1 What is the most common form of arthritis?

Osteoarthritis (at least 75% of cases), which is also called degenerative joint disease (Fig. 35-1).

2 If the cause of arthritis is in doubt, what should you do?

When in doubt, or if you suspect something other than osteoarthritis, obtain a radiograph of the affected joint and aspirate fluid. Examine the fluid for cell count and differential, glucose, bacteria (Gram stain and culture), and crystals.

3 How do you distinguish among the common causes of arthritis?

4 What other clues point to a diagnosis of osteoarthritis?

Osteoarthritis typically occurs in those older than age 40 years and has few signs of inflammation on examination, thus the joints are not hot, red, or tender like in the other four types of arthritis listed earlier. Look for Heberden nodes (visible and palpable distal interphalangeal [DIP] joint osteophytes; Fig. 35-2) and Bouchard nodes (proximal interphalangeal [PIP] joint osteophytes), worsening of symptoms after use and in the evening, bony spurs, and increasing incidence with age. Treat with weight reduction and as-needed nonsteroidal antiinflammatory drugs (NSAIDs) or acetaminophen.

5 What clues point to a diagnosis of rheumatoid arthritis?

Rheumatoid arthritis often causes systemic symptoms (fever, malaise, subcutaneous nodules, pericarditis, pleural effusion, uveitis), prolonged morning stiffness, and swan neck and boutonnière deformities. The diagnosis is often made by an elevated sedimentation rate or C-reactive protein (CRP) and positive rheumatoid factor, which is present in most adults but often negative in children. Radiographs and magnetic resonance imaging (MRI) can also support the diagnosis. General treatment strategies reflect the fact that the destruction of affected joints caused by inflammation occurs early in the course of rheumatoid arthritis. The patient should be offered treatment with disease modifying antirheumatic drugs (DMARDs) as soon as possible after the onset of disease. Escalate the intensity of treatment until synovitis and inflammation have improved.

There are five general classes of medications used for the treatment of rheumatoid arthritis, with DMARDs forming the backbone of treatment. Treatment options include the following: analgesics (from acetaminophen to narcotics), NSAIDs, glucocorticoids, nonbiologic DMARDs (methotrexate, sulfasalazine, leflunomide, hydroxychloroquine, and minocycline), and biologic DMARDs. Biologic DMARDs include tumor necrosis factor (TNF) inhibitors (etanercept, infliximab, and adalimumab), an interleukin-1 receptor antagonist (anakinra), a monoclonal antibody (rituximab), and biologic response modifiers (abatacept).

6 What clues point to a diagnosis of gout?

Gout classically begins with podagra (gout in the big toe). Also look for high uric acid levels (not always present), tophi (subcutaneous uric acid deposits that look like punched-out lesions on bone radiographs), needle-shaped crystals with negative birefringence in the joint fluid, and male gender (more commonly affected than female gender). Alcohol and protein-rich foods may precipitate an attack. Colchicine or NSAIDs (but not aspirin, which causes decreased excretion of uric acid by the kidney) are used for acute attacks. For maintenance therapy, high fluid intake, alkalinization of the urine, and/or allopurinol or probenecid (neither drug is for acute attacks) may be used.

7 What causes pseudogout? How is it diagnosed?

Pseudogout is caused by deposition of calcium pyrophosphate crystals into joints. Look for rhomboid crystals with weakly positive birefringence (vs. negative birefringence with gout crystals in the joint fluid).

8 What clues point to a diagnosis of septic arthritis? What are the common causes?

In septic arthritis, Gram stain usually reveals bacteria in the synovial fluid. Staphylococcus aureus is the most common organism except in sexually active young adults, in whom the most common pathogen is Neisseria gonorrhoeae. Obtain blood cultures in addition to synovial fluid cultures because the pathogen usually reaches the joint via the hematogenous route. Also obtain urethral swabs and cultures in appropriate patients.

9 Name some other causes of arthritis

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