Updated: 6/2/2020

Rickets

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Introduction
  • Overview
    • rickets is a defect in mineralization of osteoid matrix caused by inadequate calcium and phosphate that occurs prior to closure of the physes
      • known as osteomalacia if it occurs after physeal closure
      • can be congenital or acquired
      • treatment is usually non-operative with supplementation
  • Pathophysiology
    • Vitamin D and PTH play an important role in calcium homeostasis 
    • disruption of calcium/phosphate homeostasis
    • poor calcification of cartilage matrix of growing long bones
      • occurs at zone of provisional calcification
    • leads to increased physeal width and cortical thinning/bowing
  • Associated conditions
    • orthopaedic manifestations include
      • brittle bones with physeal cupping/widening 
      • bowing of long bones 
      • ligamentous laxity
      • flattening of skull
      • enlargement of costal cartilage (rachitic rosary) 
      • kyphosis (cat back)  
Classification
  • Vitamin D-resistant (familial hypophosphatemic)
    • most common form of heritable rickets
    • presents at 1-2 years of age
    • caused by inability of renal tubules to absorb phosphate 
      • GFR is normal
      • vitamin D3 response is impaired
    • genetics
      • X-linked dominant 
        • most common form
        • results from mutation in PHEX gene
        • leads to increased levels of FGF23, which decreases renal phosphate absorption and suppresses renal 25-(OH)-1α-hydroxylase activity
      • autosomal dominant 
        • results from mutation in FGF23
        • leads to decreased FGF23 degradation
      • autosomal recessive
        • results from mutation in dentin matrix protein 1 (DMP1) gene
        • leads to impaired osteocyte maturation and bone mineralization, and increased levels of FGF23
  • Vitamin D-deficient (nutritional)
    • results from decreased dietary intake of Vitamin D
      • rare now that Vitamin D is added to milk
    • presents at 6 months - 3 years of age
    • risk factors
      • premature infants
      • black children > 6 months who are still breastfed
      • patients with malabsorption syndromes (celiac sprue) or chronic parenteral nutrition
      • Asian immigrants
      • patients with unusual dietary choices (vegetarian diet)
    • pathophysiology
      • low Vitamin D levels lead to decreased intestinal absorption of calcium
      • low calcium levels leads to a compensatory increase in PTH and bone resorption
      • bone resorption leads to increased alkaline phosphatase levels
  • Vitamin D-dependent (type I & type II)
    • rare disorder
    • leads to clinical features similar to Vitamin D-deficient rickets but more severe
    • clinical characteristics
      • type I
        • hypotonia, muscle weakness, growth failure, hypocalcemic seizures, joint pain/deformity, fractures in early infancy
      • type II
        • hypotonia, muscle weakness, growth failure, hypocalcemic seizures, growth retardation, bone pain, severe dental caries or dental hypoplasia
    • pathophysiology   
      • type I
        • results from autosomal recessive mutation in renal 25-(OH)-1α-hydroxylase
        • prevents conversion of inactive form of vitamin D to active form
        • responsible gene 12q14
      • type II
        • results from autosomal recessive mutation in intracellular receptor for 1,25-(OH)2-vitamin D
Presentation
  • Symptoms
    • listlessness
    • irritability
    • generalized weakness
  • Physical exam
    • tibial bowing
      • due to widened proximal tibial physes
    • rachitic rosary
      • enlargement of costochondral junction
    • bowing of knees
    • retarded bone growth
    • muscle hypotonia
    • waddling gait
    • dental abnormalities
      • delayed dental eruption
      • defective enamel
    • pathologic fractures
Imaging
  • Radiographs
    • recommended views
      • AP and lateral of affected bone
    • findings
      • physeal widening
      • metaphyseal cupping
      • decreased bone density
      • Looser's zones
        • pseudofracture on the compression side of bone
      • rachitic rosary  
        • prominence of rib heads at the osteochondral junction
      • lower extremity bowing
        • often genu varum
      • codfish vertebrae 
      • cat back
        • dorsal kyphosis
Studies
  • Serum labs      

  •  Histology  
    • disordered and elongated zone of proliferation
    • poorly defined zone of provisional calcification
    • widened osteoid seams
    • "swiss cheese" trabeculae
    • abnormally arranged collagen fibers
      • run perpendicular to haversian canals
Tested Differential
  • Renal osteodystrophy 
  • Hypophosphatasia 
Treatment
  • Nonoperative
    • calcitriol
      • indications
        • Vitamin D-resistant (familial hypophosphatemic) rickets
        • type I Vitamin D-dependent rickets
    • phosphate replacement
      • indications
        • Vitamin D-resistant (familial hypophosphatemic) rickets
    • Vitamin D
      • indications
        • Vitamin D-deficient (nutritional) rickets
        • type II Vitamin D-dependent rickets
  • Operative
    • corrective surgery (multilevel osteotomy)
      • indications
        • severe tibial bowing
Techniques
  • Calcitriol
    • technique
      • 20-30 mg/kg/day split into 2-3 doses in children
      • 0.5-0.75 μg/day split into 2 doses in adults
  • Phosphate replacement
    • technique
      • 20-40 mg/kg/day split into 3-5 doses in children
      • 750-1000 mg/day split into 3-4 doses in adults
    • outcomes
      • controversial and counterintuitive
      • physiology would suggest that phosphate replacement would be beneficial and treatment of 1-3g daily was recommended
      • recent research evaluated the addition of phosphate to the standard vitamin D therapy and found no additional benefit
  • Vitamin D
    • technique
      • 5000 IU/day for 6-10 weeks
  • Corrective surgery (multilevel osteotomy)
    • technique
      • variety of fixation devices including K-wires, plates, intramedullary nails, and/or external fixation
 

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(SBQ13PE.85) A mother brings her 4-year-old daughter to your clinic for evaluation of knocked knees and short stature. On exam, the patient ambulates with a circumduction gait pattern and frequently falls. Plain radiographs are displayed in Figure A. Laboratory data is obtained and notable for calcium 9.1 mg/dL (RR 8.5-10.2 mg/dL), phosphorus 2.9 mg/dL (RR 4.3-5.4 mg/dL), alkaline phosphatase 405 U/L (RR 169-372 U/L), 25-OH vitamin D 38 ng/mL (RR 25-50 ng/mL), 1,25-OH vitamin D 21 pg/mL (RR 24-86 pg/mL), PTH 25 pg/mL (RR 15-65 pg/mL). The child is adopted and family history is not known. Which is the most likely diagnosis? Tested Concept

QID: 5247
FIGURES:
1

Physiologic genu valgum

1%

(37/2802)

2

Nutritional rickets

5%

(138/2802)

3

Familial hypophosphatemic rickets

84%

(2348/2802)

4

Renal osteodystrophy

8%

(223/2802)

5

Osteogenesis imperfecta

2%

(44/2802)

L 2 A

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(OBQ13.38) Low serum phosphate and normal calcium levels are found in what common etiology of hereditary rickets? Tested Concept

QID: 4673
1

X-linked hypophosphatemic

68%

(3826/5660)

2

Vitamin D-dependent, type I

7%

(378/5660)

3

Vitamin D-dependent, type II

6%

(330/5660)

4

Autosomal dominant hypophosphatemic

19%

(1077/5660)

5

Jansen's metaphyseal chondrodysplasia

0%

(17/5660)

L 3 A

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(OBQ10.55) Laboratory values of a normal serum calcium and parathyroid hormone can be found in which of the following disease states? Tested Concept

QID: 3143
1

Primary hyperparathyroidism

1%

(17/1539)

2

Type I vitamin D deficient rickets

9%

(132/1539)

3

Type II vitamin D deficient rickets

14%

(210/1539)

4

X-linked hypophosphatemic rickets

67%

(1034/1539)

5

Nutritional rickets

9%

(139/1539)

L 3 B

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(OBQ09.117) You are seeing a 4-year-old girl for leg deformities on a mission trip to Haiti. Clinical photograph and radiographs of her lower extremities and wrist are shown in Figures A-C. What laboratory studies would help confirm a nutritional deficiency as opposed to an X-linked genetic disorder as a cause of her condition? Tested Concept

QID: 2930
FIGURES:
1

Low serum phosphate, elevated alkaline phosphatase, elevated PTH

65%

(927/1430)

2

Low serum phosphate, elevated alkaline phosphatase, normal PTH

9%

(123/1430)

3

Low serum phosphate, elevated alkaline phosphatase, decreased PTH

5%

(65/1430)

4

Elevated serum phosphate, elevated alkaline phosphatase, elevated PTH

19%

(273/1430)

5

Elevated serum phosphate, decreased alkaline phosphatase, decreased PTH

2%

(35/1430)

L 3 C

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(OBQ08.121) Loss of function in the 25(OH) vitamin D1-alpha hydroxylase gene causes which of the following diseases? Tested Concept

QID: 507
1

Hyperphosphatemia

1%

(21/1631)

2

Vitamin D resistant rickets

24%

(387/1631)

3

Hereditary Vitamin D dependant rickets type I

62%

(1009/1631)

4

Hereditary Vitamin D dependant rickets type II

9%

(143/1631)

5

Hypophosphatemic rickets

4%

(66/1631)

L 3 D

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(SAE07PE.74) The husband of a 22-year-old woman has hypophosphatemic rickets. The woman has no orthopaedic abnormalities, but she is concerned about her chances of having a child with the same disease. What should they be told regarding this disorder? Tested Concept

QID: 6134
1

Their sons will have a 50% chance of having this X-linked dominant disorder.

21%

(33/155)

2

All of their daughters will be carriers or will have this disorder.

58%

(90/155)

3

They should be advised to not have any children as the risk of having boys with the disorder and girls who will be carriers is too hard for any parent.

1%

(1/155)

4

As long as the woman does not carry the trait, the children will not be affected because the husband has the disease and this is an X-linked dominant disorder.

11%

(17/155)

5

Their sons or daughters may be born with this disorder, but males are more severely affected.

7%

(11/155)

N/A E

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(OBQ07.271) Which of the following laboratory values would be consistent with nutritional rickets? Tested Concept

QID: 932
1

increased calcium level

1%

(8/587)

2

increased phosphate level

13%

(76/587)

3

decreased alkaline phosphatase level

8%

(49/587)

4

increased vitamin D level

1%

(7/587)

5

increased parathyroid hormone level

76%

(444/587)

L 1 C

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(OBQ04.95) The active form of vitamin-D (calcitriol) is produced by the enzyme 1-alpha-hydroxylase. What hormone activates this enzyme? Tested Concept

QID: 1200
1

thyroid stimulating hormone (TSH)

3%

(15/589)

2

parathyroid hormone (PTH)

90%

(528/589)

3

estrogen

6%

(34/589)

4

progesterone

1%

(3/589)

5

testosterone

1%

(7/589)

L 1 D

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