In-111 labeled leukocyte imaging in a case of pseudogout

In-111 labeled leukocyte scintigraphy was performed on a 90-year-old woman who had a fever and left lower extremity pain for 3 days. Leukocyte images demonstrated abnormal activity in the left knee and ankle. Aspiration of the left knee joint yielded cloudy yellow fluid with a leukocyte count of 30,000 per mm3 (75% polymorphonuclear leukocytes, 1% lymphocytes, and 24% monocytes). Cultures of the aspirate were reported as no growth. Microscopic examination of the aspirate revealed the presence of rod-shaped crystals of calcium pyrophosphate dihydrate, confirming the diagnosis of calcium pyrophosphate deposition disease, also known as pseudogout. The acute arthritis of pseudogout stimulates an intense leukocyte response; therefore, labeled leukocyte images performed on patients suspected of having this condition must be interpreted cautiously because scintigraphically it may not be possible to distinguish pseudogout from septic arthritis.