Diagnosis
A doctor can often diagnose a musculoskeletal disorder based on the symptoms and on the results of a physical examination. Laboratory tests, imaging tests, or other diagnostic procedures are sometimes necessary to help the doctor make or confirm a diagnosis.
Physical Examination
A doctor looks for certain things during a physical examination depending on what disorder is suspected. When evaluating bones, if a fracture is suspected (see Section 5, Chapter 62), the doctor may notice that the affected part (such as an arm or a leg) is abnormally shaped, suggesting that the segments of bone are out of alignment. If a bone infection (osteomyelitis) is suspected, the doctor looks for tenderness over the infected bone, together with an elevated body temperature. The doctor may feel (palpate) the surfaces of the bones, to detect any abnormal bumps, which may indicate a tumor.
When a person complains of muscle weakness, the doctor checks muscles for bulk and texture and for tenderness. Muscles are also checked for abnormal movements, which may indicate a nerve disease rather than a muscle disease. Doctors look for wasting away of muscle (atrophy), which can result from damage to the muscle or its nerves or from lack of use (disuse atrophy), as sometimes occurs from prolonged bed rest. Doctors also look for muscle enlargement (hypertrophy), which normally occurs with an exercise such as weight lifting. However, when a person is ill, hypertrophy may result from one muscle working harder to compensate for the weakness of another. Muscles can also enlarge when normal muscle tissue is replaced by abnormal tissue (increasing the size but not the strength of the muscle), which occurs in amyloidosis and in certain inherited muscle disorders, such as Duchenne muscular dystrophy.
Doctors try to establish which (if any) muscles are weak and how weak they are. The muscles are tested systematically, usually beginning with the face and neck, then the arms, and finally the legs. Normally, a person should be able to hold the arms extended for one minute without their sagging, turning, or shaking. Downward drift of the arm with palms turned inward is a sign of weakness. Strength against resistance is tested by pushing or pulling while the doctor pushes and pulls in the opposite direction.
When examining joints, the doctor tests a joint's range of motion and muscle tone by moving the limb around a joint while the person is completely relaxed (passive movement). Resistance to such movement (passive resistance) may be decreased when the nerve leading to the muscle is injured or severed; resistance may be increased when the spinal cord or brain is injured.
Laboratory Tests
Laboratory tests are often helpful in making the diagnosis of a musculoskeletal disorder. For example, the erythrocyte sedimentation rate (ESR--a test that measures the rate at which red blood cells settle to the bottom of a test tube containing blood) is increased when inflammation is present. The level of creatine kinase (a normal muscle enzyme that leaks out and is released into the bloodstream when muscle is damaged) may also be tested. In rheumatoid arthritis, a blood test to identify rheumatoid factor is helpful to diagnosis. In gout, a blood test often shows a high level of uric acid.
Laboratory tests are also often useful to help monitor the progress of treatment (for example, the ESR can be particularly useful in monitoring the progress of treatment in rheumatoid arthritis or polymyalgia rheumatica and in confirming the diagnosis of osteomyelitis).
Nerve Tests
Nerve conduction studies (see Section 6, Chapter 77) help determine if the nerves supplying the muscles are functioning normally; they are used in the diagnosis of such disorders as polyarteritis nodosa and ulnar nerve palsy. Electromyography (see Section 6, Chapter 77), often conducted at the same time as nerve conduction studies, is a test in which electrical impulses reaching muscles from the nerves are recorded to help determine whether the muscles and the connection between nerves and muscles (neuromuscular junction) are normal. The test helps determine whether there is a problem primarily in the muscles or in the nerves supplying those muscles. It is also useful in diagnosing such disorders as amyotrophic lateral sclerosis and dermatomyositis.
X-rays
X-rays are taken to evaluate painful areas of bone; often, x-rays can help to detect fractures, tumors, injuries, infections, and deformities (such as congenial hip dysplasia). To help determine whether the joint has been damaged, a doctor may use an ordinary (plain) x-ray or one taken with the joint under stress (stress x-ray).
Arthrography is an x-ray procedure in which a radiopaque dye is injected into a joint space to outline the structures, such as ligaments inside the joint. Arthrography can be used to view torn ligaments and fragmented cartilage in the joint. However, MRI is now generally used in preference to arthrography.
Dual-Energy X-ray Absorptiometry
The most accurate way to evaluate bone density, which is necessary when screening for or diagnosing osteoporosis, is with dual-energy x-ray absorptiometry (DEXA). In this test, low-dose x-rays are used to examine bone at two sites: the spine and hip. Two different energies are used to distinguish between bone and soft tissue, giving a very accurate measurement of bone density at these sites.
Computed Tomography and Magnetic Resonance Imaging
Computed tomography (CT) and magnetic resonance imaging (MRI) give much more detail than conventional x-rays and may be performed to determine the extent and exact location of damage. MRI is especially valuable for imaging muscles, ligaments, and tendons; CT is best for imaging the bone. The amount of time a person spends undergoing CT is much less than for MRI. MRI is more expensive than CT and, with the exception of when the open-sided units are used, many people feel claustrophobic inside the MRI unit.
Bone Scanning
Bone scanning is an imaging procedure that is sometimes used to diagnose a fracture, particularly if other tests do not reveal the fracture. Bone scanning involves use of a radioactive substance (technetium-99m-labeled pyrophosphate) that is taken up by any healing bone. The technique can also be used when a bone infection or a metastasis (from a cancer elsewhere in the body) is suspected. The radioactive substance is given intravenously and is detected by a bone-scanning device, creating an image of the bone that can be viewed on a computer screen.
Joint Aspiration
Joint aspiration is used to diagnose joint problems. A needle is inserted into a joint space, and fluid (synovial fluid) is sucked out (aspirated) and examined under a microscope. A doctor can often make a diagnosis after analyzing the fluid. For example, a sample of synovial fluid may contain bacteria, which confirms a diagnosis of infection. Or, it may contain urate crystals, which confirms a diagnosis of gout or pseudogout (see Section 5, Chapter 70). Usually performed in the doctor's office, this procedure is generally quick, easy, and almost painless. The risk of joint infection is minimal.
Arthroscopy
Arthroscopy is a procedure in which a small fiber-optic scope is inserted into a joint space, allowing the doctor to look inside the joint, take a piece of tissue for analysis (biopsy), and, if necessary, perform surgery to correct the condition. Disorders commonly found during arthroscopy include inflammation of the synovium lining the joint (synovitis); ligament, tendon, or cartilage tears; loose pieces of bone or cartilage. All of these conditions can be repaired or removed during arthroscopy. There is a very small risk of joint infection with this procedure.
Biopsy
A biopsy is a procedure in which a small piece of tissue is taken, usually with a needle (needle biopsy), and examined under a microscope. Biopsy samples may be taken from virtually any tissue, including muscle, bone, and joints. The risk of infection is minimal.
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