Background & aim: Autoimmune thyroid disease (AITD) is frequently accompanied by other organ-specific diseases. The aim of this study was to estimate the frequency of the association AITD-Biermers disease (pernicious anemia) by investigating the presence of intrinsic factor antibodies (IF-Ab) in the serum of patients with AITD.
Methods: Sera from patients with biological signs of AITD (increased serum TSH levels associated to detectable thyroid peroxydase autoantibodies (N=55) or very low serum TSH levels associated to detectable TSHR autoantibodies (N=58)) were screened for the presence of type I IF-Ab with an automated chimiluminometric immunoassay based on a competitive method (Access IF Ab). Matched sera from patients with hypothyroidism (N=66) or hyperthyroidism (N=47) but no detectable peroxydase or TSHR autoantibodies, respectively, were similarly tested.
Results: Sera from 4 patients were tested positive for IF-Ab. All of them suffered from an autoimmune thyroid disease (2 Graves disease, 2 Hashimotos thyroiditis). Biermers disease was previously known for 2 of them. Biermers disease is strongly suspected in the 2 other patients: for the first, presence of parietal cell autoantibodies, normal serum vitamin B12 concentration and for the second, presence of type I diabetes and vitiligo and low serum B12 concentration. Sera from patients with non autoimmune thyroid dysfunction were all IF-Ab negative.
Conclusion: The incidence of detectable IF-Ab is significantly higher (3.5%) in patients with AITD than in patients with non autoimmune thyroid disease. Testing sera for the other IF-Ab (type 2) should uncover even more patients at risk for vitamin deficiency as the presence of type 2 IF-Ab could occur alone (no type I IF-Ab) in half Biermers disease (thus potentially doubling the incidence). A prospective study looking for evidence of gastric autoimmunity and vitamin B12 deficiency in patients with AITD should establish whether the need to routinely test the patients is clinically useful or purely academic.