Infection of joints is fortunately uncommon but is important because of the damage it produces. The possibility of infection as a cause of arthritis must always be kept in mind. If its presence is suspected, synovial fluid must be obtained for culture. Infection with pyogenic organisms (septic arthritis) can be caused by a number of bacteria, including mycobacteria. Arthritis also occurs with viral infections and less commonly from infection with spirochaetes or fungi. Apart from direct infection, arthritis can also occur as a result of an immunological reaction to infection elsewhere.
Septic arthritis results from infection of joints with pyogenic organisms, of which Staphylococcus aureus is the commonest. It can also occur with other types of staphylococci, streptococci, Neisseria or Gram-negative bacilli. Organisms reach the joint in septic arthritis via the bloodstream, sometimes from an identifiable site of infection such as otitis media or a boil. Less commonly, infection spreads from osteomyelitis adjacent to the joint or the organism is introduced directly as a result of trauma, surgery or intra-articular injection.
Septic arthritis particularly occurs at the extremes of life and in immunologically compromised individuals, e.g. patients receiving immunosuppressive drugs or with RA.
The clinical features of septic arthritis are similar for all the different causative organisms. The presentation is usually dramatic. The patient typically presents with a single painful joint, often the knee. The joint is red, warm and swollen, with a demonstrable effusion. Fever is usual and there may be evidence of infection elsewhere. In RA, the presentation may be misleading; patients are often afebrile and do not necessarily have a systemic reaction or a leucocytosis. Any suddenly painful joint in a patient with RA should be aspirated to exclude infection. Systemic and local reactions can also be absent in patients receiving corticosteroids.
ASPIRATION OF THE JOINT is the only important diagnostic manoeuvre . The synovial fluid is often purulent and typically contains over 50000 x 106/litre white blood cells, predominantly neutrophils. A Gram stain may show the presence of organisms. Culture of the fluid, including special techniques for detecting anaerobes and gonococci, usually gives a definite answer.
BLOOD LEUCOCYTOSIS may be present.
BLOOD CULTURE may be positive.
X-RAYS are of no value in the diagnosis of septic arthritis; they become abnormal only when joint destruction is advanced.
This should be started immediately the diagnosis is made, as cartilage destruction can occur within a few days of the onset of the joint infection and the situation can be life-threatening. The joint should be immobilized.
The choice of antibiotic will depend upon the organism concerned. If the identification of this is delayed, ‘blind’ therapy should be started immediately with a slow i.v. infusion of flucloxacillin 500 mg 6-hourly together with clindamycin 300 mg i.v. 6-hourly or fusidic acid 500 mg 8-hourly by mouth. Antibiotics given by the intramuscular or intravenous route will pass into joints, especially when they are inflamed; antibiotics should not be injected intra-articularly. Antibiotic levels in the synovial fluid should be checked during the acute illness. Antibiotics should be continued for 6 weeks.
Drainage of infected joints is best achieved by needle aspiration, which should be performed daily until no further fluid is obtainable. For inaccessible joints such as the hip, surgical drainage may be required. If infection is allowed to continue, debris that cannot be removed with a needle collects within the joint and this delays recovery. In these circumstances, the effusion will fail to resolve and surgical debridement will be required.
The resolution of septic arthritis with complete recovery usually occurs within a few days or weeks.
SPECIFIC TYPES OF BACTERIAL ARTHRITIS
Of patients with tuberculosis, 1% have skeletal involvement. Tuberculous arthritis affecting children usually occurs in the primary stage of the disease. In adults, it is invariably secondary to pulmonary or renal disease and is due to haematogenous spread to the subchondral bone or the spinal intervertebral discs. Predisposing factors for tuberculous arthritis are those for developing tuberculosis anywhere in the body, e.g. alcohol dependence, diabetes mellitus or any other chronic debilitating disease.
The synovial membrane and periarticular tissues become inflamed and oedematous; histologically, caseating granuiomas are seen. Later there is destruction of cartilage and this may lead to fibrous ankylosis. When the spine is involved, the infection may track along the fascial planes to produce a psoas abscess.
There is usually a monoarticular arthritis affecting the hip or knee (30%) or the sacroiliac or other joints (20%); in 50% of patients there is spinal involvement. There is an insidious onset of pain and dysfunction of the joint, with swelling and synovial proliferation very like that seen in RA, and restriction of movement associated with general symptoms of malaise, anorexia and night sweats.
The mycobacterium may be cultured from the synovial fluid; however, negative results do not exclude the diagnosis and if suspicion remains, synovial biopsy is required. X-rays are at first normal but later there is narrowing of the joint space and bony erosions.
Drug treatment is as for tuberculosis elsewhere. The joint should be immobilized in the acute phase. If infection is allowed to continue, the effusion cannot be aspirated via a needle because of debris and surgical debridement is necessary.
Meningococcal arthritis usually occurs as part of a generalized meningococcal septicaemia. It is a migratory polyarthritis and organisms cannot usually be recovered from the synovial fluid. Joint destruction does not occur. This type of arthritis is due to circulating immune complexes containing meningococcal antigens. Occasionally the effusion is purulent and contains meningococcal organisms. Treatment is with penicillin.
Gonococcal arthritis is similar to meningococcal arthritis. It particularly affects young adult females and also homosexual men. It presents with a mildly inflammatory polyarthritis. It is usually asymmetrical and occasionally migratory. A useful clue to the diagnosis is the presence of small pustular skin lesions, often near the affected joints. The organism can be recovered from the bloodstream and in 25% of cases from the joints. In the remainder the arthritis is a reaction to the infection, and is probably immunologically mediated. If neglected, gonococcal septicaemia may go on to produce a typical septic arthritis. Treatment is with penicillin 1 g orally, daily for 2 weeks.
Salmonella infection differs from septic arthritis in being polyarticular. It is also less dramatic than septic arthritis and is therefore easily missed. It occurs with types of Salmonella that invade the bloodstream rather than staying within the gastrointestinal tract. Gastrointestinal features may therefore be minor or absent, deflecting attention away from the correct diagnosis. Treatment with systemic antibiotics, e.g. i.v. amoxycillin 500 mg 6-hourly, is curative.
Arthritis is seen in patients with Lyme disease, first described in the USA but now known to occur throughout the world. It is caused by a spirochaete, Borrelia burgdorferi (which has recently been detected in synovial fluid by rcn) and is transmitted from deer by a tick. It occurs mainly in children and is easily mistaken for Still’s disease. The arthritis is characteristically episodic with attacks of arthritis affecting about three large joints and lasting 1 week but may eventually become chronic. There are associated skin lesions, erythema chronicum migrans and a variety of other manifestations, particularly neurological, have been described.
Infective endocarditis may present with arthritis, which occurs particularly in the early stages of the disease. Like other clinical features, the arthritis may be due to circulating immune complexes; direct infection of the joints is much less common. Asymmetrical arthritis of a few large joints is characteristic, but other patterns may occur. Localized back pain associated with fever is another manifestation.
A number of different viral infections cause arthritis. The commonest and most important is rubella, where the virus can occasionally be isolated from the joint. Arthritis particularly a complication of the disease in young adult females, occurring in 15% of cases. Arthritis may follow either rubella or the rubella vaccine. It begins a few days after development of the rash, or 2 weeks after vaccination. It may be associated with other complications such as lymphadenopathy. It presents as a bilateral, symmetrical polyarthritis, closely resembling RA, for which it is often mistaken. However, it resolves within a few weeks in most cases. Occasionally there is persistent or recurrent arthralgia that may continue for years. Treatment is symptomatic. Arthritis may also complicate mumps. A few large joints are typically affected and, as in rubella, the condition is self-limiting.
Arthralgia and sometimes arthritis may be features of the prodromal stage of hepatitis B infection, but resolve when the jaundice appears. As in meningococcal arthritis, this prodromal syndrome is associated with circulating immune complexes. Patients with Reiter’s syndrome or psoriatic arthropathy may develop a severe exacerbation following HIV infection.
Human parvovirus B19 (see p.49) causes an acute asymmetrical short-lived polyarthritis in adults, particularly women. It often occurs without the rash. A specific anti-B19 IgM antibody is found in the serum. Transient polyarthritis is also seen in infectious mononucleosis, chickenpox and other viral infections.
FUNGAL AND OTHER INFECTIONS
Fungal infections of joints occur rarely. Actinomycosis can affect the mandible or vertebrae. Bone abscesses may be seen. Destructive joint lesions can also occur with blastomycosis. A benign polyarthritis accompanied by erythema nodosum occasionally occurs in coccidioidomycosis and histoplasmosis. Culture of purulent synovial fluid and skin tests for fungi may help the diagnosis.