A 6-year-old boy from rural Maharashtra presents with bowing of legs, delayed tooth eruption, and frontal bossing. Biochemical investigations show elevated alkaline phosphatase, low 25-hydroxyvitamin D, elevated parathyroid hormone, and hypocalcemia. All of the following are characteristic radiological findings in nutritional rickets EXCEPT:

Explanation

## Radiological Features of Nutritional Rickets ### Characteristic X-ray Findings **Key Point:** Nutritional rickets is characterized by decreased bone mineralization, leading to a radiolucent appearance on radiographs. The classic findings are centered on the growth plate (metaphysis) and reflect failure of provisional calcification. | Finding | Description | Location | |---------|-------------|----------| | Metaphyseal widening | Expansion of growth plate due to accumulation of uncalcified osteoid | Long bones (femur, tibia, humerus) | | Metaphyseal cupping | Concave deformity of metaphyseal surface | Femoral and tibial metaphyses | | Loss of sharp margins | Indistinct, frayed metaphyseal-diaphyseal junction | Femur, tibia | | Ground-glass appearance | Generalized radiolucency of bone | Throughout skeleton | | Looser zones | Pseudofractures (transverse lucencies) | Femoral neck, pubic rami, ribs | ### Why Option A is the EXCEPT Answer **High-Yield:** **Subperiosteal resorption** and **pencil-point (pencilled) cortices** are the hallmark radiological features of **primary hyperparathyroidism** (osteitis fibrosa cystica), NOT nutritional rickets. In hyperparathyroidism, excess PTH drives osteoclastic resorption along the periosteal surface, producing the characteristic lace-like cortical erosions best seen on the radial aspect of the middle phalanges. While nutritional rickets does cause secondary hyperparathyroidism (elevated PTH is seen biochemically), the dominant radiological picture is one of **metaphyseal changes and osteopenia** — not subperiosteal resorption. Subperiosteal resorption as a radiological finding is specifically attributed to primary or severe secondary hyperparathyroidism (e.g., renal osteodystrophy), not to nutritional rickets per se. ### Why Options B, C, and D Are Characteristic of Rickets - **Option B (Loss of sharp metaphyseal margins / ground-glass appearance):** Classic finding — failure of provisional calcification causes fraying and haziness of the metaphysis. - **Option C (Metaphyseal widening and cupping):** Pathognomonic of rickets — accumulation of uncalcified osteoid widens and cups the metaphysis. - **Option D (Increased bone density / sclerotic vertebral bodies):** This is NOT a feature of nutritional rickets (rickets causes radiolucency), making it an incorrect description of rickets — but it is a *less specific* distractor compared to Option A, which describes a finding actively attributed to a different disease entity (hyperparathyroidism). **Clinical Pearl:** The "rugger jersey spine" (alternating sclerotic and lucent bands in vertebral bodies) is seen in renal osteodystrophy, not nutritional rickets. Both Option A and Option D are not features of nutritional rickets, but Option A is the *better* EXCEPT answer because subperiosteal resorption is a positive feature of a distinct condition (hyperparathyroidism), whereas increased sclerosis is simply absent in rickets. ### Mnemonic: RICKETS Radiological Signs **R** — Radiolucency (ground-glass appearance) **I** — Indistinct metaphyseal margins **C** — Cupping of metaphyses **K** — Kyphoscoliosis (spinal deformity, late) **E** — Expansion of growth plate **T** — Thin cortices **S** — Splaying of metaphyses [cite: Robbins & Cotran Pathologic Basis of Disease, 10e, Ch 26; Harrison's Principles of Internal Medicine, 21e, Ch 410]