Objective: It is well-established that hyperthyroidism of Graves disease is caused by generation of TSH-receptor stimulating autoantibodies. However, in some patients TRAB titers may be in normal levels. The rate and the burden of TRAB negative disease vary between studies. In this study, we compared the clinical and laboratory parameters of 170 patients (85 TRAB positive and 85 TRAB negative) that were diagnosed to have Graves disease in our department.
Methods: Diagnostic criteria for Graves disease; i) Elevated free T3 or free T4 ii) Typical thyroid inferno pattern in ultra-sonography iii) Elevated radioiodine uptake (I-131). TRAB was measured with radioreceptor assay (RRA)-(RIAZEN-Belgium).
Results: Mean age of study group was 46.7 and female dominance was present (72%). FT4, FT3, ATPO, thyroid volume and radioiodine uptake was significantly elevated in TRAB positive disease. Mean age or the presence of thyroid nodules did not differ between groups. TRAB negative disease was more common in females (P=0.06). Thyroid ophtalmopathy was diagnosed dominantly in TRAB positive disease (41% vs %24 P=0.05). The recurrence of disease in radioactive-iodine or anti-thyroid drug treated subjects was more common in TRAB positive subjects (%25 vs %7). TRAB titers were found to be correlated with FT4, FT3, ATPO, thyroid volume and radioiodine uptake.
Conclusion: TRAB negative Graves disease is not a clinical entity on which the endocrinologists have fully agreed. It has been suggested that technical difficulties in TRAB assays might contribute to lower levels. Furthermore, some authors suggest that Hashitoxicosis should be the proper diagnosis in patients with TRAB negative thyrotoxicosis.
Our results demonstrate that TRAB negative Graves disease is associated with a milder form of thyrotoxicosis. However, either the clinical presentation of our patients or their laboratory data are distinguishable from Hashimato Thyroiditis. We suggest that TRAB negative Graves disease is a real clinical subtype of Graves disease. It must be kept in mind that, despite low TRAB levels, ophtalmopaty or recurrence of disease may occur.