Seronegative and septic arthritis: Pathology review

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Seronegative and septic arthritis: Pathology review



Seronegative and septic arthritis: Pathology review

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A 75-year-old woman presents to the emergency department for evaluation of right knee pain for the past two days. Medical history is notable for hypertension, type II diabetes mellitus, and knee osteoarthritis status post-bilateral total knee arthroplasty. Temperature is 38.5 °C (101.3 °F), blood pressure is 142/89 mmHg, pulse is 115/min, respirations are 20/min and SpO2 is 99% of room air. On physical examination, the right knee appears swollen and is tender to palpation. An arthrocentesis is performed and cultures reveal a Gram-positive coccus which is catalase-positive and coagulase-negative. Which of the following organisms was most likely identified?  

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Maurice is a 28 year old male who presents with a 2 year history of gradually progressive low back pain and stiffness. He mentions that the pain wakes him up several times at night, and that the stiffness tends to be worse when he wakes up and improves as he moves. Examination shows mild deformity of the spine and hip, as well as tenderness over the buttock. Then you see Clint, a 63 year old male shows up with a red, warm and swollen left knee, which hurts so much he can barely walk. Clint tells you that symptoms started a few days ago, after he tripped and cut his knee. His body temperature is 38 celsius degrees or 100.4 degrees Fahrenheit. X-rays are ordered in both cases, showing, in Maurice’s case, erosion of the sacroiliac joint. On the other hand, in Clint’s case, X-rays look pretty normal, so an arthrocentesis is performed, revealing that synovial fluid is purulent.

Based on the initial presentation, both cases seem to have some form of arthritis. But first, a bit of physiology real quick. There are many types of joints, including fibrous, cartilaginous, and synovial joints. synovial joints, like those of the wrist, elbow, knees, shoulders, and hips, are mobile joints that connect two bones via a fibrous capsule that is continuous with the periosteum, which is the outer layer of bones. The fibrous capsule is lined with a synovial membrane, which has cells that remove debris and produce synovial fluid. This is a viscous fluid found inside the joint capsule which lubricates joint. Together, the synovial membrane and articular cartilage form the inner lining of the joint space.

Now, arthritis refers to a group of diseases that cause destruction of one or more joints. First, we have seronegative arthritis, which is called seronegative because there’s an absence of both rheumatoid factor or RF, and anti-cyclic citrullinated peptide antibody or anti-CCP, which are commonly found in rheumatoid arthritis. Something specific to note is that seronegative spondyloarthropathies have a strong association with the gene HLA-B27, which encodes for a specific type of MHC class I molecule.


Seronegative and septic arthritis are two different forms of arthritis, each with its causes and symptoms. Seronegative arthritis refers to a type of arthritis in which a person tests negative for rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies, which are markers commonly associated with rheumatoid arthritis. Seronegative arthritis can be caused by a variety of conditions, including psoriatic arthritis, ankylosing spondylitis, reactive arthritis, etc.

Septic arthritis, on the other hand, is a severe form of arthritis, often caused by bacterial infections. The infection can enter the joint through a break in the skin, or from an infection in another part of the body that spreads through the bloodstream. Septic arthritis is a medical emergency and requires prompt treatment with antibiotics to prevent joint damage and systemic spread of the infection.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Acute monoarthritis: What is the cause of my patient's painful swollen joint?" Canadian Medical Association Journal (2009)
  4. "Septic arthritis: current diagnostic and therapeutic algorithm" Curr Opin Rheumatol (2008)
  5. "2012 Update of the 2008 American College of Rheumatology recommendations for the use of disease-modifying antirheumatic drugs and biologic agents in the treatment of rheumatoid arthritis" Arthritis Care & Research (2012)
  6. "Rheumatoid arthritis: pathological mechanisms and modern pharmacologic therapies" Bone Research (2018)
  7. "Rheumatoid Arthritis: A Brief Overview of the Treatment" Medical Principles and Practice (2018)
  8. "Ankylosing spondylitis: etiology, pathogenesis, and treatments" Bone Research (2019)
  9. "Rheumatoid arthritis" The Lancet (2016)
  10. "The lifetime risk of adult-onset rheumatoid arthritis and other inflammatory autoimmune rheumatic diseases" Arthritis & Rheumatism (2011)

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