Differential Diagnosis for a 60-year-old Male with a Red and Painful Knee
Single most likely diagnosis
- Gout: The patient's elevated uric acid level (9.3) and the acute onset of a red, painful knee with difficulty in movement are highly suggestive of gout, especially given the absence of trauma or fever. Gout often presents with sudden, severe joint pain, typically affecting the base of the big toe but can also affect the knee.
Other Likely diagnoses
- Pseudogout (Calcium Pyrophosphate Deposition Disease, CPPD): This condition can present similarly to gout, with acute joint pain and swelling, and is more common in older adults. The knee is a common site for pseudogout.
- Osteoarthritis with an acute flare: While osteoarthritis is a chronic condition, it can have acute flares that cause significant pain and swelling. The patient's age and the fact that he was biking (which could exacerbate existing joint issues) make this a plausible diagnosis.
- Meniscal tear or other internal derangement of the knee: Although the patient reports no trauma, minor injuries can sometimes be overlooked, and internal knee injuries can cause pain and swelling.
Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Septic arthritis: This is a medical emergency that requires prompt diagnosis and treatment. Although the patient has no fever, septic arthritis can occasionally present without systemic signs of infection, especially in older adults or those with compromised immune systems.
- Deep vein thrombosis (DVT): While less common, DVT can cause leg pain and swelling. Given the patient's recent physical activity (biking), there's a potential increased risk of DVT, and missing this diagnosis could be catastrophic.
Rare diagnoses
- Hemarthrosis: Bleeding into the joint space, which could be due to various causes including anticoagulant use, hemophilia, or vascular malformations. This would be an unusual presentation without a known history of bleeding disorders or anticoagulant use.
- Inflammatory arthritis (e.g., rheumatoid arthritis, lupus): These conditions can cause joint pain and swelling but typically have a more gradual onset and are associated with other systemic symptoms.
- Infection (e.g., Lyme disease, if endemic to the area): Lyme disease can cause arthritis, but this would typically follow a tick bite and might be accompanied by other symptoms like rash or fever.