Congenital Hypothyroidism

BACKGROUND

Description and Causes

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.

Diagnosis

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.

Occurrence

1:4,000 live births among Caucasian infants
1:30,000 live births among African American infants (Vanderbilt Medical Center)
Twice as many females as males are affected
Among Hispanic infants, the female to male ratio is 3:1

Characteristic Features

Most infants with CH appear normal at birth; however, some may exhibit one or more of the following characteristics.

Prolonged jaundice
Poor feeding
Poor appetite
Constipation
Respiratory distress
Delayed skeletal maturation
Lethargy
Prolonged gestation (20% > 42 weeks)
Increased birth weight (33% > 90^th percentile)
Cyanosis

Physical signs associated with CH

Macroglossia
Large fontanelle (posterior fontanelle)
Hoarse cry
Hypothermia
Ectopic thyroid gland located under the base of the tongue
Umbilical hernia

Common Associations

Pulmonary stenosis
Atrial septal defect
Ventricular septal defect

MEDICAL MANAGEMENT CONSIDERATIONS

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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.

Ongoing

Monitor thyroxine therapy throughout patient’s lifetime.

Infancy or Early Childhood (Birth to 5 years)

Immediately begin and closely monitor administration of L-thyroxine, the preferred treatment. Caution must be taken not to overtreat and produce iatrogenic hyperthyroidism.
Perform frequent laboratory evaluations of thyroid function (vs. clinical evaluation):
Two and four weeks after initiation of l-thyroxine treatment
Every one to two months during the first year of life
Every two to three months between ages one and three
Every three to 12 months thereafter until growth is completed
More frequently when compliance is questioned or abnormal values obtained
Gradually increase dose of l-thyroxine as appropriate as patient grows through infancy.
Perform routine clinical examinations, including assessment of growth and development, approximately every few months during the first three years of life.
Monitor for other congenital anomalies for which infants with congenital hypothyroidism appear to be at increased risk (10% vs. 3% in the general population).

Late Childhood (5 to 13 years)

Gradually increase dose of l-thyroxine as appropriate as patient grows through childhood.

Adolescence and Adulthood (13 years and over)

Gradually increase dose of l-thyroxine as appropriate as patient grows through adolescence.

REFERENCES

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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) 353-7878

(904) 353-8185 fax

http://www.aace.com

Batshaw, M. L. 1997. Children with disabilities. Baltimore: Brookes.

National Organization for Rare Disorders, Inc. (NORD)

PO Box 8923

New Fairfield, CT 06812-8923

(203) 746-6518

http://www.rarediseases.org

e-mail: [email protected]

The American Thyroid Association, Inc.

Townhouse Office Park

55 Old Nyack Turnpike, Suite 611

Nanuet, New York 10954

(914) 623-3736 fax

http://www.thyroid.org

e-mail: [email protected]

The Thyroid Society

7515 South Main Street

Suite 545

Houston, TX 77030

(800) 849-7643

http://www.the-thyroid-society.org/

e-mail: [email protected]

Thyroid Foundation of America

Ruth Sleeper Hall, RSL 350

40 Parkman Street

Boston, MA 02114-2698

(800) 832-8321

(617) 726-8500

(617) 726-4136 fax

http://www.tsh.org

e-mail: [email protected]

RESOURCES FOR FAMILIES

http://www.the-thyroid-society.org

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).

ADVISORY COMMITTEE

Theodore A. Kastner, M.D., M.S.

Patricia Samuelson, M.D.

Larry Yin, M.D., M.S.P.H.

PUBLICATION INFORMATION

Funded by a grant from the California Department of Developmental Services

For more information, contact:

Center for Health Improvement

1330 21st Street, Suite 100

Sacramento, CA 95814

(916) 901-9645

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.