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What is the primary mechanism by which PTH increases bone resorption?
What is the effect of excessive PTH production on serum calcium levels?
What is the primary cause of pyogenic osteomyelitis?
What is the term for the inflammation of bone and marrow?
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What is the result of increased osteoclast activity in hyperparathyroidism?
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What is the effect of PTH on the renal tubules?
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What is the result of increased PTH production in the setting of underlying renal disease?
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What is the effect of PTH on vitamin D synthesis?
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What is the consequence of decreasing bone mass in hyperparathyroidism?
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What percentage of individuals with pulmonary or extrapulmonary tuberculosis exhibit osseous infection?
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How do the organisms causing osseous infection usually originate?
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What is the typical presentation of affected individuals with mycobacterial osteomyelitis?
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What is the characteristic histologic finding in mycobacterial osteomyelitis?
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What percentage of cases of mycobacterial osteomyelitis involve the spine?
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What is the characteristic feature of tuberculous spondylitis (Pott disease)?
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What is the role of radiographic imaging studies in diagnosing bone tumors?
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What is the characteristic feature of benign bone tumors?
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What is the relative frequency of benign and malignant bone tumors?
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What is the primary cause of congenital abnormalities of the skeleton?
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What is the classification system for developmental disorders of bone?
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What is the primary characteristic of dysostosis?
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What is the most common skeletal dysplasia and a major cause of dwarfism?
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What is the normal function of FGF in endochondral growth?
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What is the characteristic head shape of individuals with achondroplasia?
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What is the primary characteristic of Osteogenesis Imperfecta (OI)?
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What is the characteristic of the teeth in individuals with Osteogenesis Imperfecta (OI)?
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What is the cause of hearing loss in individuals with Osteogenesis Imperfecta (OI)?
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What is the primary characteristic of osteoarthritis?
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What is the term for osteoarthritis that appears in younger individuals with a predisposing condition?
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What is the role of articular cartilage in the joints?
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What is the age range in which the prevalence of osteoarthritis increases exponentially?
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What percentage of people older than 70 are affected by osteoarthritis?
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What is the role of genetic factors in the development of osteoarthritis?
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What is the role of matrix metalloproteases in the development of osteoarthritis?
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What is the role of TGF-β in the development of osteoarthritis?
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What is the initial event in the development of osteoarthritis?
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What is the characteristic of the joints in severe osteoarthritis of the hip?
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What is the typical age group in which primary OA usually presents?
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What is the cause of radicular pain in OA?
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What is the primary route of infection in septic arthritis in neonates?
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What is the characteristic of Heberden nodes?
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What is the usual cause of septic arthritis in children younger than 2 years of age?
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What is the characteristic symptom of OA?
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What is the usual outcome of osteoarthritis?
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What is the common site of osteophytes in OA?
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Study Notes
Congenital Bone Diseases
- Congenital abnormalities of the skeleton can result from inherited mutations and become manifest during early stages of bone formation.
- The classification system for developmental disorders of bone is not standardized.
- Congenital anomalies can result from localized abnormalities in mesenchyme migration and condensation (dysostosis) or global disorganization of bone and/or cartilage (dysplasia).
Achondroplasia
- Achondroplasia is an autosomal dominant disorder resulting from retarded cartilage growth.
- It is the most common skeletal dysplasia and a major cause of dwarfism.
- The disease is caused by gain-of-function mutations in fibroblast growth factor receptor 3 (FGFR3).
- Affected individuals have shortened proximal extremities, a trunk of relatively normal length, and an enlarged head with bulging forehead and conspicuous depression of the root of the nose.
- The skeletal abnormalities are usually not associated with changes in longevity, intelligence, or reproductive status.
Type I Collagen Diseases (Osteogenesis Imperfecta) (OI)
- OI is the most common inherited disorder of connective tissue, caused by deficiencies in the synthesis of type I collagen.
- It is a phenotypically diverse disorder that principally affects bone and other tissues rich in type I collagen (joints, eyes, ears, skin, and teeth).
- It is autosomal dominant.
- The fundamental abnormality in OI is too little bone, resulting in extreme skeletal fragility.
- Findings include blue sclerae, hearing loss, dental imperfections, and skeletal deformities.
Hyperparathyroidism
- Excess production and activity of parathyroid hormone (PTH) result in increased osteoclast activity, bone resorption, and osteopenia.
- Isolated hyperparathyroidism peaks in middle adulthood and slightly earlier if presenting as a component of multiple endocrine neoplasia (MEN, types I and IIA).
- PTH plays a central role in calcium homeostasis through the following effects: • Osteoclast activation, increasing bone resorption and calcium mobilization • Increased resorption of calcium by the renal tubules • Increased urinary excretion of phosphates • Increased synthesis of active vitamin D, 1,25(OH)2-D, by the kidneys, which enhances calcium absorption from the gut and mobilizes bone calcium by inducing RANKL on osteoblasts
Osteomyelitis
- Osteomyelitis denotes inflammation of bone and marrow, usually secondary to infection.
- It may be a complication of any systemic infection but frequently manifests as a primary solitary focus of disease.
- Pyogenic osteomyelitis is almost always caused by bacteria and rarely by fungi.
- Mycobacterial osteomyelitis is a rare complication of tuberculosis.
Tuberculous Spondylitis (Pott Disease)
- It is a destructive infection of vertebrae, affecting the spine in 40% of cases of mycobacterial osteomyelitis.
- The infection breaks through intervertebral discs to affect multiple vertebrae and extends into the soft tissues.
Bone Tumors and Tumor-Like Lesions
- Bone tumors can present in various ways, with asymptomatic incidental findings or producing pain or a slow-growing mass.
- Radiographic imaging studies have an important role in diagnosing these lesions, providing the exact location and extent of the tumor.
- Biopsy is necessary for definitive diagnosis.
Classification of Bone Tumors
- Benign tumors greatly outnumber their malignant counterparts and occur with greatest frequency within the first three decades of life.
- In older adults, a bone tumor is more likely to be malignant.
Arthritis
Osteoarthritis (OA)
- OA is characterized by degeneration of cartilage, resulting in structural and functional failure of synovial joints.
- It is the most common disease of joints, appearing insidiously without apparent initiating cause, as an aging phenomenon (idiopathic or primary osteoarthritis).
- In about 5% of cases, OA appears in younger individuals with some predisposing condition, such as joint deformity, a previous joint injury, or an underlying systemic disease that places joints at risk.
- The prevalence of OA increases exponentially beyond the age of 50, and about 40% of people older than 70 are affected.
- Pathogenesis involves degeneration of the articular cartilage and its disordered repair, with genetic factors, including genes encoding components of the matrix and signaling molecules, playing a role.
Clinical Course of Osteoarthritis
- Primary OA usually presents in patients in their 50s.
- Characteristic symptoms include joint pain that worsens with use, morning stiffness, crepitus, and limitation of range of movement.
- Impingement on spinal foramina by osteophytes results in cervical and lumbar nerve root compression and radicular pain, muscle spasms, muscle atrophy, and neurologic deficits.
- The joints commonly involved include the hips, knees, lower lumbar and cervical vertebrae.
Septic Arthritis
- Joints can become infected from hematogenous dissemination, direct inoculation through the skin, or from contiguous spread from a soft tissue abscess or osteomyelitis.
- Septic arthritis is potentially serious, as it can cause rapid, permanent joint destruction.
Supportive Arthritis
- Bacterial infections that cause acute suppurative arthritis usually enter the joints from distant sites by hematogenous spread.
- In neonates, however, contiguous spread from underlying epiphyseal osteomyelitis may occur.
- In children younger than 2 years of age, H. influenza arthritis predominates, while in older children and adults, S. aureus predominates.
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Description
This quiz covers congenital bone diseases, including developmental disorders of the skeleton resulting from inherited mutations and abnormalities in bone formation.
