The discriminating value of serum lactate dehydrogenase levels in children with malignant neoplasms presenting as joint pain

Objectives: To determine if serum lactate dehydrogenase levels distinguish patients with malignant neoplasm presenting with musculoskeletal complaints from patients with juvenile rheumatoid arthritis who reported similar symptoms. Design: Retrospective case-comparison study. Setting: Tertiary care, outpatient clinics. Patients: Twelve patients with malignant neoplasms who presented with arthritis or arthralgias and normal complete blood cell counts and blood smears in whom rheumatologic diagnosis was initially made were compared with 24 children with a final diagnosis of juvenile rheumatoid arthritis. The patients with malignant neoplasms all had normal blood counts and elevated sedimentation rates at symptom onset. Interventions: None. Results: Serum lactate dehydrogenase levels were significantly higher in the cancer patients at 2.2 times the high normal values vs 0.8 times high normal for patients with juvenile rheumatoid arthritis (P=.004, Mann-Whitney U test). No significant differences were observed in white blood cell counts, hemoglobin levels, platelet counts, erythrocyte sedimentation rate, or uric acid or aspartate aminotransferase levels at initial evaluation. Conclusion: Serum lactate dehydrogenase values may distinguish patients with malignant neoplasms from those with rheumatic disease early in the course of illness when symptoms and other laboratory values are not helpful.