How do you approach evaluation and management of a patient with recurrent monoarticular inflammatory arthritis of unclear etiology? 

Routine testing will not identify Lyme disease, although the WBC count is higher than usual. If the antibiotic does not target B. burgdorferi, recurrence might mean inappropriate therapy previously.

WBC count is WAAAY too high for mere trauma or internal derangement.

Anything else to suggest psorias...

To add to Dr. @Dr. First Last's excellent response (and on the lines of thinking about PsA), reactive arthritis can notoriously cause a "pseudoseptic" joint, especially of the knee. I'd revisit a history of possible infections (GI/genitourinary), inflammatory lower back pain, reexamine the conjuncti...

Love this question!!!

First, I verify that the patient has monoarthritis (localized to the joint) rather than periarthritis (such as bursitis or panniculitis). In this case, it seems the patient truly does have monoarthritis.

Next, I separate between inflammatory causes and mechanical or hemorrhagic...

This is a challenging case. I would obtain an MRI of the affected joint and consider repeat synovial biopsy for histopathology and microbiologic studies. I would also pursue additional testing for culture-negative infections, including targeted PCR testing or broad-range 16S rRNA gene sequencing, de...