A 33 year Old female With Knee Pain For 2 Days

A 35 year old female presents to the clinic with a complain of pain in the right knee that started 2 days ago. The pain is associated with difficulty in walking but she denies any trauma to her knee. She has swelling ans redness in her right knee joint along with a mild fever. she denies having pain in any other joints of the body, any rash, or photo sensitivity.
Her past history is significant for an episode of acute left big toe arthritis 5 years back,

Physical Examination:

• Erythema, tenderness, pain and restricted range of motion on flexion and extension of the right knee joint.
• All other joints including the left knee are normal on examination.
• No abnormalities detected in any other organ system. 

The picture of her knee joints is shown below:

What is the Differential Diagnosis?

• Gout
• Pseudogout
• SLE
• Gonococcal septic arthritis
• Non-gonococcal septic arthritis
• Osteoarthritis

What diagnostic workup should be done in this case?

• Knee aspiration and synovial fluid analysis.
• X ray right knee
• Complete blood count
• ANA. anti ds DNA, RF
• Blood culture

Knee aspiration was done and on inspection of crystals under polarized light following was seen:

numerous multi-colored needle-shaped crystals against a purple background.

Final Diagnosis: Gout

Case discussion: Gout is an acute monoarticular, crystal induced arthrits. Foot, ankle and knee joints are most commonly affected. 

In gout , crystals of monosodium urate appear as needle shaped intracellular and extracellular crystals. When examined with a polarizing light , they are yellow when aligned parallel to the slow axis of the red compensator but turn blue when aligned across the direction of polarization (i.e they exhibit negative birefringence)

Gout is managed by treating the acute attack with NSAIDs, corticosteroids and colchicine. The long term management is focused in lowering the uric acid levels. 

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