Urgent considerations
See Differentials for more details
Septic arthritis
Infectious arthritis should be considered with any acute monoarticular joint involvement, especially in the presence of fever. Risk factors include age >80 years, diabetes mellitus, rheumatoid arthritis, joint surgery, hip or knee prosthesis, skin infection, and human immunodeficiency infection.[15][16][17][18] A recent history of joint surgery or cellulitis overlying a prosthetic hip or knee are the only clinical findings shown to significantly affect the diagnostic probability of non-gonococcal septic arthritis.[16]Staphylococcus aureus and streptococci are the most common organisms in non-gonococcal bacterial arthritis. Gram-negative bacteria or anaerobes should be considered in intravenous drug users or immunocompromised patients.[15] If the diagnosis is missed and appropriate therapy is not instituted early, rapid destruction of articular cartilage can lead to irreversible joint damage. A definitive diagnosis requires arthrocentesis and synovial fluid analysis (including cell count, Gram stain, and culture). An extreme synovial fluid WBC count (>50 x 10^9/L) increases the probability of septic arthritis.[16] Joint aspiration should be carried out before antibiotic therapy is initiated.
Systemic vasculitides
Small- to medium-vessel vasculitis may present with arthralgia, constitutional symptoms, purpura, mononeuritis multiplex, or glomerulonephritis and may suggest a more rapid work-up, with particular attention to multiple organ function. Symptoms of mesenteric ischaemia and evidence of cardiac decompensation or hypertension are suggestive of polyarteritis nodosa.[14] Acute presentations with mononeuritis multiplex, limb or visceral ischaemia, and/or renal compromise should prompt urgent assessment and management. Supportive therapy in addition to high-dose corticosteroids and broad-spectrum antibiotics may be considered in the initial phase of management.
Bacterial endocarditis
Patients often present with peripheral or central emboli or with evidence of decompensated congestive heart failure. Therefore, any patients who present with fever in conjunction with headache, meningeal signs, stroke symptoms, dyspnoea on exertion, orthopnoea, or paroxysmal nocturnal dyspnoea need to be assessed urgently. The management of infective endocarditis is guided by identification of the causative organism and whether the infected valve is native or prosthetic.
Neoplastic carcinomatosis
Patients present with constitutional symptoms, extreme pain, and monoarticular or polyarticular involvement concurrent with non-Hodgkin's lymphoma or acute and chronic leukemia. The arthritis does not respond to conventional therapy.[34][35] Palliative therapy (chemotherapy and radiotherapy) is usually the only treatment option.
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