What is the diagnostic test for Lyme disease arthritis?

Diagnostic Testing for Lyme Disease Arthritis

The recommended diagnostic test for Lyme disease arthritis is two-tiered serologic testing consisting of an enzyme-linked immunoassay (EIA/ELISA) or immunofluorescence assay (IFA) as the first tier, followed by a Western immunoblot if the first tier is positive or equivocal. 1, 2

Diagnostic Algorithm for Lyme Arthritis

1. Two-tiered serologic testing:

   • First tier: ELISA or IFA (detects both IgM and IgG antibodies)
   • Second tier: Western immunoblot (only if first tier is positive/equivocal)
     • For suspected Lyme arthritis (late disease), IgG Western blot is sufficient 1
     • IgG Western blot is considered positive if ≥5 of 10 specific bands are present (18,21-24,28,30,39,41,45,58,66,93 kDa) 2

2. Synovial fluid analysis (adjunctive testing):

   • PCR testing of synovial fluid has >75% sensitivity for Lyme arthritis 1
   • Synovial fluid typically shows:
     • Mild-to-moderate inflammation
     • Median leukocyte count of ~24,250 leukocytes/mm³
     • Predominance of granulocytes 1

Interpretation and Clinical Correlation

• All patients with Lyme arthritis should be seropositive by two-tier testing that includes an ELISA and IgG immunoblot 1
• In a seropositive patient, a positive PCR test on synovial fluid adds increased diagnostic certainty 1
• Important caveat: Positive PCR results from joint fluid in a seronegative patient should be regarded with skepticism 1

Clinical Features of Lyme Arthritis

• Lyme arthritis is typically monoarticular or oligoarticular, predominantly affecting the knee 1, 3
• Large knee effusions out of proportion to pain are characteristic 1
• Intermittent episodes of joint inflammation may spontaneously resolve after weeks to months if untreated 1

Common Pitfalls to Avoid

1. Do not rely on PCR or culture alone for diagnosis - these have limited sensitivity and should be used as adjuncts to serologic testing 1

2. Do not interpret fewer bands on Western blot as positive:

   • A positive IgG Western blot requires ≥5 of 10 specific bands
   • Interpreting fewer bands as positive leads to false positives 1, 2

3. Do not perform Western blot without first-tier EIA/ELISA:

   • Following the two-tier protocol is essential for accurate diagnosis 2
   • Western blot should only be performed if the first-tier test is positive/equivocal 2

4. Do not test patients with low pretest probability:

   • Testing has poor positive predictive value in patients without:
     • Travel to/residence in endemic areas
     • Known tick exposure
     • Compatible clinical symptoms 2

For Lyme arthritis specifically, the two-tiered serologic testing approach has excellent sensitivity (70-100%) and specificity (>95%) since it represents late disseminated disease when antibody responses are well-developed 1, 2.