The predominant manifestation of reactive arthritis is an acute, asymmetric oligoarthritis of peripheral joints, frequently 1–4 weeks after the onset of the inciting infection. Joints of the lower extremities (eg, knees, ankles, and feet) are preferentially affected compared with joints of the upper extremities. The sternoclavicular and temporomandibular joints are sometimes involved. Affected joints are usually stiff, swollen, and tender.
Axial skeleton disease most commonly presents as inflammatory low back pain, which occurs in up to half of patients with reactive arthritis. Radiographic evidence of sacroiliitis, which is often unilateral, develops in approximately 20–25% of patients. This is in contrast to the bilateral, symmetric sacroiliitis of ankylosing spondylitis. A minority of patients with sacroiliitis have spondylitis with extensive fusion of the spine resembling severe ankylosing spondylitis. The prevalence of axial skeleton disease is greater among those with chronic disease and those with HLA-B27 (90% of patients with radiographic evidence of sacroiliitis are HLA-B27 positive).
A prominent feature of reactive arthritis is enthesitis, inflammation of sites where tendons attach to bone. Common sites for enthesitis are the Achilles tendon, plantar fascia, and pelvic bones. Findings of enthesitis include soft tissue swelling with overlying warmth and tenderness to palpation.
The combination of synovitis and enthesitis in a toe or finger can cause the entire digit to become diffusely swollen, producing dactylitis or “sausage digit.” Dactylitis is a feature of the spondyloarthropathies, frequently observed in reactive arthritis and psoriatic arthritis. Toes are more commonly affected than the fingers.
Circinate balanitis is an inflammatory lesion on the glans or shaft of the penis, and it is one of the characteristic lesions associated with reactive arthritis. In an uncircumcised man, these lesions are shallow, moist, serpiginous, painless ulcers with raised borders. In a circumcised man, these lesions can appear as dry, hyperkeratotic plaques resembling psoriasis and be painful.
Another cutaneous lesion associated with reactive arthritis is keratoderma blennorrhagicum, a papular, waxy rash that affects primarily the palms and soles. At first, the rash can be vesicular and then evolve into maculopapular nodules before turning into scaly, hyperkeratotic lesions resembling psoriasis. These lesions can coalesce to cover large areas of skin, extending proximally beyond the palms and soles.
If a genitourinary infection is the initial trigger of reactive arthritis, urethritis or cervicitis (or both) can be observed.
Aphthous ulcers, usually shallow and painless, can involve both oral and genital mucosal surfaces.
Lastly, nail changes resembling those of psoriatic arthritis can occur. However, nail pitting does not usually occur. These so-called “Reiter nails” are nail beds that may become thickened and eventually undergo onychodystrophy. The clinical appearance can be confused with similarly appearing onychomycosis.
Ocular inflammation (ie, conjunctivitis, but also iritis, scleritis, episcleritis, and keratitis) is associated with reactive arthritis in up to one-fourth of cases. The ocular inflammation is often intermittent, and presents as scleral injection, eye pain, and visual changes. Corneal clouding, due to the presence of inflammatory cells and protein exudates in the anterior chamber, can be seen on slit lamp examination. A chronic uveitis that can cause permanent visual impairment or even blindness develops in a minority of patients with relapsing uveitis.
Although rare, aortitis has been reported in a few patients with long-standing reactive arthritis. In addition, valvular heart disease (specifically aortic valve regurgitation) may result with thickening of the aortic root from chronic inflammation. If the conduction system involving the atrioventricular node is affected, complete heart block may result.
There are no laboratory tests diagnostic for reactive arthritis. The diagnosis may be particularly challenging when patients have asymptomatic infections that trigger reactive arthritis. The various classification criteria for reactive arthritis rely principally on clinical symptoms of inflammatory arthritis that follow a gastrointestinal or genitourinary infection.
Synovial fluid is notable for a cloudy, viscous, nonhemorrhagic appearance. Cell count with differential normally shows 5000–50,000 white blood cells per microliter with a predominance of polymorphonuclear cells. Gram stain is absent of bacteria, and cultures of the synovial fluid are negative. Microscopic analysis of crystalline disease (eg, gout or pseudogout) would be unremarkable. Occasionally, “Reiter cells” may be found. These are large mononuclear cells that have phagocytized several polymorphonuclear cells, which themselves contain inclusion bodies. These inclusion bodies represent bacterial antigens, thus completing the link of reactive arthritis and infectious etiologies.
Because of the strong infectious link with reactive arthritis, great effort should be made to identify the causative microorganism if it is not already known. Hence, cultures should be taken from the blood, urine, stool, and throat as indicated. If a sexually transmitted infection is suspected, Neisseria gonorrhoeae, C trachomatis, and HIV should be assessed. Conversely, if gastroenteritis were the inciting event, then serologic tests for antibodies against Salmonella, Shigella, Yersinia, and Campylobacter should be considered. A negative serology does not definitively rule out infection (especially early in disease course), as antibody titers increase over time, and as the complete list of infections that can cause reactive arthritis is still unknown.
During an acute attack, acute phase reactants such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are frequently elevated. Leukocytosis, thrombocytosis, and elevated serum immunoglobulins may also be present. In long-standing disease, a mild normocytic, normochromic anemia may be found secondary to chronic inflammation.
The presence of HLA-B27 may be useful diagnostically, since it is found in up to one-half of patients with reactive arthritis. It may be important also prognostically, as HLA-B27 positivity is associated with more chronic disease.
The most common radiographic abnormalities found in reactive arthritis are fluffy periostitis, which represent proliferative changes along the shaft of bones, and bony erosions, often found at the sites of joint inflammation. Osteolytic destruction and bony ankylosis may also occur, although they occur more frequently in psoriatic arthritis.
Radiographic sacroiliitis can be detected in up to 20% of patients. When present, it is frequently unilateral. There may be syndesmophytes (abnormal ossified spinal ligaments) resembling those in ankylosing spondylitis. However, they tend to be more asymmetric and less confluent than in ankylosing spondylitis.
Most radiographic findings in reactive arthritis occur months after disease onset, and the findings can be subtle.