The effect of iodized oil on goitre size, thyroid function and the development of the Jod Basedow phenomenon.

Abstract

SUMMARYIn the Lubok Antu district of Sarawak, Malaysia, 240 subjects with 75% prevalence of goitre were studied before and at intervals of 1 and 2 years following iodized oil injection. After 1 year the prevalence of goitre was reduced to 33%, but 2 years after injection, goitres had regrown in fourteen subjects (6%). The mean urinary iodine concentration was low initially at 0±17±0±08 (SD) μmol/l, consistent with iodine deficiency, and rose to a level of 2±6 ± 2±5 μmol/l at 1 year, before falling to 0±46 ± 0±38 μmol/l, again consistent with deficiency. Such a rapid depletion of iodine may be related to the high consumption of cassava. Before injection serum TSH concentrations showed a wide scatter from normal up to 62 mU/l and at 1 year, serum TSH concentrations were undetectable. At 2 years serum TSH was again detectable in 50% of subjects with levels up to 8±6 mu/l. During the 2 years, there was a progressive rise in the mean serum T4 concentration from 92 ± 22 (SD) nmol/l to 110 ± 22 nmol/l (P < 0±05). Serum T3 concentrations rose serially in all subjects from a pre‐injection mean of 1±9 ± 0±3 nmol/l to 2±5 ± 0±9 nmol/l (P < 0±001) and then fell significantly below the baseline level to a mean of 1±7 ± 0±6 nmol/l 2 years after injection (P < 0±01). The mean serum rT3 levels followed the same trend. At 1 or 2 years following injection, eight subjects were clinically hyperthyroid. Four of these consented to venesection and hyperthyroidism was confirmed biochemically. These data reveal that: goitres decreased rapidly in size in response to iodized oil injection; 2 significant though incomplete depletion of the iodine stores occurred within 2 years of injection; the consistent increase in serum T3 was associated with a fall in serum TSH to undetectable levels; the prevalence of the Jod Basedow phenomenon was l±7%. These data suggest the need for closer biochemical monitoring of subjects receiving massive doses of iodine and a reappraisal of the use of iodized oil in the treatment of endemic goitre.