Autoimmune Myositis antibody screen
| Category | Immunology |
|---|---|
| Test background |
Myositis specific antibodies can be found in dermatomyositis (DM) and polymyositis (PM), idiopathic myositis, anti-synthetase syndrome and CTD overlap syndromes. These are a heterogeneous group of conditions characterised by proximal muscle weakness and non- infective inflammation of skeletal muscle. The anti-synthetase syndrome (ASS) consists of myositis, interstitial lung disease (ILD), mechanics hands, pyrexia, Raynauds and arthritis. Immune mediated necrotising myopathy (IMNM) is a subtype of myositis that presents with very high creatinine kinase (CK) and profound muscle weakness. Muscle biopsies show necrosis with limited infiltration of inflammatory cells. The laboratory tests for a panel of myositis specific and associated antibodies by recombinant immunoblot. The current panel contains Mi-2α, Mi2b, TIF1γ, MDA5, NXP2, SAE1, Ku, PM-Scl100, PM-scl75, SRP and the anti-synthetase antibodies; Jo1 (histidyl-tRNA synthetase), PL7 (threonyl-tRNA synthetase), PL12 (alanyl-tRNA synthetase), EJ (glycyl tRNA synthetase), OJ (isoelucyl tRNA syntheatse), and the non-specific Ro52 antibody. In ASS antibodies to Jo1, PL7 or EJ are associated with more muscle disease, and antibodies to PL7, OJ or PL12 to more severe ILD. Antibodies to SRP and HMGCoA reductase are strongly associated with IMNM. HMGCoA reductase antibodies are also associated with statin induced myositis. Antibodies to Mi2 and SAE are commonly associated with dermatomyositis with mild muscel disease. Antibodies to TIF1γ, NXP2 and MDA5 are seen in around 50% of juvenile dermatomyositis patients and identify distinct disease subsets. In adults TIF1γ and NXP2 is found with myositis-associated cancer. MDA5 antibody in myositis or dermatomyositis is a risk factor for rapidly progressing (ILD) that can result in respiratory failure. Pm/Scl antibodies are seen in scleroderma myositis overlap disease and Ku antibodies in CTD (SLE, Sjogren’s, Scleroderma)-myositis overlap syndromes. McHugh, N., Tansley, S. Autoantibodies in myositis. Nat Rev Rheumatol 14, 290–302 (2018). |
| Clinical Indications |
Suspected myositis |
| Reference range | Negative |
| Sample & container required | Serum (rust top RST tube) |
| Sample volume | 5-10 mL blood (1 mL serum) |
| Turnaround time | 10 days |
| Notes | The laboratory is currently unaccredited for this test due to a change in assay. |