|The Prevention and Control of Iodine Deficiency Disorders - Nutrition policy discussion paper No. 3 (UNSSCN, 1988, 130 p.)|
1Dr. Francois Delange is Professor of Pediatrics at the Universite Libre de Bruxelles, Chairman of the Neonatal Thyroid Committee of the European Thyroid Association, PAHO consultant for endemic goitre and ICCIDD representative for Europe.
I would like to make three short remarks on physiopathological aspects of endemic cretinism and goitre, the two principal manifestations to add to Dr. Hetzel's outstanding review.
There is general agreement that the main public-health impact of a goitrogenic environment is the impairment in brain development and that goitre represents only the tip of the iceberg of the functional consequences of such an environment. The most spectacular consequences in terms of brain damage are endemic cretinism and the endemic mental retardation observed in even non-cretinous individuals.
It should be made clear that there are two types of endemic cretinism and that neither is more "typical" than the other, as frequently stressed in this paper.
It is universally accepted that endemic cretinism is characterized by three major features:
1) Epidemiology. It is associated with endemic goitre and severe iodine deficiency;
2) Clinical manifestations. These comprise mental deficiency, together with either a) a predominant neurological syndrome including defects of hearing and speech, squint, and characteristic disorders of stance and gait of varying degree, or b) predominant hypothyroidism and stunted growth.
Although in some regions one of these two types may predominate, in other areas a combination of the two syndromes might occur;
3) Prevention. In areas where iodine deficiency has been corrected, endemic cretinism is brought under control (Delange et al., 1986a).
The abundant literature, known worldwide, on myxoedoematous cretinism is unfortunately almost ignored in such an extensive review paper.
This myxoedoematous type of endemic cretinism corresponds exactly to the picture found in sporadic congenital hypothyroidism but its frequency (when endemic) can be up to 8-10 percent of the total population Instead of the 0.025 percent for sporadic hypothyroidism in non-endemic areas. The neurological type of endemic cretinism has no specific counterpart in non-endemic areas but its occurrence is critically related to the numerous environmental, socioeconomic and genetic factors involved in the etiopathogenesis of endemic goitre.
Neonatal Thyroid Screening
One of the recently proposed indexes of severity of a goitre endemia is thyroid function in the neonate. At this critical period of brain development the neonate is hypersensitive to the effects of iodine deficiency.
It should be stressed, however, that neonatal TSH is a more sensitive index of impairment of thyroid function and regulation than neonatal T-4. It should therefore replace the latter in thyroid screening procedures in endemic areas, as has been the case in non-endemic areas (Delange et al., 1979; 1986b).
Evaluating the Severity of Endemic Goitre
Another classical index of severity is the urinary I/creatinine ratio: creatinine is used as an index of the volume of urines emitted by unit of time, as would be urinary osmolarity. Urinary creatinine is influenced by other factors as well, however, such as the dietary intake of proteins. In this case, the I/creatinine ratio constitutes a less accurate index of iodine intake than the median or mean concentration of urinary iodine, provided that for the latter a sufficient number of samples have been collected from a representative fraction of the general population (Bourdoux et al., 1986).
Bourdoux, P., C. Thilly, F. Delange and A.M. Ermans (1986). A New Look at Old Concepts in Laboratory Evaluation of Endemic Goitre. Ins J.T. Dunn, E. Pretell, C.H. Daza and E. Viteri (Eds.) Towards the Eradication of Endemic Goitre, Cretinism and Iodine Deficiency. Pan American Health Organization Publ., Washington, PAHO Scientific Publication No. 502. pp. 115-129.
Delange, P., C. Beckers, R. Hfer, M.P. Knig, F. Monaco and S. Varrone (1979). Neonatal Screening for Congenital Hypothyroidism in Europe. Report of the Nevborn Committee of the European Thyroid Association. Acta Endocrinol. Vol. 90, Suppl. 223, pp. 1-27.
Delange, P., S. Bastani, M. Benmiloud, E. DeMaeyer, M.G. Isayama, D. Koutras, S. Muzzo, H. Niepomniszcze, C.S. Pandav and G. Riccabona (1986a). Definitions of Endemic Goitre and Cretinism, Classification of Goitre Size and Severity of Endemias, and Survey Techniques. In: J.T. Dunn, E. Pretell, C.H. Daza and F.E. Viteri (Eds.) Towards the Eradication of Endemic Goitre, Cretinism and Iodine Deficiency. Pan American Health Organization Publ. Washington. PAHO Scientific Publication No. 502, pp. 373-376.
Delange, P., P. Heidemann, P. Bourdoux, A. Larsson, R. Vigneri, M. Klett, C. Beckers and P. Stubbe (1986b). Regional Variations of Iodine Nutrition and Thyroid Function During the Neonatal Period in Europe. Biol. Neonate. 49, 322-330.