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56 Cards in this Set
- Front
- Back
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Osteogenesis imperfecta (brittle bone disease) |
Autosomal dominant (AD) disease due to defective synthesis of type I collagen Clinical findings - Pathological fractures at birth - Blue sclera (reflection of underlying choroidal veins through thin sclera) - Deafness in some patients Treatment - Bisphosphonates to increase bone mineralisation |
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Achondroplasia |
Autosomal dominant disease due to mutation in fibroblast growth factor receptor 3 (FGFR3) gene. Mutations increase with paternal age. Impaired proliferation of cartilage at the growth plate. Clinical findings - Normal sized head and vertebral column - Shortened arms and legs - Normal growth hormone and insulin-like growth factor 1 levels No treatment |
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Osteopetrosis (marble bone disease) |
Autosomal recessive (severe), autosomal dominant (less severe) Pathogenesis - Deficiency in osteoclasts, normal balance of bone formation and breakdown is disrupted in favour of formation - Overgrowth and sclerosis of cortical bone (too much bone) Clinical findings - Pathologic fractures - Anaemia (replacement of marrow cavity) - Cranial nerve compression (visual and hearing loss) No treatment |
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Osteomyelitis |
In children and adults - Sepsis is the most likely cause with subsequent spread to bone (haematogenous most common, then contiguous then penetrating trauma) - Metaphysis most common site, vascular supply is best and favours haematogenous spread. Tibia and fibula most common sites in children. - Infection is most often due to Staph aureus (90% of cases), other pathogens include Strep pyogenes and Haemophilus influenzae Osteomyelitis in sickle cell - Salmonella paratyphi is the usual causative agent - Due to defective spleen unable to remove Salmonella from bloodstream Tuberculous osteomyelitis - Haematogenous spread from a primary lung focus -Targets the vertebral column (Pott disease) Pseudomonas aeruginosa osteomyelitis - Most often due to puncture of foot through rubber footwear Neutrophils enzymatically destroy bone - Devitalised bone is called sequestra - Chronic disease produces reactive bone formation in periosteum, involucrum - Draining sinus tracts to the skin surface also occur, danger of SCC developing at the orifice of sinus tracts Clinical - Fever, bone pain Diagnosis - Bone biopsy for culture - Imaging studies - CT scan or MRI Treament - Surgical debridement - Antibiotics (Flucloxacillin or Vancomycin +/- rifampicin or fusidic acid) |
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Osteoporosis: Overview |
Most common metabolic abnormality of bone Definition: Loss of both organic bone matrix (osteoid) and mineralised bone Characterised by - Decreased bone mass and density, radiographs shows osteopenia - Decreased thickness of cortical and trabecular bone More common in women as men have greater bone mass to begin with |
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Primary and Secondary Osteoporosis |
Primary - Idiopathic type which has an unknown pathogenesis and occurs in children and young adults - Osteoporosis in postmenopausal women (51-75 years) Type I - Type II (senile type) occurs in women and men over 70 and is a progressive decline in osteoblasts and increased activity of osteoclasts (bone resorption exceeds bone formation) Secondary - Underlying disease (e.g. hypocortisolism- inhibition of osteoblasts, enhance osteoclast activity) - Drugs (heparin-decreased bone formation and increased bone resorption) - Hypognoadism (hypopituitarism) - Malnutrition (anorexia nervosa) - Space travel (lack of gravity reduces bone stress) |
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Pathogenesis of postmenopausal osteoporosis |
Role of oestrogen (EGN) in maintaining bone mass - Enhances osteoblastic activity and inhibits osteoclastic activity in bone - Effect on bone mass mediated by inhibiting secretion of cytokines (IL-1, IL-6 and TNF that modulate osteoclastogenesis) EGN deficiency leads to increase in secretion of cytokines: - Enhance expression of RANK L and RANK genes which increase osteoclastogenesis - Inhibit expression of osteoprotegerin, receptor produced by osteoblasts that inhibits RANKL/RANK interaction Osteoclastic activity is greater than osteoblastic activity leading to loss of bone mass. |
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Osteoporosis: Clinical findings and Diagnosis |
Clinical findings - Compression fractures of vertebral bodies (most common leading to loss of stature) - Fractures of hip and ribs - Dowager's hump (forward bending of spine in advanced osteoporosis) - Increased risk of Colles fracture of distal radius Diagnosis - Dual photon absorptiometry (DEXA) - Non-invasive test that evaluates bone marrow density WHO uses a T-score to define osteoporosis. Calculated by subtracting mean BMD of a young adult reference population and dividing this by a standard deviation of the young adult reference population. Based on this, osteoporosis is defined as approx 2.5 S.D and below. FRAX risk calculator for fractures |
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Osteoporosis: Prevention and treatment |
Prevention - Take calcium and vitamin D supplements - Stop smoking (inhibits osteoblast activity) - Perform weight-bearing exercise that stresses bone such as weight-lifting, vigorous walking. Swimming not useful. Treatment - Bisphosphonates inhibit bone resorption and are first line treatment - Denosumab - Estrogen replacement is prescribed alone or in combination with bisphosphoantes - Strontium ranelate |
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Osteoarthritis: Overview |
Definition - progressive degeneration of articular cartilage and underlying bone. Most common disabling joint disease that is non-inflammatory and has no sex predilection. It is almost universal in people >65 years of age. Secondary cause - Legg-Calve-Perthes disease - Osteochondritis dissecans - Obesity, trauma, neuropathic joint - Meniscus injuries, hemochromatosis Common sites - Femoral head, knee - Cervical and lumbar vertebrae - Hand (usually genetic) Less common sites - Shoulder - Elbow - Feet with the exception of the first MTP joint (site for bunion formation) |
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Osteoarthritis: Pathogenesis |
Components of normal articular cartilage - Proteoglycans provide elasticity - Type II collagen that provides tensile strength In OA, cytokines activate metelloproteinases - Cause degradation of proteoglycans and collagen Joint findings - Erosions and clefts in articular cartilage - Reactive bone formation occurs at the joint margins (osteophytes) causing a slight increase in ALP - Subchondral cysts - Bone eventually rubs on bone producing dense, sclerotic bone - No ankylosis (fusion of joint) - Joint mice (fragments of articular cartilage that break free into the joint space) |
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Osteoarthritis: Clinical findings |
Pain is the most common complaint - Osteophytes irritate the synovial lining - Bone is rubbing on bone - Hip OA may refer pain to the groin - Pain is aggravated with movement of the joint, due to secondary synovitis from osteophytes Joint stiffness occurs after inactivity - Waking up in the morning - After sitting Crepitus of the joint with movement, decreased range of motion Hand involvement (osteophytes) - Enlargement of the distal interphalangeal joints (Heberden nodes) - Enlargement of the proximal interphalangeal joints (Bouchard nodes) Vertebral findings - Degenerative disk disease and compressive neuropathies |
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Osteoarthritis: Diagnosis and treatment |
Diagnosis is by imaging studies. Treatment - Heat, decrease weight bearing, range of motion exercises - Use of a cane - Analgesic (NSAIDs, paracetamol, not at same time) - Joint replacement |
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Rheumatoid arthritis overview |
Definition - Systemic disorder associated with chronic joint inflammation that most commonly affects peripheral joints Occurs more often in women 30-50 years. HLA-DR4 association Question about initial inciting agents - EBV, Parvovirus, HHV6, Mycoplasma Risk factor for septic arthritis - Medication may suppress the immune system, making infections more likely to occur |
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Rheumatoid arthritis: pathogenesis |
Type III and Type IV reactions CD4+ helper T cells are activated leading to release of pro-inflammatory agents (TNF) Inflamed synovial cells express an antigen that triggers B cells to produce rheumatoid factor (RF). This is an IgM autoantibody against Fc portion of IgG. RF and IgG join to form immunocomplexes. (Type III) ICs activate the complement system to produce C5a , chemotactic agent for neutrophils and other leukocytes to enter the joint space. Chronic synovitis ad pannus formation eventually occur, Pannus is granulation tissue formed within the synovial tissue by fibroblasts and inflammatory cells. Pannus proliferates and releases cytokines (ILs, TNF) that eventually destroys the articular cartilage leading to fusion of the joint (ankylosis) |
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Rheumatoid arthritis: Clinical Findings |
Arthritis involving second/third MCP and PIP joints Lung disease Haematologic disease Carpal tunnel syndrome Cervical spine Rheumatoid nodules Cardiovascular disease Popliteal (Baker) cyst behind the knee joint |
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Rheumatoid arthritis: Lab findings |
Positive serum ANA test Positive serum rheumatoid factor Normal to increased serum C3, decreased synovial C3 Increased serum total protein - Due to increase in gamma globulins - Polyclonal gammopathy on serum protein electrophoresis |
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Rheumatoid arthritis: Treatments |
Physical therapy emphasising movement of joints such as swimming pool exercises. Initial treatment with NSAIDs (aspirin) to relieve inflammation Early treatment with disease-modifying drugs - Minimises long-term joint damage - Methotrexate (most commonly used agent) - Cyclosporin, corticosteroids, hydroxychloroquine, gold compounds - Tumour necrosis factor (TNF)-alpha blockers are effective if disease-modifying drugs are ineffective |
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Septic arthritis: Staph and Neisseria |
Staphylococcus aureus - Most common non-gonococcal cause of septic arthritis - Treatment: nafcillin and cephalosporin (third generation) Neisseria gonorrhoea - Most common cause of septic arthritis in urban populations - May produce disseminated gonococcemia, more common in young women. Deficiency of C6-C9 predisposes to dissemination. These complement components are needed to kill the bacteria. - Septic arthritis (knee) - Tenosynovitis (wrists and ankles) - Dermatitis (pustules on wrists or ankles) Treated with ceftriaxone |
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Lyme Disease: Overview |
Borrelia Burgdorfi (spirochete) transmitted by the bite of an Ixodes tick. Different ticks produce the disease in North America, Europa and Asia. Adult ticks acquire the disease from deer, nymphs acquire it from a mouse and are responsible for most human cases. Organism has a strong tropism for skin, CNS, joints, heart and eyes. Predilection for white population. Pathogenesis due to inflammation related to organism itself, cross-reacting antibodies to spirochetal proteins against human tissue (type II) and immunocomplexes (type III HSR) have been implicated. |
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Lyme Disease: Clinical presentation |
Early localised infection (first month) - Erythema migrans develops on skin 1-2 weeks after tick removal, vesicular red center with a red expanding lesion with concentric circles (bull's eye lesion). May be single or multiple. - Only phase of disease where empirical therapy is recommended based on a clinical diagnosis without laboratory confirmation - Pathognomic lesion of LD Early disseminated disease (weeks to months post-tick bite) - Further spread to skin, lymphatics (lymphadenopathy) - Migratory poly-articular arthritis (involves bursa, tendon, joints) evolving into mono-articular (e.g. knee, wrist) - Neuroborreliosis with cranial neuropathy (particularly facial nerve palsy bilaterally), meningeal irritation (nuchal rigidity) Chronic disease (months to years after infection) - Disabling arthritis (knee) - Subacute encephalopathy, encephalomyelitis, peripheral neuropathies - Other findings include myocarditis, pericarditis, iritis, keratitis, optic neuritis |
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Lyme Disease: Diagnosis and Treatment |
ELISA (enzyme-linked immunosorbent assay) testing first as screen (highly sensitive) Western blot assay for equivocal or positive ELISA test (high specificity 94-96%) PCR test is also available Treatment - Adults - doxycycline (most often), amoxicillin, ceftriaxone. Use of doxy also covers the potential for co-infection with Ehrlichia chaffeensis - Children - amoxicillin |
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Babesiosis |
Intraerythrocytic (sometimes extaerythrocytic) protozoal disease due to Babesia microti. Secondary infection transmitted by Ixodes - Often presents concurrently with lyme disease - Fever, headache, haemolytic anaemia Diagnosis - Wright or Giemsa-stained peripheral smear to look for organisms in RBCs or free in plasma - Serologic testing Treatment - Atovaquone + azithromycin |
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Septic arthritis and tendinitis due to cat/dog bite |
Causal agent is Pasteurella multocida, a gram-negative coccobacillus with bipolar staining Most common infection is secondary to animal injury - Cat bites are more common than dog bites - Approximately 60-90% of cats normally have the organism in their mouth - Only 5-15% of dogs get infected Types of infection - Cellulitis (most common) - Septic arthritis/tendinitis - Osteomyelitis - Endocarditis, meningitis Rapid onset of infection at the bite site (usually within 24 hours) Treatment - Penicillin G, ampicillin, augmentin |
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Seronegative spondyloarthropathies: Overview |
Definition: Family of overlapping syndromes that are linked in disease manifestations and genetic susceptibility. Characteristics are: - Rheumatoid factor (RF) negative - Involve the axial skeleton (spondylitis) - HLA-B27 positive - Male dominant with reactive arthritis and ankylosing spondyltiis - Sacroilitis +/- peripheral arthritis |
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Types of spondyloarthropathy |
Ankylosing spondylitis (AS) Reactive arthritis - Reiter syndrome associated with Chlamydia Trachomatis urethritis - Arthritis associated with gastroenteritis due to Shigella, Salmonella, Campylobacter and Yersinia Psoriatic arthritis Enteropathic arthritis (UC, CD) |
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Ankylosing spondylitis |
Initially targets the sacroilial joint in young men causing bilateral sacroilitis with morning stiffness. Eventually involves the vertebral column, fusion of vertebrae (bamboo spine) causes forward curvature of the spine (kyphosis). This interferes with chest wall movement causing non-pulmonary restrictive lung disease. Schober test evaluates degree of restriction to forward bending. Aortitis with aortic regurgitation. Anterior uveitis (20% of cases) - Blurry vision - Potential for blindness Treatment - NSAIDs - Disease modifying agents (methotrexate, cyclosporin, corticosteroids) - TNF-alpha inhibitors, extremely effective in slowing down progression of the disease |
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Reiter syndrome |
Urethritis due to Chlamydia trachomatis Arthritis and Achilles tendon periostitis - Bone formation at the junction of the Achilles tendon with the plantar fascia is a confirmatory radiological sign Conjunctivitis (noninfectious) Circinate balanitis - rash on the distal shaft and glans penis that appears as vesicles, shallow ulceration or both |
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Psoriatic arthritis |
Sausage shaped DIP joints (finger or toe) Radiographs show erosive joint disease as "pencil-in-cup" deformities Extensive nail pitting |
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Paget disease (osteitis deformans) |
Mainly occurs in men over 50 Possible paramyxovirus infection of osteoclasts Targets the pelvis, skull (enlarged) and femur Pathogenesis - Early phase of osteoclastic resorption of bone, causes shaggy-appearing lytic lesions - Late phase of increased osteoblastic bone formation, markedly raised ALP and production of thick, weak bone (mosaic bone) |
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Paget Disease (clinical findings and complications) |
Clinical findings - Bone pain is the most common complaint - Headaches and hearing loss occur if it affects skull - Hat size is increased with skull involvement Complications - Pathologic fractures - Risk for developing osteogenic sarcomas - Risk for developing high output cardiac failure due to arteriovenous connections in vascular bone |
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Paget disease: Diagnosis and Treatment |
Radiographs show thickened bone with shaggy areas of radiolucency. Bone scan shows hot spots Serum alakaline phosphatase is markedly increased, but serum calcium and phosphate are normal Treatment - Bisphosphonates and calcitonin |
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Gouty arthritis: Causes and associations |
Definition - Tissue deposition of monosodium urate (MSU) due to prolonged hyperuricaemia. Occurs more often in men >30 years of age (95% of cases) and is uncommon in women before menopause. Primary gout arises from inborn errors of metabolism involving purine metabolism such as Lesch-Nyhan syndrome. Secondary causes are much more common - Underexcretion of uric acid (UA) in kidneys (80-90% of cases) can be due to lead poisoning, alcoholism, diets rick in red meat, seafood, thiazides, beer and thiazides - Overproduction of uric acid (increased nucleated cell turnover), due to treating leukaemia and psoriasis Clinical conditions associated with gout: - Urate nephropathy, renal stones - HTN, Coronary artery disease - Lead poisoning which produces interstitial nephritis that interferes with uric acid excretion |
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Gout: Pathogenesis |
Recurrent attacks of gout are usual - Most commonly involve the first MTP (podagra), polyarticular involvement in 10-15% of cases - Often precipitated by dietary indiscretions. illness, exercise or emotional stress. - Free UA crystals in the synovial fluid are pro-inflammatory activating synovial cells, leucocytes and the complement cascade. The latter releases C5a, which attracts neutrophils into the joint producing acute inflammation. Neutrophils also phagocytose uric acid crystals. - Another common site for acute gout is the extensor tenosynovium of the dorsum of the foot. |
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Gout: Clinical findings and Lab findings |
Clinical findings - Sudden onset of severe pain in the big toe - Hot, red and swollen joint - Fever, tachycardia and other constitutional signs Lab findings - Hyperuricaemia, increased serum uric acid >7mg/dL in men, >6mg/dL in women - Absolute neutrophilic leucocytosis - Joint aspiration is confirmatory, negatively birefringent MSU crystals |
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Chronic gout |
More likely if gout is poorly controlled UA crystals accumulate in the joint and produce a tophus - MSU crystals leak into the soft tissue around the joint. Distal joints are preferential sites MSU excites a brisk granulomatous reaction in the periarticular tissue - Microscopic sections reveal numerous multi-nucleated giant cells within which are MSU crystals that polarise Tophi destroy subjacent bone, causing erosive arthritis that breaks down bone and leaves overhanding edges (sometimes called rat bites) |
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Gout: Treatment |
Acutely - NSAIDs (indomethacin, ibuprofen) or colchicine - Intra-articular corticosteroids or systemic corticosteroids Chronically - Goal is to normalise serum uric acid - Uricosuric agents for underexcretors (e.g. sulfinpyrazone), if 24 hour collection of uric acid <700mg - Allopurinol or febuxostat (xanthine oxidase inhibitors) for overproducers - Pegloticases (pegylated uricase) for refractory tophaceous gout |
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Calcium pyrophosphate dihydrate deposition (CPPD) disease |
Deposition of calcium pyrophosphate in tissues - Deposition in cartilage (chondrocalcinosis) - Less commonly in tendons, ligaments, synovial tissue, bursa Incidence of CPPD increases in the presence of: - Haemochromatosis, hemosiderosis. Pyrophosphate inhibitor is increased in these diseases. Causes an increase in inorganic pyrophosphate concentration. - Primary hyperparathyroidism, increase in calcium is responsible Four variants are associated with the disease Most common variant in OA. - Most common in the elderly, present in 50% of patients who are over the age of 85 years - Degenerative arthritis with symptoms similar to OA - Most common joint involved is the knee - Calcium pyrophosphate crystals deposit in articular cartilage, crystals produce linear deposits in the cartilage. Called chondrocalcinosis when it deposits in articular cartilage. If the patient has acute pain, redness, swelling and limitation of motion in the joint, the combination is called pseudogout. Crystals phagocytosed by neutrophils show positive birefringence. Treatments - NSAIDs, colchicine, arthroscopic surgery |
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Myaesthenia Gravis (MG): Pathogenesis |
Afflicts men in 6th and 7th decade of life Afflicts women in 2nd and 3rd decade of life Pathogenesis - Definition, autonomic disorder of postsynaptic neuromuscular transmission - Autoantibody against acetylcholine (ACh) receptors, type II hypersensitivity reaction. Antibodies inhibit and/or destroy the receptors. Decrease in functional ACh receptors. - Antibody is synthesised in the thymus, thymic hyperplasia with germinal follicles (85% of cases) |
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Myaesthenia Gravis (MG): Clinical findings, diagnosis and treatment |
Clinical findings - Fluctuating muscle weakness, worsened with exercise and improved with rest - Ptosis most common initial findings, diplopia is also common and due to eye muscle weakness - Weakness in proximal muscles, diaphragm, neck extension and flexion (85% of cases) - Dysphagia for solids and liquids, occurs in the upper oesophagus (striated muscle) - Normal reflexes, sensation and coordination - Increased risk for developing a thymoma Diagnosis - Tensilon (edrophonium) test, inhibits acetycholinesterase, increase in acetylcholine reverses muscle weakness - Single fiber electromyography (abnormal in 95% of cases) Treatment - Avoid certain medications, Beta blockers, aminoglycosides, quinolone antibiotics, class 1 antiarrhythmics - Pyridostigmine (acetycholinesterase inhibitor) - Immunosuppressive drugs (corticosteroids, mycophenolate mofetil, cyclosporine) - Plasmapheresis (short-term treatment, removes antibodies) - Thymectomy (removes site for antibody production) |
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Duchenne muscular dystrophy: Overview and Pathogenesis |
X-linked recessive, 1:3500 Male births Pathogenesis - Absence of dystrophin due to frameshift mutation of the dystrophin gene on the X chromosome - Normally anchors actin to membrane glycoprotein. - Becker type has deficiency/defective dystrophin The most common childhood muscular dystrophy causing progressive degeneration of type I and type II fibres. There is fibrosis and infiltration of muscle by fatty tissue. Produces pseudohypertrophy of calf muscles. |
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Duchenne muscular dystrophy: Clinical findings, Lab findings, Diagnosis and Treatment |
Clinical findings - Symptoms occur between 2-5 years of age - Weakness and wasting of pelvic muscles, child places hands on the knees for help in standing (Gower manoeuvre), waddling gait - Cardiac involvement is present and causes a cardiomyopathy leading to heart failure and arrhythmias - Respiratory muscle weakness eventually leads to respiratory failure - Death usually occurs by 20 years of age Laboratory findings - Serum creatine kinase is increased at birth (20-100x greater), progressively declines as the muscle degenerates over time - Female carriers have increased levels of serum CK Diagnosis - Muscle biopsy, EMG - DNA testing is available (western blot), diagnosed prenatally by chorionic villous sampling Treatment - Mainly supportive |
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Myotonic dystrophy |
Autosomal dominant, most common adult muscular dystrophy. Trinucleotide repeat disorder, chromosome 19, expanded CTG repeat within the noncoding 3' untranslated region of the myotonic dystrophy protein kinase gene Selective atrophy of type I fibres. Clinical findings - Facial muscle weakness, sagging face, problems in closing the mouth - Percussion and grip myotonia, inability to relax muscles so grip sustained - Frontal balding, cataracts - Testicular atrophy, glucose atrophy - Cardiac involvement (conduction defects) Diagnosis - EMG, muscle biopsy - Raised serum CK There is no specific treatment, muscle wasting and defects in cardiac function are the most common cause of death. |
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Neoplastic disorders of the bone |
Metastasis is the most common malignancy of bone. Source are the 5 Bs: - Breast - Prostate - Lung - Kidney - Thyroid Primary malignant tumours of bone in descending order of frequency: - Multiple myeloma - Osteogenic sarcoma - Chondrosarcoma - Ewing sarcoma |
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Osteochondroma |
Males 10-30 years, solitary or multiple Metaphysis of distal femur Outgrowth of bone (exostosis), capped by benign cartilage. Most common benign tumour. |
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Endochondroma |
Equal distribution M=F, 20-50 years Solitary or multiple Medullary location. Small tubular bones in arms and feet. Multiple endochondromas. Risk for chondrosarcoma. |
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Osteoma |
Males, any age Facial bones Associated with Gardner polyposis syndrome |
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Osteoid osteoma |
Males, 10-20 years Cortex of proximal femur Radiographic finding: radiolucent focus surrounded by sclerotic bone Nocturnal pain relieved by aspirin |
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Osteoblastoma |
Males, 10-20 years Vertebra Similar to osteoid osteoma. |
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Giant cell tumour |
Females 20-40 years Epiphysis of distal femur or proximal tibia Reactive multinucleated giant cells resemble osteolasts Neoplastic mononuclear cells |
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Chondrosarcoma |
Males, 30-60 years Pelvic bones, proximal femur Grade determines biological behaviour. Metastasises to lungs |
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Osteogenic sarcoma (osteosarcoma) |
Male 10-25 years Risk factors - Paget disease - Familial retinoblastoma - Irradiation - Fibrous dysplasia Metaphysis of distal femur, proximal tibia Most common primary bone cancer (some say MM) Malignant osteoid Radiographic findings - Sunburst appearance (spiculated pattern from calcified malignant osteoid) - Codman triangle (tumour lifting the periosteum) Metastasises to lungs |
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Ewing sarcoma |
Males, 10-20 years Pelvic girdle, diaphysis and metaphysis of proximal femur or rib Small round blue cell tumour t(11:22) chromosome rearrangement Radiographic finding - Onion skin appearance around bone (periosteal reaction) - Possible fever and anaemia |
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Polymyositis: Overview and Pathogenesis |
Female dominant disease with increased incidence in the black population. Normally occurs aged 40-60. Associated with an increased risk of malignant neoplasms (15-20% of cases), particularly lung and bladder cancer, and non-Hodgkin malignant lymphomas. Aetiopathogenesis Cytotoxic CD8 T cells (predominant cells) and CD4 TH1 subset cells that activate macrophages damage unidentified antigens in myocyte fibers in skeletal muscle. - Triggers for he T cell response may be associated with viruses including human retroviruses (HIV, HTLV1 and Coxsackie B) - The viruses damage skeletal muscle leading to altered class I and class II MHC antigens |
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Polymyositis: Clinical findings and lab findings |
Clinical findings - Constitutional signs includes fever, morning stiffness, fatigue and weight loss - Symmetrical, proximal muscle weakness (+/- pain), in both the upper and lower extremities, trunks, shoulders and hips - Dysphagia for solids and liquids and oropharynx and upper oesophagus, these areas contain skeletal rather than smooth muscle. - Respiratory difficulties are related to interstitial lung disease. Lab findings - Serum creatine kinase (CK) and aldolase are markedly increased - Antibody findings, Serum ANA increased in 30-60% of cases, anti-transfer RNA synthetase (Jo-1) antibodies increased in 25% of cases - EMG shows myopathic dysfunction - Muscle biopsies show necrotic and regenerating muscle and a lymphocytic and macrophage infiltrate, muscle atrophy is not a prominent feature. Treatment and prognosis - Corticosteroids are the first line treatment - Majority respond well to therapy (80% 5 year survival) |
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Dermatomyositis |
Epidemiology similar to polymyositis, including risk of malignancy. Aetiopathogenesis - Activated CD4 T cells primarily target the capillaries in skeletal muscle - Antibodies and complement are involved in the capillary damage - Foci of myofiber injury accompanies microvascular changes Clinical findings - Muscle complaint like in PM - Cutaneous findings are key, reddish-purple papules called Gottron patches noted over the knuckles and proximal inter-phalangeal joints in both hands. Purple-red eyelid discoloration occurs (heliotrope eyelids or "raccoon eyes") Lab findings - Similar to PM - Muscle biopsies show an inflammatory reaction (mainly lymphocytes), atrophy of muscle fibers is a prominent feature. Damage to capillaries in muscle leads to ischaemia and atrophy of muscle fibers Treatment - Corticosteroids is first line |
