3.2 Diagnostic Tests

anterior uveitis tends to increase in frequency and severity as the scleral inßammation progresses and, if the uveitis is uncontrolled, visual loss is guaranteed. Anterior uveitis may result from the spread of the adjacent scleral inßammation or from the same process which also affects the sclera. Because a variety of scleritisassociated systemic diseases may involve the anterior uvea, immunologic mechanisms responsible for the scleral and uveal reactions may be interrelated.

Lens

Cataract formation can be caused by long-stand- ing anterior uveitis-associated scleritis and is one of the primary causes of visual loss in patients with scleritis. The detection of a cataract in a young patient with scleritis may, in the absence of other etiologies, be an indication of the severity of the disease. Rapid lens opaciÞcation may occur in some eyes with circumferential scleral inßammation. Posterior subcapsular cataracts can appear in patients receiving local or systemic corticosteroids. It has been reported that the risk of developing a posterior subcapsular cataract in a patient with anterior scleritis receiving corticosteroid therapy is three times higher than the same risk in a patient receiving corticosteroid therapy for any other reason.

Fundus

Direct and indirect ophthalmoscopy and fundus examination, with the 90-, 78-, and 60-diopter lenses, may reveal inßammation of the choroid, ciliochoroidal effusions, choroidal detachments, retinal vasculitis, retinal detachment, macular edema, or optic nerve pathology in association with scleral inßammation. Posterior uveal involvement is always present in posterior scleritis, but only rarely in anterior scleritis. Therefore, the detection of posterior uveitis in association with anterior scleritis mandates a search for the presence of posterior scleritis. The posterior uveal involvement is believed to be caused by inßamed sclera overlying the choroid or by the same processes responsible for some scleritisassociated systemic diseases.

Intraocular Pressure

Tonometry, by Schištz tonometer, applanation tonometer, or pneumotonometer, should always be performed because the onset of glaucoma during the course of scleritis, as with the onset of uveitis, may be an ominous sign of further complications and progressive visual loss. High intraocular pressure is believed to be caused primarily by overlying scleral inßammation, damage to the trabecular meshwork secondary to anterior uveitis, or peripheral anterior synechiae secondary to anterior uveitis. Glaucoma, particularly in combination with uveitis, is the most common reason for enucleation in uncontrolled scleritis.

3.2Diagnostic Tests

Once the history of the present illness, review of systems, and physical examination have been completed, diagnosis of the type of scleral disease has been reached, and some preliminary systemic diagnoses have emerged as the most likely causes. The second phase of the approach to scleral diseases includes the selection of diagnostic tests for conÞrming or rejecting the possibilities suspected in the former phase (Table 3.7). It is important to emphasize that, unless the cause of scleritis is infectious, blood and urine laboratory tests alone rarely establish a systemic disorder diagnosis; rather they conÞrm it in the context of the clinical characteristics discovered in the Þrst phase. Therefore, ÒblanketÓ testing in scleritis is both expensive and wasteful.

Once the diagnosis has been established, selected laboratory testing is helpful in monitoring the effect of therapy on disease activity.

3.2.1Blood Tests

3.2.1.1 Rheumatoid Factor

Rheumatoid factor (RF) is generally deÞned as an autoantibody speciÞc for epitopes in the Fc fragment of immunoglobulin G (IgG). RF was discovered by E. Waaler [3] in 1937 while he was

working with a complement test using sheep erythrocytes (srbc) coated with anti-srbc rabbit antibodies. Waaler noted that serum from rheumatoid arthritis (RA) patients contained a factor that could agglutinate the antibody-coated erythrocytes, and the antibodies were necessary to obtain agglutination [3]. Later, in 1948, Rose et al. [4]. also noted, while working with a complement test for Rickettsia, agglutination induced by the sera of RA patients.

Approximately 80% of the patients with RA exhibit RF positivity (seropositive RA) [5]. However, RF is not speciÞc for RA. Rather, it is found in the sera of a variable portion of patients with other rheumatic diseases and with nonrheumatic diseases (Table 3.8) [6Ð8]; many of these conditions are associated with the presence of IgM RF. RF is also found in 5% of apparently normal individuals and in 10Ð20% of nonrheumatic individuals over 65 years old who will not

develop RA. RF positivity frequently precedes the onset of RA [9, 10].

The presence of RF does not establish the diagnosis of RA as the predictive value of the presence of RF in determining that diagnosis of RA is poor. Thus, fewer than one-third of unselected patients with a positive RF are found to have RA. Therefore, RF test is not useful as a screening procedure. However, the presence of RF can be of prognostic signiÞcance because patients with high titers tend to have more severe and progressive disease (rapid radiographic deterioration of involved joints and greater functional impairment), with extraarticular manifestations (e.g., subcutaneous nodules, vasculitis, neuropathy, ulcers, FeltyÕs syndrome, SjšgrenÕs syndrome) [5, 11Ð16]. In summary, RF test can be employed to conÞrm a diagnosis in individuals with a suggestive clinical presentation and, if present in high titer, to designate patients at risk for severe systemic disease.

Table 3.8 Diseases commonly associated with rheumatoid factor

Connective tissue disease

Rheumatoid arthritis

Systemic lupus erythematosus

Scleroderma

SjšgrenÕs syndrome

PolymyositisÐdermatomyositis

Acute viral infection

Rubella

Cytomegalovirus

Hepatitis

Infectious mononucleosis

Inßuenza

Chronic bacterial infection

Tuberculosis

Leprosy

Syphilis

Brucellosis

Salmonellosis

Subacute bacterial endocarditis

Parasitic infections

Malaria

Trypanosomiasis

Filariasis

Chronic inßammatory disease

Sarcoidosis

Chronic pulmonary disease

Chronic liver disease

Mixed cryoglobulinemia

Hypergammaglobulinemic purpura

RF can be IgG, IgM, or IgA antibody class. Most procedures used to detect RF activity are based on the agglutination of carrier particles (polystyrene latex or red blood cells) passively coated with human or rabbit IgG preparations. These techniques are modiÞcations of the originally described sensitized sheep cell agglutination test (WaalerÐRose) or latex Þxation tests and detect primarily IgM RF. IgM RF is not speciÞc of RA because it is found in a wide variety of acute and chronic inßammatory diseases, and even in some normal individuals. Interest in improving sensitivity, quantitative accuracy, and detection of other isotypes of RF has led to the development of speciÞc radioimmunoassays (RIAs) and enzyme-linked immunoabsorbant assays (ELISAs) capable of measuring nanogram quantities of IgA and IgG RF [17, 18]. The detection of IgG RF presents special problems in that both the RF activity and the antigenic sites are

located in the IgG molecule. Furthermore, nonRF IgG present as antigen bound to IgM RF can contribute to false-positive results. Thus, most immunoassays for IgG RF require tubes or microtest wells coated with rabbit IgG and often incorporate procedures to remove or destroy IgM RF [19, 20]. The speciÞcity of the RF for RA increases when IgM RF, IgA RF, and IgG RF are positive.

3.2.1.2 Anticyclic Citrullinated Peptide Antibodies

Antibodies to cyclic citrullinated peptide (antiCCP) can also be used to evaluate patients with RA [21]. Although these antibodies are most commonly found in RF-positive patients, on occasion they can be detected in the absence of RF. In addition, the anti-CCP test has a similar sensitivity and a better speciÞcity for RA than does RF, and, therefore, some have advocated its use to evaluate RA patients instead of RF. This is particularly the case in individuals with early RA, in whom assessment of anti-CCP may be the most useful to conÞrm the diagnosis and establish a likely prognosis. The presence of anti-CCP is most common in patients with aggressive disease, with a tendency for developing bone erosions [22]. The development of anti-CCP is most frequent in individuals with an RA associated HLA-b1 allele and in those who smoke cigarettes, and may occur before the development of clinical manifestations of RA. However, as with RF, the presence of anti-CCP is not useful to predict the future development of RA because it can be found in 1.5% of normal individuals, most of whom will not develop RA, and occasionally in patients with other rheumatic diseases. However, it is a useful test to conÞrm a diagnosis of RA and to estimate prognosis.

3.2.1.3 Antinuclear Antibodies

In 1948, Hardgraves and colleagues initiated the study of antibodies to nuclei with the description of the lupus erythematosus (LE) phenomenon [23], which demonstrates the ingestion of traumatized cells from systemic lupus erythematosus (SLE) patients by neutrophils [24]. The phenomenon is now known to be caused by the reaction

Table 3.9 Antibodies to nuclear or cytoplasmic antigens

SLE systemic lupus erythematosus, MCTD mixed connective tissue disease, PM polymyositis, PSS progressive systemic sclerosis, RA rheumatoid arthritis H homogeneous P peripheral, S speckled, CYT cytoplasmic, Sjšgren SjšgrenÕs syndrome

of antibodies against nucleoprotein (DNAÐ histone) with cell nuclei and the subsequent phagocytosis of such ÒsensitizedÓ nuclei. The LE test has been replaced by a more sensitive and speciÞc test, the indirect immunoßuorescent assay (IFA) for the detection of antinuclear antibodies (ANAs) [25Ð27].

The Þnding of ANAs indicates, in the majority of cases, an ongoing or latent inßammatory condition within the broad classiÞcation of connective tissue diseases [28]. However, infections, such as chronic active hepatitis, infectious mononucleosis, and lepromatous leprosy, and other autoimmune diseases, such as primary biliary cirrhosis and chronic glomerulonephritis, also are characterized by this serologic abnormality [27]. ANA may occasionally be found in normal subjects, although usually in low titers; the frequency increases with age.

The normal titer of ANA is 1:40 or less. Higher titers are indicative of an autoimmune disease. ANAs really actually compose a family of autoantibodies directed against components of the cell nucleus; they are important markers of SLE and

related syndromes (Table 3.9). Among the ANAs, antibodies to DNAÐhistone, double-stranded DNA (ds DNA), single-stranded DNA (ssDNA), RNA, histone, nuclear ribonucleo protein (nRNP), and Small RNP (Sm), all occur in SLE, whereas antibodies to Ro/SSA and La/SSB/Ha occur in SLE and SjšgrenÕs syndrome; antibodies to nRNP also can be detected in patients with mixed connective tissue disease, an entity whose features overlap those of SLE, scleroderma, and polymyositis; antibodies to PM-Scl, Mi1, Mi2, Jo2, and Ku all are found in patients with polymyositis; antibodies to Scl70 and centromere occur in patients with progressive systemic sclerosis, whereas antibodies to anti-DNAÐhistone occur in patients with rheumatoid arthritis [29]. Some of these entities are not associated with episcleritis or scleritis; however, they are important in the differential diagnosis of other connective tissue diseases that may be associated with episcleritis and scleritis (Table 3.2). The pattern of immunoßuorescence positivity revealed by an ANA test is of considerable diagnostic signiÞcance. Major ßuorescence patterns include homogeneous, peripheral (rim), speckled, and nucleolar. The ANA pattern is relatively valuable but is much less important than the identiÞcation of a speciÞc ANA or anticytoplasmic antibody (ACA) (e.g., anti-nRNP, anti-La/SSB, and anti- PM-Scl). The homogeneous pattern can be produced by anti-DNAÐhistone and ds DNA antibodies associated with the LE phenomenon; the peripheral pattern also can be caused by antibodies to DNAÐhistone and dsDNA; the speckled pattern correlates with anti-Sm, anti-nRNP, anti-La/SSB, and anti-Scl70 antibodies; the nucleolar pattern can be produced by anticentromere antibodies. Disease associations with typical staining patterns are shown in Table 3.9 [30Ð36].

The ANA test is an indirect ßuorescence reaction in which a droplet of patient serum is reacted with substrate cells Þxed with acetone or methanol on a slide. As many as 20 or 30 different sera can be examined on the same slide. After a certain reaction period has elapsed, all excess serum is washed off to remove other serum components, except bound ANA. In the next step, the preparation is then covered with ßuorescein-tagged