ENA

The term “ENA” stands for “Extractable Nuclear Antigens.” The ENA panel is a group of tests used to detect the presence of specific autoantibodies against these antigens in the serum. The antibodies are associated with a variety of connective tissue diseases and autoimmune disorders. Here are some of the specific antibodies that might be tested in an ENA panel and the diseases they are associated with:

1. Anti-SSA (Ro) and Anti-SSB (La):
   1. Sjögren’s Syndrome: Primary Sjögren’s is a common association, especially in those with positive anti-SSA/Ro antibodies.
   2. Systemic Lupus Erythematosus (SLE): Especially those with cutaneous manifestations or neonatal lupus.
2. Anti-Sm:
   1. Systemic Lupus Erythematosus (SLE): The presence of anti-Sm antibodies is highly specific for SLE, although it’s not found in all SLE patients.
3. Anti-RNP (Ribonucleoprotein):
   1. Systemic Lupus Erythematosus (SLE)
   2. Mixed Connective Tissue Disease (MCTD): High titers are especially characteristic of MCTD.
4. Anti-Topoisomerase I (Scl-70):
   1. Systemic Sclerosis (Scleroderma): Particularly associated with the diffuse cutaneous form.
5. Anti-Centromere:
   1. Systemic Sclerosis (Scleroderma): More commonly associated with the limited cutaneous form, often referred to as CREST syndrome (Calcinosis, Raynaud’s phenomenon, Esophageal dysmotility, Sclerodactyly, and Telangiectasia).
6. Anti-Jo-1 (and other anti-synthetase antibodies):
   1. Associated with anti-synthetase syndrome, which often presents with myositis, interstitial lung disease, non-erosive arthritis, and other features.
7. Anti-dsDNA:
   1. Systemic Lupus Erythematosus (SLE): This antibody is quite specific for SLE and is often associated with lupus nephritis.
8. Anti-Histone:
   1. Drug-Induced Lupus: Certain medications can induce a lupus-like syndrome, and patients with drug-induced lupus often have positive anti-histone antibodies.
9. Anti-PM/Scl:
   1. Overlap syndrome between systemic sclerosis (scleroderma) and polymyositis/dermatomyositis.
10. Anti-Ku:
    1. Associated with overlap syndromes of SLE, systemic sclerosis, and inflammatory myopathies.

While ENA antibodies can be helpful in the diagnosis and classification of connective tissue diseases, the results should always be interpreted in the context of the clinical picture. Not all patients with these conditions will have positive ENA antibodies, and not all patients with positive ENA antibodies will have or develop these conditions. Clinical judgment, physical examination, and comprehensive evaluation are critical.