The patient is a 20 y.o. man referred by his dentist after he developed recurrent deep dental caries complicated by mandibular osteomyelitis. Initial mandibular films showed marked bony sclerosis. The patient recently moved to the area, but he reports that he has sustained several femoral and rib fractures over the last several years. He relates that his doctors told him that he has thick bones, and never could understand why he should be so prone to fracture. He is otherwise well, and has no systemic symptoms. He does divulge that several other family members have a similar history, including his father. Thinking that this scenario sounded familiar, confirmatory radiographs of the spine were obtained.
Spine radiographs reveal the classic sandwich vertebrae of osteopetrosis (red arrows). This is manifested as thickening and sclerosis of the vertebral endplates, and of the bone adjacent to the endplates. There is also marked thickening of the posterior vertebrae (yellow arrows), especially in the vertebral arch. Skull X-ray (not shown) reveals basilar sclerosis with sparing of the calvaria, and films of the pelvis (not shown) show a bone-within-bone appearance of the iliac wings.
Diagnosis and Discussion
Correct Diagnosis: Type II Autosomal Dominant Osteopetrosis (Albers- Schnberg Disease)
Type II Autosomal Dominant Osteopetrosis (Type II ADO), also known as Albers- Schnberg Disease, is a rare bone dysplasia characterized by diffuse and symmetric bony sclerosis most often affecting the long bones, skull, ribs, and spine. A rarer autosomal recessive form affects children, and is often fatal by the end of the first decade of life. Patients with Type II ADO often present by the early 20s with a history of recurrent long bone fractures, deep dental caries complicated by abscesses, mandibular osteomyelitis, or cranial nerve palsies secondary to basilar skull sclerosis. Early degenerative joint disease, especially in the hips is also seen. Despite their diffusely thickened bone, these patients are prone to fracture, likely due to the thickened bonesdecreased torsional strength. However, this same property likely protects patients from vertebral fractures, which are quite rare in this condition. The condition is easily diagnosed radiographically with its characteristic sandwich vertebrae seen on spine films. A similar appearance may also be seen in patients with renal osteodystrophy (the rugger jersey vertebrae), but the clinical setting helps distinguish between the two entities.
Orthopedic surgery is notoriously difficult in these patients; drill bits often break, intraoperative fractures occur due to the surprisingly brittle and inelastic bone, and postoperative infections and abscesses are common due to decreased bone vascularity. The disease is thought to be due to defective osteoclast function, although an exact etiology remains unknown. An increased serum acid phosphatase is generally seen in these patients and they may be mildly anemic due to a decreased marrow space. Treatment is largely symptomatic and often involves meticulous fracture management and close postoperative care.
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