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Diagnostic Tests – DEXA Scanning (Dual-Energy X-ray Absorptiometry)
1. What does it show?
A DEXA scan measures bone mineral density (BMD) and is the standard test used to diagnose osteoporosis. It compares a patient’s bone density to that of a healthy young adult population and reports results as T-scores, allowing assessment of fracture risk and bone loss severity.
2. When do you answer a DEXA scan?
You should select DEXA scanning when evaluating patients at high risk for osteoporosis, including:
Exam pearl:
Any condition causing increased bone resorption or decreased bone formation → think DEXA scan.
3. What is the treatment?
Management of osteoporosis includes:
1. What does it show?
A DEXA scan measures bone mineral density (BMD) and is the standard test used to diagnose osteoporosis. It compares a patient’s bone density to that of a healthy young adult population and reports results as T-scores, allowing assessment of fracture risk and bone loss severity.
2. When do you answer a DEXA scan?
You should select DEXA scanning when evaluating patients at high risk for osteoporosis, including:
- Postmenopausal women
- Patients with high cortisol states, such as:
- Cushing’s syndrome
- Chronic exogenous steroid use
- Patients with hyperthyroidism
- Patients with hyperparathyroidism
Exam pearl:
Any condition causing increased bone resorption or decreased bone formation → think DEXA scan.
3. What is the treatment?
Management of osteoporosis includes:
- Estrogen therapy (selected postmenopausal patients)
- Bisphosphonates (first-line therapy for most patients)
- Selective estrogen receptor modulators (SERMs) such as:
- Raloxifene
- TamoxifeN
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Diagnostic Tests – Anticentromere Antibodies
1. What condition is it associated with?
Anticentromere antibodies are highly specific for CREST syndrome, which represents the limited cutaneous form of systemic sclerosis.
CREST is an acronym for:
By contrast, anti–topoisomerase I (Scl-70) antibodies are associated with diffuse systemic sclerosis, the more severe, systemic form of the disease.
2. When do you answer anticentromere antibodies?
You should select anticentromere antibody testing as the best initial or confirmatory test when a clinical scenario describes:
Exam pearl:
Limited scleroderma / CREST → Anticentromere antibodies
Diffuse systemic sclerosis → Scl-70 antibodies
1. What condition is it associated with?
Anticentromere antibodies are highly specific for CREST syndrome, which represents the limited cutaneous form of systemic sclerosis.
CREST is an acronym for:
- Calcinosis
- Raynaud phenomenon
- Esophageal dysmotility
- Sclerodactyly
- Telangiectasia
By contrast, anti–topoisomerase I (Scl-70) antibodies are associated with diffuse systemic sclerosis, the more severe, systemic form of the disease.
2. When do you answer anticentromere antibodies?
You should select anticentromere antibody testing as the best initial or confirmatory test when a clinical scenario describes:
- A woman aged 30–50 years
- Symptoms suggestive of limited systemic sclerosis (e.g., Raynaud phenomenon, skin tightening of fingers, telangiectasias)
- Positive antinuclear antibody (ANA)
- Often a positive rheumatoid factor
Exam pearl:
Limited scleroderma / CREST → Anticentromere antibodies
Diffuse systemic sclerosis → Scl-70 antibodies
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Diagnostic Tests – ANA, Anti–Double-Stranded DNA (anti–dsDNA), and Anti-Smith (anti-Sm) Antibodies
1. What diseases are they associated with?
These antibodies are classically associated with systemic lupus erythematosus (SLE), with different roles in screening versus confirmation:
2. When do you answer ANA, anti-dsDNA, and anti-Sm?
You should select this antibody panel when a clinical vignette suggests systemic lupus erythematosus, especially in:
High-yield exam pearl:
If you want, I can also create a JPEG comparison diagram (ANA vs dsDNA vs anti-Sm) like your other rheumatology visuals.
1. What diseases are they associated with?
These antibodies are classically associated with systemic lupus erythematosus (SLE), with different roles in screening versus confirmation:
- ANA (Antinuclear Antibody)
- >98% sensitive for SLE
- Not specific
- A negative ANA essentially rules out SLE (≈98% negative predictive value)
- Anti–double-stranded DNA (anti–dsDNA)
- Highly specific (~99%) for SLE
- Often correlates with disease activity, especially lupus nephritis
- Anti-Smith (anti-Sm)
- Extremely specific for SLE
- Lower sensitivity, but when present, it is diagnostic
2. When do you answer ANA, anti-dsDNA, and anti-Sm?
You should select this antibody panel when a clinical vignette suggests systemic lupus erythematosus, especially in:
- A young woman
- Rash (e.g., malar rash, photosensitivity)
- Arthralgias or arthritis
- History of multiple spontaneous abortions (suggesting lupus anticoagulant / antiphospholipid syndrome)
High-yield exam pearl:
- Suspected SLE → ANA first
- Confirm SLE → anti-dsDNA and anti-Sm
- Negative ANA → SLE is essentially excluded
If you want, I can also create a JPEG comparison diagram (ANA vs dsDNA vs anti-Sm) like your other rheumatology visuals.
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Diagnostic Tests-ANA, Anti–Double-Stranded DNA (anti-dsDNA), and Anti-Smith (anti-Sm) Antibodies
1.
What diseases are they associated with?
- ANA (Antinuclear Antibody)
- More than 98% sensitive for systemic lupus erythematosus (SLE)
- Not specific for SLE (can be positive in other autoimmune diseases and even in healthy individuals)
- A negative ANA essentially excludes SLE, with about a 98% negative predictive value
- Anti–double-stranded DNA (anti-dsDNA)
- Approximately 99% specific for SLE
- Levels often correlate with disease activity, particularly lupus nephritis
- Anti-Smith (anti-Sm)
- Extremely specific for SLE
- Less sensitive, but when present, it is diagnostic of lupus
2.
When do you answer/order this test?
Answer ANA, anti-dsDNA, and anti-Sm antibodies when the clinical presentation suggests systemic lupus erythematosus, classically:
- Young female with:
- Multiple spontaneous abortions (suggesting lupus anticoagulant / antiphospholipid antibodies)
- Rash (malar or photosensitive)
- Joint pains / inflammatory arthritis
- May also have renal disease, cytopenias, or serositis
- ANA → screening test (rules out SLE if negative)
- Anti-dsDNA & Anti-Sm → confirmatory tests (rule in SLE if positive)
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Diagnostic Tests – Muscle Biopsy
1. For which clinical condition(s) would you use this test?
A muscle biopsy is used to diagnose primary myopathies, particularly when a structural, metabolic, inflammatory, or genetic muscle disorder is suspected. Conditions commonly diagnosed with muscle biopsy include:
2. When do you answer muscle biopsy?
You should choose muscle biopsy when the clinical scenario describes:
Proximal weakness + myalgias + suspected intrinsic muscle disease → Muscle biopsy
3. For which muscle diseases would you
not
answer muscle biopsy?
Despite overlapping symptoms of weakness, muscle biopsy is NOT the correct test in the following situations:
1. For which clinical condition(s) would you use this test?
A muscle biopsy is used to diagnose primary myopathies, particularly when a structural, metabolic, inflammatory, or genetic muscle disorder is suspected. Conditions commonly diagnosed with muscle biopsy include:
- Glycogen storage diseases
- Mitochondrial myopathies
- Dystrophinopathies (e.g., Duchenne and Becker muscular dystrophy)
- Inflammatory myopathies, such as dermatomyositis and polymyositis
2. When do you answer muscle biopsy?
You should choose muscle biopsy when the clinical scenario describes:
- Proximal muscle weakness, such as:
- Difficulty with shoulder abduction
- Trouble rising from a chair
- Associated myalgias (muscle soreness)
- Evidence of myopathy, such as:
- Elevated muscle enzymes
- Recurrent rhabdomyolysis
- A possible family history of similar symptoms, suggesting an inherited muscle disorder
Proximal weakness + myalgias + suspected intrinsic muscle disease → Muscle biopsy
3. For which muscle diseases would you
not
answer muscle biopsy?
Despite overlapping symptoms of weakness, muscle biopsy is NOT the correct test in the following situations:
- Endocrine-related myopathies
- Examples: thyroid disease, diabetes
- Appropriate tests: specific endocrine laboratory testing
- Neuromuscular junction disorders
- Example: myasthenia gravis
- Appropriate tests:
- Edrophonium (Tensilon) testing
- Anti–acetylcholine receptor antibodies
- Electromyography (EMG)
- Muscle fiber disease → muscle biopsy
- Endocrine or neuromuscular junction disease → targeted labs or electrophysiologic testing
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Diagnostic Tests – Rheumatoid Factor (RF)
1. What disease is it associated with?
Rheumatoid factor (RF) is most commonly associated with rheumatoid arthritis (RA). It is present in over 70% of patients with RA, making it a useful supportive test. However, RF is not specific for RA and may also be positive in other autoimmune diseases, chronic infections, and even in some healthy older adults.
2. When do you answer rheumatoid factor?
You should select RF testing when the clinical scenario describes:
Symmetric small-joint inflammatory arthritis with morning stiffness → think rheumatoid arthritis → order rheumatoid factor (often along with anti-CCP antibodies).
1. What disease is it associated with?
Rheumatoid factor (RF) is most commonly associated with rheumatoid arthritis (RA). It is present in over 70% of patients with RA, making it a useful supportive test. However, RF is not specific for RA and may also be positive in other autoimmune diseases, chronic infections, and even in some healthy older adults.
2. When do you answer rheumatoid factor?
You should select RF testing when the clinical scenario describes:
- A woman with symmetric inflammatory arthritis
- Morning stiffness that improves with activity
- Involvement of the wrists, metacarpophalangeal (MCP) joints, and proximal interphalangeal (PIP) joints
- Laboratory evidence of inflammation, such as:
- Elevated ESR
- Synovial fluid WBC count between 2,000 and 20,000 cells/µL (inflammatory range)
Symmetric small-joint inflammatory arthritis with morning stiffness → think rheumatoid arthritis → order rheumatoid factor (often along with anti-CCP antibodies).
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Diagnostic Tests – Allergy Testing (Skin Prick / Intradermal Testing)
1. For which clinical scenario is this test used?
Allergy testing involves subdermal or skin exposure to small amounts of suspected allergens, followed by observation for a localized hypersensitivity reaction. It is used when a patient has allergic symptoms and the specific trigger is unclear, such as:
2. When is allergy testing contraindicated?
Allergy testing is contraindicated in patients with:
High anaphylaxis risk or unstable asthma → do NOT perform skin allergy testing
3. What medication must be stopped before allergy testing?
Beta blockers (e.g., propranolol) must be stopped prior to allergy testing or desensitization when possible.
Why?
Allergy testing + beta blocker = dangerous combination
1. For which clinical scenario is this test used?
Allergy testing involves subdermal or skin exposure to small amounts of suspected allergens, followed by observation for a localized hypersensitivity reaction. It is used when a patient has allergic symptoms and the specific trigger is unclear, such as:
- Allergic rhinitis (runny nose, sneezing, watery eyes)
- Suspected allergies to:
- Foods
- Pets
- Aeroallergens (pollens, dust mites, molds)
- Venoms (bees, wasps)
2. When is allergy testing contraindicated?
Allergy testing is contraindicated in patients with:
- A high risk of anaphylaxis based on prior severe reactions
- Uncontrolled or severe asthma, due to increased risk of life-threatening reactions during testing
High anaphylaxis risk or unstable asthma → do NOT perform skin allergy testing
3. What medication must be stopped before allergy testing?
Beta blockers (e.g., propranolol) must be stopped prior to allergy testing or desensitization when possible.
Why?
- If anaphylaxis occurs, epinephrine is the life-saving treatment
- Beta blockers blunt the response to epinephrine, making treatment of anaphylaxis less effective
Allergy testing + beta blocker = dangerous combination
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Diagnostic Tests – Anti-Ro (SSA) and Anti-La (SSB) Antibodies
1. What diseases are they associated with?
Anti-Ro (SSA) and Anti-La (SSB) antibodies are most strongly associated with Sjögren’s syndrome. Patients with Sjögren’s syndrome classically have:
These antibodies may also be seen in other connective tissue diseases, but their strongest association is with Sjögren’s syndrome.
2. When are they the answer?
You should select anti-Ro and anti-La antibody testing when the clinical scenario describes the classic sicca triad, which includes:
Dry eyes + dry mouth + arthritis → think Sjögren’s syndrome → order anti-Ro / anti-La antibodies.
1. What diseases are they associated with?
Anti-Ro (SSA) and Anti-La (SSB) antibodies are most strongly associated with Sjögren’s syndrome. Patients with Sjögren’s syndrome classically have:
- Positive ANA
- Anti-Ro and/or Anti-La antibodies
- Often a positive rheumatoid factor
These antibodies may also be seen in other connective tissue diseases, but their strongest association is with Sjögren’s syndrome.
2. When are they the answer?
You should select anti-Ro and anti-La antibody testing when the clinical scenario describes the classic sicca triad, which includes:
- Dry eyes (keratoconjunctivitis sicca)
- Dry mouth (xerostomia)
- Arthritis or arthralgias
Dry eyes + dry mouth + arthritis → think Sjögren’s syndrome → order anti-Ro / anti-La antibodies.
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Diagnostic Tests – Anti–Scl-70 (Anti–Topoisomerase I) Antibodies
1. What is this?
Anti–Scl-70 antibodies are autoantibodies directed against topoisomerase I, a nuclear enzyme. They are associated with systemic sclerosis, particularly the diffuse cutaneous form. Their presence supports the diagnosis and helps with risk stratification.
2. When do you answer anti–Scl-70 antibodies?
Order anti–Scl-70 when the clinical picture suggests diffuse systemic sclerosis, such as:
Exam pearl: Diffuse scleroderma features → think anti–Scl-70.
3. How would a negative test affect management?
A negative anti–Scl-70 does not rule out systemic sclerosis because the test has low sensitivity (~30%).
If clinical suspicion remains high, management and further evaluation should continue despite a negative result.
4. What is the patient at risk for if anti–Scl-70 is positive?
A positive anti–Scl-70 is most strongly associated with severe pulmonary involvement, especially:
This finding signals a higher-risk disease course and warrants close pulmonary monitoring.
High-yield contrast
1. What is this?
Anti–Scl-70 antibodies are autoantibodies directed against topoisomerase I, a nuclear enzyme. They are associated with systemic sclerosis, particularly the diffuse cutaneous form. Their presence supports the diagnosis and helps with risk stratification.
2. When do you answer anti–Scl-70 antibodies?
Order anti–Scl-70 when the clinical picture suggests diffuse systemic sclerosis, such as:
- Polyarthralgia
- Raynaud phenomenon
- Thick, tight (“hide-bound”) skin
- Dysphagia and GI hypomotility
- Evidence of pulmonary and/or renal involvement
Exam pearl: Diffuse scleroderma features → think anti–Scl-70.
3. How would a negative test affect management?
A negative anti–Scl-70 does not rule out systemic sclerosis because the test has low sensitivity (~30%).
If clinical suspicion remains high, management and further evaluation should continue despite a negative result.
4. What is the patient at risk for if anti–Scl-70 is positive?
A positive anti–Scl-70 is most strongly associated with severe pulmonary involvement, especially:
- Interstitial lung disease
- Pulmonary fibrosis
This finding signals a higher-risk disease course and warrants close pulmonary monitoring.
High-yield contrast
- Limited systemic sclerosis (CREST) → Anticentromere antibodies
- Diffuse systemic sclerosis → Anti–Scl-70 antibodies
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Diagnostic Tests – Aldolase
1. What is it associated with?
Aldolase is an enzyme released from damaged skeletal muscle. It is elevated in inflammatory myopathies, particularly:
2. When do you answer aldolase?
You should choose aldolase (or CPK) as the best initial diagnostic test when the clinical vignette suggests an inflammatory myopathy, such as:
Exam pearl:
Proximal muscle weakness + dermatomyositis rash → check aldolase or CPK first
3. What is the most accurate test?
While aldolase is useful for initial screening, the most accurate diagnostic tests for polymyositis and dermatomyositis are:
1. What is it associated with?
Aldolase is an enzyme released from damaged skeletal muscle. It is elevated in inflammatory myopathies, particularly:
- Polymyositis
- Dermatomyositis
2. When do you answer aldolase?
You should choose aldolase (or CPK) as the best initial diagnostic test when the clinical vignette suggests an inflammatory myopathy, such as:
- An older woman with proximal muscle weakness
- Difficulty rising from a chair or lifting arms
- Associated myalgias
- Characteristic skin findings, including:
- Heliotrope rash
- Gottron’s papules
Exam pearl:
Proximal muscle weakness + dermatomyositis rash → check aldolase or CPK first
3. What is the most accurate test?
While aldolase is useful for initial screening, the most accurate diagnostic tests for polymyositis and dermatomyositis are:
- Electromyography (EMG)
- Muscle biopsy
