Reactive arthritis:

Definition: Reactive arthritis is arthritis which developed soon after or during an infection elsewhere in the body, but in which the microorganisms cannot be recovered from the joint.(Time duration between the infection and arthritis between several days to weeks)It is a very uncommon disease that typically occurs in young adults, affecting both men and women.

Specific infections have been associated with reactive arthritis: Genitourinary infections: Chlamydia trachomatis Enteric infections: Salmonella, Shigella, Yersinia, Campylobacter & Clostridium difficile+ Reactive arthritis has been reported in patients with HIV infection.

Symptoms: Symptoms of the infection: diarrhea or urethritis. But by the time the patient presents. These might not be present.

Musculoskeletal signs & symptoms include two major manifestations: Arthritis: The arthritis is usually acute onset asymmetric mono or oligoarthritis, often affecting the lower extremities. However, around 50% of patients have arthritis in the upper extremities, and some have polyarthritis in the small joints. Some even develop dactylitis (sausage digits) Enthesitis: Swelling at the heels is among the most characteristic symptom of enthesitis. Common sites of heel involvement are at the insertions of the Achilles tendon and of the plantar fascia on the calcaneus. Pain, swelling, and local tenderness are suggestive clinical features. Note: Enthesis is the site of insertion of ligaments, tendons, joint capsule or fascia to bone

Extraarticular signs and symptoms: Conjunctivitis and less frequently anterior uveitis GU symptoms such as dysuria, urethritis, prostatitis Mucosal ulcers Constitutional symptoms initially Nail changes that resemble those seen in psoriasis (minus the pitting of the nails) Rashes such as erythema nodosum

Reiter syndrome: uveitis; urethritis; arthritis

Labs and imaging: Evidence of antecedent or concomitant infection (ex: stool cultures). But generally not helpful due to the time lapse between infection and the arthritis Elevated acute-phase reactants (CRP, ESR) Genetic testing: Positive testing for HLA-B27 Inflammatory synovitis: finding in synovial fluid are nonspecific but indicative of inflammatory arthritis with elevated leukocyte counts predominantly neutrophils Plain radiographs: joint swelling consistent with inflammatory arthritis

Diagnosis: Clinical diagnosis; No single definitive diagnostic test + no validated diagnostic criteria. Generally, the diagnosis can be made in patients with Characteristic musculoskeletal findings Evidence of a preceding extra articular infection but the inability to identify the causative pathogen does not exclude the diagnosis Lack of evidence for another more likely cause of the oligoarthritis

Treatment: Treat the infection (but this doesnt affect the arthritis) NSAIDs where an adequate trial is usually at least two weeks in duration If that doesnt work intra-articular or systemic glucocorticoids If that doesnt work disease modifying anti-rheumatic drug such as Leflunomide. This is used in those who have not responded adequately to at least two different NSAIDs over a total of four weeks and who require ongoing therapy with more than 7.5 mg of Prednisone or equivalent for more than three to six months.

Differential diagnosis:

Diarrhea with arthritis: Inflammatory bowel diseases, Behcets disease, Celiac disease as well as certain parasitic infections. BUT in these conditions chronicity of the GI symptoms + the presence of other features

Genitourinary symptoms with arthritis: Disseminated gonococcal infection (DIG) in case of urethral, uterine, cervical or tuboovarian inflammation occurs. Here, culture of synovial fluid, the urethra and other potentially infected mucosal sites is helpful in the diagnosis or exclusion of DGI or gonoccocal arthritis.

Bacterial infection: septic arthritis, identified by joint fluid examination and culture

Crystal- induced inflammation: upon examination of joint fluid monosodium urate (gout) or calcium pyrophosphate (pseudogout)

Poststreptococcal arthritis: patients with acute rheumatic fever (ARF) following streptococcal pharyngitis Undifferentiated spondyloarthritis: No history of an infection