ACUTE PRE-TIBIAL MYXEDEMA FOLLOWING RADIOIODINE THERAPY FOR THYROTOXIC GRAVES-DISEASE

A 54-year-old woman was treated with an oral dose of 555MBq of I-131 r adioiodine for thyrotoxicosis. She had no clinically detectable extrat hyroidal manifestations of Graves' disease at the time, but within two months developed moderately severe ophthalmopathy and very extensive thyroid dermopathy affecting her face, arms, hands and feet, in additi on to the classic pre-tibial area. Although she developed mild post ra dioiodine hypothyroidism, this was detected at an early stage and its treatment had no effect on the extrathyroidal signs. Thyrotrophin rece ptor antibodies (TRAb) were positive before treatment (22% inhibition of TSH binding in neat serum), rose to very high levels following radi oiodine (97.6% inhibition), and fell progressively over the following year during treatment with prednisolone. Thyroglobulin autoantibodies became detectable following radioiodine but thyroid peroxidase antibod ies were undetectable throughout. Serum and purified IgG from blood sa mples obtained prior to steroid therapy and over the subsequent year w ere tested on a dermal fibroblast cell line in vitro for the stimulati on of synthesis of glycosaminoglycans, protein and DNA, but no increas e in radiolabel incorporation was apparent for any sample when compare d to controls. The temporal relation between the radioiodine and the a cute onset of dermopathy and ophthalmopathy, together with the abrupt rise in TRAbs, indicates a probable causal association. However, the a bsence of in-vitro fibroblast stimulation would suggest that the patho genesis of Graves' dermopathy is not dependent solely on any simple hu moral factor.