Extra-osseous 99mTc methylene diphosphonate uptake detected enlargement of the knee joint in patient with polyarthritis

Bone scintigraphy is a nuclear scanning test used to find abnormalities in the skeleton. Certain abnormal processes involving soft tissues can also cause skeletal accumulation of radiotracer during bone scintigraphy. We present a case of periarticular knee soft tissue 99mTc methylene diphosphonate uptake in a patient with asymmetric polyarthritis. A 33-year-old patient with asymmetric polyarthritis, skin lesions and joint pain underwent bone scintigraphy. Total body examination showed an extra-osseous uptake in periarticular soft tissue of knees joints. A detailed history checkup, physical examination and laboratory tests were carried out to understand the link between the extra-osseous uptake and the phosphonate binding in periarticular soft tissue. To improve the anatomical description of the soft tissue of the knees and to clarify the nature of the extra-skeletal 99mTc methylene diphosphonate uptake, magnetic resonance imaging scan was performed. 99mTc-labeled phosphonate binding has been reported in a number of extra-osseous conditions, but to our knowledge, there are a few cases showing bone tracer uptake in polyarthritis. In polyarthritic patients, whole-body bone scintigraphy were useful in examining the whole joints and detecting possible dubious extra-osseous uptake; in fact, it is able to select subjects who require further in-depth analysis, for example, magnetic resonance imaging.