Extra MSK Flashcards
- What is the HLA-B27?
- What is the function?
It is the Human Leucocyte Antigen, which a class I surface antigen present on all cells except RBC. It plays a role in immunity and self-recognition as an antigen presenting cell. Essentially you are either HLA-B27 positive or negative.
What proportion of the UK population is HLAB27 positive?
9% in the UK, more common in the northern hemispheres.
Describe the basic concept behind the misfolding and the heavy chain homodimer hypothesis
the molecules in both can join together and accumulate in the ER which triggers an inflammatory response called the endoplasmic reticulum UPR response. This then triggers a cascade of inflammatory cytokines e.g. IL23 or IL17.
Give 9 Signs of spondyloarthritis. SPINEACHE
1) Sausage digits (dactylitis)
2) Psoriasis
3) Inflammatory back pain
4) NSAID good response
5) Enthesitis (particularly in the ankle tendons, plantar fasciitis
6) Arthritis
7) Crohn’s/ Colitis/elevated CRP
8) HLA-B27
9) Eye (Uveitis)
What clinical features do all the spondyloarthritis conditions share?
1) Axial inflammation
2) Asymmetrical peripheral arthritis
3) Absence of rheumatoid factor “seronegative”
4) Strong association with HLAB27
Ankylosis
Abnormal stiffening and immobility of joint due to new bone formation.
Pathophysiology behind Ankylosing Spondylitis
1) Repeated inflammation of the spine leads to erosive damage.
2) Lymphocyte and plasma infiltration occurs with local erosion of bone at the attachments of the intervertebral which heals with new bone formation. (SYNDESMOPHYTE)
3) This leads to Enthesitis and irreversible fusion of the spine
What is enthesitis?
Inflammation where tendons/ligaments insert into bone
What is syndesmophyte?
New bone formation and vertical growth from anterior vertebral corners.
Give two spinal abnormalities that is usually found in ankylosing spondylitis
1) Loss of lumbar lordosis and increased kyphosis.
2) Limitation of lumbar spine motility in both sagittal and frontal planes. (Schober test)
Schober test
A mark is made at the 5th lumbar spinous process and 10cm above, with the patient in the erect position.
On bending forward, the distance should increase to more than 15 cm in normal individuals.
What is the use of TNF- alpha blockers? When should they be used?
- Improves spinal and peripheral joint inflammation, the earlier you start the less syndesmophyte form.
What is asymmetrical oligoarthritis?
- Involves the knee or any large joint with a few small joints in the fingers and toes.
What is symmetrical seronegative polyarthritis?
Polyarthritis is any type of arthritis that involves 5 or more joints simultaneously.
What proportion of people with psoriatic arthritis are HLA-B27 positive?
50%
What is the most typical pattern of joint involvement in psoriatic arthritis?
Distal interphalangeal joint
What is dactylitis?
Sausage shaped fingers due to inflammation of the flexor tendons and synovium.
What is arthritis mutilans?
Destruction of the small bones in the hands and feet due to periarticular osteolysis and bone shortening
Name 5 hidden sites for psoriasis
1) Behind ear/inside ear
2) Scalp
3) Umbilicus
4) Natal cleft
5) Genitalia
What is the pathophysiology of reactive arthritis?
- Bacterial antigens or bacterial DNA have been found in the inflamed synovium of affected joints- suggesting that this persistent antigenic material is driving the inflammatory response.
SEPTIC ARTHRITIS
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Describe the tests that you would perform to find Staphylococcus aureus and what would the results be?
1) Gram stain and shape = Purple as gram +ve cocci
2) Clusters/Chains? = Clusters»_space;>staphylococcus
3) Coagulase test: +ve»_space;>aureus
Describe the tests that you would perform to find Streptococci and what would the results be?
1) Gram stain = purple as gram +ve cocci
2) Clusters/chains? = Chains»»streptococci
3) Haemolysis on blood agar and Lancefield grouping to see which type
Describe the tests that you would perform to find and Neisseria gonorrhoea what would the results be?
1) Gram staining and shape = pink as gram -ve cocci
Nesseria= N for negative
MOST COMMON CAUSE OF SEPTIC ARTHRITIS IN YOUNG SEXUALLY ACTIVE WOMEN AND MEN WHO HAVE SEX WITH MEN
Describe the tests that you would perform to find Haemophilus influenzae and what would the results be?
1) Gram stain= pink as gram -ve coccobacillus
2) Blood culture on blood and chocolate agar:
No growth on blood agar as they need factor X(haem) and V (NAD).
Growth on chocolate agar as blood agar heated to release haem.
Name 3 different types of bacterial arthritis
1) Gonococcal arthritis
2) Meningococcal arthritis
3) Tuberculous arthritis
READ UP ON THESE
Pathophysiology of osteomyelitis: describe the 3 ways in which the pathogen can get into bone.
Is it polymicrobial or monomicrobial?
- Easy: DIRECT inoculation of infection into the bone e.g. trauma/open wound. POLY/MONOMICROBIAL
- Quite easy: contiguous spread of infection to bone from adjacent soft tissues. POLY/MONOMICROBIAL
- Difficult: hematogenous seeding, from skin to blood to bone e.g. due to cannula infection. MONOMICROBIAL
Why do long bones tend to be affected by hematogenous seeding in children?
In children the metaphysis of long bones has a slow blood flow, capillaries lack or have inactive phagocytic lining cells and endothelial BM is absent meaning bacteria can move from the blood to bone and predispose growth of bacteria in the bone.
Why do vertebrae tend to be affected by hematogenous seeding in adults?
With age, the vertebrae become more vascular meaning bacterial seeding and vertebral endplate is more likely.
In chronic histopathological changes of osteomyelitis, what is the name for new bone formation?
Involucrum
Why does chronic osteomyelitis lead to sequestra and new bone formation?
Inflammatory exudate( formed in response to bacteria in marrow)»>increased intamedullary pressure»ruptures through periosteum -> periosteum blood supply impaired -> necrosis -> pieces of separated bone known as sequestra -> new bone forms called involucrum.
OSTEOPOROSIS
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What is a DEXA scan?
Dual Energy X-ray Absorptiometry. Low energy x-rays to see how dense bone is. It is used to get the T-score.
What is the T-score for established osteoporosis?
Less than or equal to -2.5 + 1or more fragility fractures
Define osteopenia
Pre-cursor to osteoporosis characterised by low bone density, due to loss of calcium.
What age is peak bone mass achieved?
25 yrs
What is a Z-score?
How far this individual is from the gender AND age-matched mean BMD given in standard deviations.
Name some other drugs other than steroids that can cause osteoporosis
- Heparin
- Ciclosporin
- PPIs
- Anticonvulsants
- GnRH Analogues
- SSRI’s
- Depo-provera