MEDizzy - A 68-year-old Muslim woman, wearing a classic black hijab,

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Musculoskeletal and Integumentary Systems

A 68-year-old Muslim woman, wearing a classic black hijab, presents with pain in the lower spinal and pelvic region. She describes the pain as dull and especially prominent when walking or carrying something. X-ray images of the spine show microfractures. Serum calcium and phosphorus concentrations are within reference ranges. Serum alkaline phosphatase and parathyroid hormone levels are elevated. 25-hydroxyvitamin D is decreased. Which of the following is the most likely diagnosis?

ExplanationThe woman suffers from vitamin D deficiency, most likely caused by reduced sun exposure due to whole body clothes. When exposed to sunlight, cutaneous vitamin D (7-dehydrocholesterol) is converted to cholecalciferol, which is metabolized in the liver to 25-hydroxycholecalciferol (25[OH]D). Moreover, cutaneous production of vitamin D decreases with age, and dietary vitamin D intake is often low in older people, both further reducing her 25(OH)D production. At very low levels, there is not enough substrate for its conversion to 1,25-dihydroxy vitamin D, leading to reduced intestinal absorption of calcium and phosphorus. Initially, hypocalcemia leads to increased release of parathyroid hormone (PTH). The consequent bone demineralization can normalize serum calcium and phosphorus but leads to osteomalacia, which presents with bone pain (especially when weight-bearing), microfractures, muscle weakness, and difficulty walking. Serum alkaline phosphatase (ALP) is elevated and indicates increased osteoblastic activity and bone turnover in general.