Rickets/Osteomalacia

Basics

DESCRIPTION

  • Osteomalacia refers to impaired bone mineralization, caused primarily by deficiencies in vitamin D, calcium, and/or phosphate.
  • In children, osteomalacia can lead to growth plate abnormalities, termed rickets.

EPIDEMIOLOGY

  • The prevalences of rickets and osteomalacia are very high in many parts of the world.
  • Reported with increasing frequency in the United States since the 1980s

GENERAL-PREVENTION

  • Vitamin D supplements should be provided to breastfed infants and high-risk individuals.
  • In the United States and Canada, cow’s milk, infant formula, and cereals are fortified with vitamin D.

PATHOPHYSIOLOGY

Rickets arises due to decreased availability of phosphorus and calcium to mineralize the skeletal matrix, leading to growth plate disorganization and accumulation of undermineralized osteoid. This results in growth plate expansion, bone weakening, and skeletal deformities.

ETIOLOGY

Primary causes include the following:

  • Nutritional
    • Insufficient vitamin D and/or calcium intakes (common)
    • Insufficient phosphorus intake (rare)
  • Deficient sunlight exposure
  • Malabsorption
    • Celiac disease
    • Cystic fibrosis
    • Liver disease
  • Renal tubular defects
    • Cystinosis
    • Fanconi syndrome
    • Renal tubular acidosis
  • Abnormalities in vitamin D metabolism
    • Anticonvulsant use
    • Liver disease
  • Genetic forms (see “Table 1”)
Table 1. Biochemical Features of Rickets/Osteomalacia
CaPhosAlk phosiPTH25-(OH)D1,25-(OH)2DUrine Ca/ CrTRP
Nutritional/insufficient sunlightN or ↓↓↑↑↓↑↓↑
MalabsorptionN or ↓↓↑↑↓↑↓↑
Renal tubular defectsN or ↓↓↑↑N↑↑N or ↓
Altered vitamin D metabolismN or ↓↓↑↑↓↑↓↑
Genetic forms of rickets
X-linked, AD, and AR hypophosphatemic ricketsN↓↑N or ↑NN or ↑N or ↓↓
1α-hydroxylase deficiency↓↓↑↑N↓↓↑
Vitamin D receptor mutations (Vitamin D resistance)↓↓↑↑N↑↓↑
Hereditary hypophosphatemic rickets with hypercalciuriaN or ↓↓↑↑N↑↑↓
HypophosphatasiaN or ↑N or ↑↓N or ↓NN or ↓N or ↑N

Ca indicates calcium; Phos, phosphorus; Alk phos, alkaline phosphatase; iPTH, intact parathyroid hormone; 25-(OH)D, 25-vitamin D; 1,25-(OH)2D, 1,25-dihydroxyvitamin D; Ca/Cr, calcium/creatinine ratio; TRP, tubular reabsorption of phosphorus ([1− (U phos × P Cr/U Cr × S Phos)] × 100, normal 85–95%); N, normal; AD, autosomal dominant; AR, autosomal recessive.

RISK-FACTORS

  • Infants born to vitamin D–deficient mothers
  • Low birth weight and/or prematurity
  • Breastfeeding without vitamin D supplementation
  • Poor nutrition
  • Increased skin pigmentation
  • Higher latitudes and winter months
  • Sunscreen use
  • Malabsorption
  • Renal tubulopathies

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