Tc99m MDP bone scan in fragilitas ossium

Sir,

We present the bone scan findings in a 15-year-old female, a known case of osteogenesis imperfect (OI). The patient had a normal appearance on birth, and the classical signs such as blue sclera and short stature were absent. The patient had a complaint of pain at multiple sites in the body, mainly in limbs. As she grew up, she suffered spontaneous fracture at multiple sites due to trivial/no trauma. Tc99m methylene diphosphonate planar bone scan [Figure 1] performed to look for fracture sites showed the entire axial and appendicular skeleton to be amorphous, deformed, and curvaceous. The long bones appeared asymmetrical and angulated at places. Heterogenous tracer uptake was seen in the diaphysis of long bones. Focus of increased tracer uptake was noted in bilateral ribs anteriorly giving a beaded appearance. Severe kyphoscoliosis was also noted. Increase tracer uptake was also seen in the epiphyseal region of long bones. Both femori and humeri appeared unstructured with multiple foci of abnormal osteoblastic activity. Pelvis also appeared deformed with multiple foci of increased tracer uptake. These findings are consistent with multiple fractures sites in the deformed skeleton of diagnosis OI type III. Furthermore, termed as fragilitas ossium, that signifies brittleness of bone.[1]

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Figure 1 Tc99m methylene diphosphonate planar bone scan in a case of osteogenesis imperfecta

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Clinical features of this disease are bone fragility, high frequency of fractures usually with minimal trauma, bone deformity, joint hyper mobility, subnormal or short stature, dentinogenesis imperfecta, bluish/grayish hue of sclera, and hearing loss due to otosclerosis in adulthood. OI was classified in types I through IV by David Sillence (created 1979) based on the variability of the modes of inheritance, family history, clinical features, and radiologic findings and it forms the basis for the currently accepted classification system of OI.[2] Currently, OI is classified into nine clinically different types (I–IX).

Collagen is the major protein of the body tissue that forms the framework of skeletal system. The first four types are associated with a mutation in genes responsible for collagen type I synthesis. This mutation results in either decreased production of the concerned protein or synthesis of structurally defective collagen molecules. The inheritance is predominantly autosomal dominant, resulting in a qualitative reduction of type 1 collagen. In recessive type, there is a quantitative reduction in type 1 collagen.[3] A mutation in genes encoding type 1 collagen is predominantly found in 80% of OI cases.[4] Defective collagen synthesis leads to pathologic changes in all tissues of which type 1 collagen is an important constituent such as bones, sclera, teeth, ligament, and skin. The result is a weak bone that easily breaks.[3] The clinical and radiological signs have got a wide spectrum of severity, ranging from mild to perinatal lethal form. Patients with a nonlethal form of OI, usually live their full life, interrupted by frequent fractures and bone deformities secondary to malunion or joint contractures.

Type III OI exhibits one of the severe forms of skeletal manifestation, in which the first fracture can occur during perinatal period or during birth, and this form is probably best known to radiologists and orthopedic surgeons. Its hallmark feature is severe bone fragility and osteopenia. Multiple fractures and progressive deformity affect the long bones, skull, and spine and are often present at birth. Kyphoscoliosis is common. Children with this type of OI tend to have severe dwarfism caused by spinal compression fractures, limb deformities, and disruption of growth plates. These patients usually have short height/subnormal stature; their extremities are short and bones are deformed. Other distinctive clinical manifestations are barrel-shaped chest, weak muscles, severe scoliosis, triangular face, and blue sclera that usually turns white with age.[5] Vertebral bodies tend to be wedged, translucent, and shallow. Thinning of the skull with multiple ossification centers (wormian bones) and under-mineralized calvarium is noted in a radiograph of infants.[5] In adults, the metaphyses are broad, while the diaphysis is thin. There are osteopenia and joint hyper mobility leading to kyphoscoliosis. Osteopenia in the metaphyses and popcorn calcification in the epiphysis causes the disruption of growth plate and reduces the length of long bones.