General Medicine
Autoimmunity and Joint Pain
Autoimmunity and joint pain for MBBS: inflammatory versus mechanical patterns, rheumatoid arthritis, lupus and crystal arthropathies with key antibodies, mapped to NMC codes IM7.1 to IM7.14.
MedNext Academy | 3 min read
Autoimmunity and Joint Pain
Autoimmunity and joint pain for MBBS: inflammatory versus mechanical patterns, rheumatoid arthritis, lupus and crystal arthropathies with key antibodies, mapped to NMC codes IM7.1 to IM7.14.
This chapter builds a structured approach to joint pain, separating inflammatory from mechanical patterns and articular from periarticular disease. It introduces the pathophysiology of autoimmunity and the clinical and serological features that distinguish rheumatoid arthritis, lupus, the crystal arthropathies and the spondyloarthropathies.
High-yield: Autoimmunity and Joint Pain
- Joint pain is first separated into articular and periarticular, then into inflammatory and mechanical patterns.
- Inflammatory joint pain shows morning stiffness lasting over 30 to 60 minutes that eases with activity.
- Mechanical joint pain worsens with use and improves with rest, typical of osteoarthritis.
- The pattern of joint involvement, symmetry and number of joints narrows the differential quickly.
- Rheumatoid arthritis is a symmetrical small-joint polyarthritis sparing the distal interphalangeal joints.
- Rheumatoid factor and anti-cyclic citrullinated peptide antibodies support rheumatoid arthritis, the latter being more specific.
- Systemic lupus erythematosus is a multisystem disease with a positive antinuclear antibody in nearly all patients.
- Anti-double-stranded DNA and anti-Smith antibodies are specific for systemic lupus erythematosus.
- Acute monoarthritis must be treated as septic arthritis until joint aspiration proves otherwise.
- Gout is caused by monosodium urate crystals that are negatively birefringent and needle-shaped under polarised light.
- Pseudogout is caused by calcium pyrophosphate crystals that are positively birefringent and rhomboid.
- Spondyloarthropathies are associated with HLA-B27 and cause inflammatory back pain and enthesitis.
- Extra-articular features such as rash, serositis, eye and lung involvement point to a systemic rheumatologic disease.
- A prioritised differential guides which serological and imaging tests to order rather than testing indiscriminately.
- Fever with joint pain always demands exclusion of infection before an autoimmune label is applied.
Sorting out joint pain
- **Inflammatory versus mechanical:** Inflammatory pain gives prolonged morning stiffness easing with use; mechanical pain worsens with use.
- **Rheumatoid arthritis:** Symmetrical small-joint polyarthritis; anti-cyclic citrullinated peptide is the specific antibody.
- **Lupus:** Multisystem disease, antinuclear antibody positive; anti-double-stranded DNA and anti-Smith are specific.
- **Red flag:** Acute monoarthritis is septic until joint aspiration proves otherwise.
NMC competencies in this chapter
- **IM7.1:** Pathophysiology of autoimmune disease
- **IM7.3:** Pathophysiologic classification of joint pain
- **IM7.5:** Acute, subacute and chronic joint pain
- **IM7.6:** Arthralgia, arthritis, mechanical and inflammatory pain
- **IM7.8:** Causes based on the features of joint involvement
- **IM7.10:** Systemic manifestations of rheumatologic disease
- **IM7.13:** Prioritised differential diagnosis from clinical features
- **IM7.14:** Diagnostic workup based on the presumed aetiology
Frequently Asked Questions
How do you tell inflammatory from mechanical joint pain?
Inflammatory pain causes early morning stiffness lasting more than 30 to 60 minutes that eases with activity, while mechanical pain worsens with use and improves with rest.
Which antibody is most specific for rheumatoid arthritis?
Anti-cyclic citrullinated peptide antibody is more specific than rheumatoid factor and also carries prognostic value for erosive disease.
Why is acute monoarthritis an emergency?
Acute monoarthritis must be treated as septic arthritis until joint aspiration excludes infection, because delayed treatment can rapidly destroy the joint.
How does this chapter help for NEET-PG?
Inflammatory versus mechanical patterns, specific autoantibodies and crystal characteristics under polarised light are common exam points that map directly to questions.
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