A 3-year-old boy is evaluated for delayed developmental milestones, including short stature. There is no family history of bone conditions. The family recently immigrated to the United States. The patient was exclusively breastfed until age 6 months and has since had a varied diet of fruits, vegetables, and meats. He takes no medications or supplements. Vital signs are normal. Physical examination reveals frontal bossing, dental enamel defects, and bilateral, symmetric, bead-like enlargement of the costochondral junctions. If a histologic examination of the bone is performed, which of the following changes is most likely to be seen in this patient?

Question

A 3-year-old boy is evaluated for delayed developmental milestones, including short stature.  There is no family history of bone conditions.  The family recently immigrated to the United States.  The patient was exclusively breastfed until age 6 months and has since had a varied diet of fruits, vegetables, and meats.  He takes no medications or supplements.  Vital signs are normal.  Physical examination reveals frontal bossing, dental enamel defects, and bilateral, symmetric, bead-like enlargement of the costochondral junctions.  If a histologic examination of the bone is performed, which of the following changes is most likely to be seen in this patient?

Quizplus · Accepted Answer

11ec160b_3a6c_7382_9249_e561c15f0cbe_MD0001_00 Vitamin D is derived from food and generated in the skin due to sunlight exposure (ie, conversion of 7-dehydrocholesterol to cholecalciferol). Endogenous production from sunlight accounts for approximately half of daily requirements (~200-400 IU/day [required: 600]). The dietary share is usually obtained primarily from fortified dairy/dairy-alternative foods; oily fish (eg, salmon, herring) is also an abundant source. Other foods contain vitamin D but are often insufficient to meet requirements. Vitamin D deficiency reduces intestinal absorption of calcium. Parathyroid hormone secretion increases to mobilize calcium from bone and maintain plasma calcium levels but causes renal phosphate wasting. The resulting hypophosphatemia causes impaired mineralization of bone. In children, this manifests as rickets, characterized by excessive unmineralized osteoid matrix at the epiphyseal (growth plate) cartilage. Clinical manifestations of rickets include frontal bossing, craniotabes (softened skull bones), and costochondral widening from cartilage overgrowth (rachitic rosary). Dental enamel hypoplasia can also be seen. Weight-bearing children may show lower extremity bowing (genu varum). Radiographs of growth plates (eg, distal ulna) often reveal metaphyseal plate widening and cupping. (Choice A) Glucocorticoids (eg, prednisone) cause osteoporosis because they inhibit proliferation and differentiation of osteoblast precursors and increase apoptosis of mature osteoblasts. Fragility fractures may occur, but this patient's deformities are more consistent with rickets. (Choice B) The early osteolytic phase of Paget disease of bone is characterized by proliferation of abnormally large, hypernucleated osteoclasts. Paget disease causes bone pain and deformity (eg, frontal bossing, bowing of long bones) but findings are typically focal and asymmetric and usually occur in adults age >50. (Choice C) Replacement of bone with disorganized fibrous connective tissue (fibrous dysplasia) can occur in a single bone (eg, femur) or multiple bones (polyostotic). Polyostotic fibrous dysplasia (McCune-Albright syndrome) is typically associated with café au lait macules and pituitary endocrine disorders (eg, precocious puberty, thyrotoxicosis, acromegaly). (Choice D) Osteosarcoma, the most common malignant bone tumor in children, is characterized by excessive production of mineralized bone. The lesions are typically single and would not cause short stature, frontal bossing, or enamel defects. Educational objective: Vitamin D deficiency decreases intestinal absorption of calcium. Parathyroid hormone secretion increases to maintain plasma calcium, which causes renal phosphate wasting and impaired bone mineralization. In children, this causes rickets characterized by excessive unmineralized osteoid matrix at the epiphyseal cartilage.

A 3-Year-Old Boy Is Evaluated for Delayed Developmental Milestones, Including