U1RNP– see Antibodies against U1RNP and Sm antigen.

UCTD – see Undifferentiated connective tissue disease (UCTD).

Ultrasound The principle is the transformation of the electrical energy of a high-frequency current into mechanical energy of longitudinal vibration of the physical environment with a frequency above the level of audibility (approximately 20,000 Hz). The vibration of all atoms and molecules, or of entire cells, occurs in the trajectory of the ultrasound ray leading to micro-massages with subsequent dispersal effects (the transformation of gel into fluidity, gel fluidisation) and the transformation of mechanical energy into thermal energy and thereby to the heating up of deep tissues.

Ultrasound in rheumatology (arthrosonography) A diagnostic method using ultrasound to measure the varying degree of its reflection when passing through tissues of the body and produces a two- or three-dimensional reconstruction images of the examined area. It is a promising noninvasive method, which is easily available, reproducible and economically advantageous, but is dependent on a well-trained operator. It is particularly used in the detection of joint effusions, changes in muscles, periarticular structures, ligaments, tendons, bursae, cartilage and the bone surface. High-frequency probes (above 10–15 MHz) can detect the early erosive changes around joints. Doppler’s mode enables assessment of blood flow.