Osteomalacia and Rickets

A 6-year-old boy from rural Bihar presents with bowing of legs, delayed tooth eruption, and frontal bossing. Serum calcium is 7.2 mg/dL, phosphate 3.8 mg/dL, and alkaline phosphatase 180 IU/L. A 35-year-old woman from the same village presents with bone pain, muscle weakness, and a serum calcium of 7.8 mg/dL, phosphate 3.2 mg/dL, and alkaline phosphatase 95 IU/L. Which feature best distinguishes nutritional rickets in the child from osteomalacia in the adult?

A 3-year-old girl with vitamin D-dependent rickets type 1 (VDDR-1) has a serum 25-hydroxyvitamin D level of 28 ng/mL and a 1,25-dihydroxyvitamin D level of 8 pg/mL. A 4-year-old boy with vitamin D-dependent rickets type 2 (VDDR-2) has a serum 25-hydroxyvitamin D level of 32 ng/mL and a 1,25-dihydroxyvitamin D level of 680 pg/mL. Which biochemical finding best distinguishes VDDR-1 from VDDR-2?

A 3-year-old child from rural Bihar presents with bowing of legs, delayed fontanelle closure, and frontal bossing. Serum calcium is 7.2 mg/dL, phosphate 3.5 mg/dL, and alkaline phosphatase is markedly elevated. What is the most common cause of rickets in this clinical scenario?

A 38-year-old woman from rural Bihar presents with progressive bone pain, muscle weakness, and difficulty climbing stairs for 8 months. She reports dietary restriction of dairy and minimal sun exposure due to cultural practices. On examination, she has generalized bone tenderness and proximal muscle weakness (grade 4/5). Serum calcium is 7.8 mg/dL (normal 8.5–10.5), phosphate 2.1 mg/dL (normal 2.5–4.5), alkaline phosphatase 156 IU/L (normal 30–120), and 25-hydroxyvitamin D is 12 ng/mL (normal >30). X-ray shows loss of sharp cortical margins and generalized osteopenia. What is the most likely diagnosis?

A 35-year-old woman with chronic kidney disease stage 4 (eGFR 22 mL/min/1.73 m²) presents with bone pain, muscle weakness, and a serum calcium of 7.8 mg/dL (corrected). Laboratory studies show phosphate 5.2 mg/dL, alkaline phosphatase 420 IU/L, PTH 580 pg/mL (normal 15–65), and 25-hydroxyvitamin D 28 ng/mL. 1,25-dihydroxyvitamin D level is 18 pg/mL (normal 20–60). What is the most appropriate immediate next step in management?