Hyperplastic callus formation in both femurs in osteogenesis imperfecta

Natural history of hyperplastic callus formation in osteogenesis imperfecta type V

Hyperplastic callus formation was assessed in 23 patients with osteogenesis imperfecta type V. Hyperplastic callus mostly affected long bones in the lower extremities and occurred predominantly during phases of rapid growth.

INTRODUCTION

Hyperplastic callus (HPC) formation is one of the most conspicuous features of osteogenesis imperfecta (OI) type V, but the natural history of HPC has not been well characterized.

MATERIALS AND METHODS

In this retrospective single-center study, we assessed HPC in 23 OI type V patients (9 females and 14 males).

RESULTS

Fifteen patients (65%) had HPC at 48 skeletal sites, 30 of which affected the lower limbs. The number of HPC sites per patient ranged from 0 to 7, with an average of 2.6 for men and 1.1 for women (p = 0.047 for this sex difference; t-test). New HPC formation was observed both after fractures and outside of the context of fractures. Only a minority of lower limb fractures (26%) precipitated HPC formation. After an initial enlargement phase, HPC lesions usually stabilized, but could also resolve completely (n = 2) or progress and lead to bone deformation. The most common complication of HPC was a fracture through the lesion (n = 7). Neither pamidronate nor indomethacin seemed to influence the course of HPC.

CONCLUSIONS

HPC is a potentially serious complication of OI type V. Given the rarity of the disorder, treatment studies will require multicenter collaborations.

Hyperplastic callus formation in osteogenesis imperfecta type V mimicking osteosarcoma: 4-year follow-up with resolution

We report a case of hyperplastic callus formation that occurred in both femurs in a patient with type V osteogenesis imperfecta (OI), with 4-year follow-up and resolution. The clinical, histological and imaging aspects of this condition are discussed. Recognition of the hyperplastic callus formation in this particular type of OI is important in order to avoid misdiagnosis.

Syndromes with congenital brittle bones

Background

There is no clear definition of osteogenesis imperfecta (OI). The most widely used classification of OI divides the disease in four types, although it has been suggested that there may be at least 12 forms of OI. These forms have been named with numbers, eponyms or descriptive names. Some of these syndromes can actually be considered congenital forms of brittle bones resembling OI (SROI).

Discussion

A review of different syndromes with congenital brittle bones published in the literature is presented. Syndromes are classified in "OI" (those secondary to mutations in the type I pro-collagen genes), and "syndromes resembling OI" (those secondary to mutations other that the type I pro-collagen genes, identified or not). A definition for OI is proposed as a syndrome of congenital brittle bones secondary to mutations in the genes codifying for pro-collagen genes (COL1A1 and COL1A2).

Summary

A debate about the definition of OI and a possible clinical and prognostic classification are warranted.

Type V osteogenesis imperfecta: a new form of brittle bone disease

Osteogenesis imperfecta (OI) is commonly subdivided into four clinical types. Among these, OI type IV clearly represents a heterogeneous group of disorders. Here we describe 7 OI patients (3 girls), who would typically be classified as having OI type IV but who can be distinguished from other type IV patients. We propose to call this disease entity OI type V. These children had a history of moderate to severe increased fragility of long bones and vertebral bodies. Four patients had experienced at least one episode of hyperplastic callus formation. The family history was positive for OI in 3 patients, with an autosomal dominant pattern of inheritance. All type V patients had limitations in the range of pronation/supination in one or both forearms, associated with a radiologically apparent calcification of the interosseous membrane. Three patients had anterior dislocation of the radial head. A radiodense metaphyseal band immediately adjacent to the growth plate was a constant feature in growing patients. Lumbar spine bone mineral density was low and similar to age-matched patients with OI type IV. None of the type V patients presented blue sclerae or dentinogenesis imperfecta, but ligamentous laxity was similar to that in patients with OI type IV. Levels of biochemical markers of bone metabolism generally were within the reference range, but serum alkaline phosphatase and urinary collagen type I N-telopeptide excretion increased markedly during periods of active hyperplastic callus formation. Qualitative histology of iliac biopsy specimens showed that lamellae were arranged in an irregular fashion or had a meshlike appearance. Quantitative histomorphometry revealed decreased amounts of cortical and cancellous bone, like in OI type IV. However, in contrast to OI type IV, parameters that reflect remodeling activation on cancellous bone were mostly normal in OI type V, while parameters reflecting bone formation processes in individual remodeling sites were clearly decreased. Mutation screening of the coding regions and exon/intron boundaries of both collagen type I genes did not reveal any mutations affecting glycine codons or splice sites. In conclusion, OI type V is a new form of autosomal dominant OI, which does not appear to be associated with collagen type I mutations. The genetic defect underlying this disease remains to be elucidated.