Differential Diagnosis for Knee Pain, Redness, and Warmth
- Single Most Likely Diagnosis
- Septic Arthritis: This condition is characterized by joint pain, redness, warmth, and swelling, often due to a bacterial infection. The knee is a commonly affected joint, and the presentation matches the symptoms described.
- Other Likely Diagnoses
- Gout: An inflammatory arthritis that can cause sudden, severe pain, redness, and warmth in the affected joint, often the knee. Urate crystals in the joint fluid are diagnostic.
- Pseudogout (Calcium Pyrophosphate Deposition Disease, CPPD): Similar to gout, but caused by calcium pyrophosphate dihydrate crystals. It can present with acute knee pain, redness, and warmth.
- Osteoarthritis with an acute inflammatory flare: While typically a chronic condition, osteoarthritis can have acute flares that present with increased pain, redness, and warmth due to inflammation.
- Meniscal Tear or Ligament Sprain: Acute injuries to the knee can cause pain, swelling, and sometimes warmth and redness due to the inflammatory response.
- Do Not Miss Diagnoses
- Septic Bursitis: Infection of the bursae around the knee can present similarly to septic arthritis and requires prompt antibiotic treatment.
- Osteomyelitis: Bone infection that can cause pain, redness, and warmth over the affected bone. It's less common in the knee but critical to diagnose early.
- Deep Vein Thrombosis (DVT): While DVT typically presents with swelling and pain in the calf, it can occasionally present with redness and warmth in the thigh or knee area. It's a medical emergency due to the risk of pulmonary embolism.
- Rare Diagnoses
- Rheumatoid Arthritis (RA) flare: While RA is not rare, an acute flare presenting for the first time with significant knee involvement might be less common. It's an autoimmune disorder that causes inflammation in the joints.
- Hemarthrosis: Bleeding into the joint space, which can occur due to trauma, bleeding disorders, or anticoagulant use. It's less common but can present with acute pain, swelling, and possibly warmth.
- Neuropathic Arthropathy (Charcot Joint): A condition that occurs in people with nerve damage (usually due to diabetes or syphilis), leading to progressive degeneration of a weight-bearing joint, which can present with pain, redness, and warmth.