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DIAGNOSTIC REASONING IN RHEUMATOLOGY

  • Most rheumatologic diseases are diagnosed “clinically” – e.g., a rheumatologist weighs the exam findings, labs, imaging and/or tissue biopsy results and makes a (sometimes tentative) diagnosis based on the strength of concordance between these findings and a given disease entity.

  • Classification criteria: Diagnostic criteria exist to ensure homogeneity of patients with rheumatologic diseases who enroll in clinical trials. Therefore, these criteria are biased in favor of specificity and NOT intended to diagnose rheumatic diseases.

APPROACH TO READING A HAND X-RAY

  • Alignment: Misaligned joints can help suggest specific pathologies. For example, ulnar deviation of the metacarpophalangeal joints (MCPs) is suggestive of rhematoid arthritis (RA).

  • Bone density: Lucency can be used to assess bone density; denser regions of bone are brighter on x-ray. When the lucency of juxta-articular bone is similar to that of the central metacarpal, there is said to be periarticular osteopenia, which is an early pathologic change in RA. Conversely, subchondral sclerosis (increased brightness of the juxta-articular bone) is suggestive of osteoarthritis (OA).

  • Cortical edges: Erosions appear as interruptions in the smooth contour of the peri-articular cortex and raise concern for the inflammatory arthropathies or erosive OA. Osteophytes appear as irregular outgrowths of bone and suggest OA.

  • Joint spaces: Joint space narrowing suggests arthritis, but does not distinguish inflammatory from non-inflammatory pathology.

  • Soft tissues: The triangular fibrocartilage sits between the ulna and the carpal bones and is a good site to assess for chondrocalcinosis (i.e., calcium pyrophosphate crystal build-up, commonly due to pseudogout).

FIGURE 9.3

Hand x-ray and joints typically affected by rheumatologic and non-rheumatologic diseases. A) Hand x-ray with anatomy labeled. B) Joints in the hand and differential diagnosis of rheumatologic and non-rheumatologic conditions that typically affect these joints. Abbreviations: CMC, carpometacarpal joint; DIP, distal interphalangeal joint; MCP, metacarpophalangeal joint; OA, osteoarthritis; PIP, proximal interphalangeal joint; RA, rheumatoid arthritis; SLE, systemic lupus erythematosus.

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