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 initial diagnosis of gout may have been incorrect or that there is a co-existing condition.
• Other Likely diagnoses
  • B. active gout arthritis: Although the patient was initially diagnosed with gout and treated with allopurinol, the presence of high uric acid levels and the recurrence of symptoms could suggest that the gout is not well-controlled. However, the involvement of multiple joints simultaneously is less typical for gout.
  • A. active pseudo-gout arthritis: This condition, also known as calcium pyrophosphate deposition disease (CPPD), can present with acute arthritis, often involving the knee. However, it is less commonly associated with psoriasis compared to gout or psoriatic arthritis.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Septic arthritis: Although not directly suggested by the information provided, any patient presenting with acute joint pain, especially if there's a history of recurrent joint issues, should be evaluated for septic arthritis, which is a medical emergency.
• Rare diagnoses
  • Other rheumatologic conditions: Such as rheumatoid arthritis, although less likely given the patient's history of psoriasis and the specific joints involved.
  • Seronegative spondyloarthropathies: Besides psoriatic arthritis, other conditions in this category (like ankylosing spondylitis, reactive arthritis, enteropathic arthritis) could be considered, but they are less likely given the specific presentation and the lack of other suggestive symptoms.