Crystal arthropathy of the lumbar facet joint is a rare but benign differential diagnosis of spondylodiscitis.
A 70-year-old woman with a recent sigmoid diverticulitis was examined for a suspicion of infectious spondylodiscitis. She had inflammatory low back pain for a month with low-grade fever and C-reactive protein (CRP) up to 3 mg/dl. Magnetic resonance imaging of the spine suggested a septic localization with T2 short-tau inversion recovery hypersignal on the left lumbar facet joints L3–L4 and L4–L5 (Figure 1).
A bone biopsy of lumbar facet joints was performed with computed tomography guidance and showed no microorganism on bacteriological direct examination, and culture was sterile at 48 h. CRP was 1.6 mg/dl. Pathological examination revealed that bone, cartilage, and synovial tissues contained basophilic material including numerous rhomboidal crystals birefringent in polarized light (calcium pyrophosphate crystal deposits; Figure 2). Symptoms disappeared with nonsteroidal antiinflammatory drugs.
Calcium pyrophosphate crystal deposition in the spine is well known in 2 cases: crown dens syndrome, which is a classic differential diagnosis of meningitis in older people1, and paralyzing sciatica due to a synovial facet joint cyst filled with crystal deposits2.
Septic arthritis of lumbar facet joints is rare, but is more frequently described than the microcrystalline etiology. A review counted 34 cases of septic arthritis of facet joints3, whereas a single case of crystal lumbago was reported by a Japanese team, with involvement in the L4–L5 facet joints4.
Arthritis of lumbar facet joints could be due to crystal lumbago, if no microorganism is found.
Acknowledgment
We thank Dr. Anna Ludig and Professor Jean Sibilia.