while 15% are hereditary. The etiology of congenital hypothyroidism can be classified under one of six categories: aplasia, hypoplasia, radioiodine, thyrotropin deficiency, thyroid hormone unresponsiveness, and defective synthesis of thyroxine. Developmental defects of the thyroid gland are the most common causes of sporadic congenital hypothyroidism.
The majority (over 90%) of affected babies in North America have a permanent, life-long type of CH. About 10% of babies diagnosed with CH have a transient form which varies in duration for several days to several months.
Although this disorder is detectable at birth, most newborns with CH appear normal. Recent data suggest that the hypothyroid fetus is protected to a certain extent by placental transfer of maternal thyroid hormone. Clinical signs of hypothyroidism often do not appear until the infant is three to four months old, at which time affected infants most likely will already have suffered irreversible brain damage.
Untreated or unrecognized congenital hypothyroidism has grave consequences, with moderate to severe mental retardation, growth failure, deafness, and neurological problems resulting. Clear evidence exists that infants with low serum T4 levels (below 10 mug/dL [129 nmol/L]) during the first year of life, particularly if those levels are accompanied by a TSH concentration greater than 15 mU/L, have lower IQ values than patients whose T4 levels were held constant at higher concentrations. However, early detection and treatment of congenital hypothyroidism have the potential to completely reverse the effects of fetal hypothyroidism in all but the most severe cases.
Early detection before clinical signs are evident is key to avoiding lifelong morbidity of affected infants, and early diagnosis relies almost solely on the results of a routine newborn screening test (NBS). In the United States, state law mandates that every infant born must have an NBS performed.
Since the early 1970’s, newborn screening for CH has become routine in most industrialized nations, including North America and Europe, and is under development in Eastern Europe, South America, Asia, and Africa. At this time, physicians in the United States are more likely to encounter congenital hypothyroidism in either individuals born before 1970 in the Untied States or in infants and children immigrating to the United States from less developed countries. Members of the former group are generally recognized and receive replacement therapy. However, the latter group can represent a challenge. In most cases, these children have already begun to develop clinical sequella of CH.
Most North American screening programs use a two-tiered approach: an initial filter paper blood spot T4 measurement is followed by a measurement of TSH in filter paper specimens with low T4 values. This approach will identify infants with primary hypothyroidism but will miss infants who have normal T4 values but elevated TSH values. Test results can come in various combinations of normal and low readings. Therefore, physicians cannot and must not relinquish their clinical judgment and experience in the face of normal newborn thyroid test results; failure of normal development can result from hypothyroidism in infants who have had normal T4 and TSH screening results. In confirming test results, thyroid scintigraphy, using 99mTc or 123I, is the most accurate diagnostic test to detect suspicious structural thyroid abnormalities.
It is highly desirable that the blood for testing be collected when the infant is between two and six days of age as specimens collected in the first 24 – 48 hours of life may lead to false-positive TSH elevations. However, screening before discharge is preferable to missing the diagnosis of hypothyroidism.
Most infants with CH appear normal at birth; however, some may exhibit one or more of the following characteristics.
Physical signs associated with CH
MEDICAL MANAGEMENT CONSIDERATIONS
Note: These considerations are in addition to the normal medical care provided to an individual without Congenital Hypothyroidism. Most recommendations can be addressed through clinical examination by the primary care provider.
It is strongly recommended that routine visits are made to a pediatric endocrinologist for routine follow-up throughout childhood and adolescence.
Infancy or Early Childhood (Birth to 5 years)
Late Childhood (5 to 13 years)
Adolescence and Adulthood (13 years and over)
Peer-reviewed Journal Articles/Academies
American Academy of Pediatrics. 1993. Policy Statement: Newborn screening for congenital hypothyroidism: Recommended guidelines (RE9316) Pediatrics 91 (6): 1203-1209.
Bargagna, S., Canepa, G., Costagli, C., Dinetti, D., Marcheschi, M., Millepiedi, S., Montanelli, L., Pinchera, A., and Chiovato, L. 2000. Neuropsychological follow-up in early-treated congenital hypothyroidism: A problem-oriented approach. Thyroid 10 (3): 243-249.
Harrell, G. B. and Murray, P. D. 1998. Diagnosis and management of congenital hypothyroidism. J Perinat Neonatal Nurs 11 (4): 75-83.
LaFranchi, S. 1999. Congenital hypothyroidism: Etiologies, diagnosis, and management. Thyroid 9 (7): 735-740.
Lorey, F. W. and Cunningham, G. C. 1992. Birth prevalence of primary congenital hypothyroidism by sex and ethnicity. Human Biology 64 (4): 531-538.
Rovet, J. F. and Ehrlich, R. 2000. Psychoeducational outcome in children with early-treated congenital hypothyroidism. Pediatrics 105 (3 Pt. 1): 515-522.
Selva, K. A., Mandel, S. H., Rien, L., Sesser, D., Miyahira, R., Skeels, M., et al. 2002. Initial treatment dose of L-thyroxine in congenital hypothyroidism. The Journal of Pediatrics. 141 (6): 786-792.
Van Vliet, G. 1999. Neonatal hypothyroidism: treatment and outcome. Thyroid 9 (1): 79-84.
Van Vliet, G. 2001. Treatment of congenital hypothyroidism. Lancet 358 (9276): 86-87.
Verrotti, A., Grego, R., Altobelli, E., Morgese, G., and Chiarelli, F. 1998. Bone metabolism in children with congenital hypothyroidism — a longitudinal study. J Pediatr Endocrinol Metab 11 (6): 699-705.
Waller, D. K., Anderson, J. L., Lorey, F., and Cunningham, G. C. 2000. Risk factors for congenital hypothyroidism: An investigation of infant’s birth weight, ethnicity, and gender in California, 1990-1998. Teratology 62 (1): 36-41.
Wang, S. T., Pizzolato, S., and Demshar, H. P. 1998. Diagnostic effectiveness of TSH screening and of T4 with secondary TSH screening for newborn congenital hypothyroidism. Clin Chim Acta June 22; 274 (2): 151-158.
Special Interest Groups/Other Publications
American Association of Clinical Endocrinologists
1000 Riverside Ave.; Suite 205
Jacksonville, FL 32204
(904) 353-8185 fax
Batshaw, M. L. 1997. Children with disabilities. Baltimore: Brookes.
National Organization for Rare Disorders, Inc. (NORD)
PO Box 8923
New Fairfield, CT 06812-8923
The American Thyroid Association, Inc.
Townhouse Office Park
55 Old Nyack Turnpike, Suite 611
Nanuet, New York 10954
(914) 623-3736 fax
The Thyroid Society
7515 South Main Street
Houston, TX 77030
Thyroid Foundation of America
Ruth Sleeper Hall, RSL 350
40 Parkman Street
Boston, MA 02114-2698
(617) 726-4136 fax
RESOURCES FOR FAMILIES
Comprehensive article for laymen written for the newsletter of The Thyroid Society by John S. Dallas, MD (practicing pediatric endocrinologist, Associate Professor at the University of Texas Medical Branch in Galveston, and member of The Thyroid Society’s Medical Advisory Board).
Theodore A. Kastner, M.D., M.S.
Patricia Samuelson, M.D.
Larry Yin, M.D., M.S.P.H.
Funded by a grant from the California Department of Developmental Services
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This document does not provide advice regarding medical diagnosis or treatment for any individual case, and any opinions or statements contained in this document are not intended to serve as a standard of medical care. Physicians are encouraged to view the considerations presented in this document in light of evolving scientific information. This document is not intended for use by the layperson. Reproduction of this document may be done with proper credit given to California Department of Developmental Services and the Center for Health Improvement.
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