Page 607 - Concise Pathology for Exam Preparation ( PDFDrive )

592 SECTION II Diseases of Organ Systems

• Monostotic form of the disease usually remains asymptomatic (discovered incidentally
on radiological examination).
• Polyostotic form, however, is more widespread and may produce pain, fractures,
skeletal deformities, bone overgrowth (leontiasis ossea: overgrowth of the craniofacial
skeleton), and occasionally, sarcomatous transformation.
May also manifest with platybasia (flattening of the base of skull due to weakened bone),
chalkstick type of fractures in the long bones or severe secondary osteoarthritis with
marked elevation of serum alkaline phosphatase and normal-to-high serum calcium level.

Pathology

Three sequential stages have been identified in Paget disease:
• Initial osteolytic stage: Large areas of osteoclastic resorption produced by increased
number of osteoclasts are seen.
• Mixed osteolytic–osteoblastic stage: Imbalance between osteoblasts laying down new
bone and osteoclastic resorption occurs so that mineralization of the newly laid matrix
lags behind, resulting in development of a characteristic mosaic pattern of osteoid
seams or cement lines.
• Quiescent osteosclerotic stage: After many years, excessive bone formation results
so that the bone becomes more compact and dense, producing osteosclerosis.
However, newly formed bone is poorly mineralized, soft and susceptible to frac-
tures. Radiologically, this stage produces characteristic cotton-wool appearance of
the affected bone.

Q. Classify fibro-osseous lesions of bone. Outline the salient
clinicopathological features of its different types.
Ans. Fibro-osseous lesions of bone include

Fibrous Dysplasia (FD)

• Benign condition, possibly of developmental origin characterized by the presence of
localized area of replacement of bone by fibroconnective tissue with a characteristic
whorled pattern containing trabeculae of woven bone.
• Radiologically, the typical focus of FD is well-demarcated and has a ground-glass
appearance.
• FD has three subtypes:
1. Monostotic FD
(a) Monostotic FD usually affects a solitary bone.
(b) It is the most common type of FD and comprises about 70% of all cases.
(c) Most patients are between 20 and 30 years of age.
(d) Bones most often affected, in descending order of frequency are ribs, cranio-facial
bones (especially maxilla), femur, tibia and humerus.
(e) The condition generally remains asymptomatic, and is discovered incidentally, but
infrequently may produce tumour-like enlargement of the affected bone.
2. Polyostotic FD
(a) This form of fibrous dysplasia comprises 25% of all patients and affects several
bones.
(b) Earlier onset than the monostotic form.
(c) Most frequently affected bones are craniofacial bones, ribs, vertebrae and long
bones of the limbs.
(d) Spontaneous fractures and skeletal deformities are common in the childhood poly-
ostotic form of the disease.
3. Albright syndrome
(a) Also called McCune–Albright syndrome
(b) A form of polyostotic FD associated with endocrine dysfunction
(c) Accounts for less than 5% of all cases

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