Musculoskeletal Pathology Flashcards
What kind of condition are connective tissue diseases?
Autoimmune conditions = inflammatory conditions characterised by the presence of autoantibodies
What are some specific autoantibodies that have strong links with specific diseases?
Rheumatoid factor = rheumatoid arthritis
Structural parts of DNA = SLE
Anticentromere, antitelomere = Scleroderma
Anti Jo = Dermatomyositis
What occurs in rheumatoid arthritis?
Inflammation of joints = cartilage is destroyed by inflammatory process causing loss of joint space
What is rheumatoid factor?
Autoantibody against Fc IgG
What occurs in the acute and chronic phases of rheumatoid arthritis?
Acute = Pannus formation (inflammatory granulation tissue), hyperplastic/reactive synovium Chronic = fibrosis, deformity
What occurs in SLE?
Prototypic autoimmune disease where autoantibodies are directed at the structural parts of DNA
What are some autoantibodies involved in SLE?
ANA (>95%), Anti double stranded DNA (40-60%), Anti-Sm, RNP, SS-A and B
What occurs in inflammatory arthritis usually?
Chronic inflammation = lymphocytes and plasma cells
What are some acute features of inflammatory arthritis?
Oedema, fibrin, reactive features in synovial cells
When should a biopsy be taken in inflammatory arthritis?
To exclude other conditions
What are some examples of metabolic diseases that affect the joints?
Crystal arthropathies, Paget’s disease, osteomalacia
How can gout arise?
Urate formed in DNA replications as adenine and guanine are purine based, uric acid is the end product of purine synthesis, leads to needle shaped crystal formation
What are the two ways hyperuricaemia can arise?
Increased production
Reduced excretion = under-excretion most common cause, drug side effect (thiazide diuretics reduce urate excretion)
What are some causes of increased uric acid production?
Usually idiopathic (unknown enzyme defect in 90%) HGPRT deficiency = Lyoch Nyhan syndrome (rare) Increased cell turnover (e.g cancer, psoriasis)
Where do urate crystals tend to form?
In joints (lower temperatures)
What is the name for the deposition of urate crystals in soft tissue?
Gouty tophus
What are some clinical manifestations of crystal arthropathies?
Precipitation of crystals (reduced solubility)
Acute inflammatory reaction
Gouty tophus
Secondary degenerative changes in joint
Renal disease (stones and direct deposition in tubules and interstitium)
How is cytology performed of crystal arthropathies?
Joint fluid examined under cross-polarised light to detect needle shaped crystals
What does histology of crystal arthropathies show?
Amorphous eosinophilic debris and inflammation (giant cells), crystals lost during tissue processing, pyrophosphate arthropathy
What crystal arthropathies can calcium pyrophosphate cause?
Pseudogout or chondrocalanosis, usually older patients in large joints, idiopathic
What are some causes of calcium pyrophosphate crystal arthropathies?
Hypercalcaemia (e.g hyperparathyroidism), haemachromatosis, hypomagnesaemia, ochronsis, hypothyroidism
How does calcium pyrophosphate appear on x-rays?
Dense deposits
What are some features of pseudogout?
Usually asymptomatic, incidental finding, range of joint pain, crystals aren’t distinct histologically, weak positive birefringence on fresh microscopy
How are pseudogout crystals different from the crystals of regular gout?
Rhomboid shaped crystals (rather than needle shaped), thicker and bigger than urate crystals
What is Paget’s disease?
Abnormality of bone turn-over, increased osteoclastic activity, more bone but not structured normally
What are some suggested mechanisms of Paget’s disease?
Genetic elements = SQSTM1/p62
RANKL = osteoclast receptor activator Nf kb ligand
Viral infection = paramyxovirus, RSV ,measles (virus capsule protein MVNP stimulates osteoclast activity)
What are the three stages of Paget’s disease?
Osteolytic, mixed, burnt out
What is the net result of Paget’s disease?
Thick excess bone with abnormal reversal lines (mosaic patterns)
How can pain arise in Paget’s disease?
From microfracture or nerve compression
What are some features of the abnormal growth and enlargement that occurs in Paget’s disease?
Leontiasis ossea (new hates), platybasia (skull base abnormality), sabre tibia
Which bones are less affected by Paget’s disease?
Axial or small bones
What are some results of the high metabolism caused by Paget’s disease?
Heat, warm skin, AV shunt, high output cardiac failure
What secondary malignancy can arise from Paget’s disease?
Osteosarcoma
What is osteomalacia, and how does it manifest?
Abnormal vitamin D metabolism related to sun-exposure; manifests as Rickets in young = bowed legs, square heads, pigeon chests, rickety rosary
What occurs when a fracture initially happens?
Trauma, bone breaks causing pain (from periosteum), haemorrhage
What occurs in the initial phase of fracture healing?
Haematoma (fibrin mesh), influx of inflammatory cells, cytokine release to recruit osteoprogenitor cells form periosteum and medullary cavity
What should have occurred one week after a fracture occurs?
Callus formed, organised haematoma, early recruitment and remodelling at ends of bone
What is present between two and three weeks after a fracture has occurred?
Maximum girth of callus, woven bone deposits perpendicular to cortical bone, some cartilage deposition at fracture site (undergoes endochondral ossification), bridging with bony callus
What occurs in remodelling of a bone?
Woven bone in callus constantly remodelled, areas under less stress are resorbed and eventually bone returns to normal shape
What are some features of pathological fractures?
Most common cause for hips to come to pathology, bone isn’t normal prior to break, bone breaks with low level of injury
What are some causes of pathological fractures?
Osteoporosis, tumours = benign (children, primary tumours) or malignant (adults, metastatic disease)
What cancers tend to cause bony metastases?
Lung, kidney, breast and prostate
What are the three kinds of metastatic bone disease?
Osteolytic = most common, bone is resorbed, appear as radiolucent Osteosclerotic = prostate cancer, appear as opacity Myeloma/plasmacytoma = malignant proliferation of plasma cells causes bony lesions
What is the first thing that occurs when a joint is changing?
Small cracks in cartilage, followed by fibrillation
What occurs once cartilage has been completely worn away at a joint?
The surface become polished (eburnation) and the cortical bone thickens greatly to cope with the load
What do fractures cause to happen in a changing joint?
Leakage of synovial fluid through bone, forming small cysts
What occurs as a result of rapid remodelling to cope with stress at a changing joint?
Remodelling is disorganised and produced abnormal outgrowths (osteophytes)
What are some radiological appearances of joint changes?
Loss of joint space = cartilage loss
Subchondral sclerosis = eburnation
Subchondral cysts = synovial fluid accumulation
Osteophytes = disorganised bone remodelling
