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2001 |
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Question
A 60-year-old woman undergoes a bone scan because laboratory studies show an elevated alkaline phosphatase level. Results show increased uptake in multiple sites, including her skull. A lateral radiograph of the skull is shown in Figure 1a, and a CT scan is shown in Figure 1b. What is the most likely diagnosis?
1 – Eosinophilic granuloma
2 – Multiple myeloma
3 – Lymphoma
4 – Paget’s disease
5 – Polyostotic fibrous dysplasia
Figures
Answer (click for answer)
Correct Answer: 4- Paget’s disease Figure 1a shows a lateral radiograph of the skull showing what appears to be a large continuous lytic lesion involving the frontal and temporal areas of the skull. Figure 1b is a CT of the skull confirming decreased bone mass in the involved lytic area. The lytic area is a continuous region, unlike the multiple lytic areas usually seen in multiple myeloma. The elevated alkaline phosphatase level is secondary to the increased bone turnover involved in Paget’s disease. Note also that Paget’s disease is most commonly diagnosed during the fifth decade of life and so is a reasonable diagnosis in this 60-year-old patient. The bone scan confirms the marked bone-remodelling that occurs in Paget’s disease. Often the hardest part of diagnosing Paget’s is differentiating it from metastatic cancer. While the clinical picture can be confusing, the overall picture here fits best with the Paget’s disease diagnosis. Also, per the reference, the given radiographic findings are apparently classic for Paget’s. Regarding the skull film, the figure provided is classic for the early phase of Paget’s in which you see a sharply circumscribed focus of lysis without a sclerotic rim (osteoporosis circumscripta). The focus usually begins in the frontal or occipital region from where it may spread to involve the entire skull. In the middle phase you see "cotton-wool" exudates which develop mostly along the base of the inner table within the lytic zone. This represents a combined bone lytic and blastic phase. In the late phase, the osteoporosis circumscripta resolves and is replaced by condensing foci of bone sclerosis.
Reference: Reference: Mirra JM, Brien EW, Tehranzadeh J: Paget’s disease of bone: Review with emphasis on radiologic features. Part II. Skeletal Radiol 1995;24:173-184.