Differential Diagnosis for Soft Tissue Swelling of the IP Joint

Single Most Likely Diagnosis

• Pseudogout (Calcium Pyrophosphate Deposition Disease, CPPD): This condition can present similarly to gout, with sudden onset of joint pain and swelling, but it does not respond to colchicine. The absence of erythema does not rule out pseudogout, as it can sometimes present without significant inflammation.

Other Likely Diagnoses

• Osteoarthritis: While osteoarthritis is more chronic, an acute flare can cause soft tissue swelling around the IP joints. The lack of response to colchicine and absence of erythema could suggest osteoarthritis, especially if there's a history of joint pain or trauma.
• Trauma or Sprain: Acute injury to the IP joint can cause swelling that does not respond to colchicine. The history might reveal a recent injury, and the physical exam could show tenderness and limited range of motion.
• Infectious Arthritis: Although less likely given the absence of erythema, infectious arthritis (septic arthritis) can present with joint swelling and does not respond to colchicine. It's crucial to consider this diagnosis, especially if there's a history of recent infection or immune compromise.

Do Not Miss Diagnoses

• Septic Arthritis: As mentioned, this is a critical diagnosis to consider due to its potential for severe consequences, including joint destruction and systemic infection. Even without erythema, septic arthritis should be ruled out, especially in immunocompromised patients or those with a history of intravenous drug use.
• Ganglion Cyst: While typically not an emergency, a ganglion cyst can cause soft tissue swelling around the IP joint. It's essential to consider this diagnosis to avoid missing a condition that might require surgical intervention.

Rare Diagnoses

• Hemochromatosis: This genetic disorder can lead to iron deposition in joints, causing arthritis and swelling. It's a rare condition but should be considered in patients with unexplained joint symptoms and other signs of iron overload.
• Sarcoidosis: This systemic disease can cause arthritis and joint swelling, including in the hands. It's rare but should be considered in patients with other symptoms suggestive of sarcoidosis, such as lung disease or skin lesions.
• Amyloidosis: Amyloid deposits can accumulate in joints, leading to swelling and arthritis. This condition is rare and typically associated with other systemic symptoms, but it should be considered in the differential diagnosis of unexplained joint swelling.