Osteopetrorickets

Jimmy Wang, MD

Andrew Poznanski, MD

Childrens Memorial Hospital

Abstract

6 month old male presents with blindness and bulging anterior fontanelle. A noncontrast head CT was ordered.

Keywords

Osteopetrosis Rickets Osteopetrorickets 1385

Publication Date: 2008-01-29

History

6 month old male presents with blindness and bulging anterior fontanelle. A noncontrast head CT was ordered.

Findings

Noncontrast Head CT: Diffusely dense, thickened, and sclerotic calvarium, particularly at the skull base. Mild to moderate hydrocephalus. A skeletal survey was recommended.

Skeletal Survey: Diffuse sclerosis of all bones, with absence of medullary space in long bones. Bone on bone appearance and “mephistophelean” orbits. Additionally, metaphyseal fraying at the ends of long bones and cupping at the anterior rib ends (rachitic rosary). Diffuse periosteal reaction of all long bones (with appearance of “periosteal cloaking”).

Diagnosis

Osteopetrosis complicated by rickets, also termed "osteopetrorickets."

DDx

None

Discussion

Osteopetrosis, also known as Albers-Schonberg disease is a rare disorder characterized by osteoclast dysfunction leading deficient bone resorption, a process necessary in the growth and maturation of bone. This leads to increasing accumulation of dense sclerotic of bone generally without significant changes in shape or contour unless the process is advanced. Increasing bone density and sclerosis can be pronounced in the calvarium, resulting in narrowing of neural foramina in the skull base and patients can present with blindness, deafness, cranial nerve palsies, or ischemic cerebrovascular events. There is also narrowing of marrow spaces of long bones, leading to decreased intramedullary hematompoiesis causing anemia, leukopenia, and thrombocytopenia. Compensatory extramedullary hematopoiesis is manifested by hepatosplenomegaly. These patients can be lethargic and weak, and are susceptible to infections with deadly consequences.

Rickets is a disorder of bone due to absolute or relative insufficiency of vitamin D or its derivatives leading to insufficient mineralization of cartilage into mineralized cartilage and mineralized osteoid.

There is a rare paradoxical association reported in the literature between osteopetrosis, a condition characterized by elevated calcium levels, and rickets, a condition that can result from low calcium states. It has been theorized that osteopetrosis can predispose to the development of rickets when the available extracellular calcium level is low. Although the total body calcium is markedly elevated in osteopetrosis, over 99% is sequestered in the skeleton, unavailable for use. The body sees a paradoxically low serum calcium level, which leads to renal wasting of phosphorus. Calcium levels can be further lowered by decreased calcium intake as advised by the physician once a diagnosis of osteopetrosis is made, and glucocorticoid therapy. Low serum calcium and low serum phosphorus levels leads to insufficient mineralization of newly formed osteoid, a setup for the development of rickets. This condition has been referred to as osteopetrorickets.

One of the primary roles of radiology in osteopetrosis is the recognition of superimposed rickets as a potential complication of osteopetrosis, as this can have important implications on the treatment plan. If rickets is present, the established therapy of bone marrow transplant is likely to fail, due to the inability of newly generated osteoclasts to resorb hypomineralized osteoid. Therefore, rickets should be treated first with calcitriol and increased dietary intake of calcium before bone marrow transplantation is initiated.

References

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3. Bukte Y, Gurkan F, Davutoglu M, et al. Infantile Osteopetrosis Associated with Rickets. Eur J Gen Med 2005; 2(1):32-34.
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