Introduction: Crystal arthropathy of lumbar facet joint is quite rare, but it is a benign differential diagnosis of spondylodiscitis.
Case report: A 70-year-old woman with episodic lower back pain and gonalgia over the last 3 years, presented with inflammatory lower back pain increased since a month with low-grade fever and C-Reactive Protein (CRP) up to 3 mg/dL. Magnetic Resonance Imaging (MRI) of lumbar spine showed STIR-sequences hypersignal on the left lumbar facet joints L3-L4 and L4-L5, suggesting a septic grafting (Picture 1). At arrival in rheumatology unit, 48 hours past MRI, the patient had no fever and few pain with analgesic. Rachis palpation was lightly painful on L4-L5 level, without stiffness. There was no other articular or extra-articular sign. CRP was at 1.65 mg/dL, uric acid level was 263 µmol/L, complete blood cell count was normal, notably there was no leukocytosis. Blood culture was sterile. A bone biopsy of lumbar facet joints was realized with CT guidance and showed no microorganism on bacteriological direct examination, culture was sterile at 48 hours. Anatomopathological examination of bone tissue finally gives the diagnosis: numerous crystal deposits were found in bone, cartilage and synovial tissue (Figures 1 and 2). Actually this patient had a crystal lumbago with calcium phosphate crystal deposition of facet joints. Chondrocalcinosis of femoro-tibial joints was visible on X-ray. Symptoms disappeared with Non-Steroidal Anti-Inflammatory drugs (NSAI).
Discussion: Calcium phosphate crystal deposition in rachis is well known in 2 cases: 1/ Crown dens syndrome (CDS) is a classic differential diagnosis of meningitis in older people. 2/ Paralyzing sciatica could be due to a synovial cyst issue from facet joint and fill with crystal deposit. Nevertheless, isolated lower back pain due to calcium phosphate deposition is quite infrequent. To the best of our knowledge, a single case of crystal lumbago was described by a Japanese team (1), with L4-L5 facet joints involvement. The lack of symptom (low pain, no stiffness), low level of CRP, presence of meniscal chondrocalcinosis and fact that two homolateral lumbar facet joints were touched led to look forward crystal deposit and allow the final diagnosis of crystal lumbago. Septic arthritis of lumbar facet joints is rare, but is more frequently described than microcrystalline arthritis. A 2001 review counted 34 cases of septic arthritis of facet joints (2).