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The Child with Possible Rickets (Case 7)

 An 8-month-old child has a 24-hour history of increased crying when she moves her right leg. She has a prominent bulge over the mid-right thigh where she had received an immunization yesterday. She has not had fever nor change in appetite, and she seems upset only when the leg is disturbed. The child underwent a failed Kasai procedure for biliary atresia and is awaiting a liver transplant. A radiograph of the leg demon-strates a mid-shaft fracture and poor mineralization.

What is the mechanism for this condition?

What are the best diagnostic tests to diagnose this condition?

ANSWERS TO CASE 7: 

Rickets

Summary: An 8-month-old child with a chronic medical condition, including biliary atresia, poor bone mineralization, and a fracture.

Mechanism: Malabsorption of vitamin D (among other fat-soluble vitamins) due to lack of intestinal secretion of bile salts, resulting in rickets.
Best diagnostic tests: Serum 25(OH)D, calcium, phosphorus, and alkaline phosphatase levels. Radiographs demonstrate poor bone mineralization.

ANALYSIS

Objectives

1. Become familiar with the clinical presentation of rickets.
2. Understand the pathophysiology behind nutritional and nonnutritional rickets.
3. Appreciate some of the other metabolic causes of childhood fractures.

Considerations
This child has biliary atresia and underwent a failed Kasai procedure. Metabolic aberrations are expected while this child awaits liver transplanta-tion. A review of her medications and compliance in receiving them is war-ranted. Because of the brittle nature of her bones, her leg was fractured while receiving immunizations.

APPROACH TO 

The Child with Possible Rickets



DEFINITIONS

BILIARY ATRESIA: A congenital condition affecting approximately 1 in 16,000 live births in which the liver’s bile ducts become blocked and fibrotic, resulting in reduced bile flow into the bowel.
GENU VALGUM: “Knock” knees.
GENU VARUM: “Bowed” legs.

KASAI PROCEDURE: An operative procedure in which a bowel loop forms a duct to allow bile to drain from a liver with biliary atresia.
RICKETS: Poor mineralization of growing bone or of osteoid tissue.
CLINICAL APPROACH
A patient with liver failure has poor bile salt secretion, resulting in poor fat-soluble vitamin absorption, including vitamin D. The poor vitamin D absorption causes low serum 25(OH)D, occasionally reduced serum calcium levels, markedly elevated serum alkaline phosphatase, poor bone mineral-ization, and an increased risk of fractures. Children with liver failure and ascites are treated with loop diuretics, which often cause urinary calcium losses. Treatment, aimed at restoring normal bone mineralization, consists of high vitamin D doses and calcium supplementation.
Nutritional rickets, resulting from inadequate dietary vitamin D or a lack of sunlight exposure (Figure 7–1), is rare in industrialized countries in healthy children. It is occasionally seen in dark-skinned infants who do not receive vitamin D supplementation or in breast-fed infants not exposed to sunlight. More common causes of rickets are liver or renal failure and a variety of bio-chemical abnormalities in calcium or phosphorus metabolism (Table 7–1).
The most common form of nonnutritional rickets is familial, primary hypophosphatemia (X-linked dominant) in which phosphate reabsorption is defective, and conversion of 25(OH)D to 1,25(OH)2D in the proximal tubules of the kidneys is abnormal. Low serum 1,25(OH)2D, low–normal serum calcium, moderately low serum phosphate, and elevated serum alkaline phosphatase levels, hyperphosphaturia, and no evidence of hyperparathy-roidism results. Children at the age of walking present with smooth lower-extremity bowing (as compared to angular bowing of calcium-deficient rickets), a waddling gait, genu varum, genu valgum, coxa vara, and short stature. Other findings of calcium-deficient rickets (myopathy, rachitic rosary, pectus deformities, tetany) usually are not seen. Familial hypophosphatemia can cause intraglobular dentin deformities, whereas calcium-deficient rickets causes enamel defects. Radiologic findings include coarse-appearing trabecu-lar bone and widening, fraying, and cupping of the metaphysis of the proxi-mal and distal tibia, distal femur radius, and ulna.



Comprehension Questions
7.1     A 14-month-old child has lower-extremity bowing, a waddling gait, genu varum, and is at the fifth percentile for height. Laboratory data include low–normal serum calcium, moderately low serum phosphate, and elevated serum alkaline phosphatase levels, hyperphosphaturia, and normal parathyroid levels. Which of the following is the most likely diagnosis?

A. Fanconi syndrome
B. Genetic primary hypophosphatemia
C. Malabsorption of vitamin D
D. Phosphate malabsorption
E. Renal osteodystrophy

7.2    An 8-month-old African-American baby arrives to the emergency department with his mother with the complaint of decreased left arm movement. He is the product of a normal term pregnancy, has had no medical problems, and was in good health when his mother dropped him off at the day care center. Upper arm radiographs show a left humerus spiral fracture. Which of the following is the most appropri-ate next step in management?

A. Admit the child and call child protective services.
B. Obtain serum 1,25(OH)2D levels.
C. Order serum alkaline phosphatase levels.
D. Obtain stool for analysis for fat-soluble vitamins.
E. Send chromosome sample for osteogenesis imperfecti analysis.

7.3    The diet of a 3-year-old child with cystic fibrosis should be supple-mented with which of the following?

A. Folate
B. Sodium
C. Vitamin C
D. Vitamin B12
E. Vitamin D

7.4    A 5-year-old girl is somewhat short and has mild leg bowing. Her med-ical history is significant only for well-controlled seizure disorder. Serum calcium, phosphorus, and alkaline phosphatase levels and uri-nary amino acid concentration are normal. A bone age is notable for abnormal distal radius and ulna mineralization. Which of the follow-ing is the most likely diagnosis?

A. Cystic fibrosis
B. Fanconi syndrome
C. Genetic primary hypophosphatemia
D. Rickets associated with anticonvulsive drug use
E. Schmid metaphyseal dysplasia

ANSWERS

7.1    B. Lower-extremity bowing, low–normal calcium and phosphate lev-els, and normal parathyroid hormone levels suggest familial primary hypophosphatemia.
7.2    A. A spiral fracture of the humerus is suspicious but not diagnostic for child abuse. While further laboratory testing is appropriate, the next step in the management of this child is to provide a safe envi-ronment until more data are available.
7.3    E. In addition to pancreatic enzyme replacement therapy, supple-mentation with fat-soluble vitamins (A, D, E, and K), often iron, and sometimes zinc is recommended.
7.4    E. All of the rickets syndromes present with elevated alkaline phos-phatase levels. Schmid metaphyseal dysplasia, an autosomal domi-nant condition, presents in a similar way with short stature, leg bowing, and waddling gait. Radiographs show irregular long bone mineralization. Biochemically, Schmid-type metaphyseal dysostosis presents with normal serum calcium, phosphorus, and alkaline phos-phatase activity and normal urinary amino acid levels.

Clinical Pearls
Nutritional rickets (inadequate dietary vitamin D or sunlight exposure) is rare in healthy children in industrialized countries. Medical conditions (liver or renal failure) or abnormalities in calcium and phosphorus metab-olism usually are responsible.
Primary hypophosphatemia (X-linked dominant) is the most common cause of nonnutritional rickets; proximal kidney tubule defects in phos-phate reabsorption and conversion of 25(OH)D to 1,25(OH)2D are seen. Findings include low–normal serum calcium, moderately low serum phos-phate, elevated serum alkaline phosphatase, and low serum 1,25(OH)2D levels, hyperphosphaturia, and no evidence of hyperparathyroidism.

REFERENCES


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The Child with Possible Rickets (Case 7) The Child with Possible Rickets (Case 7) Reviewed by WebofPediatric on December 15, 2021 Rating: 5

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