Endemic cretinism in Thailand: a multidisciplinary survey

Abstract

Endemic cretinism has been classified into neurological and myxedematous types. Profound mental deficiency, deaf-mutism and cerebral diplegia are predominantly found in the former. The latter have been described as less mentally retarded but with severe growth retardation and myxedematous features. The pathogenesis of different clinical types of endemic cretinism is still unclear. Recently, a unifying hypothesis suggested that iodine deficiency, severe enough to cause maternal and fetal hypothyroxinemia, results in neurological defects in all cretins.We conducted the present study in northern Thailand to determine the validity of this hypothesis in another geographical area. The study consisted of a multidisciplinary survey on 112 endemic cretins aged 2-66 years in Nan. They were categorized clinically into three types of endemic cretins, neurological (n = 57), myxedematous (n = 19) and mixed form (n = 36). The subjects were generally short and the majority had severe mental retardation (mean intellectual quotient (I.Q.) 30.8 Ϯ 8.8), psychomotor defect and profound sensorineural hearing loss. The I.Q. score and proportion of cretins with sensorineural hearing loss and psychomotor defect were similar among the three types of cretins. The most frequent neurological abnormalities were spasticity, hyper-reflexia, the presence of primitive reflexes and gait disturbance. These abnormalities were distributed equally among the three types of endemic cretins. Delayed skeletal maturation and abnormal epiphysis were also present in all types of cretins. However, myxedematous cretins were shorter (P < 0.01), having more myxedematous features (P < 0.05 to P<0.001) and less sexual maturation (P < 0.05). Thyroid volume was lower in cretins with hypothyroidism (P < 0.01).In conclusion, our findings support the hypothesis that neurological features are present in all types of cretins, and are the consequence of maternal and fetal hypothyroxinemia due to severe iodine deficiency. The clinical manifestations of the cretins were subsequently modified by the length and severity of postnatal iodine deficiency and hypothyroidism.

Thyroid Hormone and the Mammalian Auditory System

“…Endemic iodine defi ciency is commonly associated with deafness or deaf-mutism as well as mental and physical retardation (Goslings et al 1975 ;Rajatanavin et al 1997 ). Neurological symptoms and deafness are most prominent in the offspring when iodine is lacking during early pregnancy as this probably deprives the fetus of thyroid hormone at vulnerable stages in the development of the nervous system (Fig.…”

“…Abnormalities of the thyroid gland have long been associated with hearing loss in human disease. For example, deafness is well-known in geographical regions in which endemic goiter and cretinism exist (DeLong et al 1985 ;Rajatanavin et al 1997 ). This developmental disorder of neurological and physical retardation results from chronic defi ciency of dietary iodine, an essential element required for the synthesis of thyroid hormone.…”

Iodine and the brain: evidence from the mountains of Thailand

“…prenatal hypothyroidism), Rajatanavin et al (2) confirm that the distinction between the types of endemic cretin could be related to the length and severity of postnatal thyroid hormone deficiency. Endemic cretins with predominant neurological features appeared to have had only transient hypothyroidism in the postnatal period, evidenced by their near normal thyroid function and by a lack of hypothyroid clinical features.…”

“…The remoteness of most endemias has been one of the major factors which has hindered progress in the understanding of this complex disorder and, as a consequence, modern clinical methods using multidisciplinary teams have, until recently, rarely been applied to its investigation. Rajatanavin et al in this issue (2) provide the most recent evidence, from an iodine deficiency endemia in a remote, moutainous area of Thailand, which helps to further unravel the puzzle of endemic cretinism. This new evidence supports the two-step hypothesis of the pathogenesis of endemic cretinism, as well as highlighting the important contribution of prenatal thyroid hormone from maternal sources to normal brain development (3).…”

“…Rajatanavin et al report the results of an extensive multidisciplinary study of a large cohort of people with endemic cretinism who had been traditionally classified as neurological, myxoedematous or mixed in type (2). Despite this physiognomic classification they found that a specific pattern of neurological damage, including audiometric and intellectual damage, was present in all types of endemic cretin.…”