Connective Tissue Disorders
Some autoantibodies are more specific for rheumatic illness and, in particular, connective tissue diseases and vasculitis.
Anti-double Stranded DNA Antibodies (dsDNA)
- dsDNA autoantibodies are highly specific for SLE and are detected in many (approximately 2/3) children with lupus nephritis.
- Titres can correlate with renal disease activity in some children with SLE.
- Other extractable nuclear antigens (including anti-RNP antibodies, anti-Sm antibodies, anti-Ro and anti-La antibodies) occur with variable frequencies in children with SLE and related connective tissue disorders.
Anti-Neutrophil Cytoplasmic Antibodies
- The clinical settings where antiphospholipid antibodies should be ordered are arterial or venous thrombosis, recurrent miscarriages, or unexplained thrombocytopenia.
- The clinically relevant antiphospholipid antibodies include anticardiolipin (IgG and IgM) and lupus anticoagulant.
- Not all antiphospholipid antibodies are pathogenic and are known to occur in the normal adult population. In view of this, antiphospholipid antibodies should only be considered positive if present on at least two occasions at least three months apart.
- Antiphospholipid antibodies can be found in association with viral infections and may be drug induced.
- Antiphospholipid antibodies may occur in primary antiphospholipid syndrome, JSLE and some vasculitides.
- Children with persistently positive antiphospholipid antibodies should be commenced on prophylactic low-dose aspirin to modify the risk of thromboembolic phenomena.
Autoantibodies in Complex Connective Tissue Diseases
- This group of antibodies exhibit two main patterns of immunofluorescent staining: perinuclear (pANCA) and cytoplasmic (cANCA).
- About 90% of cANCA is directed against proteinase 3 (PR3) and around 70% of pANCA against myeloperoxidase (MPO).
- ANCAs can be detected in chronic infection (including TB, the viral hepatides and HIV), malignancy, inflammatory bowel disease and sclerosing cholangitis and can be drug-induced.
- PR3-ANCA is commonly found in granulomatosis with polyangiitis (previously known as Wegener's granulomatosis) and can be found in microscopic polyangiitis.
- MPO-ANCA is typically associated with microscopic polyangiitis or occasionally with Eosinophilic Granulomatosis with Polyangiitis (EGPA) - formerly known as Churg-Strauss syndrome).
- The autoantibody profile can predict the disease pattern in some children with complex multi-system connective tissue disease.
- Autoantibodies can predict the extent and risk of skin and other organ involvement in systemic sclerosis.
- Anti-topoisomerase 1 (Scl 70) antibody occurs in systemic sclerosis and is associated with lung fibrosis and renal disease.
- Anti-PM-Scl antibody is associated with a combination of myositis and scleroderma.
- Anti-U1RNP antibody is associated with Mixed Connective Tissue Disorders and overlap syndromes.
- Anti-centromere antibody is found in limited cutaneous systemic sclerosis and is associated with an increased risk of pulmonary hypertension.
- Anti-RNA antibody is associated with diffuse cutaneous systemic sclerosis.
- Anti-Jo antibodies predict lung involvement in children with Juvenile Dermatomyositis.
Juvenile Systemic lupus Erythematosus (JSLE) is important to consider in the context of non-specific symptoms of malaise or arthralgia. JSLE is more common in Asian, Africa and First Nations populations, with a predominance of girls affected in the adolescent group and a more equal sex distribution in young children (9:1 female to male ratio in adulthood versus 5:1 in childhood). Extra-articular features are common and include rashes which can be photosensitive and characteristically in malar distribution (over the cheeks, forehead and sparing nasal folds), mouth ulcers, Raynaud's phenomenon and hair loss. The arthritis of JSLE is usually non-erosive and polyarticular, often the pain is the major symptom but there is little objective swelling. Renal involvement can be asymptomatic and suggested by haematuria or proteinuria or raised blood pressure. Investigations in suspected JSLE will need to exclude infection, malignancy and other rheumatic disease. Blood counts, peripheral blood smear, blood cultures, chest radiograph and urinalysis are the basic tests.
The diagnosis of JSLE combines clinical and laboratory features.
Common presenting symptoms of JSLE include:
- Skin - malar rash (photosensitivity), Alopecia, vasculitis rashes, Raynaud ’s phenomenon.
- Arthritis - polyarticular (small joints mainly).
- Constitutional features - fatigue / fever / weight loss / pallor.
- Mucositis - oral / nasal ulcers.
- Pleuritis/pericarditis - chest pain, breathlessness.
- Central nervous system - headaches, seizures, psychosis, neuropathy, worsening school performance).
- Lymphadenopathy, hepatosplenomegaly.
Laboratory findings in JSLE:
- Anaemia (may be haemolytic with positive red cell autoantibodies detected on a Coomb's test or direct antiglobulin test).
- Leukopaenia, lymphopaenia, thrombocytopaenia.
- Elevated liver enzymes (AST, ALT).
- Elevated kidney function tests (blood urea nitrogen, creatinine).
- Decreased complement components C3 and C4.
- Positive antinuclear antibody.
- High titre positive dsDNA antibody.
- Positive autoantibodies to extractable antigens (anti - Ro (SSA); anti - La (SSB); anti - Sm; anti - RNP).
- Positive antiphospholipid antibodies (anti - cardiolipin, lupus anticoagulant) and antihistone antibodies can be present in drug induced lupus (e.g., with anticonvulsants).
- Proteinuria, Haematuria and active urine sediment.