Gout Examinationsss

7/29/2019 Gout Examinationsss

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Approach Considerations

Arthrocentesis of the affected joint is mandatory for all patients with new-onset acute monoarthritis and isvery strongly recommended for those with recurrent attacks whose diagnosis has never been proved bymicroscopic visualization of crystals. Tophi also may be aspirated for crystal analysis under polarizingmicroscopy.

A prior history of gout or pseudogout does not rule out the possibility of acute septic arthritis. In fact, thelatter is more common in patients with a history of crystal-induced arthritis. Septic arthritis must bediagnosed and treated promptly, because irreversible damage can occur within 4-6 hours and the jointcan be completely destroyed within 24-48 hours.

Send joint fluid for fluid analysis, including cell count and differential, Gram stain, culture and sensitivity,and microscopic analysis for crystals. If crystals are seen, their shape and appearance under polarizedlight are diagnostic.

In gout, crystals of monosodium urate (MSU) appear as needle-shaped intracellular and extracellularcrystals. When examined with a polarizing filter and red compensator filter, they are yellow when alignedparallel to the slow axis of the red compensator but turn blue when aligned across the direction ofpolarization (ie, they exhibit negative birefringence). Negatively birefringent urate crystals are seen onpolarizing examination in 85% of specimens.

Microscopic analysis in pseudogout shows calcium pyrophosphate (CPP) crystals, which appear shorterthan MSU crystals and are often rhomboidal. Under a polarizing filter, CPP crystals change colordepending upon their alignment relative to the direction of the red compensator. They are positivelybirefringent, appearing blue when aligned parallel with the slow axis of the compensator and yellow whenperpendicular.

In crystal arthritis, the white blood cell (WBC) count in the synovial fluid is usually 10,000-70,000/L.However, it may be as low as 1000/L or as high as 100,000/L.

Even in the presence of crystals in the joint fluid, blood cultures are indicated if any sign of systemictoxicity is present. Septic arthritis can occur in patients with active crystalline arthropathy.

Gouty attacks are not related to serum levels of uric acid. Thus, an elevated serum uric acid level does

not prove the diagnosis of acute gout, though hyperuricemia is present in 95% of cases, and a normallevel does not exclude the diagnosis. Renal uric acid excretion should be measured in high-risk patients,including those with renal calculi, a strong family history of gout, and a first attack before age 25 years.

Pseudogout attacks can be triggered by many metabolic abnormalities. Thus, patients who have an initialattack of arthritis with CPP crystals should have a workup that includes a chemistry screen; serummagnesium, calcium, and iron levels; and thyroid function tests.

The WBC count in peripheral blood is usually elevated, with a left shift during acute attacks. Theerythrocyte sedimentation rate (ESR) usually is elevated during acute attacks.

Imaging studies of the affected joint or joints are indicated. Patients with new onset of acute gout usuallyhave no radiographic abnormalities. In established disease, radiographs may reveal punched-outerosions or lytic areas with overhanging edges.

Magnetic resonance imaging (MRI) is capable of detecting crystal deposits but is not part of any routineevaluation for acute arthritis. MRI can be very useful in determining the extent of the disease and mayhelp in the differential diagnosis.

Patients with pseudogout usually have degenerative joint changes evident on imaging studies. Inaddition, they may have calcifications in the soft tissues, tendons, or bursae.

Synovial Fluid Analysis


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When a patient presents with acute inflammatory monoarticular arthritis, aspiration of the involved joint iscritical to rule out an infectious arthritis and to attempt to confirm a diagnosis of gout or pseudogout on thebasis of identification of crystals (see the image below). Minute quantities of fluid in the shaft or hub of theneedle are sufficient for synovial fluid analysis.

Gout. Fluid obtained from tophaceous deposit in patient with gout.Urate crystals are shaped like needles or toothpicks with pointed ends (see the first image below). Underpolarizing light microscopy, urate crystals are yellow when aligned parallel to the axis of the red

compensator and blue when aligned across the direction of polarization (ie, they exhibit negativebirefringence). Finding negatively birefringent urate crystals (see the second image below) firmlyestablishes the diagnosis of gouty arthritis.

Gout. Needles of urate crystals seen on polarizing microscopy.

Gout. Strongly negative birefringent, needle-shaped crystals diagnostic of goutobtained from acutely inflamed joint.Pseudogout crystals (CPP) are rod-shaped with blunt ends and are positively birefringent. Thus,pseudogout crystals are blue when aligned parallel to the slow ray of the compensator and yellow whenthey are perpendicular.

Crystals must be distinguished from birefringent cartilaginous or other debris. Debris may have fuzzyborders and may be curved, whereas crystals have sharp borders and are straight. As alkalizationreduces uric acid crystal solubility and the enzyme uricase can dissolve these crystals, reduction byaddition of sodium hydroxide or uricase to suspected gout crystal can be helpful.

Corticosteroids injected into joints have a crystalline structure that can mimic either MSU or CPP crystals.They can be either positively or negatively birefringent.
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The sensitivity of a synovial fluid analysis for crystals is 84%, with a specificity of 100%. If gout remains aclinical consideration after negative analysis findings, the procedure can be repeated in another joint orwith a subsequent flare. Crystals may be absent very early in a flare.

Although the sensitivity of this test is inferior, aspiration of synovial fluid from previously inflamed jointsthat are not currently inflamed may reveal urate crystals. Such crystals are generally extracellular.

Synovial fluid should also be sent for cell count. During acute attacks, the synovial fluid is inflammatory,with a WBC count higher than 2000/L (class II fluid) and possibly higher than 50,000/L, with apredominance of polymorphonuclear neutrophils, though low WBC counts are occasionally found.

Synovial fluid glucose levels are usually normal, whereas they may be depressed in septic arthritis andoccasionally in rheumatoid arthritis. Measurement of synovial fluid protein has no clinical value.

Crystalline arthritis and infectious arthritis can coexist. Indeed, infectious arthritis is more common inpreviously damaged joints, which may occur in patients with chronic gouty arthritis. Consequently, inpatients with acute monoarticular arthritis, send synovial fluid for Gram stain and culture and sensitivity.

The pathologic specimens must be processed anhydrously. MSU is water-soluble and dissolves informalin; therefore, only the ghosts of urate crystals may be seen if formalin is used. Absolute (100%)alcoholfixed tissue is best for identification of urate crystals.

Once a diagnosis of gout is established by confirmation of crystals, repeat aspiration of joints withsubsequent flares is not necessary unless infection is suggested or the flare does not respondappropriately to therapy for acute gout.

Serum Uric Acid

Measurement of serum uric acid is the most misused test in the diagnosis of gout. The presence ofhyperuricemia in the absence of symptoms is not diagnostic of gout. In addition, as many as 15% ofpatients with symptoms from gout may have normal serum uric acid levels at the time of their attack.Thus, the diagnosis of gout can be missed if the joint is not aspirated. Remember that situations thatdecrease uric acid levels can trigger attacks of gout. In such cases, the patients medical re cords mayreveal prior elevations of uric acid.

Approximately 25% of the population has a history of elevated serum uric acid, but only a minority ofpatients with hyperuricemia develop gout. Thus, an abnormally high serum uric acid level does notindicate or predict gout. As noted, gout is diagnosed by the presence of urate crystals in the synovial fluidor soft tissues. More important, some patients who present with a hot swollen joint and an elevated serumuric acid level in fact have infectious arthritis, which may be mismanaged if their synovial fluid is notexamined.

Asymptomatic hyperuricemia generally should not be treated. However, patients with levels higher than11 mg/dL and overexcretion of uric acid are at increased risk for renal stones and renal impairment;therefore, renal function should be monitored in these individuals.[30]

The level of serum uric acid does correlate with the risk for developing gout. The 5-year risk fordeveloping gout is approximately 0.6% if the level is below 7.9 mg/dL, 1% if it is 8-8.9 mg/dL, and 22% if itis higher than 9 mg/dL.

Urinary Uric Acid

A 24-hour urinary uric acid evaluation is generally performed if uricosuric therapy is being considered. Ifpatients excrete more than 800 mg of uric acid in 24 hours while eating a regular diet, they areoverexcretors and thus overproducers of uric acid. These patients (approximately 10% of patients withgout) require allopurinol instead of probenecid to reduce uric acid levels. Furthermore, patients whoexcrete more than 1100 mg in 24 hours should undergo close renal function monitoring because of therisk of stones and urate nephropathy.


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In patients in whom probenecid is contraindicated (eg, those with a history of renal stones or renalinsufficiency), a 24-hour urine test of uric acid excretion need not be performed, because the patientclearly will need allopurinol.

Blood Studies

Blood studies may reveal abnormalities associated with gout or common comorbid conditions. In addition,

abnormal results on renal function or liver function studies may affect the selection of therapy.

Obtaining an accurate measure of the patients renal function before deciding on therapy for gout isimportant. The glomerular filtration rate can be estimated by using formulas such as theModification ofDiet in Renal Disease (MDRD) Study equationor theChronic Kidney Disease Epidemiology Collaboration(CKD-EPI) equation. Serum creatinine evaluation alone can underestimate renal dysfunction in elderlypatients or in patients with low muscle mass.

The WBC count may be elevated in patients during the acute gouty attack, particularly if it is polyarticular.Hypertriglyceridemia and low levels of high-density lipoprotein (HDL) are associated with gout. Glucosemeasurement is useful because patients with gout are at increased risk for the development of diabetesmellitus.

Pseudogout attacks can be triggered by many metabolic abnormalities. Thus, patients who have an initial

attack of arthritis with CPP crystals should have a workup that includes a chemistry screen; serummagnesium, calcium, iron and iron-binding levels; and thyroid function tests.

Radiography

Plain radiographs may show findings consistent with gout, but these findings are not diagnostic. Early inthe disease, radiographs are often normal or show only soft-tissue swelling. Radiographic findingscharacteristic of gout, which generally do not appear within the first year of disease onset, consist ofpunched-out erosions or lytic areas with overhanging edges (see the image below). Haziness suggestiveof tophi can be seen in late gout, and tophi may calcify.

Gout. Radiograph of erosions with overhanging edges. Erosions with overhanging edges generally are considered pathognomonic for gout but also can be foundinamyloidosis,multicentric reticulohistiocytosis, and type IIAhyperlipoproteinemia. Characteristics oferosions that are typical of gout but not of rheumatoid arthritis include the following:

Maintenance of the joint space[82, 83]

Absence of periarticular osteopenia

Location outside the joint capsuleAnother characteristic of erosions typical of gout is sclerotic borders, sometimes called cookie-cutter orpunched-out borders. In addition, erosions in gout may be distributed asymmetrically among the joints,with strong predilection for distal joints, especially in the lower extremities (see the images below).
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Gout. Plain radiograph showing typical changes of gout in first metatarsophalangeal joint and

fourth interphalangeal joint. Gout. Plain radiograph showing chronic tophaceous gouty arthritis inhands.

Ultrasonography

At the first attack, sites affected with gout may be anechoic on ultrasonography. Later, diffuseenhancement may be evident on the articular cartilage surface.[84]Chondrocalcinosis show up as a thin,hyperechoic band within hyaline cartilage and punctuated pattern on fibrocartilage.

Ultrasonographic findings in established gout include the following

[85, 86, 87]

:

A double-contour sign, consisting of a hyperechoic, irregular line of MSU crystals on the surface ofarticular cartilage overlying an adjacent hyperechoic bony contour

Wet clumps of sugar, representing tophaceous material, described as hyperechoic and hypoechoicheterogeneous material with an anechoic rim

Bony erosions adjacent to tophaceous depositsUltrasonography may demonstrate urate crystal deposition in tissues of asymptomatic patients withhyperuricemia. Pineda et al found double-contour signs in the first metatarsal-phalangeal joints of 25% of50 asymptomatic patients with hyperuricemia but in none of 52 normouricemic subjects.[88]

In a study by DeMiguel et al, ultrasonography identified urate crystal deposition in 11 of 26 patients whohad asymptomatic hyperuricemia for 2-28 years (average, 6.2 years), affecting the knee in 9 cases andthe first metatarsal-phalangeal joint in 6. These results document that asymptomatic gout may not be as

innocuous as was once believed.[89]

Computed Tomography

Plain radiography and computed tomography (CT) are complementary for recognizing erosions ingout.[90] Dual-energy CT, using a renal stone color-coding protocol, assesses chemical composition,labeling urate deposits in red.[91]

In a study comparing CT imaging versus a history of urinary tract calculus for identification ofnephrolithiasis in gout patients, 62% of the patients with CT-documented scans had no history of
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urolithiasis. In 383 male patients with primary gout, CT scanning confirmed nephrolithiasis in 103 (26.9%),whereas the history of urinary tract calculus was positive in only 65 (17%). The authors concluded thatthe prevalence of urolithiasis cannot be accurately determined on the basis of patients histories.[92]

Magnetic Resonance Imaging

MRI is not part of any routine evaluation for acute arthritis. MRI evidence of edema is minimal in gout,

unless concomitant osteomyelitis is present.[93]

However, MRI with gadolinium is recommended whentendon sheath involvement must be evaluated and when osteomyelitis is in the differential diagnosis.Large deposits of crystals may be seen in bursae or ligaments.

Tophi usually have low or intermediate signal intensity on T1-weighted spin echo images. Signal intensityalso tends to be low on T2-weighted images. In the absence of inflammation, the tophi are sharplydelineated. Presence of inflammation results in increased perilesional signal intensity. Tophi and thesurrounding area of inflammation enhance with gadolinium.[94]

Histology

Chronic tophaceous gouty deposits frequently show large pale pink acellular areas, which representdissolved urate crystals, surrounded by histiocytes and multinucleated giant cells (see the image below).

Gout. Hematoxylin and eosin (H&E) stain, low power, showing abundant pale pinkareas surrounded by histiocytes and multinucleated giant cells.The crystals are water-soluble and thus are dissolved during routine tissue processing. If there are a largenumber of crystals, however, some may survive processing and appear as pale brown-gray refractilematerial (see the image below), or they may be seen on unstained sections. The urate crystals are easily

seen on polarized light.

Gout. H&E stain, high power, showing that most urate crystals have been dissolvedbut that some pale brown-gray crystals did survive processing.Pseudogout also demonstrates pale pink areas that may be surrounded by histiocytes and multinucleatedgiant cells. On higher-power views, however, the crystals are purple and rhomboid and therefore can bedistinguished from gout on routine histology (see the images below).
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H&E stain, medium power, of pseudogout with pale pink fibrocartilage in upper

portion and purple crystals of calcium pyrophosphate in lower portion. Pseudogout.

H&E stain, high power, under polarized light to highlight rhomboidal crystals.Pseudogout. H&E stain, high power, of calcium pyrophosphate crystals, demonstrating their rhomboidal structure.
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Gout Examinationsss