Pathophysiology
1) functional vitamin D deficiency causing inadequate mineralization of bones and the matrix of growth plates 2) two forms – type 1 (vitamin D dependent) and type 2
Signs and Symptoms
1) type 1 – usually presents in first year of life 2) type 2 – usually presents early in life but not uncommon for first signs to appear in childhood up to puberty 3) bowed legs 4) slipped capital femoral epiphysis 5) short stature 6) patients dit in a Buddha-like posture 7) flattened skull 8) prominent forehead (frontal bossing) 9) classic rachitic rosary chest (knobs on costochondral cartilage) 10) pectus carinatum 11) potbelly 12) weak muscles 13) irritability 14) apathetic 15) difficulty in focusing on tasks 16) severe dental caries
Characteristic Test Findings
Laboratory – 1) type 1 – increased serum PTH and alkaline phosphatase, hypocalcemia, hypophosphatemia 2) type 2 – increased 1,25-(OH)2DÂ Radiology – 3) flared and cup-shaped epiphysis
Histology/Gross Pathology
hypertrophy of growth plate (5-15) times thicker than normal) as osteoclasts do not resorb this plate
Associated Conditions
increased incidence secondary to – 1) phenytoin use 2) phenobarbital use 3) hypoparathyroidism 4) tumor-induced osteomalacia 5) chronic renal disease
Biochemistry
1) vitamin D can be ingested in food or synthesized from 7-dehydrocholesterol in the skin by exposure to the UV component of sunlight 2) type 1 – deficiency in renal 1-alpha-hydroxylase, which prevents conversion from precursor form 3) type 2 – defect in vitamin D receptor, making end organs functionally resistant to 1,25-(OH)2D
Inheritance/Epidemiology
1) virtually eliminated in developed nations by addition of vitamin D to foodstuffs and generally improved nutrition 2) vitamin D-dependent rickets is autosomal recessive
Treatment
1) type 1 – 1,25-(OH)2D 2) type 2 – repeat IV calcium
Tips for USMLE
1) if rachitic rosary chest is mentioned, think rickets 2) if bowed legs are mentioned think rickets 3) if anything about deficient vitamin D functioning is mentioned, think rickets
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