Osteomalacia, Rickets, and Vitamin D Insufficiency Flashcards
What is Osteomalacia?
Disorder of mature (adult) bone; inadequate or delayed mineralization of osteoid.
What is Rickets?
Disorder of growing bone; defective chondrocyte differentiation and mineralization in epiphyseal growth plates, causing growth retardation and skeletal deformities.
What historical condition was common due to vitamin D deficiency?
Rickets.
Who is at higher risk for vitamin D deficiency in the U.S.?
- Elderly women with osteoporosis
- Patients with chronic diseases affecting vitamin D metabolism.
What are the sources of Vitamin D?
- Dietary intake
- UV irradiation of 7-dehydrocholesterol in the skin.
What happens in the liver regarding Vitamin D metabolism?
Conversion to 25-hydroxy (25-OH) vitamin D.
What is the active form of Vitamin D produced in the kidney?
1,25-dihydroxy (1,25(OH)2) vitamin D.
What are the functions of Vitamin D?
- Increases calcium absorption in the intestine
- Increases calcium reabsorption in the kidney
- Decreases PTH secretion
- Stimulates osteoblast maturation and bone matrix synthesis.
What are the three categories of causes for Osteomalacia and Rickets?
- Low calcium intake or abnormal vitamin D metabolism/action
- Abnormal phosphorus metabolism
- Normal vitamin D and mineral metabolism (rare).
What are common causes affecting Vitamin D metabolism?
- Limited sunlight exposure
- Malabsorption (e.g., celiac disease, Crohn’s disease)
- Chronic liver or kidney disease
- Medications (e.g., phenytoin, barbiturates).
What is VDDR Type I?
Deficiency of renal 1-alpha-hydroxylase.
What is VDDR Type II?
Mutation in vitamin D receptor (end-organ resistance).
What regulates serum phosphorus?
- 1,25(OH)2 vitamin D: Increases intestinal phosphate absorption
- PTH: Promotes renal phosphate excretion
- FGF 23: Enhances renal phosphate loss and reduces intestinal absorption.
What genetic syndrome is associated with X-linked hypophosphatemic rickets (XLHR)?
Mutation in PHEX gene → increased FGF 23.
What is a common disorder seen in chronic renal failure?
Osteoporosis, osteomalacia, osteitis fibrosa cystica, adynamic bone, mixed renal osteodystrophy.
What symptoms are associated with Osteomalacia?
- Bone pain (back, hips, knees)
- Muscle weakness (proximal muscles)
- Fractures from minor trauma.
What symptoms characterize Rickets?
- Widened metaphyses
- Growth retardation
- Skeletal deformities
- Craniotabes (soft skull)
- Rachitic rosary (costochondral swelling)
- Bowing of legs.
What biochemical abnormalities are seen in Vitamin D deficiency?
- Low serum calcium → secondary hyperparathyroidism
- Low serum phosphate, elevated alkaline phosphatase.
What distinguishes VDDR Type I in terms of Vitamin D levels?
Low 1,25(OH)2 vitamin D, normal/high 25-OH vitamin D.
What characterizes VDDR Type II in vitamin D levels?
High 1,25(OH)2 and 25-OH vitamin D.
What are radiographic findings in Osteomalacia?
- Reduced bone mass
- Pseudofractures (Looser’s zones).
What radiographic features are seen in Rickets?
- Fraying of metaphyses
- Widened growth plates
- Bowing of legs.
What histologic features are seen in Osteomalacia?
- Widened osteoid seams
- Increased mineralization lag time (measured by tetracycline labeling).
What is the treatment for Vitamin D deficiency?
Calcium supplements + vitamin D (D2, D3, or calcitriol).
