Differential Diagnosis

• Single most likely diagnosis
  • C. Psoriasis arthritis: The patient is a known case of psoriasis and presents with multiple joint pain (right big toe, right ankle, and bilateral knee pain) which is not typical for gout. Psoriatic arthritis often presents with oligoarthritis or polyarthritis, and the patient's lack of response to allopurinol (a medication primarily used for gout) suggests that the current symptoms may not be due to gout.
• Other Likely diagnoses
  • B. Active gout arthritis: Although the patient was initially diagnosed with gout and is on allopurinol, the presence of high uric acid levels and the recurrence of symptoms could suggest active gout, especially if the allopurinol dose is not adequate or if the patient is not adherent to the medication.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • A. Active pseudo-gouty arthritis: This condition, also known as calcium pyrophosphate deposition disease (CPPD), can mimic gout and other forms of arthritis. It's less likely given the patient's history of psoriasis, but missing a diagnosis of pseudo-gout could lead to inappropriate treatment and potential worsening of symptoms.
• Rare diagnoses
  • Other rare forms of arthritis, such as rheumatoid arthritis or infectious arthritis, could be considered but are less likely given the patient's history and presentation. However, they should be kept in mind if the patient does not respond to treatment for the more likely diagnoses.