Reactive arthritis


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Reactive arthritis


Pediatric musculoskeletal conditions

Radial head subluxation (Nursemaid elbow)

Developmental dysplasia of the hip

Legg-Calve-Perthes disease

Slipped capital femoral epiphysis

Transient synovitis

Osgood-Schlatter disease (traction apophysitis)

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Radial head subluxation (Nursemaid elbow)

Winged scapula

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Unhappy triad

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Osteomalacia and rickets


Paget disease of bone


Lordosis, kyphosis, and scoliosis

Joint disorders



Spinal stenosis

Rheumatoid arthritis

Juvenile idiopathic arthritis


Calcium pyrophosphate deposition disease (pseudogout)

Psoriatic arthritis

Ankylosing spondylitis

Reactive arthritis


Septic arthritis


Baker cyst

Muscular disorders

Muscular dystrophy



Inclusion body myopathy

Polymyalgia rheumatica



Neuromuscular junction disorders

Myasthenia gravis

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Other autoimmune disorders

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Musculoskeletal system pathology review

Back pain: Pathology review

Rheumatoid arthritis and osteoarthritis: Pathology review

Seronegative and septic arthritis: Pathology review

Gout and pseudogout: Pathology review

Systemic lupus erythematosus (SLE): Pathology review

Scleroderma: Pathology review

Sjogren syndrome: Pathology review

Bone disorders: Pathology review

Bone tumors: Pathology review

Myalgias and myositis: Pathology review

Neuromuscular junction disorders: Pathology review

Muscular dystrophies and mitochondrial myopathies: Pathology review

Pediatric musculoskeletal disorders: Pathology review


Reactive arthritis


0 / 7 complete

USMLE® Step 1 questions

0 / 2 complete

High Yield Notes

15 pages


Reactive arthritis

of complete


USMLE® Step 1 style questions USMLE

of complete

A 42-year-old man comes to his primary care physician’s office for evaluation of right knee pain, red eyes, and lesions on soles of his feet. The patient states he had a “urinary tract infection” that was treated with antibiotics 3 weeks ago, and his symptoms appeared shortly thereafter. He has multiple sexual partners, and he uses condoms occasionally. Vitals are within normal limits. Physical examination shows bilateral conjunctival injection with scant purulent discharge at the lid margins. The right knee is mildly swollen with associated tenderness to palpation. Examination of the soles of feet is demonstrated below. Arthrocentesis of the right knee joint shows a leukocyte count of 40,000/mm3 but no organisms on gram-stain or culture. Which of the following is the most likely diagnosis?  

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Arthritis p. 476

reactive arthritis p. 479

Campylobacter spp.

reactive arthritis and p. 479

Chlamydia spp. p. 146

reactive arthritis p. 479

Conjunctivitis p. 553

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Campylobacter jejuni p. , 143

chlamydia p. 146, 180

HLA-B25 and p. 98

presentation p. 718

Salmonella spp.

reactive arthritis p. 479

Shigella spp.

reactive arthritis p. 479


reactive arthritis p. 479, 718

Yersinia spp.

reactive arthritis p. 479


Content Reviewers

Rishi Desai, MD, MPH

Marisa Pedron


Harry Delaney, MBChB

Tanner Marshall, MS

Reactive arthritis, formerly known as Reiter’s syndrome, is inflammation of a joint which usually develops after an infection, and that infection is typically a sexually transmitted disease or gastroenteritis. Reactive arthritis is part of a group of diseases called seronegative spondyloarthropathies. Spondyloarthropathies are autoimmune, inflammatory joint diseases, and they’re seronegative, which refers to the fact that an auto-antibody called rheumatoid factor is absent from the blood.

Normally, the immune cells are ready to spot and destroy anything foreign that could cause the body harm. To help with this, most cells in the body have a set of proteins that combine together to form something called a major histocompatibility complex, or MHC, and this is a molecule that sits on the surface of their cell membrane. There are two kinds of MHC molecules, class I and class II. Class I molecules are found on most cells in the body, and they present molecules from within the cell for the immune system to continually sample. Normally the molecule’s just a sample from inside the cell, also known as a self-antigen. When immune cells pass by, they recognize this self-antigen as harmless so there’s no response.

MHC class II molecules are found specifically on phagocytic cells like macrophages which destroy and digest foreign pathogens like bacteria. Once a macrophage destroys a bacterium, it presents a piece of that bacterium on its MHC class II receptor, and the macrophage then makes its way to the lymph node to find some T-lymphocytes. A type of T-lymphocyte, called a CD4+ T-cell, also known as a helper T-cell, uses its T-cell receptors to bind to the foreign antigen presented by the MHC class II molecule. If the helper T-cell binds strongly, the antigen is recognized as foreign, and the helper T-cell switches on the corresponding B-cell, so it can start producing a whole lot of antibodies. These antibodies bind to the specific pathogen, and typically prevent it from attacking the host’s cells and, at the same time, they “tag” the pathogen for further destruction by other immune cells.


Reactive arthritis, originally referred to as Reiter's arthritis, is an autoimmune condition commonly affecting the joints, skin, and eyes, which develops in response to an infection in another part of the body. Reactive arthritis commonly presents as inflammatory arthritis of large joints, conjunctivitis or uveitis, and urethritis in men or cervicitis in women. Symptoms include joint pain and swelling, pain and swelling in the eyes, pain with urination, pain with sexual intercourse in females, and skin rashes. Treatment focuses on identifying and treating the culprit infection with antibiotics, and anti-inflammatory drugs to dampen the inflammation.


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  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Poststreptococcal Arthritis" Canadian Journal of Infectious Diseases (1995)
  6. "Risk Factors for Progression from Subclinical to Clinical Phase of Psoriatic Arthritis: A Case–Control Study" Rheumatology and Therapy (2021)

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