Gout: A Clinical Overview
Gout, a metabolic disorder that affects more than six million people in the United States, most commonly presents as an acute inflammatory arthritis—usually manifesting in an acutely painful, tender, and inflamed joint. Because gout can affect every organ system, however, patients with gout are vulnerable to other significant pathologies that may also require timely intervention.
The social history should address alcohol use or abuse. The clinician should also inquire about how gout is impacting the daily life of the patient. Diet and exercise habits should be assessed37 (see “Patient Education,” below).
PHYSICAL EXAMINATION
The physical exam begins with evaluation of the skin and extremities for the classic features of gout. Affected joints will be exquisitely tender, and patients may be febrile. Most cases are monoarticular, but polyarticular involvement is likely in patients with advanced disease (and can, particularly in women, be mistaken for rheumatoid arthritis).2,16 In patients with chronic tophaceous gout, there may be whitish-yellow skin deposits, subcutaneous nodules, and areas of taut skin. The lower-extremity joints and tendons, as well as the wrists, fingers, and elbows, are commonly affected16 (see Figure 2).
DIAGNOSIS
Diagnostic criteria that are currently available (and have long been in use) include the American College of Rheumatology/American Rheumatism Association (ACR/ARA) preliminary criteria,34 the New York criteria,21 and the Rome criteria.38 The specifics of each are listed in Table 2.21,34,38,39
The gold standard for gout diagnosis is detection of MSU crystals in a sample of synovial fluid aspirated from the affected joint or from a tophus and examined by polarized light microscopy.24 This is of significant importance to the clinician who is faced with a questionable diagnosis.16 However, crystal visualization is not ordinarily available to the primary care clinician,2,17,40 and it is not always necessary if a careful history and physical exam are conducted in a patient with hyperuricemia or other risk factors for gout. A presumptive diagnosis may be acceptable in a patient with the classic presentation of acute gout: rapid onset of severe pain in a swollen, erythematous joint and symptoms peaking within 24 hours. The presence of tophi is pathognomonic for chronic tophaceous gout.41
In cases of questionable or unusual manifestation of gout, however, various imaging techniques and crystal visualization may be indicated.32
In order to compare the effectiveness of the latter technique with conventional diagnostic criteria for gout, Malik et al39 conducted a pilot study involving 82 patients who had undergone synovial fluid analysis with polarized light microscopy. Patients were surveyed about the clinical features of their disease, as listed in the three standard sets of criteria for diagnosis of gout. Compared with the “gold standard” of urate crystal detection (which is one of the Rome criteria38), the study authors found the ACR/ARA preliminary criteria,34 the New York criteria,21 and the Rome criteria38 generally unsatisfactory.
In the study, among patients with confirmed presence of MSU crystals:
• 87% reported more than one attack of acute arthritis (ACR/ARA34)
• 86% reported monoarthritis attack (ACR/ARA34)
• 89% had hyperuricemia (ACR/ARA34 and Rome,38 with the latter giving effective, specific parameters)
• 100% had negative results on joint fluid culture (ACR/ARA34)
• 90% reported an attack starting at night (ACR/ARA34).
The positive predictive values for these signs and symptoms are 38%, 39%, 74%, 50%, and 45%, respectively, according to Malik et al.39 The presence of tophi (cited by all three sets of criteria but “proven or suspected” in the ACR/ARA34) had the highest positive predictive value for gout (91%) and a likelihood ratio of 15.56, which was at least three times higher than any of the other listed criteria. A verified response to colchicine, one of the New York criteria,21 had the second highest positive predictive value at 86%.39
In summary, the ACR/ARA,34 the New York,21 and the Rome criteria38 had specificity of 79%, 83%, and 89%, respectively; sensitivity of 70%, 70%, and 67%, respectively; and positive predictive values for gout of 66%, 70%, and 77%, respectively. The Rome criteria38 had the highest specificity and highest positive predictive value, perhaps making them most helpful for clinicians who lack access to synovial fluid analysis.
DIFFERENTIAL DIAGNOSIS
Conditions to be considered and ruled out before a diagnosis of gout can be made are:
• Pseudogout
• Septic arthritis
• Psoriatic arthritis
• Rheumatoid arthritis
• Erosive osteoarthritis
• Bacterial cellulitis
• Sarcoid arthropathy.16,28,42,43
Unlike gout (in which compensated polarized light microscopy reveals needle-shaped urate crystals with strong negative birefringence), pseudogout is characterized by calcium pyrophosphate dihydrate crystals; these are rhomboid-shaped, with weak positive birefringence.42 Additionally, radiographic imaging will reveal soft tissue swelling and chondrocalcinosis of the joint in pseudogout.44
The patient with septic arthritis, most likely affecting the knee, will have a white blood cell (WBC) count exceeding 50,000/mm3 and a positive culture of the synovial fluid, with absence of crystals.28
Chronic tophaceous gout can mimic rheumatoid arthritis in appearance and joint distribution, and patients affected by either condition may develop a positive rheumatoid factor. Examination of synovial fluid for MSU crystals and radiographic imaging will be of value in making a distinction.
