ultrasound At the simplest level, ultrasound consists of placing a probe against the patient's skin. The probe then emits a pulse of sound and receives and records its echo or echoes. Sound waves bounce off tissue interfaces (e.g., the interface between fat and tendon) particularly well and will also reflect the homogeneity (sameness) of a tissue. Sound waves do not pass easily through solid material such as bone, and therefore, gallstones and kidney stones will cast an echo-free shadow behind them. A special type of ultrasound has been developed to measure the density of bones. Many developments have occurred in ultrasound over the past three decades, and it is now a very sophisticated method of imaging the body. Of all forms of imaging, ultrasound is most dependent on the ultrasonographer. In addition to interpreting the images obtained the ultrasonogra-pher has to use the probe to interrogate the area of interest.
Advantages of ultrasound compared with other musculoskeletal imaging techniques are that it is quick, widely available, noninvasive, and fairly cheap. it is also very effective when used as a guide to needle placement when taking a biopsy or aspirating a collection of fluid. in musculoskeletal practice, ultrasound is most frequently used to assess tendons. it demonstrates tendinitis, tears, and complete rupture very accurately. At the shoulder, for example, it can also show that the rotator cuff tendons are bunching up as the arm is lifted, thus confirming mechanical impingement. In many countries it has become the imaging modality of choice at the shoulder. Ultrasound is extremely effective at demonstrating bursitis from any cause. increasingly ultrasound is being used to demonstrate joint effusions, and a few rheumatologists even have portable machines in their offices to extend their examination of joints. Ultrasound is particularly helpful in demonstrating effusions in joints that are difficult to assess clinically such as shoulders, hips, and wrists. if, for example, septic arthritis were suspected in a hip joint, the absence of an effusion on ultrasound would virtually exclude that diagnosis. Although not good at imaging, bone ultrasound can show signs very suggestive of OSTEOMYELITIS.
uric acid The uric acid level in a blood test is often elevated in patients with gout but is often mistakenly thought to be a diagnostic test for gout. The blood urate levels are not very useful in making the diagnosis during an acute attack of gout. Many people with mildly raised urate levels will never develop gout, and 40 percent of people with acute gout will have a normal level during the attack. Most of this second group will, however, have a raised uric acid level later when the attack has settled. The best way to diagnose gout is to identify uric acid crystals in synovial fluid (see joint aspiration).
urinalysis A urinalysis is a urine test to detect blood, glucose (sugar), and protein, all of which should be negative. Urine is usually tested using a dipstick with small squares that change color in the presence of blood, sugar, or protein. Some dipsticks also detect nitrite and leukocyte esterase—substances that indicate the presence of a urinary infection. if the test for blood or protein is positive, the urine is examined under a microscope and further tests performed to identify the cause. A positive test for glucose usually indicates a diagnosis of diabetes mellitus. However, some healthy people without diabetes have an abnormally low threshold for spilling glucose into the urine.
There are many causes of an abnormal urinaly-sis, but the most common ones are menstrual blood, infections of the bladder and urinary tract, drugs, kidney stones, tumors, and autoimmune diseases affecting the kidney. Drugs such as cyclophosphamide can damage the bladder and cause blood in the urine, and gold and penicil-lamine can cause glomerulonephritis so that protein leaks into the urine.
X rays Also known as radiography, X-ray images are often used to diagnose bone and chest diseases. X rays, a type of radiation, pass through the body, but different tissues absorb them differently. Tissues that absorb well, such as bone appear white on the image. Those that do not absorb much, such as air, appear black. X rays are very useful for diagnosing abnormalities of bones and joints but not very useful for lesions in soft tissues such as muscles. X rays are used to help with the diagnosis and monitoring of many rheumatic diseases. The typical X ray changes of rheumatoid arthritis and gout for example, differ, and this can be very useful for making the correct diagnosis. Many patients with early arthritis have normal X rays because at this stage most of the damage occurs in the cartilage, a tissue that does not show up well on X rays other than as space between bones. There is a lot of research trying to use MRi, which provides much more detailed images of soft tissues such as cartilage, to diagnose early arthritis and measure its response to treatment. The advantages of X rays are that the test is quick, relatively cheap, widely available, and easy to perform. The disadvantages are that it exposes patients to a small dose of radiation, and is therefore avoided in pregnant women, and that it does not provide much detail about soft tissues.
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