7.1 DEFINITION OF GOITRE STAGES
7.2 DEFINITION OF ENDEMIC GOITRE AS A PUBLIC HEALTH PROBLEM
7.3 ENDEMIC CRETINISM AND ADDITIONAL DEVELOPMENTAL ABNORMALITIES
In public-health programmes carrying out iodine supplementation, the problem is to assess a population or group living in an area or region that is suspected of being iodine-deficient. Only a brief outline of the methods can be given here. For additional information, the reader is referred to comprehensive studies elsewhere (e.g., Stanbury and Hetzel, 1980).
The data required include the following:
(1) The total population including the number of children under 15 years of age (in which the effects of iodine deficiency are so important);Basic population data are usually available and make a reference point of obvious importance in developing an iodization programme if it is to be comprehensive. There are difficulties in reaching the whole iodine-deficient population, especially because of the remoteness of many of these communities. Observing school children is one method with advantages of access and convenience, and this has been used extensively in most surveys.(2) The goitre rate, including the prevalences of palpable or visible goitre classified according to accepted criteria;
(3) The rates of cretinism and 'cretinoidism' in the population;
(4) Urinary iodine excretion;
(5) The level of iodine in the drinking water;
(6) The level of serum thyroxine (T-4) in various age groups. Particular attention is now focussed on the levels in the neonate because of the importance of the T-4 level for early brain development.
A classification of goitre severity has been adopted by the World Health Organization (Thilly et al., 1980). There are still minor differences in technique among different observers. In general visible goitre is more readily verified than the palpable type. The most recent authoritative review of the classification of goitre and cretinism was carried out at the PAHO/WHO meeting in Lima, November 1983, (Dunn et al., 1986 p.373-4). The following extract is taken from that review.
Definition of Goitre
A normal thyroid gland should have the minimal size compatible with euthyroidism under conditions of normal iodine intake (100 to 150 mcg/day). This gland would be non-palpable or barely palpable. For practical purposes, the definition of goitre of Perez et al., (1960) is recommended: "A thyroid gland whose lateral lobes have a volume greater than the terminal phalanges of the thumbs of the person examined will be considered goitrous".
Estimation of Thyroid Size
A slight modification of the system of Perez et al. (1960) is recommended.
Stage 0. No goitre.In case of doubt between any two of these stages, the lower should be recorded.Stage 1a. Goitre detectable.
Stage 1b. Goitre palpable and visible only when the neck is fully extended. This stage also includes nodular glands, even if not goitrous; see Section C below.
Stage 2. Goitre visible with the neck in normal position; palpation is not needed for diagnosis.
Stage 3. Very large goitre that can be recognized at a considerable distance.
Measurement of thyroid surfaces by the procedure of MacLennan and Gaitan (1974) is particularly recommended for standardization of technique among different examiners and for comparison of surveys in different areas and at different times.
The total goitre rate is the prevalence of stage 1+2+3; the visible goitre rate is the prevalence of stages 2+3.
This classification is appropriate to field surveys for public health purposes. For clinical purposes, more precise information can be obtained by other techniques including scintigraphy and sonography.
Estimation of the Consistency of the Thyroid by Palpation
The diffuse or nodular consistency of the thyroid should be recorded, for nodules usually occur in areas where marked iodine deficiency has been long-standing. This estimation should be independent of that for the size of the thyroid, with the following exception: when one or more nodules are found in a non-goitrous gland, it will be recorded as Stage 1b since nodularity implies marked modifications in the structure of the gland.
An area is arbitrarily defined as endemic with respect to goitre if more than 10 percent of the population or of the children aged six to 12 years are found to be goitrous. The figure 10 percent was chosen because a higher prevalence usually implies an environmental factor, while a prevalence of several percent is common even when all known environmental factors are controlled.
Definition by Three Main Features
1. Epidemiology. It is associated with endemic goitre and severe iodine deficiency.Other Developmental Abnormalities2. 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; orAlthough in some regions one of the two types may predominate, in other areas a combination of the two syndromes will occur.b. Predominant hypothyroidism and stunted growth.
3. Prevention. In areas where adequate correction of iodine deficiency has been achieved, endemic cretinism has been prevented.
It has now become increasingly clear that endemic cretinism represents only the extreme stage of a broader spectrum of developmental abnormalities including decreased intellectual potential. These abnormalities are also prevented by correction of iodine deficiency."
The prevalence rates of cretinoids and 'cretinoidism' may be difficult to determine. Observations of school children will not detect those most severely affected who are likely not to be attending school. Studies of I.Q. provide additional important evidence justifying programmes.
Urinary iodine excretion can be determined appropriately on 24-hour samples. The difficulties of collection may be insurmountable, however. For this reason, as originally suggested by Follis (1963), determinations may be made on casual samples from a group of approximately 30 subjects (Thilly et al., 1980). The iodine levels are expressed as mcg/g of creatinine excretion and the range plotted out as a histogram. This provides a reference point for the level of iodine excretion which is also a good index of the level of iodine nutrition. Modern automated equipment (autoanalyser) is making the analysis of large numbers of samples quite feasible. Methods have been recently improved so that reliable results can be obtained (Belling, 1983; Garry et al., 1973).
It has been suggested that there are three grades of severity of iodine deficiency in a population that may be determined by urinary iodine excretion (Querido et al., 1974). These are as follows:
Grade 1 Goitre endemias with an average urinary iodine excretion of more than 50 mcg/g of creatinine1. At this level, a thyroid hormone supply adequate for normal mental and physical development can be anticipated. This group could be described as suffering from 'mild IDD';The level of iodine in drinking water indicates the level of iodine in the soil which in turn determines the level of iodine in the crops and animals in the area. Iodine levels of water in iodine-deficient areas are usually below 2 mcg/litre (2 ppm).1See footnote in Section 4.8Grade 2 Goitre endemias with an average urinary iodine excretion of between 25 and 50 mcg/g of creatinine. In these circumstances, adequate thyroid hormone formation may be impaired. This group is at risk of hypothyroidism but not of overt cretinism ('moderate IDD');Grade 3 Goitre endemias with an average urinary iodine excretion below 25 mcg/g of creatinine. Endemic cretinism is a serious risk in such a population ('severe IDD').
The level of serum thyroxine (T-4) provides an indirect measure of iodine nutritional status. Radio-immunoassay methods with automated equipment have greatly assisted this approach. Particular attention should be given to levels of T-4 in the neonate; levels below 4 mcg percent must be regarded as prejudicial to brain development (Burrow, 1980).
In most of the industrialized countries of the world, where iodine deficiency in humans' is rare, all babies born are screened to ensure they have adequate thyroid hormone levels. These screening programmes use blood from heel pricks of neonates, spotted on to filter paper which is dried and sent to a regional laboratory. Blood levels of either T-4 or TSH or both are measured by immuno-assay techniques. The detection rate of neonatal hypothyroidism requiring treatment is about 1 per 3,500 babies screened. This rate varies little among developed countries (Burrow, 1980).
Neonatal hypothyroid screening has been initiated in several less-developed and iodine-deficient regions. As already noted in Section 2, Kochupillai et al. (1984) in India and Ermans et al. (1980a) in Zaire have reported severe biochemical hypothyroidism. T-4 concentrations of less than 3 mcg/dl occurred in 4 percent and 10 percent of neonates respectively. It is evident from these and other reports that within an iodine-deficient population, serum T-4 levels are lowest at birth and lower in children than in the adult population. In addition goitrogens such as cassava seem to be much more potent at reducing serum T-4 levels in neonates and children than in adults (Delange et al., 1982). This may be a critical factor since T-4 levels are lowest at the most crucial time of development, especially brain development. There is thus a strong argument for extending neonatal hypothyroid screening beyond the developed countries to regions where iodine deficiency may be a problem.
To summarize, the most critical evidence is that available from measuring urinary iodine and from measuring T-4, including in the neonate. The results of these two determinations indicate the severity of the problem. They can also be used to assess the effectiveness of remedial measures.
