A Rare Case of Possible Iron Overload and B12 Deficiency in Autoimmune Polyglandular Syndrome Type 3B

Autoimmune polyglandular syndromes (APS) are a rare group of disorders characterized by the dysfunction of multiple endocrine and non-endocrine organs due to autoimmune destruction. APS type 3B (APS3B) is a subtype characterized by the coexistence of autoimmune thyroiditis and pernicious anemia, more commonly observed among middle-aged females. Here, we describe a unique case, workup, and diagnosis of APS3B in a 58-year-old Hispanic male who presented with an atypical presentation of APS3B complicated by metformin use and possible transfusional iron overload. Workup revealed positive intrinsic factor antibodies and elevated homocysteine and methylmalonic acid levels, confirming pernicious anemia. Thyroid studies demonstrated markedly positive anti-thyroid peroxidase antibodies and elevated thyroid-stimulating hormone, consistent with autoimmune thyroiditis. He was treated with blood transfusions, initiation of intramuscular vitamin B12 injections, and discontinuation of metformin. This case highlights how APS may be overlooked in patients with multiple chronic comorbid conditions and should be considered in those presenting with several endocrine abnormalities.