Case Presentation: A 58-year-old Hispanic male with type 2 diabetes on Metformin, chronic B12 deficiency with macrocytic anemia requiring recurrent transfusions, hypothyroidism, peripheral neuropathy, and chronic myositis presented with 1.5 months of worsening fatigue, dyspnea, dizziness, and generalized edema. He had poor outpatient follow-up and had not seen his primary care provider in years. He was first diagnosed with chronic anemia 15–20 years ago and required transfusions approximately every 6 months since then. Labs revealed severe macrocytic anemia (Hb 5.6 g/dL), markedly low vitamin B12, elevated homocysteine and methylmalonic acid, and positive intrinsic factor antibodies confirming pernicious anemia. Iron studies suggested secondary iron overload, and thyroid studies showed elevated TSH with markedly positive anti-thyroid peroxidase antibodies, consistent with autoimmune thyroiditis. These findings confirmed the diagnosis of autoimmune polyglandular syndrome type 3B (APS3B), a rare disorder characterized by both autoimmune thyroiditis and pernicious anemia. The patient received blood transfusions, intramuscular B12 supplementation, and discontinuation of Metformin, with improvement in symptoms. Outpatient follow-up was arranged for continued B12 therapy, monitoring for iron-related complications, and management of thyroiditis.
Discussion: This case demonstrates the diagnostic complexity of APS3B with overlapping metabolic and hematologic disorders. Iron overload from chronic transfusions and Metformin-associated B12 deficiency initially masked the autoimmune etiology and delayed recognition. APS3B typically occurs in middle-aged females; this atypical male presentation underscores the need for high suspicion in patients with multiple endocrine abnormalities. Hospitalists are uniquely positioned to identify rare autoimmune syndromes, coordinate acute management, and address underlying causes. Recognizing conditions like APS3B prevents patients from undergoing repeated admissions for blood transfusions without treating the root problem, reducing morbidity and long-term complications such as iron overload.
Conclusions: APS3B can present atypically in male patients and can be masked by iron overload and B12 deficiency. Hospitalists play a critical role in uncovering underlying causes, avoiding repeated symptomatic management, and ensuring appropriate follow-up. Recognizing APS3B enables monitoring for other autoimmune disorders, emphasizing the importance of comprehensive inpatient evaluation to prevent recurrent hospitalizations and optimize patient outcomes.