Clinical Information

Connective tissue diseases (CTD) constitute diverse disorders affecting the joints, skin, eyes, heart, lungs, and gastrointestinal tract.(1) The diseases may be caused mainly by inheritable disorders of the connective tissue or autoimmune mechanisms.(1,2) The most common autoimmune-mediated CTD include rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), systemic sclerosis (SSc) including CREST syndrome (calcinosis, Raynaud phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia), Sjogren syndrome (Sjs), mixed connective tissue disease (MCTD), and idiopathic inflammatory myopathies (IIM).(1-3) Collectively, these diseases are also referred to as antinuclear antibody (ANA)-associated CTD or ANA-associated systemic autoimmune rheumatic diseases (ASARD). These diseases are generally accompanied by antibodies to nuclear and cytoplasmic autoantigens when tested by indirect immunofluorescence assay (IFA) using HEp-2 substrate (HEp-2 IFA).(2,3) In addition to the ANA-CTD, RA (another CTD with overlapping clinical features) is an important consideration in the early detection of patients at-risk for CTD.(2,4,5)

The diagnosis of any CTD is based on the patient’s personal and family medical histories, clinical presentation, radiographic and histopathologic features, presence of specific autoantibodies, and other laboratory findings.(6-8) Certain CTD subsets are characterized by autoantibodies that are highly specific for individual diseases as outlined in the Table below. The detection of ANA in certain clinical subsets of CTD is generally dependent on the type of immunoassay employed and the reference intervals.(5,9) Clinically, patients with CTD often present with signs and symptoms that are nonspecific such as fever, weight loss, fatigue, and arthralgias.

Table. Autoantibodies and Clinical Associations with Specific Connective Tissue Diseases

In the Connective Tissue Cascade, serum is tested initially for the presence of ANA and for cyclic citrullinated peptide (CCP) antibodies using solid-phase immunoassays (SPAs). The presence of significantly elevated CCP antibodies is suggestive of RA or risk for developing disease in at-risk individuals.(5,6) However, additional testing for rheumatoid factor (RF) and inflammatory markers, which are not included in the cascade, are important for optimal diagnosis as per the 2010 American College of Rheumatology/European League Against Rheumatism RA classification criteria.(6) The presence of ANA detected with SPAs such as enzyme-linked immunosorbent assay maybe useful in identifying patients with specific CTD subsets (ANA-associated CTD), notably Sjogren’s syndrome, mixed connective tissue disease MCTD), systemic lupus erythematosus.(2,3) The CTD cascade employs a cut-off based on degree of ANA positivity to identify sera for second-order testing for first-line antibodies (dsDNA. SSA, SSB, Scl 70. Centromere B, U1RNP, Smith) and anti-CCP antibodies allowing for identification of the common autoantibodies in the classification criteria for RA, SLE and SSc.(6-8) The decision threshold for performing second-order tests is based on empirical data derived from testing patients with varying levels of ANA and is chosen to minimize testing in situations in which positive results for dsDNA and other antibodies is less likely.(9) However, a negative ANA enzyme immunoassay result does not rule out a diagnosis of CTD as has been reported in a number of studies.(reviewed in 3,10) Therefore, in patients with a strong clinical suspicion of CTD, testing for ANA using HEp-2 IFA may be warranted.(3,10)