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BMJ Case Rep. 2010; 2010: bcr06.2009.2012.
Published online 2010 March 23. doi:  10.1136/bcr.06.2009.2012
PMCID: PMC3028213
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Osteopetrorickets: a twin paradox

Description

A 4½-month-old previously well male child presented with fever, rapid breathing for 5 days, and abdominal distension for the preceding 3 months. He was born to a non-consanguineous marriage and had been fed with diluted cow’s milk since the age of 2 months. On examination, the child had tachypnoea, intercostal retractions, crackles in the chest, pallor, frontoparietal bossing, and hepatosplenomegaly. Anthropometric parameters were below the 3rd centile of the WHO National Center for Health Statistics (NCHS) reference standards (weight 4 kg, length 50 cm, head circumference 39.4 cm). Fundus and the rest of the systemic examination were normal. Laboratory parameters showed haemoglobin 6.5 g/dl, total leucocyte count of 28×109/l, platelet count of 330×109/l, and a normal reticulocyte count. Chest x-ray showed infiltrates with dense bones which prompted a skeletal survey (fig 1). Radiological examination showed metaphyseal fraying and splaying at the lower end of femur and proximal end of the tibia and fibula, thickening of the base of the cranium, and a generalised increase in bone density with “bone in bone” appearance (fig 1). Biochemical investigations revealed low serum calcium (7.0 mg/dl), phosphorus (2.8 mg/dl) and elevated alkaline phosphatase (824 U/l). Thus, a diagnosis of osteopetrorickets was established. After stabilisation, the child was started on calcium, phosphorus, calcitriol supplementation and prednisolone along with nutritional rehabilitation. At 4 months follow-up the child showed improvement in serum calcium (9.2 mg/dl), phosphorus (3.6 mg/dl) and alkaline phosphatase (537 IU/l), and the x-ray showed features of healing.

Figure 1
(A) Dense bones on chest x-ray. (B) Metaphyseal fraying and splaying at the lower end of femur and proximal end of the tibia and fibula. (C) Thickening of the base of the cranium.

Osteopetrorickets is a rare paradoxical feature of infantile osteopetrosis, characterised by osteoclast dysfunction and failure of resorption of calcified cartilage leading to insufficient mineralisation of newly formed chondroid and osteoid, even in the presence of an intensely positive calcium balance.1,2 More than 99% of the calcium gets sequestrated in the bone and calcium phosphorus product falls to <40, which is insufficient for mineralisation. In addition, decreased dietary calcium intake contributes to rickets, as did faulty feeding in the index case. Clinical signs of rickets may not be obvious, therefore a high index of suspicion and regular monitoring of biochemical and probably radiological parameters is essential to diagnose and treat the above entity at the earliest opportunity, since appropriate treatment leads to improvement in general well being and protects against respiratory tract infections.1,3 Furthermore, management of osteopetrorickets has important connotations for the outcome of bone marrow transplantation which is the treatment of choice for osteopetrosis. The mainstay of management is 1,25-hydroxyvitamin D3 and high dose calcium supplementation.

Footnotes

Competing interests: None.

Patient consent: Patient/guardian consent was obtained for publication.

REFERENCES

1. Kaplan FS, August CS, Fallon MD, et al. Osteopetrorickets: the paradox of plenty. Pathophysiology and treatment. Clin Orthop 1993; 294: 64–78. [PubMed]
2. Kirubakran C, Ranjani K, Scott JX, et al. Osteopetrorickets. J Trop Pediatr 2004; 50: 185–6. [PubMed]
3. Banco R, Siefert MF, Marks SC, et al. Rickets and osteopetrosis: the osteosclerotic mouse. Clin Orthop 1985; 201: 238–42. [PubMed]

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