Pediatric Examination and Board Review (66 page)

8.
(E)
All of the above. Craniotabes is a generalized softening of the calvaria that can be seen in younger infants with rickets, along with frontal bossing and parietal flattening. Rachitic rosary is caused by prominence of the costochondral junction of the ribs. This is typically palpable on the lateral aspect of the chest in a young child because the ribs are not fully formed. Harrison groves are indentations of the lower ribs from the vessels that run under the ribs and indent the soft bone. Genu varum (bowleg deformity) is also a common rachitic bone deformity, which becomes more pronounced with weight bearing. Children also present with thickening of the wrists and ankles. There is an increased risk of fracture in children with rickets.

9.
(C)
Hypomagnesemia. Low magnesium levels inhibit both PTH secretion and action of PTH at bone and kidney, which will hinder the correction of serum calcium. Serum magnesium should be corrected.

10.
(C)
Liver. PTH promotes calcium mobilization from bone by osteoblast-mediated activation of bone resorbing osteoclasts. In the proximal tubule of the kidney, PTH increases the reabsorption of calcium while inhibiting phosphate reabsorption, and it activates the enzyme 1-α-hydroxylase, which catalyzes the conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D. PTH indirectly promotes the absorption of calcium and phosphate in the intestinal tract through the action of 1,25-dihydroxyvitamin D. PTH does not control calcium through effects on the liver.

11.
(E)
1,25-Dihydroxyvitamin D. The skin produces vitamin D
₃
from 7-deoxycholesterol after exposure to the sun. People with increased skin melanin pigmentation have decreased photosynthesis of vitamin D, and thus they require more time in the sun to make the same amount of vitamin D as those with lighter skin color. Season of the year and geographic latitude can greatly affect the production of vitamin D in the skin. The natural sources of vitamin D include fatty fish, such as salmon, and fatty fish oils, such as cod liver oil. Most vitamin D obtained from the diet comes from fortified foods, such as milk and bread. Vitamin D
₃
is biologically inert and must undergo 25-hydroxylation in the liver, with subsequent 1-α-hydroxylation in the kidney to form the biologically active form of vitamin D, 1,25-dihydroxyvitamin D. 24,25-Dihydroxyvitamin D is biologically inert and one of the first steps of vitamin D degradation.

12.
(C)
Intestinal tract. 1,25-Dihydroxyvitamin D has its major impact in the gut because it promotes the reabsorption of calcium and phosphate in the duodenum and jejunum.

13.
(C)
Congenital hypoparathyroidism. Early neonatal hypocalcemia is characteristically seen in premature infants, infants with asphyxia at birth, and infants of diabetic mothers. Premature infants often have an exaggerated postnatal depression of serum calcium. In addition, both premature infants and asphyxiated infants tend to have an exaggerated rise in calcitonin, which antagonizes the effect of PTH on bone and kidney and may provoke hypocalcemia. Infants of mothers with diabetes may also have an exaggerated postnatal depression of serum calcium, and maternal glycosuria is accompanied by significant losses of magnesium, which predisposes the infant to total body magnesium losses. Hypomagnesemia in turn inhibits both PTH secretion and action.

14.
(A)
Asphyxia. An asphyxiated infant is more likely to present with early neonatal hypocalcemia rather than late neonatal hypocalcemia.

15.
(B)
Phosphate supplementation. Children with rickets because of vitamin D deficiency typically require calcium supplementation and calcitriol acutely to raise their calcium into the normal range. Ergocalciferol is used to replenish the vitamin D stores, but its effects are typically not seen for 4-7 days, hence the use of the biologically active calcitriol acutely. Phosphate supplementation is typically not used unless the rickets is caused by phosphate depletion (as is sometimes seen in premature infants or patients on total parenteral nutrition) or if the patient has hypophosphatemic rickets (in which case the patient would not have hypocalcemia).

16.
(E)
Patient has 1-α-hydroxylase deficiency. In 1-α-hydroxylase deficiency, or what is also termed vitamin D–dependent rickets (VDDR) type I, 25-hydroxyvitamin D is not converted into the biologically active 1,25-dihydroxyvitamin D in the kidney because of a deficiency of 1-α-hydroxylase. These patients cannot make biologically active vitamin D when treated with ergocalciferol, and they must be maintained on calcitriol. This disorder usually presents between 3 and 12 months of life, and children have similar symptoms and signs as children with nutritional rickets. Vitamin D–resistant rickets or vitamin D–dependent rickets (VDDR) type II is caused by a defect in the vitamin D receptor, leading to resistance to vitamin D. They can present with both hypocalcemia and hypophosphatemia.

17.
(D)
Hypercalcemia. Mild hypercalcemia can present with generalized weakness, anorexia, constipation, and polyuria. More severe hypercalcemia can present with nausea, vomiting, dehydration, seizures, and coma. Patients who are hypercalcemic can also present with significant psychological changes such as depression or paranoia.

18.
(E)
A and C. Children with DiGeorge syndrome typically present with transient or permanent hypocalcemia because of hypoplasia of the parathyroid glands, hypoplasia or aplasia of the thymus leading to impaired cell-mediated immunity, and anomalies of the outflow tract of the heart. Abnormalities in the chest radiograph are common, and absence of the thymic shadow should be looked for. Mutations in chromosome 22q11 have been described in DiGeorge syndrome. Other clinical characteristics include facial malformations, short stature, and developmental delay. Mutations in chromosome 15q11 are seen in Prader-Willi syndrome.

S
UGGESTED
R
EADING

Diaz R. Abnormalities in calcium homeostasis. In: Radovick S, MacGillivray MH, eds.
Pediatric Endocrinology
,
A Practical Clinical Guide
. Totowa, NJ: Humana Press; 2003:343-363.

Levine B-S, Carpenter TO. Rickets: the skeletal disorders of impaired calcium or phosphate availability. In: Radovick S, MacGillivray MH, eds.
Pediatric Endocrinology
,
A Practical Clinical Guide
. Totowa, NJ: Humana Press; 2003:365-379.

Root AW, Diamond FB. Disorders of mineral homeostasis in the newborn, infant, child and adolescent. In: Sperling MA, ed.
Pediatric Endocrinology.
3rd ed. Philadelphia, PA: WB Saunders; 2008:686-769.

Rosen CJ, ed.
Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism
7th ed. Washington, DC: American Society for Bone and Mineral Research; 2008.

CASE 42: A 12-YEAR-OLD GIRL WITH NAUSEA, ABDOMINAL PAIN, AND VOMITING

A 12-year-old girl comes to your office with complaints of nausea, abdominal pain, and emesis for the past 24 hours. She has previously been healthy, but her parents believe she has lost weight over the summer despite a very good appetite. She has been drinking more water during the day, which her parents relate to it being summertime. She also complains of nocturia for the last few months. She is not taking any medications. On examination, she appears ill, with dry mucous membranes. She is afebrile. Respirations are deep and rapid.

SELECT THE ONE BEST ANSWER

1.
What diagnosis would be at the top of your differential?

(A) appendicitis

(B) gastroenteritis

(C) diabetes insipidus

(D) diabetes mellitus

(E) psychogenic polydipsia

2.
What test would you do first?

(A) serum amylase

(B) abdominal ultrasound

(C) liver function tests

(D) hemoglobin A1c

(E) urinalysis

3.
Diabetic ketoacidosis (DKA) is typically characterized by all of the following except

(A) hyperkalemia

(B) hyperglycemia

(C) ketosis

(D) acidosis

(E) osmotic diuresis

4.
The following hormones play a role in DKA except

(A) cortisol

(B) growth hormone

(C) epinephrine

(D) prolactin

(E) B and D

5.
Your patient has a serum blood glucose of 900 mg/dL, pH 7.0, large serum ketones, sodium 126, potassium 4.2, chloride 102, bicarbonate less than 5, and phosphate 4.2 mEq/L. Which of the following is true?

(A) she should be treated for hyponatremia

(B) the blood glucose should be lowered to normal as quickly as possible

(C) she should receive an ampule of sodium bicarbonate

(D) she should have additional potassium in the intravenous (IV) fluids

(E) further monitoring of phosphate is not necessary

6.
Potential drawbacks to the use of sodium bicarbonate in DKA include each of the following except

(A) cerebral edema

(B) rebound alkalosis

(C) sodium overload

(D) hypokalemia

(E) rise in cerebrospinal fluid (CSF) pH

7.
What would the most appropriate initial management be if her serum blood sugar was 800 mg/dL, serum and urine ketones were large, and pH was 7.12?

(A) bolus of normal saline