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Spondyloarthritis more active bowel inflammation and may predict develop ment of IBD. Reactive Anhritis Reactive arthritis occurs after specific bacterial infections. It is classified as a spondyloarthropathy and represents only 2'7, of patients in this category. The most common organism responsible for reactive arthritis is Chlomydio trachomatis; 4% to 8"/,' of infected patients develop reactive arthritis. Gastrointestinal pathogens include several species of Salmonella and Shigella, Campylobacter jejuni, and Yersiniq species; reactive arthritis occurs in approximately 1'X, of infected indMduals. Respiratory pathogens, including Chlamydia pneumoniae and Mycoplosma tl G U R E 2 I . Keratoderma blennorrhagicum on the palms and circinate balanitis on the glans penis are psoriasiform skin rashes seen in this patient with reactive pneumoniae, are also known causes of reactive arthritis. arthritis. Clostridioides difficileis an uncommon but important cause of reactive arthritis given its frequency in hospitalized patients. persistent disease. Complications of reactive arthritis can Approximately 7.4% of patients with C. dfficile colitis will include erosive joint disease, especially at the metatar develop reactive arthritis. An inciting organism is identifled in sophalangeal joints; aortitis with aortic valve insufficiency; only about 50% of patients. Women develop reactive arthritis atrioventricular conduction block: and uveitis. more commonly than men (relative risk, 1.5). H[A-B27 is found in 50'/" to 80% of patients with reactive arthritis; the highest rEY PO I l{TS frequency (90%) is seen in those who develop reactive arthritis . AnMosing spondylitis is a chronic inflammatory disease from Yersin io infection. affecting the axial skeleton (including sacroiliac joints), Reactive arthritis develops 2 to 3 weeks after genitouri entheses, and peripheral joints. nary and gastrointestinal infections. Synovial fluid Ieukocyte . Psoriatic arthritis is an inJlammatory ioint disease asso- counts can be elevated, often around 50,000/pL (50 x 10e/L) ciated with psoriasis, multiple possible joint patterns, with a predominance olneutrophils. Synovial fluid in reactive enthesitis, tenosynovitis, and dactylitis. arthritis can also demonstrate rice bodies: small pieces ol . Ankylosing spondyloarthritis, isolated sacroiliitis, and hypertrophic synovial tissue that are sloughed and accumulate peripheral arthritis can occur in patients with inflam in the joint and may require a large bore needle to aspirate. matory bowel disease. The arthritis is typically pauciarticular and involves larger joints. Enthesitis of the Achilles tendon or plantar fas . Reactive arthritis can occur 2 to 3 weeks following spe- cific gastrointestinal and genitourinary infections; the cia is commoni enthesitis may also occur in the knee, a joint with multiple entheses. Dactylitis of fingers and toes is also arthritis is tlpically pauciarticular and involves larger joints, and dactylitis and enthesitis can occur. common in reactive arthritis. Sacroiliac joint and spine inflammation and pain are less common than peripheral manifestations. Mucocutaneous manifestations include genitourinary dis Diagnosis ease (such as urethritis, cervicitis, cystitis, or prostatitis). Laboratory Studies Patients can have painless oral ulcers, tlpically affecting the Except for incidental overlap with other conditions, patients hard palate. Conjunctivitis is the most common eye finding, but with spondyloarthritis are negative fbr rheumatoid factor. anterior uveitis and even keratitis can occur. Keratoderma blen anti cyclic citrullinated peptide, and antinuclear antibodies. norrhagicum, a psoriasiform skin rash, occurs on the palms and Serologic testing should be performed only if an alternative soles but occasionally can become generalized (Figure 21). The diagnosis is being considered. lesions begin as discrete plaques and then enlarge and coalesce. For patients with inflammatory low back pain but normal Circinate balanitis is a similar psoriasiform lesion on the glans or nondiagnostic plain radiographs ofthe spine and sacroiliac penis in men. Erythema nodosum is rare. joints, a positive result on a test for HLA B27 antigen can be Important differential diagnostic considerations include useful for deciding to pursue advanced imaging. HLA-B27 infectious arthritis, disseminated gonococcal infection, antigen testing is never diagnostic but can help determine risk Whipple disease, IBD, or Behqet syndrome. for spondyloarthritis in uncertain situations. A patient with The typical course ofa reactive arthritis flare is 6 weeks to inflammatory low back pain, uveitis, and radiographic evi 6 months. Manifestations can last I year. Episodes may recur dence of bilateral sacroiliitis does not need HLA B27 antigen in some patients; about 25% of patients will have chronic testing because the diagnosis is clear.

Reactive Anhritis Reactive arthritis occurs after specific bacterial infections. It is classified as a spondyloarthropathy and represents only 2'7, of patients in this category. The most common organism responsible for reactive arthritis is Chlomydio trachomatis; 4% to 8"/,' of infected patients develop reactive arthritis. Gastrointestinal pathogens include several species of Salmonella and Shigella, Campylobacter jejuni, and Yersiniq species; reactive arthritis occurs in approximately 1'X, of infected indMduals. Respiratory pathogens, including Chlamydia pneumoniae and Mycoplosma tl G U R E 2 I . Keratoderma blennorrhagicum on the palms and circinate balanitis on the glans penis are psoriasiform skin rashes seen in this patient with reactive pneumoniae, are also known causes of reactive arthritis. arthritis. Clostridioides difficileis an uncommon but important cause of reactive arthritis given its frequency in hospitalized patients. persistent disease. Complications of reactive arthritis can Approximately 7.4% of patients with C. dfficile colitis will include erosive joint disease, especially at the metatar develop reactive arthritis. An inciting organism is identifled in sophalangeal joints; aortitis with aortic valve insufficiency; only about 50% of patients. Women develop reactive arthritis atrioventricular conduction block: and uveitis. more commonly than men (relative risk, 1.5). H[A-B27 is found in 50'/" to 80% of patients with reactive arthritis; the highest rEY PO I l{TS frequency (90%) is seen in those who develop reactive arthritis . AnMosing spondylitis is a chronic inflammatory disease from Yersin io infection. affecting the axial skeleton (including sacroiliac joints), Reactive arthritis develops 2 to 3 weeks after genitouri entheses, and peripheral joints. nary and gastrointestinal infections. Synovial fluid Ieukocyte . Psoriatic arthritis is an inJlammatory ioint disease asso- counts can be elevated, often around 50,000/pL (50 x 10e/L) ciated with psoriasis, multiple possible joint patterns, with a predominance olneutrophils. Synovial fluid in reactive enthesitis, tenosynovitis, and dactylitis. arthritis can also demonstrate rice bodies: small pieces ol . Ankylosing spondyloarthritis, isolated sacroiliitis, and hypertrophic synovial tissue that are sloughed and accumulate peripheral arthritis can occur in patients with inflam in the joint and may require a large bore needle to aspirate. matory bowel disease. The arthritis is typically pauciarticular and involves larger joints. Enthesitis of the Achilles tendon or plantar fas . Reactive arthritis can occur 2 to 3 weeks following spe- cific gastrointestinal and genitourinary infections; the cia is commoni enthesitis may also occur in the knee, a joint with multiple entheses. Dactylitis of fingers and toes is also arthritis is tlpically pauciarticular and involves larger joints, and dactylitis and enthesitis can occur. common in reactive arthritis. Sacroiliac joint and spine inflammation and pain are less common than peripheral manifestations. Mucocutaneous manifestations include genitourinary dis Diagnosis ease (such as urethritis, cervicitis, cystitis, or prostatitis). Laboratory Studies Patients can have painless oral ulcers, tlpically affecting the Except for incidental overlap with other conditions, patients hard palate. Conjunctivitis is the most common eye finding, but with spondyloarthritis are negative fbr rheumatoid factor. anterior uveitis and even keratitis can occur. Keratoderma blen anti cyclic citrullinated peptide, and antinuclear antibodies. norrhagicum, a psoriasiform skin rash, occurs on the palms and Serologic testing should be performed only if an alternative soles but occasionally can become generalized (Figure 21). The diagnosis is being considered. lesions begin as discrete plaques and then enlarge and coalesce. For patients with inflammatory low back pain but normal Circinate balanitis is a similar psoriasiform lesion on the glans or nondiagnostic plain radiographs ofthe spine and sacroiliac penis in men. Erythema nodosum is rare. joints, a positive result on a test for HLA B27 antigen can be Important differential diagnostic considerations include useful for deciding to pursue advanced imaging. HLA-B27 infectious arthritis, disseminated gonococcal infection, antigen testing is never diagnostic but can help determine risk Whipple disease, IBD, or Behqet syndrome. for spondyloarthritis in uncertain situations. A patient with The typical course ofa reactive arthritis flare is 6 weeks to inflammatory low back pain, uveitis, and radiographic evi 6 months. Manifestations can last I year. Episodes may recur dence of bilateral sacroiliitis does not need HLA B27 antigen in some patients; about 25% of patients will have chronic testing because the diagnosis is clear. 38

Spondyloarthritis Patients with spondyloarthritis may have anemia of Figure 23 with findings seen in Figure 24. Radiographs of the inflammation as a result of chronic inflammation. Erythroclte spine can show squaring of the vertebrae anteriorly (due to sedimentation rate and C reactive protein help confirm an erosion at the insertion of entheses); sclerosis at the anterior inflammatory process and can be monitored during therapy. edges of the vertebrae ("shiny corner" sign [Figure 25]); However, these values are not always elevated, particularly in ankylosing spondylitis. All patients with chronic spondyloar- thritis should be monitored for standard risk factors for car diovascular disease. lmaging Studies Radiography ofthe sacroiliac joints is an initial test for patients suspected of having ankylosing spondylitis. Anteroposterior radiography ofthe pelvis or a Ferguson view ofthe pelvis (in which the x ray beam is directed 20 degrees cephalad to show all sacroiliac joints in one plane) can depict the changes of sacroiliitis (Figure 22). The radiographic changes are initially more intense on the iliac side of the joint, with sclerosis and erosions. Erosive changes lead to a pseudo-widening appear- ance of the sacroiliac joints; in advanced cases, ankylosis of the sacroiliac joints can occur; compare normal findings in FIGU R E 24. CIscan of the sacroiliac joints in a patientwith sacroiliitis (same patient shown in Figure 22). Note the marked sclerosis/new bone formation, especially on the iliac side of the joint and erosions of the sacroiliac joints. t IGU R E 22. Radiograph of the sacroiliac joints (Ferguson view) in a patient with sacroiliitis (same patient shown in Figure 24). Note the iliacside sclerosis and ! i nd istinctness of the sacroi liac joi nts on both sides of the joi nt, i nd icati ng erosions.

lmaging Studies Radiography ofthe sacroiliac joints is an initial test for patients suspected of having ankylosing spondylitis. Anteroposterior radiography ofthe pelvis or a Ferguson view ofthe pelvis (in which the x ray beam is directed 20 degrees cephalad to show all sacroiliac joints in one plane) can depict the changes of sacroiliitis (Figure 22). The radiographic changes are initially more intense on the iliac side of the joint, with sclerosis and erosions. Erosive changes lead to a pseudo-widening appear- ance of the sacroiliac joints; in advanced cases, ankylosis of the sacroiliac joints can occur; compare normal findings in FIGU R E 24. CIscan of the sacroiliac joints in a patientwith sacroiliitis (same patient shown in Figure 22). Note the marked sclerosis/new bone formation, especially on the iliac side of the joint and erosions of the sacroiliac joints. t IGU R E 22. Radiograph of the sacroiliac joints (Ferguson view) in a patient with sacroiliitis (same patient shown in Figure 24). Note the iliacside sclerosis and ! i nd istinctness of the sacroi liac joi nts on both sides of the joi nt, i nd icati ng erosions. F IG U R E 2 5. Lateral lumbosacral spine radiograph in a patient with ankylosing spondylitis. Note the squared appearance of the anterior aspect of the lumbar vertebrae and the "shi ny corner" sig n on the anterosu perior aspect of the L3 (anow) FIGU RE 2 3. Normal CT scan of the sacroiliac joints. Note the intact sacroiliac vertebrae. The "fl uffy" appea rance to the facet joints posteriorly is typical of the new joints and lack of subchondral sclerosis. bone formation seen in ankylosing spondylitis. 39