Addison-like Clinical Phenotype Without Adrenal Insufficiency: A Rare Manifestation of Pernicious Anemia.

Severe vitamin B12 deficiency can clinically mimic Addison disease, with hyperpigmentation despite preserved adrenal function. We report a 34-year-old woman presenting with fatigue, an unintended weight loss of about 20 kg, and mucocutaneous hyperpigmentation raising concern for primary adrenal insufficiency. Examination showed pallor, mild scleral icterus, and elevated blood pressure. Laboratory testing demonstrated severe cobalamin deficiency with macrocytic anemia and biochemical evidence of intramedullary hemolysis, whereas morning cortisol and ACTH levels excluded adrenal failure. Intrinsic factor antibodies confirmed pernicious anemia. Notably, cancer antigen 15-3 was elevated at presentation but normalized after intramuscular vitamin B12 replacement, indicating a benign hematologic rather than oncologic etiology. Treatment triggered an appropriate reticulocyte response with subsequent hematologic recovery and gradual resolution of the hyperpigmentation. Pernicious anemia should be considered in the differential diagnosis of Addison-like pigmentation without adrenal insufficiency. Recognizing that tumor marker elevation may occur in severe megaloblastic anemia is essential to prevent unnecessary oncologic workup.