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e-TABLE 94.13 CLINICAL AND LABORATORY FEATURES DIFFERENTIATING PYOGENIC SEPTIC ARTHRITIS FROM LYME ARTHRITIS Variable Pyogenic Lyme disease Clinical Swollen, exquisitely tender Refusal to bear weight Range of motion severely limited Fever is common Joint erythema is common Swollen, less tender than with pyogenic arthritis Usually can walk without difficulty Range of motion diminished, but can still flex and extend to some degree Fever is uncommon Joint erythema is less common Laboratory a ESR/CRP elevated ESR/CRP normal or elevated Synovial fluid WBC Synovial fluid—variable, and over ½ >100,000 cells/mm3 have synovial fluid WBC >100,000 cells/mm3 Does not improve Can have spontaneous resolution after without treatment several weeks Outcome a Data from Dart AH, Michaelson KA, Aronson PL, et al Hip synovial fluid cell counts in children from a Lyme disease endemic area Pediatrics 2018;141(5):e20173810 ESR, erythrocyte sedimentation rate; CRP, C-reactive protein; WBC, white blood cell count