Rickets

Definition

 

Rickets

- paediatric disorder characterised by deformity and growth retardation

- secondary to defective mineralisation of the growth plate

 

Osteomalacia

- adult disorder

- defective mineralisation of osteoid

 

Physiology

 

Generation of Vit D

 

Vitamin D3 ingested and absorbed

- activated by sunlight

- need 10 - 15 minutes 3 x per week

 

25 hydroxylated in liver

 

1 alpha-hydroxylase in kidney

- active 1,25 vit D3

- calcitriol

- this is under PTH control

 

Action Vit D

 

Intestine

- increases Ca and PO4 absorption

 

Kidney

- decreases Ca and PO4 excretion

 

Bone

- increases Ca and PO4 release

 

Pathology

 

Physis

- hypertrophic zone widens

- provisional zone never forms

- no mineralisation of osteoid

 

Clinical

 

Osteopenia

 

Bowing

- usually develops during periods of rapid growth

- not seen in newborn

- see in toddlers

 

Fractures

- recurrent clavicle fractures

- stress fractures

 

Teeth

- delayed formation

- increased dental caries

 

Kyphoscoliosis

 

Short stature

- adults < 5 foot

 

Xray

 

Tibial and femoral bowing

 

Pathognomonic signs

- widened physeal plate

- cupping of the metaphysis

 

Blood Results

 

Ca2+ low

Phosphorus low

Alk Phos high

Vit D low

Electrolytes

 

Causes

 

1.  Vitamin D deficiency

 

Causes

- inadequate sun exposure

- low dietary intake

 

More common in dark skinned children

- exclusively breastfed

- live in northern cities with low sunlight

- vegetarian diet

 

Treatment

- daily vitamin D

- 30 minutes daily sunshine

 

2.  Congenital disease

 

A.  Vitamin D dependent rickets Type 1

- defect in 1 alpha hydroxylase

- converts 25 (OH) to 1,25 (OH)

- 1,25 biologically active

 

B.  Vitamin D independent rickets Type 2

- mutations in the vitamin D receptor

- more than 10 types

 

C. Familial X linked hypophosphataemic rickets

- AD, most common form

- vitamin D resistant rickets

- impaired tubular resorption phosphate

- treatment phosphate + calcitriol

 

3.  Vitamin D metabolism abnormalities

 

Causes

- renal failure

- phenytoin