Clinical Presentation

A short, lethargic 21/2-year-old boy presents with enlarged wrists and knees.

Figure 96A

Figure 96B

Radiologic Findings

Rickets

Differential Diagnosis

• Hypophosphatasia (often has prominent lucent extensions into metaphysis and craniosynostosis; wormian bones)
  
• Metaphyseal chondrodysplasia, Schmid type (short stature, metaphysis is well mineralized, and generally has benign course)

Discussion

Background

Rickets can be described as an alteration in the orderly mineralization and development of the growing skeleton generally related to defective vitamin D metabolism. The disease process was first recognized in the 1600s during the industrial revolution. Lack of sun exposure due to the smog, high buildings, and crowded streets in urbanized centers was the primary initiating factor at that time. In 1900 it was estimated that ~80% of children <2 years of age had evidence of rickets in the Boston area. The availability of synthesized vitamin D in the 1920s nearly eradicated vitamin D-deficiency rickets. The most common causes of rickets in the United States today are vitamin D-resistant or vitamin D-dependent disorders and renal osteodystrophy. In regions of Asia and Africa, the prevalence of vitamin D-dependent rickets is ~40%. There are >50 disease processes, with a vast spectrum of etiologies and clinical presentations, that can result in rickets.

Etiology

The causes of rickets can be categorized into the following groups:

• Abnormalities of vitamin D metabolism, which are divided into:
  
  
  
  • Deficiency of intake (nutritional) or gastrointestinal malabsorption
    
  • Liver disease (prevents normal 25-hydroxylation of vitamin D): anticonvulsant treatment, biliary atresia, total parenteral nutrition, tyrosinemia
    
  • Renal disease (prevents 1-hydroxylation of vitamin D): renal osteodystrophy, vitamin D-dependent rickets, tumor-associated rickets, and parathyroid disorders (hypo-, hyper-, and pseudohypoparathyroidism)
  
  
• Alterations in phosphorus or calcium metabolism due to renal tubular disorders:
  
  
  
  • X-linked hypophosphatasia rickets
    
  • Fanconi’s syndrome
    
  • Tumor-associated rickets

Histology/Pathology