Describe the vitamin D Deficiency of Nutritional Rickets.

Definition

• Rickets is a disease of the growing bone due to defective mineralisation of the growth plate (physis) and osteoid, most commonly from vitamin D deficiency.
• The equivalent in adults (after epiphyseal fusion) is osteomalacia.

Vitamin D Metabolism

Skin: 7-dehydrocholesterol + UVB → Cholecalciferol (D3) → Liver: 25-hydroxylase → 25-OH-D (storage form; best marker of status) → Kidney: 1-α-hydroxylase → 1,25-(OH)2-D (active form / calcitriol) → Gut: ↑ Ca & PO4 absorption → bone mineralisation

Etiology

• Deficient sunlight exposure (dark skin, pollution, purdah, indoor living) and low dietary vitamin D.
• Exclusive breastfeeding without vitamin D supplementation; prematurity (low stores).
• Malabsorption (coeliac disease, cholestasis); chronic liver / renal disease; anticonvulsants (enzyme induction increases vitamin D breakdown).
• Rarer inherited forms — vitamin-D-dependent rickets, X-linked hypophosphataemic (vitamin-D-resistant) rickets.

Types of Rickets

Clinical Features

General: hypotonia, delayed milestones, pot-belly, growth failure, tetany/seizures (hypocalcaemia), and increased infections.

Head:

• Craniotabes (soft, ping-pong skull — earliest sign in infancy); frontal & parietal bossing (caput quadratum).
• Delayed closure of the anterior fontanelle; delayed dentition and enamel defects.

Chest:

• Rachitic rosary (beading at the costochondral junctions); Harrison's sulcus (a groove at the diaphragm's insertion); pigeon-chest deformity.

Limbs & spine:

• Widening of the wrists & ankles; 'double malleoli'.
• Once weight-bearing — bow legs (genu varum) or knock-knees (genu valgum); coxa vara.
• Kyphoscoliosis and pelvic deformities (important in girls for later childbirth).

Investigations

X-ray (wrist — most useful): cupping, fraying and splaying of the metaphysis; widened, hazy growth plate; generalised osteopenia; greenstick fractures in advanced disease.

Management

• Vitamin D — either daily oral (2000–5000 IU/day for ~6–12 weeks) or 'Stoss' therapy (a single large dose, e.g. ~6 lakh IU) followed by a maintenance dose.
• Calcium supplementation — dietary + oral calcium, especially to prevent 'hungry-bone' hypocalcaemia after starting vitamin D.
• Treat symptomatic hypocalcaemia (IV calcium gluconate for tetany/seizures, with monitoring).
• Correct any underlying cause (malabsorption, renal disease); orthopaedic correction of residual deformity later.

Monitoring Response (radiological Healing)

A dense 'line of provisional calcification' appears at the metaphysis within 2–4 weeks; ALP falls and biochemistry normalises — confirming a good response.

Complications

• Permanent bony deformities; short stature; pathological fractures; pelvic contraction.
• Hypocalcaemic seizures/tetany, laryngospasm; recurrent respiratory infections; anaemia.

Prevention

• Adequate sunlight exposure; routine vitamin D supplementation (400 IU/day) for all infants, especially exclusively breastfed and preterm babies.
• Maternal vitamin D during pregnancy & lactation; food fortification; nutrition education.

Differential Diagnosis of Bow Legs

• Physiological bowing — normal up to ~2 years; symmetrical, painless, resolves spontaneously.
• Blount disease (tibia vara) — pathological, often unilateral/asymmetric.
• Skeletal dysplasia (e.g. Achondroplasia) — disproportionate short stature.
• Rickets is distinguished by the widened wrists, rosary, biochemistry (↑ALP, ↓PO4) and X-ray changes.

Prognosis

• Nutritional rickets responds well and heals completely with vitamin D and calcium if treated early.
• Long-standing disease may leave residual bony deformities (bow legs, pelvic contraction) that need orthopaedic correction; timely treatment prevents these.

WHY Rickets Persists in Sunny India

• A paradox that must be understood is why vitamin D deficiency is common in a country flooded with sunshine.
• The skin makes vitamin D from UVB radiation — but a surprising number of factors block this.
• Skin pigmentation: melanin absorbs UVB, so darker skin requires several times more sun exposure to make the same amount of vitamin D.
• Clothing and custom: covering the body, purdah, and keeping infants indoors.
• Urban living: air pollution and smog absorb UVB; tall buildings shade the streets; and people work indoors and avoid the midday sun.
• Exclusive breastfeeding beyond 6 months without supplementation — because breast milk is a poor source of vitamin D (this is precisely why vitamin D supplementation of all infants is recommended).
• And a diet poor in vitamin D, with little fortification.
• Add prematurity, malabsorption, chronic kidney or liver disease and anticonvulsants, and the picture is complete.
• Hence the answer is not merely 'go outside': it is routine vitamin D supplementation of infants and at-risk groups, food fortification, and treatment of established rickets with vitamin D and calcium — after which the biochemistry corrects in weeks and the deformities largely remodel.