| Abstract |
Bone disease, i.e. renal osteodystrophy, is commonly seen in patients with chronic renal failure. It encompasses all the disorders of mineral and bone metabolism associated with chronic renal insufficiency, i.e. secondary hyperparathyroidism, retention and accumulation of beta 2 microglobulin and aluminum. The most frequent cause of renal osteodystrophy is secondary hyperthyroidism, with a consequence of high turnover bone disease. Secondary hyperparathyroidism, i.e. increased parathyroid hormone (PTH) secretion and parathyroid gland hyperplasia, develops early in the course of chronic renal insufficiency. Hypocalcemia, phosphate retention and deficiency of calcitriol stimulate PTH synthesis and secretion and parathyroid cell proliferation, i.e. hyperplasia. Parathyroid cell proliferation is initially polyclonal (diffuse hyperplasia), and later it is monoclonal or multiclonal (nodular hyperplasia). Calcitriol receptors as well as calcium-sensing receptors are significantly reduced in parathyroid glands in nodular hyperplasia. Patients with such parathyroid gland hyperplasia are often resistant to vitamin D therapy. A specific form of bone disease is beta 2 amyloidosis. Destructive arthropathy, cystic changes and carpal tunnel syndrome are clinical manifestations of dialysis-related amyloidosis, which is one of the major complications in patients on longterm hemodialysis. Aluminum intoxication leads to the low turnover bone disease and consequential osteomalacia or aplastic bone lesions, the cause of which has not yet been fully clarified. Ultrasound can be a useful, economical and noninvasive method in the evaluation of renal osteodystrophy. Ultrasound waves are very important for noninvasive imaging of soft tissue, especially parathyroid glands, pathologic changes of the joints, and for detection of metastatic calcifications. They are also useful in the evaluation of skeletal status in dialysis patients. Ultrasound waves of a frequency above the limit of human hearing are used in the morphological diagnosis of parathyroid gland. Today, because of its simplicity and non-invasiveness, it is a generally accepted method for the detection of enlarged parathyroid gland in patients with secondary hyperparathyroidism, for the monitoring of pathologic changes, and for making decisions on the method of treatment based on the size and number of parathyroid glands. Ultrasound can distinguish nodal from diffuse parathyroid hyperplasia. Under ultrasound guidance it is possible to perform fine needle aspiration biopsy, to confirm ultrasound findings, and percutaneous inactivation of parathyroid gland (PEI) with alcohol. Ultrasound is useful in the diagnosis of pathologic changes of the musculoskeletal system in patients with beta 2 amyloidosis, to assess the process of its spread, especially in the shoulder joint where the changes are most pronounced (rotator cuff thickness, amyloid deposits as hyperechogenic pads, and detection of fluid in the joint), but it can also be used to examine other joints as well as soft tissue in which metastatic calcifications may occur. Standard ultrasound equipment (pulse-echo) and linear probe of 5-13 MHz are used, also serving for ultrasound examination of the neck, joints and soft tissue. Quantitative bone ultrasonometry is based on different physical characteristics of the ultrasound including: transmission, Speed Of Sound (SOS) in meters/sec and Broad Band Attenuation (BUA) in dB/MHz, and different concepts of the apparatus. These parameters depend on the strength and architecture of the bones and describe better the changes in bone structure in dialysis patients by calculation of the Stiffness Index (QUI), better than the standard bone densitometry by dual-energy x-ray absorptiometry, which only measures bone density. Combined ultrasound measurement of the bone in several locations may be successful in monitoring dialysis patients.
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