ABC of Rheumatology: RHEUMATOID ARTHRITIS—I: CLINICAL FEATURES AND DIAGNOSIS

Clinical features Joint damage

The start of the disease is usually insidious but can be episodic or acute. Rheumatoid arthritis usually presents as a polyarthritis affecting small joints or small and large joints. Early disease is characterised by pain and other cardinal signs of inflammation (heat, swelling, functional loss, and possible erythema over the joints) but not by damage and deformity. If the disease remains active and uncontrolled the inflammation will usually spread to additional joints and gradual irreversible tissue damage will occur, causing deformity and instability of joints. The most serious long term disability is associated with damage to the larger weight bearing joints.

FIG 1

Effect of rheumatoid arthritis on the hand: (left) early changes and (right) later deformity

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Inflammation of other synovial structures is common, and a similar process may occur in tendon sheaths, progressing to serious dysfunction and rupture. The typical rheumatoid deformities—such as ulnar deviation of the fingers, z deformity of the thumb, and swan neck and boutonniere deformities—are mostly due to damage or displacement of tendons. Palpable thickening or nodularity of tendons is common.

The spine—Although rheumatoid arthritis predominantly affects peripheral joints, discovertebral joints of the cervical spine are often affected. This may lead to atlantoaxial subluxation or, less commonly, subluxation at lower levels, with subsequent compression of the spinal cord. The earliest and most common symptom of cervical subluxation is pain radiating up into the occiput. Other symptoms include paraesthesia, sudden deterioration in hand function, sensory loss, abnormal gait, and urinary retention or incontinence.

Effusion of the knee may produce a popliteal (Baker's) cyst. This may rupture to cause diffuse pain and swelling in the calf that mimics deep vein thrombosis.

FIG 2

Magnetic resonance image of cervical spine showing spinal cord compression at C1 and C2.

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FIG 3

Rheumatoid nodule (above) and rheumatoid vasculitis (right).

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Non-articular manifestations

Non-articular manifestations of rheumatoid arthritis are common. Rheumatoid nodules—which affect about a fifth of patients—may occur anywhere but are most common at sites of pressure, notably the extensor surfaces of the forearms and the posterior surface of the Achilles tendon.

A wide variety of other systems may be damaged by the rheumatoid process. Disease of small and sometimes larger blood vessels may be caused by deposition of immune complex in the vascular walls. This can lead to digital infarction, larger skin ulcers, and mononeuritis because of damage to the vasa nervorum.

Renal disease is rare but may occur as a result of amyloidosis, which presents as proteinuria or drug toxicity.

FIG 4

Renal amyloid (Congo red stain.)

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Eye complications

Sjogren's syndrome—The sicca complex results in dry gritty eyes with slight redness but normal vision. It is confirmed with the Schirmer test, which measures the wetting of a strip of sterilised filter paper when one end is placed under the eyelid. It is usually a late feature in women with seropositive rheumatoid arthritis.

Episcleritis is ocular irritation with nodules. Vision is normal.

Scleritis causes severe pain and occasionally reduces vision. There is diffuse or nodular redness, and the end stage of the condition is healing, with atrophy producing a bluish-grey sclera.

FIG 5

Scleritis associated with rheumatoid arthritis

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Felty's syndrome

This is a combination of seropositive rheumatoid arthritis (often with relatively inactive synovitis) with splenomegaly and neutropenia. It is associated with serious infections, vasculitis (leg ulcers, mononeuritis), anaemia, thrombocytopenia, and lymphadenopathy.

Neurological complications

These include entrapment of peripheral nerves (carpal tunnel, ulnar, lateral popliteal, tarsal, etc); mononeuritis multiplex; peripheral neuropathy—either associated with the disease or caused by drugs; compression of nerve roots; and compression of the cervical region of the spinal cord.

Investigations Immune abnormalities

Rheumatoid factors are antiimmunoglobulins, and anti-IgG IgM is the immunological hallmark of rheumatoid arthritis. It is detected with the Rose-Waaler assay, but it is neither universally present in, nor specific for, rheumatoid arthritis: it is found in the sera of 80% of patients with rheumatoid arthritis, but the remainder are persistently seronegative despite otherwise typical disease. These patients may, however, be found to carry rheumatoid factors of other isotypes. The extra-articular features of rheumatoid arthritis are much commoner in patients with high concentrations of rheumatoid factor, but it is a poor guide to the severity of joint disease and to the success or otherwise of treatment.

Antinuclear antibodies may be present in some patients. The test for antinuclear antibody is widely used to screen for systemic lupus erythematosus, but it should be remembered that some patients with lupus will have positive tests for rheumatoid factor while some patients with rheumatoid arthritis will have positive tests for antinuclear antibody. Thus neither test is a universal diagnostic tool.

Indicators of acute phase response

A raised erythrocyte sedimentation rate (or plasma viscosity) and the presence of acute phase proteins such as C reactive protein are commonly found in patients with rheumatoid arthritis, especially when the disease is active. They reflect the severity of acute inflammation and thus may be a reasonable guide to the success of drug treatment, though they are not specific to rheumatoid arthritis. The disease is likely to progress if a raised erythrocyte sedimentation rate (or presence of C reactive protein) persists, but progression can still occur if they do not persist.

Liver function

Tests for liver function may give abnormal results in patients with rheumatoid arthritis. Serum concentrations of transaminases and alkaline phosphatase may be moderately elevated when the disease is active.

Radiography

Radiographs of the hands often are normal at presentation or may show swelling of soft tissue, loss of joint space, or periarticular osteoporosis. Erosions typical of rheumatoid arthritis develop within three years of the start of the disease in over 90% of patients who ultimately develop the erosions.

FIG 6

Radiograph of hands showing rheumatoid erosions.

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Unusual presentations

Symmetrical small joint polyarthritis, with or without large joints also being affected, is the commonest presentation. In elderly patients the start of rheumatoid arthritis may be indistinguishable from polymyalgia rheumatica. Occasionally, rheumatoid arthritis may present as a monoarthritis. Other conditions (such as infection, crystal arthritis, other inflammatory arthritis, etc) must be excluded before a diagnosis of rheumatoid arthritis is made.

Palindromic rheumatism is characterised by recurrent episodes of mostly oligoarticular arthritis that leave no residual clinical or radiological changes. Up to half of patients with this condition later develop typical rheumatoid arthritis, often accompanied by conversion to seropositivity for rheumatoid factor.