Acute pseudogout presenting as an exception to Musculoskeletal Infection Society criteria in total knee arthroplasty: a case report

Abstract

In this case, a 78-year-old female with no previous medical history of crystalline arthropathy presented with pain, effusion, and erythema about a total knee arthroplasty (TKA) performed 13 years prior. Implementation of a novel synovial fluid alpha-defensin assay ruled out periprosthetic joint infection (PJI) despite a positive 2018 Musculoskeletal Infection Society (MSIS) minor criteria score of 8 points, a significant diagnostic differentiation which prevented secondary invasive debridement or joint irrigation intervention. Confirmatory histologic study was positive for calcium pyrophosphate crystals, indicative of acute pseudogout inflammation rather than PJI or septic arthritis manifestation. The patient was then conservatively managed medically for a pseudogout flare and had no evidence of infection with normal physical exam and laboratory study at one- and two-years post treatment, respectively. Given the predominantly clinical nature of current PJI assessment in-clinic coupled with notable risks associated with aggressive re-intervention in the setting of suspected infection, critical need exists for the maturation of sensitive, reliable empiric measures which may assist in guiding orthopaedic surgeon evaluation of patients presenting with inflammatory symptomology around a previous surgical site. In this case, we conclude that patients with a negative alpha-defensin assay alongside crystalline arthropathy on histology may be cautiously yet successfully treated non-operatively despite clinical MSIS criteria concerning for PJI.

Keywords: Musculoskeletal Infection Society (MSIS) criteria; Pseudogout; alpha-defensin; calcium pyrophosphate dihydrate (CPPD); case report; periprosthetic joint infection (PJI).

Figure 1

Radiographs taken on office presentation with erythematous, painful, swollen knee. Hardware components are in satisfactory alignment without any significant osteolysis thirteen years after index total knee arthroplasty.

Figure 2

Cytopathologic findings on CPPD depositions. (A) Aggregate of crystals on fine needle aspirate, Diff-Quik stain; (B) aggregate of crystals and few mononuclear cells, FNA cell-block, H&E stain; (C) birefringent crystals on polarized light microscopy of same area from cell block; (D) darkfield image showing crystals, same area from cellblock; (E) aggregate of crystals surrounded by mononuclear and multinucleated giant cells in tissue section, H&E stain; (F) SEM/EDS of cellblock material, showing crystals at low and higher magnification, and EDS spectrum confirming presence of Ca and P in a single crystal (arrow). Reproduced from Naqvi et al. (CytoJournal, 2008) (21).

Figure 3

Case report clinical and histopathologic timeline. Representative depiction of described time-course and relevant clinical progression for patient within the present case report.