Lumbar Pseudogout Mimicking Pyogenic Spondylitis in an Older Patient: A Diagnostic Pitfall in Emergency Care.

Lumbar pseudogout, or calcium pyrophosphate dihydrate deposition disease (CPPD), is an uncommon manifestation of a crystal-induced arthropathy that typically affects peripheral joints. Spinal involvement, particularly in the lumbar region, is rare and may closely mimic infectious conditions such as pyogenic spondylitis. An 85-year-old man was hospitalized for pneumococcal pneumonia and subsequently developed severe low back pain on day 7 of admission. Although his pneumonia improved with antimicrobial therapy, inflammatory markers remained elevated, raising suspicion of pyogenic spondylitis. Computed tomography and magnetic resonance imaging of the lumbar spine demonstrated compression fractures and inflammatory changes at the L2/3 intervertebral disc but were insufficient to establish a definitive diagnosis. A diagnostic intervertebral disc biopsy was therefore performed, and polarized light microscopic examination revealed calcium pyrophosphate dihydrate crystals, confirming the diagnosis of lumbar pseudogout. Nonsteroidal anti-inflammatory drugs were discontinued because of renal dysfunction, and the patient's symptoms improved rapidly after corticosteroid therapy. This case highlights the diagnostic challenge of lumbar pseudogout, which can closely resemble infectious or neoplastic spinal disease. Although imaging plays an important role in excluding alternative diagnoses, definitive diagnosis of CPPD relies on crystal identification, most commonly through synovial fluid analysis or, when not feasible, tissue biopsy. Lumbar pseudogout should be considered in older adults presenting with acute inflammatory low back pain to facilitate timely diagnosis and appropriate management.