PHYSIOLOGICAL ABNORMALITIES OF SKELETAL-MUSCLE IN DIALYSIS PATIENTS

Background. Muscle weakness is a commom but unexplained feature of dia lysis patients. This study investigated the prevalence and causes of m uscle weakness in dialysis patients by examining the quadriceps muscle force and contractile properties. Methods. The quadriceps femoris was studied in terms of force, force-frequency curve, and speed of muscle relaxation in 49 dialysis patients and 27 healthy subjects. In additi on nutritional, haematological, biochemical, and histological assessme nts were performed, and steps of force generation were analysed to rea ch the possible mechanisms leading to the observed weakness. Results. Muscle weakness, though invariable as a symptom, was subtle or absent on clinical examination. Quadriceps force measurements, however, revea led unequivocal weakness in most of the patients (71%). The quadriceps muscle was weaker (317 +/- 115 versus 460 +/- 159 N, P<0.01) compared to healthy individuals, but there was no evidence of impaired excitat ion-contraction coupling (0.79 +/- 0.05 versus 0.76 +/- 0.07, P=0.1). Among dialysis patients the older and the malnourished (n=23) were the weaker but there was no relationship to the type or duration of dialy sis. The serum albumin was the only biochemical parameter related to t he muscle force (r=0.6, P=0.01). The other most prominent abnormality of quadriceps muscle function observed in this study was slowing of re laxation (patients versus controls; 8.7 +/- 1.8% versus 10.8 +/- 1.1% force loss/10 ms, P < 0.0001) particularly in the malnourished group ( malnourished versus well nourished; 8.3 +/- 2.1 versus 9.4 +/- 0.95, P =0.03). Muscle histology was investigated (n=12) and revealed that typ e II fibres were mildly atrophic in 40% of the biopsies in most areas, but predominantly type IIB. Although type IIB fibre areas are slightl y smaller in the dialysis patients compared to the controls, this was not statistically significant (3025 +/- 578 ver sus 4406 +/- 1582, P=0 .1) except in the malnourished group compared to the well-nourished di alysis patients (2092 +/- 304 versus 4346 +/- 1496, P=0.04), and in th e malnourished dialysis patients type IIB fibre area was significantly correlated to the strength (r=0.6, P=0.02). Conclusions. The only sig nificant predictor of loss of muscle strength and abnormality of relax ation in this study was the nutritional state. A regular assessment of the nutritional state is required to ensure adequate nutrition to pre vent the observed abnormalities of the skeletal muscles.