Arthritis Curehow to Arthritis Cure for Diagnosis and Diagnostic Tests
Whenever bacterial arthritis is suspected, the most important diagnostic procedures are arthrocentesis and examination of the synovial fluid. Arthrocentesis and synovial fluid analysis should be performed in patients who are seen with an inflamed joint for which alternative explanations are not immediately apparent. For example, a patient with a history of gout or evidence of a generalized flare of rheumatoid arthritis might not require arthrocentesis. However, the clinician should follow up carefully and reassess for an infectious process if the decision is made to treat for a diagnosis other than infection. For joints that are deep and more difficult to aspirate, ultrasound-guided or fluoroscopy-guided needle aspiration should be done.
Normal joints contain a small amount of synovial fluid that is clear, is highly viscous, and has few white blood cells (WBCs). The protein concentration is approximately one-third that of plasma, and the glucose concentration is similar to that of plasma. Infected synovial fluid is usually purulent with an elevated leukocyte count typically greater than 50,000 WBC/mm3 and often exceeding 100,000 WBC/mm3 with polymorphonuclear cell predominance. Synovial fluid levels of glucose, lactate dehydrogenase, and total protein have limited value in the diagnosis of septic arthritis. Although a low synovial fluid glucose (<40 mg/dL or less than half the serum glucose concentration) and an elevated lactate dehydrogenase suggest bacterial infection, they are not sufficiently sensitive or specific for the diagnosis.48 Figure 109-2 is an algorithm for synovial fluid analysis, and Table 109-4 lists the differential diagnoses of septic arthritis and the known causes of pseudoseptic arthritis.49
A definite diagnosis of bacterial arthritis can be made only by visualizing bacteria on a Gram-stained smear or by culturing bacteria from the synovial fluid. In patients not previously treated with antibiotics, synovial fluid cultures are positive in 70% to 90% of cases of nongonococcal bacterial arthritis.4,50 Blood cultures are positive in 40% to 50% of cases of septic arthritis and are the only method of identifying the pathogen in approximately 10% of cases.51,52 Occasionally, an extra-articular site of infection offers a clue to the etiologic organism infecting the joint. Examples include septic arthritis in association with pneumococcal pneumonia, E. coli urinary tract infection, and cellulitis caused by staphylococci or streptococci. Gram-positive cocci are identified in 50% to 75% of synovial fluid Gram-stained smears, but Gram-negative bacilli are identified less than 50% of the time in culture-proven cases.50
Arthritis Curehow to Arthritis Cure for Inflammatory markers such as erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and WBC are usually raised, but the sensitivity is low, and their absence does not exclude the diagnosis of septic arthritis.43,53 Procalcitonin, the peptide precursor of calcitonin, has been extensively investigated as a biomarker for bacterial infection.54 Procalcitonin levels are elevated in bacterial infections, and the levels return to normal relatively rapidly once the bacterial infection is controlled. Unlike the ESR and CRP, procalcitonin levels are not elevated in many other inflammatory conditions, such as gout, systemic lupus erythematosus, or Still's disease.55 Also, the levels are not affected by NSAIDs or glucocorticoids. It is postulated that cytokines and endotoxins released from bacteria inhibit conversion of procalcitonin to calcitonin. Viral infections are not associated with procalcitonin elevations because viruses stimulate release of IFN, which blocks procalcitonin production in human cells. The majority of procalcitonin is produced in nonthyroidal tissue. Therefore procalcitonin elevations may occur in post-thyroidectomy patients who have a bacterial infection. In healthy individuals, serum procalcitonin levels are less than 1 ng/mL. A meta-analysis of studies on the use of procalcitonin for the diagnosis of septic arthritis recommended that procalcitonin be used as a rule-in test at the cutoff value of 0.5 ng/mL and as a rule-out test at the cutoff value of 0.3 ng/mL, with specificity and sensitivity in the range of 90%.56 In this meta-analysis, procalcitonin was more sensitive and specific than CRP for diagnosing or ruling out septic arthritis.
Culture for N. gonorrhoeae is almost always negative in skin lesions and is positive in less than 50% of synovial fluid samples and in less than one-third of blood cultures; this phenomenon may be the result of the fastidious growth requirements of N. gonorrhoeae. The organism can often be easily recovered from other sites, such as urethral, cervical, rectal, or pharyngeal specimens (i.e., the genitourinary tract). In culture-negative septic arthritis in which N. gonorrhoeae is suspected, polymerase chain reaction techniques can be used to detect gonococcal DNA in the synovial fluid. Unfortunately, the technique is not standardized and is not widely avilable.Arthritis Curehow to Arthritis Cure for 57
When culturing the synovial fluid, it should be brought directly to the laboratory and placed on conventional broth and solid media or into aerobic and anaerobic blood culture bottles. Inoculating blood culture bottles with 5 to 10 mL of joint fluid or smaller volumes into isolator tubes may increase the yield of positive cultures beyond that of standard techniques.58,59 Synovial the 1 last update 2020/05/31 fluid culture can use specialized collection and detection systems that can identify significantly more pathogens and fewer contaminants than culture by the agar-plate method.60When culturing the synovial fluid, it should be brought directly to the laboratory and placed on conventional broth and solid media or into aerobic and anaerobic blood culture bottles. Inoculating blood culture bottles with 5 to 10 mL of joint fluid or smaller volumes into isolator tubes may increase the yield of positive cultures beyond that of standard techniques.58,59 Synovial fluid culture can use specialized collection and detection systems that can identify significantly more pathogens and fewer contaminants than culture by the agar-plate method.60
Plain radiographs in septic arthritis are usually normal early in the course of the infection, but baseline films should be obtained to look for evidence of other disease and for 1 last update 2020/05/31 contiguous osteomyelitis. Radiographs often show nonspecific changes of inflammatory arthritis, including periarticular osteopenia, joint effusion, soft tissue swelling, and joint space loss. In more advanced infection, periosteal reaction, marginal or central erosions, and destruction of subchondral bone may be seen. Bony ankylosis is a late sequela of septic arthritis. Dislocation or subluxation of the femoral head is unique to hip infection of neonates.61Plain radiographs in septic arthritis are usually normal early in the course of the infection, but baseline films should be obtained to look for evidence of other disease and contiguous osteomyelitis. Radiographs often show nonspecific changes of inflammatory arthritis, including periarticular osteopenia, joint effusion, soft tissue swelling, and joint space loss. In more advanced infection, periosteal reaction, marginal or central erosions, and destruction of subchondral bone may be seen. Bony ankylosis is a late sequela of septic arthritis. Dislocation or subluxation of the femoral head is unique to hip infection of neonates.61
Ultrasound of the hip is the modality of choice to detect fluid collections in this deep joint and can serve as a guide in its aspiration. Ultrasound can be similarly used in other joints, such as the popliteal cyst of the knee, shoulder, acromioclavicular, or sternoclavicular joints. Triple-phase bone scan using technetium 99m is often done in children to identify an associated metaphyseal osteomyelitis or avascular necrosis of the femoral head. Whole-body bone scan is preferred in young children because, despite focal symptoms, septic arthritis and osteomyelitis may be multifocal in this age group.62 In septic arthritis of all age groups, the periarticular distribution of increased uptake is seen on the early “blood-pool” phase and the delayed images of the joint. Bone scans provide only nonspecific information, however, and cannot differentiate septic from noninfectious causes of joint inflammation. Bone scans are more sensitive than standard radiography in the diagnosis of arthritis because radionuclide uptake precedes morphologic bone changes that are seen on radiograph. A suggestive bone scan must be interpreted in the proper clinical context and supported by microbiologic data for a definitive diagnosis of joint or bone infection.
In joints that are difficult to evaluate otherwise or that have complex anatomic structures, computed tomography (CT) and MRI can provide useful images to delineate the extent of the infection.63 MRI is highly sensitive in early detection of joint fluid and is superior to CT in the delineation of soft tissue structures and soft tissue abscess. These images can show early bone erosion, reveal soft tissue extension, and facilitate arthrocentesis of joints such as shoulders, hips, acromioclavicular,64 sternoclavicular, sacroiliac, and facet joints of the spine. MRI findings such as reactive bone marrow can suggest the presence of secondary osteomyelitis, which can complicate septic arthritis. When multiple joint involvement is suspected, triple-phase bone scintigraphy is the preferred modality of investigation.