Rickets is defined as failure of mineralization of the growing bones, which should not be confused with osteomalacia i.e. defective mineralization of mature bones, or osteoporosis i.e. de-mineralization of pre-mineralized bones.
Rickets may be broadly divided into two categories Vitamin D deficiency or nutritional rickets, and Vitamin D-resistant or refractory rickets. Nutritional rickets accounts for over 90% cases in childhood.
Vitamin D deficiency
Vitamin D is a fat-soluble vitamin, essential for normal mineralization of growing bones.
Physiology of Rickets: Cholecalciferol (Vitamin D3) is the natural form of vitamin D, present as a preformed vitamin in animal sources e.g. fats and fish liver oils. However, the major bulk of Vitamin D3 in humans is synthesized endogenously on exposure to ultraviolet rays in sunlight, from a natural pro-vitamin (7-dehydrocholesterol), present under the human skin. Plants do not contain Vitamin D3, though another variant (calciferol or Vitamin D2) may be derived by irradiation of a plant sterol – Ergosterol.
A. Vitamin D deficiency (Nutritional) Rickets: Higher requirements in growing child, Inadequate dietary intake, Lack of exposure to sunlight, Poor stores at birth — preterms, IUGR, Malabsorption states & Anticonvulsant therapy
B. Vitamin D resistant (refractory) Rickets: Chronic hepatic disease, Chronic renal disease (Renal osteodystrophy), Hypophosphatemic Rickets (Familial hypophosphatemia and Renal tubular acidosis or Fanconi syndrome)
C. Vitamin D dependent Rickets: Type 1: Autosomal I -hydroxylase deficiency, Type 2: End-organ resistance to Vitamin D
Vitamin D at a glance
RDA: 200 lU/day
Sources: Endogenous synthesis, Animal sources: animal fats and fish liver oils & Fortified foods
Functions: Gut absorption of calcium & phosphorus, Bone mineralization, Renal reabsoption of phosphates and calcium Deficiency states: Rickets (in children) and Osteomalacia (in adults)
Hypervitaminosis D (develops after 1-3 months): Renal: polyuria, polydipsia, renal failure; GIT anorexia, vomiting; CNS: irritability, hypotonial; Metastatic: soft-tissue calcifications, osteopetrosis
Cholecalciferol, itself an inactive substance, needs to be sequentially hydroxylated in the liver and kidneys, to convert into either an active metabolite (1, 25 dihydroxy cholecalciferol) or relatively inactive metabolite (24, 25 dihydroxy cholecalciferol), depending on the needs. Active metabolite promotes CaIP absorption from gut & kidneys as well as bone mineralization.
Etiologically, Vitamin D deficiency Rickets is rarely dietary, mainly seen in rapidly-growing children, due to relatively higher requirements. Inadequate endogenous synthesis due to limited sun-exposure in dark-skinned population or veil-wearing communities e.g. muslims, is another contributory factor for rickets in India.
Pathophysiology of Rickets: Vitamin D deficiency leads to reduced Ca’and P absorption from gut & kidneys and consequent rise in parathormone levels to maintain normocalcemia. This high parathormone activity stimulates calcium mobilization from bones and reabsorption from kidneys.
Mobilization of skeletal calcium leads to Deficient mineralization of growing osteoid tissue, with typical clinico-radiological changes in rickets; Increased osteoblastic activity with elevated serum alkaline phosphate levels – the first biochemical change in rickets. Increased renal reabsorption of calcium leads to compensatory phosphorus excretion and low serum phosphorus levels — the second biochemical change. Normocalcemia is usually maintained in rickets by elevated PTH levels, except in severe cases.
Rickets commonly present at 6 months – 2 years of age with bony deformities and hypotonia of supporting ligaments/muscles. Important changes in Rickets are —
a) Craniofacial changes:
• Craniotabes – softening and thinning of skull bones with pin-pong ball like resilience on pressure over parietal bones (normal <3 months).
• Frontal bossing – prominence of frontal bones
• Caput quadratum – Box-head or hot cross-bun appearance due to fronto-panetal bossing,
• Delayed closure of anterior fontanel,
• Delayed dentition.
b) Thoracic changes:
• Rachitic rosary – round, non-tender beading due to widening of costochondral junctions,
• Harrison sulcus – a groove/depression along the lower costal margins,
• Sternal deformities like Pectus excavatum i.e. depression of sternum, Pectus carinatuin i.e. forward projection of sternum, or pigeon-chest deform it
c) Limb deformities:
• Widening of wrist/ankles (double malleolus) due to widened epiphysis and metaphysis,
• Gait abnormalities e.g. Knock-knee (Genu incurvatum), Bow-legs and Coxa-vera,
• Green-stick pathological fractures of long bones.
d) Spinal deformities:
• Kyphosis or scoliosis due to lax ligaments,
• Short stature due to deformed spinal curvature.
e) Generalized hypotonia with —
• Pot-belly, due to abdominal muscle hypotonia,
• Visceroptosis due to ligamental laxity,
• Hyper-extensible joints (acrobatic rickets).
h) Other manifestations e.g. excessive sweating over forehead, recurrent respiratory infections etc.
Rickets in severely malnourished children may present without clinical signs despite extensive radiological changes (atrophic rickets).
Diagnosis of rickets
a) Typical clinical defomities,discussed above,
b) Characteristic radiological changes, best demonstrated at wrist joint, showing —
• Widening of epiphyseal ends with increased space between diaphysis and epiphysis, due to poor visibility of thickened but uncalcified metaphysis.
• Fraying at the visible end of long bones, (raveled sleeve appearance), due to irregular mineralization of metaphysis.
• Cupping i.e. concavity at the visible end of long bones, due to poor mineralization of relatively less vascular center and pressure changes
• Splaying of the ends of long bones, due to pressure changes on poorly mineralized bones
Other late changes include delayed bone age, costochondral widening with spatulate ribs, tn-radiate pelvis and spinal defonnities.
After Vitamin D administration, radiological recovery is visible in 7-10 days with appearance of provisional zone of preparatory calcification – a transverse line beyond the visible end of shaft, suggestive of healing rickets. Absence of this zone till 3 weeks indicates possibility of refractory rickets. Complete X-ray clearance takes 2-3 months, though deformities may persist for many years.
c) Biochemical changes depend on severity of disease and differentiate active disease from old deformities. Important changes in order of appearance are —
— Elevated S. alkaline phosphatase (>20 KA units),
— Low S. Phosphorus levels (<4 mgldl)
— Low Ca x P index (<30)
— Low S. Calcium levels (<9-11 mg/dl)
DID: Nutritional rickets need to be differentiated from Vitamin D resistant/refractory rickets.
Treatment: Stoss regimen is the most widely used method of treatment in nutritional rickets as well as to differentiate them from resistant rickets, as follows —
a) Confirm rickets on X-ray of the wrist joint,
b) Give single dose of oral or IM Vitamin D3 6,00,000111 on diagnosis, along with oral calcium supplementation.
c) Repeat X-ray after 2-3 weeks, to see for zone of preparatory calcification.
d) If present, indicates deficiency rickets.
e) If absent, repeat same dose of Vitamin 03, Repeat X-ray again after 2-3 weeks.
g) Absence of the line of preparatory calcification till 4- 6 weeks despite 2 mega doses of Vitamin D3 indicate
Vitamin D resistant rickets & need for detailed investigations.
Nutritional rickets may also be treated with daily Vitamin D therapy (P0 2000-6000 lU/day) for 2-4 week.
Prevention of rickets involves adequate exposure to sunlight and Vitamin D supplement (P0 4001U/day) in preterms or rapidly-growing children.
VITAMIN D RESISTANT Rickets
Vitamin D resistant rickets are less common but important indicators of many systemic or metabolic defects. Some important causes of resistant rickets are as follows —
Familial hypophosphatemia, an X-linked dominant disease, is a leading cause of non-nutritional rickets due to defects in — a) renal reabsorption of phosphates, with consequent phosphaturia and hypophosphatemia, b) conversion of 25(OH)D3 into 1,25(OH)2D3.
Clinically, these cases usually present as toddlers with severe bow-legs and waddling gait, typically more severe in males.
Diagnosis rests on — a) no response to Vitamin D therapy, b) similar family history c) heavy phosphaturia. despite hypophosphatemia, and d) absence of glucosuria, aminoaciduria and bicarbonaturia (did Renal tubular acidosis).
Treatment includes daily phosphate supplements as Joulie solution (P0 0.5-1.0 gm/d q4hr), along with Vitamin D2 (2000 lLTikgid) or preferably, 1,25 (OH)2D3 (50-60 ngikgid). Mega Vitamin D therapy, as used in nutritional rickets, should be avoided due to the risk of hypercalcemia and nephrocalcinosis.
Vitamin D-Dependent rickets manifest at 3-6 months of age and are of two types —
• Type I, due to 25(OH)D3 -lct- hydroxylase deficiency that prevents renal conversion of Vitamin D into active form, and
• Type II, due to inherited end-organ resistance.
While type I may be treated with massive doses of Vitamin D7 (2-10 lac lU/day), type II needs to be treated with 1 ,25(OH)2D3 (15-30 jag/kg/day).
Check out the below video on Rickets –