Bone and Soft Tissue Pathology Practice Questions

Q: Identify the lesion in a 20-year-old male whose foot X-ray is shown below:

Mycetoma. ***Mycetoma*** - The X-ray image shows a **lytic lesion** with surrounding sclerosis in the calcaneus, indicated by the arrow, which is characteristic of **mycetoma**. The histological image reveals an inflammatory infiltrate with **pigmented fungal grains (brown aggregates)**, confirming the diagnosis. - Mycetoma is a chronic granulomatous infection of subcutaneous tissues, often extending to bone, particularly in the foot. Its characteristic features include **grains (colonies of microorganisms)** within the lesions. *Ochronosis* - Ochronosis would show **dark discoloration of cartilage** and connective tissues due to **homogentisic acid** deposition, leading to degenerative arthritis. This would appear on X-ray as **calcification of cartilage** (e.g., intervertebral discs, menisci) rather than focal lytic lesions with grains. - The histological image would show characteristic **ochre-colored pigment deposits**, not fungal grains. *Haemophilic pseudo-tumour* - A haemophilic pseudo-tumour is a rare complication of hemophilia, often presenting as a **large, expanding lesion** within bone or soft tissue, typically due to recurrent hemorrhage. - X-rays would reveal a **well-defined, expansile lesion** with cortical thinning or bone destruction, and histology would show features of chronic hemorrhage, fibrous tissue, and hemosiderin deposition, not fungal grains. *Pigmented villonodular synovitis* - This condition involves **proliferation of synovial tissue**, often affecting large joints like the knee or hip, leading to bone erosions and cysts. - Histology would show **hyperplastic synovium** with hemosiderin deposition, multinucleated giant cells, and lipid-laden macrophages, but not fungal grains as seen in the microscopy image.

Q: Bone biopsy specimen is shown below. Diagnosis is:

Paget's disease. ***Paget's disease*** - The image shows a **mosaic pattern of woven and lamellar bone**, with prominent **cement lines** (dark wavy lines). This disorganized bone remodeling is characteristic of Paget's disease. - Paget's disease involves excessive and disorganized bone turnover, leading to structurally abnormal and weakened bone. *Osteomalacia* - Characterized by **deficient mineralization of osteoid**, leading to accumulation of unmineralized matrix. - Histologically, this would present as wide, unmineralized osteoid seams, which are not seen in the image. *Osteoporosis* - Defined by a **reduction in bone mass** and microarchitectural deterioration, leading to increased fracture risk. - Histologically, osteoporosis would show **thinner trabeculae** and **larger marrow spaces**, but the bone itself would be normally mineralized, lacking the disorganized mosaic pattern. *Osteosclerosis* - Refers to an **increase in bone density**, often due to increased bone formation or decreased bone resorption. - While Paget's disease can lead to increased bone density in affected areas, osteosclerosis as a primary diagnosis would typically involve uniformly dense, often thickened bone without the classic mosaic pattern seen here.

Q: A muscle biopsy shows 'moth-eaten' fibers. Which histochemical finding would confirm mitochondrial myopathy?

Ragged red fibers on MGT. ***Ragged red fibers on MGT*** - The presence of **ragged red fibers** on a **modified Gomori trichrome (MGT) stain** is the histological hallmark of **mitochondrial myopathies**. - These fibers represent abnormal accumulation of **dysfunctional mitochondria** beneath the sarcolemma. *Type 1 fiber predominance* - While some myopathies may show type 1 fiber predominance, it is a **non-specific finding** and does not confirm mitochondrial myopathy. - It can be seen in various conditions, including **neurogenic atrophy** or some **congenital myopathies**. *Rimmed vacuoles* - **Rimmed vacuoles** are characteristic of **inclusion body myositis** (IBM) and some **distal myopathies**. - They are not a specific finding for mitochondrial myopathy. *Nemaline rods* - **Nemaline rods** are pathognomonic for **nemaline rod myopathy**, a distinct form of congenital myopathy. - They are composed of **actin filament aggregates** and are unrelated to mitochondrial dysfunction.

Q: Albers-Schönberg disease is:

Osteopetrosis. ***Osteopetrosis*** - **Albers-Schönberg disease** is another name for **osteopetrosis**, also known as **marble bone disease** [1]. - It is a group of rare genetic disorders characterized by abnormally **dense bones** due to a defect in **osteoclast** function, leading to impaired bone resorption [1]. *Osteoporosis* - **Osteoporosis** is characterized by decreased bone density and structural deterioration of bone tissue, leading to an increased risk of fractures. - It results from an imbalance where **bone resorption outpaces bone formation**, the opposite of osteopetrosis. *Paget* (Paget's disease of bone) - **Paget's disease of bone** involves localized areas of increased bone turnover, leading to disorganized bone remodeling and weakened, enlarged bones. - It is distinct from osteopetrosis, which involves a generalized increase in bone density. *Osteogenesis imperfecta* - **Osteogenesis imperfecta** (OI), or brittle bone disease, is a genetic disorder causing extremely fragile bones prone to fractures, often due to defects in **collagen production** [1]. - This condition presents with bone fragility and often blue sclera, which is the opposite of the increased bone density seen in osteopetrosis. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1188-1189.

Q: Marble bone disease is:

Osteopetrosis. ***Osteopetrosis*** - **Osteopetrosis**, also known as **marble bone disease**, is a rare genetic disorder characterized by abnormally dense bones due to a defect in **osteoclast function** [1]. - Impaired bone resorption leads to an accumulation of woven bone, causing bones to be fragile despite their density [1]. *Osteosclerosis* - **Osteosclerosis** is a general term for increased bone density and can be a feature of various conditions, including osteopetrosis. - However, it is a descriptive term rather than a specific disease diagnosis equivalent to marble bone disease. *Histiocytosis X* - **Histiocytosis X**, also known as **Langerhans cell histiocytosis**, is a rare disorder involving the proliferation of Langerhans cells. - It primarily affects bone but can also involve other organs, presenting with lytic lesions rather than increased bone density. *Osteomalacia* - **Osteomalacia** is a condition characterized by inadequate mineralization of bone tissue, leading to soft and weakened bones. - It is typically caused by **vitamin D deficiency** and is the opposite of increased bone density. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1188-1189.

Q: Crystals deposited in Pseudogout:

Calcium pyrophosphate dihydrate. ***Calcium pyrophosphate dihydrate*** - **Calcium pyrophosphate dihydrate (CPPD)** crystals are characteristic of pseudogout, also known as **CPPD deposition disease**. [1] - These crystals typically appear **rhomboid-shaped** and show **positive birefringence** under polarized light microscopy. [1] *Calcium oxalate* - **Calcium oxalate** crystals are primarily associated with **kidney stones** and severe kidney disease. - They are not the causative agent for pseudogout, which involves different crystal types and joint pathology. *Monosodium urate* - **Monosodium urate** is the crystal form associated with **gout**, forming needle-shaped crystals with **negative birefringence**. [2] - This is distinct from pseudogout, which involves CPPD crystals and a different clinical presentation. [1], [2] *Amyloid* - **Amyloid** refers to insoluble, misfolded proteins that can deposit in various tissues and organs, causing **amyloidosis**. - Amyloid deposits are associated with organ dysfunction but do not form the characteristic crystals found in pseudogout. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 683-684. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1218-1220.

Q: Osteogenesis imperfecta is due to

Defective synthesis of type I collagen. ***Defective synthesis of type I collagen*** - **Osteogenesis imperfecta** is primarily caused by mutations in genes (COL1A1 or COL1A2) that encode **Type I collagen**, leading to defective collagen synthesis [1]. - This defective collagen results in **fragile bones**, leading to recurrent fractures, which is the hallmark of the disorder [1]. *Inborn error of the methionine metabolism* - An inborn error of methionine metabolism, such as **homocystinuria**, affects multiple systems including bone, but it causes **osteoporosis** and marfanoid habitus, not the typical features of osteogenesis imperfecta. - Homocystinuria is characterized by **thromboembolism**, **ectopia lentis**, and developmental delay, which are not features of osteogenesis imperfecta. *Growth hormone dysfunction* - **Growth hormone dysfunction** primarily leads to growth disturbances like **dwarfism** or **gigantism**, but does not directly cause the characteristic bone fragility and connective tissue defects seen in osteogenesis imperfecta. - While growth hormone can influence bone metabolism, its dysfunction is not the underlying genetic defect responsible for osteogenesis imperfecta. *Bony abnormality confined to the metaphysis* - A bony abnormality confined to the **metaphysis** is characteristic of conditions like **rickets** or **achondroplasia**, where there are issues with cartilage growth and ossification. - **Osteogenesis imperfecta** affects the entire bone structure due to a systemic defect in collagen, not just a confined region like the metaphysis. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, p. 1188.

Q: Mutations in type I collagen fibres results in:

Osteogenesis imperfecta. ***Osteogenesis imperfecta*** - This condition is primarily caused by **genetic defects** in the genes encoding **Type I collagen**, particularly *COL1A1* and *COL1A2*. - It leads to **fragile bones** that fracture easily, **blue sclera**, **hearing loss**, and **dentinogenesis imperfecta**, due to the impaired formation of collagen, a major component of bone and connective tissues. *Osteosclerosis* - This refers to a general term for **increased bone density** and hardening of bone, which can be a symptom of various conditions. - It is not caused by a specific mutation in Type I collagen but rather points to an **imbalance in bone remodeling** where bone formation outpaces resorption. *Osteopetrosis* - Also known as **Albers-Schönberg disease** or **marble bone disease**, this condition is characterized by **abnormally dense bones** due to a defect in **osteoclast function**, which impairs bone resorption [1]. - It is primarily caused by mutations in genes involved in osteoclast development and acidification, such as *CLCN7*, not Type I collagen genes [1]. *Marfan's syndrome* - This is a **connective tissue disorder** caused by a mutation in the *FBN1 gene* encoding **fibrillin-1**, a protein essential for the formation of elastic fibers. - It affects the **skeleton, eyes, heart, and blood vessels**, leading to features like tall stature, long limbs, and cardiovascular abnormalities, distinct from collagen defects causing bone fragility. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, p. 1188.

Question 1

Identify the lesion in a 20-year-old male whose foot X-ray is shown below:

Accepted Answer

Mycetoma

Answer

Ochronosis

Answer

Haemophilic pseudo-tumour

Answer

Pigmented villonodular synovitis

Question 2

Bone biopsy specimen is shown below. Diagnosis is:

Accepted Answer

Paget's disease

Answer

Osteomalacia

Answer

Osteoporosis

Answer

Osteosclerosis

Question 3

A 5 year old child who presented with proptosis of one of the eyes was found to have a desmin positive tumour. What is the probable diagnosis?

Accepted Answer

Rhabdomyosarcoma

Answer

Neuroblastoma

Answer

Retinoblastoma

Answer

Ewing's sarcoma

Question 4

A 12-year-old Caucasian male presents with his mother to the pediatrician’s office complaining of right thigh pain. He reports that he has noticed slowly progressive pain and swelling over the distal aspect of his right thigh over the past two months. He denies any recent trauma to the area and his temperature is 100.9°F (38.3°C). On exam, there is swelling and tenderness overlying the distal right femoral diaphysis. Laboratory evaluation is notable for an elevated white blood cell (WBC) count and elevated erythrocyte sedimentation rate (ESR). A radiograph of the patient’s right leg is shown. Biopsy of the lesion demonstrates sheets of monotonous small round blue cells with minimal cytoplasm. Which of the following genetic mutations is most likely associated with this patient’s condition?

Accepted Answer

t(11;22)

Answer

RB1 inactivation

Answer

TP53 inactivation

Answer

t(8;14)

Answer

t(X;18)

Question 5

A muscle biopsy shows 'moth-eaten' fibers. Which histochemical finding would confirm mitochondrial myopathy?

Accepted Answer

Ragged red fibers on MGT

Answer

Type 1 fiber predominance

Answer

Rimmed vacuoles

Answer

Nemaline rods

Question 6

Albers-Schönberg disease is:

Accepted Answer

Osteopetrosis

Answer

Osteoporosis

Answer

Paget

Answer

Osteogenesis imperfecta

Question 7

Marble bone disease is:

Accepted Answer

Osteopetrosis

Answer

Osteosclerosis

Answer

Histiocytosis X

Answer

Osteomalacia

Question 8

Crystals deposited in Pseudogout:

Accepted Answer

Calcium pyrophosphate dihydrate

Answer

Calcium oxalate

Answer

Amyloid

Answer

Monosodium urate

Question 9

Osteogenesis imperfecta is due to

Accepted Answer

Defective synthesis of type I collagen

Answer

Inborn error of the methionine metabolism

Answer

Growth hormone dysfunction

Answer

Bony abnormality confined to the metaphysis

Question 10

Mutations in type I collagen fibres results in:

Accepted Answer

Osteogenesis imperfecta

Answer

Osteosclerosis

Answer

Osteopetrosis

Answer

Marfan's syndrome

Bone and Soft Tissue Pathology — MCQs

Bone and Soft Tissue Pathology — MCQs

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