A 13-month-old boy is brought to the clinic for a well-child visit. The patient has been walking since age 10 months. He can say "mama" and "dada." Solid food intake consists of homegrown baby food, including small portions of fruits, vegetables, eggs, and grains once a day. He breastfeeds 8-10 times a day. The patient was born full-term and has no chronic medical conditions. He takes no medications or vitamins. He has a cousin with achondroplasia. On examination, the anterior fontanel is wide open. The skull bones are pliable to palpation. Bony prominences are palpated at the costochondral junctions bilaterally. Bilateral legs appear bowed; the left leg appears more bowed than the right. The remainder of his examination is normal. Which of the following is the most likely cause of this patient's findings?

Question

A 13-month-old boy is brought to the clinic for a well-child visit.  The patient has been walking since age 10 months.  He can say "mama" and "dada."  Solid food intake consists of homegrown baby food, including small portions of fruits, vegetables, eggs, and grains once a day.  He breastfeeds 8-10 times a day.  The patient was born full-term and has no chronic medical conditions.  He takes no medications or vitamins.  He has a cousin with achondroplasia.  On examination, the anterior fontanel is wide open.  The skull bones are pliable to palpation.  Bony prominences are palpated at the costochondral junctions bilaterally.  Bilateral legs appear bowed; the left leg appears more bowed than the right.  The remainder of his examination is normal.  Which of the following is the most likely cause of this patient's findings?

Quizplus · Accepted Answer

11ec25c8_d748_ec66_bc81_79a20ade3121_MD0003_00 This infant likely has nutritional rickets due to a deficiency in vitamin D, which is necessary for calcium metabolism and skeletal growth. Clinical manifestations typically appear after several months of deficiency and reflect defective mineralization, particularly at growth plates and sites of rapid bone growth. Findings include enlarged or delayed closure of fontanels, wrist enlargement, and craniotabes (soft skull bones). Progressive, symmetric or asymmetric bowing of the femurs and tibias may occur after children become weight-bearing, as seen here. Widening of the costochondral joints ("rachitic rosary") on the anterior chest is common and may appear as bony prominences on examination. wrist enlargement "rachitic rosary" Vitamin D is made naturally within the skin on exposure to ultraviolet rays. Therefore, risk factors for vitamin D deficiency include limited sun exposure and increased skin pigmentation (melanin partially blocks ultraviolet rays from reaching the skin). In addition, infants who are primarily breastfed without vitamin D supplementation are at risk because breast milk does not provide adequate vitamin D (particularly if the mother is deficient) and few natural foods contain vitamin D. Therefore, homemade baby food without vitamin D fortification, as in this case, is likely also inadequate. (Choice A) Achondroplasia features include limb shortening, tibial bowing, frontal bossing, and gross motor delay. This patient's gross motor skills are appropriate for age, and craniotabes and costochondral joint hypertrophy are not associated with achondroplasia. (Choice B) Although often asymptomatic at birth, congenital syphilis is associated with early bony destruction that can cause limited extremity movement or pain, which is not seen here. Additional bony findings (eg, frontal bossing, anterior bowing of tibia ["saber shins"]) develop age >2. (Choice C) Congenital hypothyroidism can present with lethargy, constipation, and feeding difficulties; examination may reveal large fontanels and macroglossia. Most neonates are identified by newborn screening, and bone abnormalities are not seen. (Choice D) Without additional findings, this infant's open anterior fontanel could be normal because closure typically occurs at age 12-15 months. In addition, physiologic varus (symmetric bowing) is normal until age 2. However, craniotabes, asymmetric bowing, and costochondral joint hypertrophy are abnormal and require evaluation. Educational objective: Rickets presents with craniotabes (soft skull bones), enlarged costochondral joints, and progressive genu varum. Risk factors for nutritional rickets due to vitamin D deficiency include increased skin pigmentation, limited sun exposure, and insufficient dietary intake (eg, exclusive breastfeeding without vitamin D supplementation). References: Prevention of rickets and vitamin D deficiency in infants, children, and adolescents. (http://www.ncbi.nlm.nih.gov/pubmed/18977996) Nutritional rickets. (http://www.ncbi.nlm.nih.gov/pubmed/21274312)

A 13-Month-Old Boy Is Brought to the Clinic for a Well-Child