Renal tubular acidosis type 2 with Fanconi's syndrome, osteomalacia, osteoporosis, and secondary hyperaldosteronism in an adult consequent to vitamin D and calcium deficiency: effect of vitamin D and calcium citrate therapy.

ABSTRACT

OBJECTIVE: To describe a unique example of renal tubular acidosis type 2 (RTA 2) in conjunction with Fanconi's syndrome and osteomalacia consequent to vitamin D and calcium deficiency in an adult without underlying gastrointestinal disease. METHODS: We review the clinical, hormonal, histomorphometric, and micro-computed tomographic findings and the response to therapy with vitamin D and calcium in our patient. RESULTS: On admission, a 33-year-old African American woman had the following laboratory findings: serum ionized calcium 3.8 mg/dL (0.95 mmol/L), venous pH 7.26, bicarbonate 20 mEq/L, chloride 111 mEq/L, alkaline phosphatase 1,192 U/L (20.26 microkat/L) (normal, 40 to 136 U/L), 25-hydroxyvitamin D <5 ng/mL (<12 nmol/L) (normal, 10 to 60 ng/mL), parathyroid hormone 1,620 pg/mL (165.2 pmol/L) (normal, 10 to 60 pg/mL), aldosterone 68.4 ng/dL (1,894.7 pmol/L) (normal, 4.5 to 35.4 ng/dL), supine plasma renin activity 19.8 ng/mL per hour (5.35 ng/L per second) (normal, 0.5 to 1.8 ng/mL per hour), and aminoaciduria. A lumbar spine bone density T-score was -4.6, and a femoral neck T-score was -4.9. An undecalcified tetracycline-labeled bone biopsy specimen showed severe osteomalacia, severe osteoporosis, and peritrabecular fibrosis. A small intestinal biopsy revealed normal findings. Results of an ammonium chloride loading test and a bicarbonate infusion test were consistent with RTA 2. After 24 months of vitamin D and calcium therapy, results of serum and urine chemistry studies and bicarbonate infusion normalized. The lumbar spine T-score improved to -2.0, and the femoral neck T-score improved to -2.7. Bone biopsy specimens demonstrated resolution of the osteomalacia. CONCLUSION: Nutritional vitamin D and calcium deficiency may cause RTA 2, Fanconi's syndrome, and osteomalacia in adults as well as in children.