SAT-735 Chronic Giardiasis as a Cause of Malabsorption-Induced Osteomalacia

Abstract Disclosure: T. Rizwan: None. K. Bayrakdar: None. U.N. Syed: None. Background: Osteomalacia results from defective mineralization of newly formed osteoid due to prolonged vitamin D deficiency, often caused by limited sun exposure, poor dietary intake, or malabsorption. We report a case of a 38-year-old woman who developed osteomalacia secondary to chronic giardiasis, leading to vitamin D deficiency through malabsorption. Clinical Case: A 38-year-old female immigrant from India with a history of iron deficiency anemia presented with severe left thigh pain for two days after a fall. She reported chronic bilateral lower extremity pain, worsening post-fall, and intermittent watery diarrhea. She was hemodynamically stable, with restricted lower extremity movement due to pain. Laboratory tests showed normal electrolytes, eGFR > 60, and microcytic anemia. Vitamin B12 and folic acid were low-normal. Bilateral hip X-rays revealed linear lucency in the medial femoral necks with adjacent sclerosis, consistent with Looser zones. Further testing showed elevated PTH (419.7 pg/mL), severe vitamin D deficiency (<7 ng/mL), and 1,25-OH vitamin D (46 pg/mL), ionized calcium of 1.17 mmol/L, and phosphate of 2.9 mg/dL. The patient was diagnosed with osteomalacia due to severe vitamin D deficiency. She received IV iron, vitamin B12, and ergocalciferol 50,000 units weekly, later increased to 100,000 units. Given concerns about malabsorption, further tests, including a celiac panel, fecal fat analysis, and stool ova and parasite exam, were ordered. She was also started on elemental calcium 60 mg twice daily and advised to increase dietary calcium intake. After medical optimization, she underwent bilateral hip fracture fixation. Stool tests later confirmed the presence of Giardia lamblia. She was treated for giardiasis, which was ultimately determined to be the underlying cause of her osteomalacia due to vitamin D deficiency. Discussion and Conclusion: Osteomalacia results from impaired mineralization of newly formed osteoid at bone turnover sites. Proper mineralization requires normal osteoid quality and quantity, adequate calcium and phosphate, normal pH, sufficient alkaline phosphatase activity, and minimal calcification inhibitors. Vitamin D, obtained through diet or skin, is absorbed in enterocytes, hydroxylated in the liver to 25-hydroxyvitamin D, and converted in the kidneys to active 1α,25-dihydroxyvitamin D, which regulates calcium, phosphate balance, and other functions. Giardiasis, caused by Giardia lamblia, is common in low-resource settings. Chronic infection can lead to villous atrophy and malabsorption syndromes. It should be considered a potential cause of vitamin D deficiency in patients with osteomalacia. Timely diagnosis and treatment are crucial to managing malabsorption, correcting vitamin D deficiency, and preserving bone health. Presentation: Saturday, July 12, 2025