Evaluation of the Patient With Joint Symptoms

Blood tests should be selected based on history and examination findings. Some tests, although not specific, can be helpful in supporting or excluding the possibility of certain systemic rheumatic diseases Introduction to Autoimmune Rheumatic Disorders Autoimmune rheumatic disorders include diverse syndromes such as Autoimmune myositis Eosinophilic fasciitis Mixed connective tissue disease Relapsing polychondritis read more , as for the following:

Tests such as white blood cell count, erythrocyte sedimentation rate (ESR), and C-reactive protein may help determine the likelihood that arthritis is inflammatory due to infectious or other systemic disorders, but these tests are not highly specific or sensitive. For example, an elevated ESR or C-reactive protein level suggests articular inflammation or may be due to a large number of nonarticular inflammatory conditions (eg, infection, cancer). Also, such markers may not be elevated in all inflammatory disorders.

Imaging studies are often unnecessary. Plain x-rays in particular reveal mainly bony abnormalities, and most joint disorders do not affect bone primarily. However, imaging may help in the initial evaluation of relatively localized, unexplained, persistent or severe joint and particularly spine abnormalities; it may reveal primary or metastatic tumors, osteomyelitis, bone infarctions, periarticular calcifications (as in calcific tendinitis), or other changes in deep structures that may escape physical examination. If chronic rheumatoid arthritis Diagnosis Rheumatoid arthritis is a chronic systemic autoimmune disease that primarily involves the joints. Rheumatoid arthritis causes damage mediated by cytokines, chemokines, and metalloproteases.... read more , gout Diagnosis Gout is a disorder caused by hyperuricemia (serum urate > 6.8 mg/dL [> 0.4 mmol/L]) that results in the precipitation of monosodium urate crystals in and around joints, most often causing recurrent... read more , or osteoarthritis Diagnosis Osteoarthritis is a chronic arthropathy characterized by disruption and potential loss of joint cartilage along with other joint changes, including bone hypertrophy (osteophyte formation). Symptoms... read more is suspected, erosions, cysts, and joint space narrowing with osteophytes may be visible. In calcium pyrophosphate arthritis (pseudogout) Diagnosis Calcium pyrophosphate arthritis (CPP arthritis) involves intra-articular and/or extra-articular deposition of calcium pyrophosphate dihydrate (CPPD) crystals. Manifestations are protean and... read more , calcium pyrophosphate deposition may be visible in intra-articular cartilage.

For musculoskeletal imaging, plain x-rays may be obtained first, but they are less sensitive, particularly during early disease, than MRI, CT, or ultrasonography. MRI is the most accurate study for fractures not visible on plain x-rays, particularly in the hip and pelvis, and for soft tissues and internal derangements of the knee. CT is useful if MRI is contraindicated or unavailable. Ultrasonography, arthrography, and bone scanning may help in certain conditions.

Arthrocentesis is the process of puncturing the joint with a needle to withdraw fluid. If there is an effusion and arthrocentesis is done correctly, fluid can typically be withdrawn. Examination of synovial fluid is the most accurate way to exclude infection, diagnose crystal-induced arthritis Overview of Crystal-Induced Arthritides Arthritis can result from intra-articular deposition of crystals: Monosodium urate Calcium pyrophosphate dihydrate Basic calcium phosphate (apatite) Rarely, others such as calcium oxalate crystals read more , and help determine the cause of joint effusions. This procedure is indicated for all patients with acute or unexplained monarticular joint effusions and for patients with unexplained polyarticular effusions.

Arthrocentesis is done using strictly sterile technique. Infection or other rash over the site used to enter the joint is a contraindication. Preparations for collecting samples should be made before doing the procedure. Local anesthesia, with lidocaine and/or difluoroethane spray, is often used. Many joints are punctured on the extensor surface to avoid nerves, arteries, and veins, which are usually on the joint’s flexor surface. As much fluid as is possible should be removed. Specific anatomic landmarks are used (see figures , , and ). Ultrasound guidance has been shown to increase the likelihood of a successful aspiration.

At the bedside, gross characteristics of the fluid are assessed, such as its color and clarity.

Gross characteristics allow many effusions to be tentatively classified as noninflammatory, inflammatory, or infectious (see table ). Effusions can also be hemorrhagic. Each type of effusion suggests certain joint diseases (see table ). So-called noninflammatory effusions are often mildly inflammatory but tend to suggest diseases such as osteoarthritis Osteoarthritis (OA) Osteoarthritis is a chronic arthropathy characterized by disruption and potential loss of joint cartilage along with other joint changes, including bone hypertrophy (osteophyte formation). Symptoms... read more , in which inflammation is not severe.

Laboratory tests commonly done on joint fluid include cell count, leukocyte differential, Gram stain Gram stain Light microscopy can be done quickly, but accuracy depends on the experience of the microscopist and quality of equipment. Regulations often limit physicians’ use of microscopy for diagnostic... read more and culture Culture Culture is microbial growth on or in a nutritional solid or liquid medium; increased numbers of organisms simplify identification. Culture also facilitates testing of antimicrobial susceptibility... read more (if infection is a concern), and wet drop examination for cells and crystals. However, the exact tests often depend on which diagnoses are suspected.

Microscopic examination of a wet drop preparation of synovial fluid for crystals (only a single drop of fluid from a joint is needed) using polarized light is essential for definitive diagnosis of gout Diagnosis Gout is a disorder caused by hyperuricemia (serum urate > 6.8 mg/dL [> 0.4 mmol/L]) that results in the precipitation of monosodium urate crystals in and around joints, most often causing recurrent... read more , calcium pyrophosphate arthritis Diagnosis Calcium pyrophosphate arthritis (CPP arthritis) involves intra-articular and/or extra-articular deposition of calcium pyrophosphate dihydrate (CPPD) crystals. Manifestations are protean and... read more , and other crystal-induced arthritides Overview of Crystal-Induced Arthritides Arthritis can result from intra-articular deposition of crystals: Monosodium urate Calcium pyrophosphate dihydrate Basic calcium phosphate (apatite) Rarely, others such as calcium oxalate crystals read more . A polarizer over the light source and another polarizer between the specimen and the examiner’s eye allow visualization of crystals with a shiny white birefringence. Compensated polarized light is provided by inserting a first-order red plate, as is found in commercially available microscope kits that can be adapted to standard light microscopes.

The most common crystals seen are those diagnostic of gout Gout Gout is a disorder caused by hyperuricemia (serum urate > 6.8 mg/dL [> 0.4 mmol/L]) that results in the precipitation of monosodium urate crystals in and around joints, most often causing recurrent... read more (monosodium urate, negatively birefringent needle-shaped crystals) and calcium pyrophosphate arthritis (calcium pyrophosphate, rhomboid- or rod-shaped crystals that are positively birefringent or not birefringent). If crystals appear atypical in a wet drop, several less common crystals (cholesterol, liquid lipid crystals, oxalate, cryoglobulins) or artifacts (eg, depot corticosteroid crystals) should be considered.

Other synovial fluid findings that occasionally make or suggest a specific diagnosis include the following: