Monoarticular Arthritis

Acute Monoarticular Arthritis

Pretest Probabilities

In otherwise healthy adult patients, acute monarthritis is usually caused by gonococcal arthritis or gout.
Gonococcal arthritis typically occurs in healthy young persons.
Acute gouty arthritis is uncommon in pre-menopausal women.
Co-occurrence of gout and rheumatoid disease is rare.
Nongonococcal joint infection usually occurs in elderly and chronically ill patients.

Diagnostic Strategies

In virtually all cases of monarthritis, joint aspiration and synovial fluid analysis are essential to making a definitive diagnosis for infectious and crystal-induced arthritis (Table 3). A clinical history of gout and identification of a tophus may provide near certainty without a joint aspirate. The serum uric acid is a poor test for the presence or absence of gout. A Gram stain and culture should be obtained in the elderly or chronically ill patient, regardless of crystal examination results. Gram stain of synovial fluid is fairly sensitive for nongonococcal joint sepsis. Gonococcal arthropathy is rapidly responsive to antibiotic therapy. A therapeutic trial may be the only method to confirm the diagnosis.

In a previously healthy young woman with monarthritis,
gonococcal disease should be presumed present if gout cannot be proved by crystal examination. Although Gram stain or cultures of joint fluid are positive in less than 25% of cases, the chance of a bacteriologic diagnosis is vastly improved by culturing the blood, urinary tract, and all other possible sources of gonococcal bacteremia (1). A prompt response (48 to 72 hours) to appropriate antibiotics supports the diagnosis.
A similar strategy applies to young men, unless they have a tophus or more than four criteria for the diagnosis of gout.

In healthy older men and postmenopausal women,
gout becomes more likely. In the absence of a diagnosis supported by crystal examination or Gram stain, five or more clinical criteria strongly suggest gout, especially if clinical features of disseminated gonococcal disease are absent. In the absence of five or more criteria for gout, empiric treatment for gonococcal disease may be given as a therapeutic and diagnostic maneuver, anticipating prompt response to antibiotics or confirmation by culture results.

In the elderly or chronically ill patient with acute monarthritis, joint sepsis should be suspected even in the absence of fever and leukocytosis. Treatment for joint sepsis should be initiated unless crystals are identified and the Gram stain is negative. The presence of hyperuricemia (which may be due to renal insufficiency, salicylates, or diuretics) is difficult to interpret in this group and should not influence therapy.

Differential Diagnosis of monoarticular arthritis:

Infectious or Septic Arthritis
Historically, gram-positive organisms (particularly Staphylococcus aureus) have been the most common etiologic pathogens in patients with septic arthritis. The spectrum of septic arthritis has changed gradually. Gram-negative, mycobacterial, or fungal infections, which were previously rare causes of joint space infections, are now seen more commonly in clinical practice. This change in disease expression is likely due to the presence of comorbid diseases or aberrant immune surveillance in seriously ill patients. Most cases of bacterial arthritis develop because of transient bacteremia and secondary hematogenous spread of pathogens (for example, following dental or urologic procedures) or because of sustained intravascular sepsis (for example, in an immunocompromised host).

Fungal or mycobacterial pathogens should be considered in immunocompromised hosts with new-onset synovitis or in patients with unexplained monoarticular arthritis. Diagnosis usually requires synovial biopsy with appropriate diagnostic stains and cultures. Infection with the recently characterized etiologic agent of Whipple's disease (Tropheryma whippelli) may result in multisystem disease, including a peripheral arthritis that may antedate signs or symptoms of intestinal malabsorption; synovial biopsy or jejunal biopsy may be useful in establishing the diagnosis of this disorder.

Psoriatic Arthritis
The patterns described include: (1) a symmetric polyarthritis similar to seronegative RA, which is seen in about 25% of all patients with psoriasis and arthritis; (2) monoarticular or pauciarticular arthritis, which may include sausage digits; (3) spondylitis or sacroiliitis, which occurs more often in the patients who also have arthritis of pattern 2 than it does as an isolated entity; (4) distal interphalangeal joint arthritis, which frequently accompanies psoriasis of the corresponding nails; and (5) a severe destructive arthritis ("arthritis mutilans"), with ankylosis of some joints and dissolution of juxta-articular bone at others. This is the most severe type, but rare.

Other CrystalsOther Crystals Associated with Arthritis
Acute arthritis, including podagra, bursitis, and tendonitis, has been associated with calcium oxalate crystals due to primary oxalosis or oxalate accumulation secondary to end-stage renal failure. Although cholesterol and other lipid crystals are frequent in rheumatoid synovial and bursal effusions, they have recently been suggested as a rare cause of acute monoarthritis, bursitis, and unexplained polyarthritis. Eosinophilic monoarticular synovitis following minor trauma in allergic patients has been linked to the presence of Charcot-Leyden crystals. Other rare causes that have been hypothesized to result in crystal-induced arthritis include crystals due to immunoglobulin, cystine, xanthine, hypoxanthine, and aluminum phosphate.

Of 117 patients followed for a mean of 2 years, 17 developed monoarticular or polyarticular arthritis, usually in the setting of advanced HIV infection. "Rheumatic symptoms and human immunodeficiency virus infection. The influence of clinical and laboratory variables in a longitudinal cohort study." Arthritis Rheum. 1991:34:257-63.