vitamin d deficiency_rickets

8/12/2019 Vitamin D Deficiency_Rickets

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Rickets of Vitamin D Deficiency

Rickets is failure in mineralization of growing bone

early changes are seen at the ends of long bones in x ray

evidence of demineralization exists in the shafts.

Failure of mature bone to mineralize is called osteomalacia.

ETIOLOGY.

Lack of -direct exposure to ultraviolet rays in sunlight 296310 nm

these rays do not pass through ordinary window glass

intake of vitamin D

Two forms of vitamin D

Vitamin D2 , or calciferol, available as irradiated ergosterol,

Vitamin D3 , available synthetically, is naturally present in human skin in the provitamin

stage as 7-dehydrocholesterol.It is activated photochemically to cholecalciferol and transferred to the liver.

These irradiated sterols are hydroxylated in the liver to 25-OH-cholecalciferol and,subsequently, in the renal cortical cells to 1, 25-dihydroxycholecalciferol, which

functions as a hormone.

Receptors of the hormone are found in the kidneys, intestine, osteoblasts of bone,parathyroid, islet cells of the pancreas, cells in the brain, mammary epithelium,

Functions =

facilitation of intestinal absorption of calcium and phosphorusreabsorption of phosphorus in the kidneys

direct effect on mineral metabolism of bone (deposition and reabsorption).homeostasis of calcium and phosphorus in the body's fluids and tissues.

Egg yolk contains 310 mg/g. 1 mg = 40 IU.exposure to ultraviolet irradiation,

PATHOLOGY.

New bone formation is initiated by osteoblasts,

osteoblasts are responsible for matrix deposition and mineralization.

Osteoblasts secrete collagen,changes in polysaccharides, phospholipids, alkaline phosphatase, and pyrophosphatase

mineralization occurs in the presence of adequate calcium and phosphorus.

Resorption of bone occurs when osteoclasts secrete enzymes on the bone surface,dissolving and removing matrix and mineral.

Osteocytes resorb and redeposit bone.

Factors affecting bone growth are phosphorus, calcium, fluoride, and growth hormone

In rickets,

suppression of normal growth of epiphyseal cartilage and of normal calcification.


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deficiency in serum of calcium and phosphorus salts

Cartilage cells fail to complete their normal cycle of proliferation and degenerationfailure of capillary penetration occurs in a patchy manner.

result is a frayed, irregular epiphyseal line at the end of the shaft.

Failure of osseous and cartilaginous matrix to mineralize in the zone of preparatory

calcification,deposition of newly formed uncalcified osteoid, results in a wide, irregular, frayed zone

of nonrigid tissue (the rachitic metaphysis)

This zone, responsible for many of the skeletal deformities, becomes compressed andbulges laterally, producing flaring of the ends of the bones and the rachitic rosary

Mineralization is lacking in subperiosteal bone

pre-existing cortical bone is resorbed in a normal manner but is replaced by osteoidtissues over the entire shaft, which fails to mineralize.

If this continues, the shaft loses its rigidity,

softened and rarefied cortical bone is distorted by stress

deformities and fractures result.

Healing Rickets.

With healing, degeneration of cartilage cells occurs along the metaphyseal-diaphyseal

border, capillary penetration of the resultant spaces is resumed, and calcification takes

place in the zone of preparatory calcification.calcification, occurring at the line at which normal calcification would have occurred had

the rachitic process not supervened, produces a line clearly demonstrable in x ray

healing progresses, the osteoid tissue between this line of preparatory calcification andthe diaphysis also becomes mineralized

Osteoid tissue in the cortex and the shaft becomes mineralized.

Chemical Pathology.

In Vitamin Ddeficient rickets

body attempts to maintain normal serum calcium levels

In the absence of vitamin D, less calcium is absorbed from the intestine.

With lowered serum calcium level, parathormone is secreted,leads to mobilization of calcium and phosphorus from the bone.

serum calcium concentration is thus maintained,

secondary effects occur, including the changes of rickets in bone and the lowered serumphosphorus concentration

parathormone decreases phosphorus reabsorption in the kidneys

elevated serum phosphatase levels (due to increased osteoblastic activity).

alkaline phosphatase of serum, in normal children is less than 200 IU/dL,

elevated in mild rickets to more than 500 IU/dL.

As rickets heals, the phosphatase value returns to the normalSerum alkaline phosphatase levels may be normal in infants who have rickets and who

are protein or zinc depleted.


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Calcium and phosphorus = calcium absorption occurs in humans when the ratio ofcalcium to phosphorus in the diet is about 2:1

increase in phosphate decreases absorption of calcium.

increase in calcium absorption occurs with acidity of intestinal contents or when lactose

is the dietary sugar.Chelating agents such as ethylenediaminetetraacetic acid or the phytates of cereals may

decrease calcium absorption,

dietary iron may decrease absorption of phosphateHigh dietary levels of stearic and palmitic acids, decrease calcium absorption.

Calcium absorption is facilitated by 1, 25-dihydroxycholecalciferolCalcium deficiency alone leads to the failure of calcification as seen in rickets and

osteomalacia

it results in a diminished amount of bone.

Vitamin D deficiency is also accompanied by

generalized aminoaciduriaa decrease of citrate in bone and its increased urinary excretion

decreased ability of the kidneys to make an acid urinephosphaturia, ,

mellituria.

parathyroid glands hypertrophy in rickets,urinary cyclic adenosine monophosphate level is increased.

CLINICAL MANIFESTATIONS.

breast-fed infants whose mothers have osteomalacia, rickets may develop within 2 mo.rickets appears at thr end of the 1st and during the 2nd yr of life.

early signs of rickets, craniotabes, is due to thinning of the outer table of the skulldetected by pressing firmly over the occiput or posterior parietal bones.

Ping-Pong-ball sensation is felt.

Craniotabes near the suture lines is normal

Palpable enlargement of the costochondral junctions (the rachitic rosary)thickening of the wrists and ankles

Increased sweating, around the head

softness of the skull may result in flattening and asymmetry of head.anterior fontanel is larger than normal

its closure may be delayed until after the 2nd yr of life.

central parts of the parietal and frontal bones are often thickened, forming prominences orbosses, which give the head a boxlike appearance (caput quadratum).

Eruption of the temporary teeth may be delayed,

there may be defects of the enamel and extensive caries.

permanent teeth that are calcifying may be affected;permanent incisors, canines, and first molars show enamel defects.


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exposure to ultraviolet light

by oral administration of vitamin D.daily requirement of vitamin D is 10 mg or 400 IU.

Premature infants or breast-fed infants whose mothers are not exposed to adequate

sunlight should receive supplemental vitamin D daily.

Vitamin D should also be administered to pregnant and lactating mothers.

TREATMENT.

Natural sun light

oral administration of vitaminDaily administration of

50150 mg of vitamin D3 or

0.52 mg of 1,25-dihydroxycholecalciferol

produces healing demonstrable on roentgenograms within 24 wk, except in cases of

vitamin D refractory rickets.

Administering 15,000 mg of vitamin D in a single dose, repeat x ray if no line appears by4 weeks repeat Vit D if still no healing line it is resistant

rapid healing follows,

earlier differential diagnosis from genetic vitamin Dresistant ricketsless dependence on parents for daily administration of the vitamin.

If no healing occurs, the rickets is probably resistant to vitamin D

After healing is complete, the dose of vitamin D should be lowered to 10 mg/24 hr.

Nelson Textbook of Paediatrics16th Edition (2000), W.B. Saunders. All rights reserved.

Buy this book at 10% discount and The Isabel Medical Charity will

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