These are found in the antiphospholipid syndrome, which is described Antineutrophil cytoplasmic antibodies (ANCA) These are detected by immunofluorescence and by enzyme-linked immunosorbent assay (ELISA) in the serum, and are of two types:
1 cANCA (cytoplasmic staining) is directed against serine proteinase C.
2 pANCA (perinuclear staining) is mainly directed against myeloperoxidase. cANCA is seen in Wegener’s granulomatosis with a specificity of about 90%. It is found in 50% of early cases and almost 100% of cases with full-blown systemic disease. It disappears with treatment and rising titres may predict relapse, making it a very useful marker of progress. It is very occasionally found in other types of vasculitis such as microscopic polyarteritis.
pANCA is much less specific and is found in:
• Various types of vasculitis including microscopic polyarteritis, Churg-Strauss syndrome and sometimes polyarteritis nodosa
• Rheumatoid arthritis
• Connective tissue disorders such as SLE and Sjogren’s syndrome, not necessarily associated with vasculitis
• Chronic inflammatory bowel disease, in primary sclerosing cholangitis and in autoimmune hepatitis
• Drug treatment, e.g. hydralazine.
A raised serum uric acid is a good confirmatory test for gout, but is not diagnostic. A low level of uric acid excludes gout. In known cases of gout, the uric acid level is helpful in deciding treatment.
SYNOVIAL FLUID EXAMINATION
The characteristics of synovial fluid in normal and diseased joints are shown Polarized light microscopy reveals the presence of negatively birefringent crystals in gout. In pyrophosphate arthropathy, crystals of calcium pyrophosphate, which are ‘eakly positively birefringent, are seen. Crystals of hydroxyapatite are too small to be seen in polarized light microscopy and need to be identified using electron microscopy. Gram stain may identify organisms in septic arthritis but the fluid should also be cultured.
X-rays show characteristic abnormalities in many rheumatic conditions; these are described in the appropriate sections. Degenerative changes are present in almost everyone by the age of 65 years and often before; their presence on an X-ray does not necessarily therefore mean osteoarthritis. X-rays are of little value in acute conditions such as
OCCASIONALL Y USEFUL TESTS
“WHITE BLOOD CELL COUNT is useful in infections and eukaemia presenting with arthritis.
RAISED SERUM ALKALINE PHOSPHATASE is characteristicof Paget’s disease (see p. 428) but is also sometimes seen in active rheumatoid arthritis and polymyalgia rheumatica.
A MONOCLONAL PROTEIN BAND on serum electrophoresis is found in myeloma.
RAISED ANTISTREPTOLYSIN-O (ASO) titre indicates recent streptococcal infection. Very high levels are characteristic of rheumatic fever.
HIGH SERUM TRANSFERRIN SATURATION OR FERRITIN LEVEL occurs in haemochromatosis, which may present with arthritis.
Low SERUM COMPLEMENT may be found in the active phase of SLE.
ARTHR0SCOPY is useful for the demonstration of mech anicallesions in the knee joint such as a torn meniscus and if necessary a synovial biopsy can be obtained during the procedure. This investigation is particularly useful in persistent mono articular arthritis, e.g. in tuberculosis.
AN ARTHROGRAM can also be used to visualize the meniscus or to demonstrate knee-joint rupture.
RADIOISOTOPE BONE SCAN is useful in demonstrating malignant deposits. Increased uptake also occurs around osteoarthritic joints and also in inflammatory arthropathies, but these abnormalities can usually be distinguished from malignant disease.
HISTOCOMPATIBILITY ANTIGEN HLA-B27 is found in 96% of patients with ankylosing spondylitis and only 5% of normal people in the UK. There are marked differences between the incidence of the antigen in different populations that roughly parallel the frequency of ankylosing spondylitis. In addition, about 60% of patients with Reiter’s disease are B27 positive.
M R I SCANNING is useful for the detection of mechanical problems in joints, for example a torn meniscus or ruptured cruciate ligament in the knee or a rotator cuff tear in the shoulder. It is also useful to detect avascular necrosis for example in the hip joint, and is replacing myelography for the detection of spinal disease.