title: Vitamin D, surface electromyography and physical function in uraemic patients.
abstract: BACKGROUND
  Muscle function is impaired in uraemic patients and several causes have been proposed. Deficiency of 25-hydroxyvitamin D (25-OHD), which affects muscle function in non-uraemic patients, may very well also be associated with the myopathy found in these patients. The aim of this study was to investigate the association between 25-OHD and muscle function as well as physical function in chronic kidney disease (CKD) and peritoneal dialysis (PD) patients.
  
  
  METHODS
  In this cross-sectional study, 21 adult patients with CKD stage 3-5 and 21 patients treated with PD were included. Standard biochemistry parameters were measured including 25-OHD, 1,25-dihydroxycholecalciferol (1,25-OHD) and parathyroid hormone analysis. Muscle function was determined by 30-second surface electromyography (sEMG) recordings of a right thigh muscle (vastus lateralis) and a second left finger muscle (second dorsal interosseous) under voluntary contractions. Physical function was determined using a 30-second Chair Stand Test and the Short Form 36 quality of life questionnaire. Clinical characteristics were collected from the patient records.
  
  
  RESULTS
  Moderate vitamin 25-OHD deficiency (<40 nmol/l) was measured in 52% of patients with CKD and in 71% of the patients on PD. Severe deficiency (<15 nmol/l) was measured in 14% of patients on PD. There were no significant differences between the CKD and PD patients in terms of sEMG results. 25-OHD was not correlated to any results from the tests of sEMG or physical function. However, a higher sEMG frequency and signal root mean square (RMS) were positively associated with a higher Chair Stand Test score. Time to maximum sEMG frequency was negatively correlated to the Chair Stand Test score (p < 0.05), and positively correlated to the level of comorbidity (p < 0.05). sEMG signal peak-peak amplitude, frequency and RMS were positively correlated to the quality of life scales Physical Function, Role Physical, General Health, Vitality, Social Function, Mental Health, and Physical Component Scale (p < 0.001).
  
  
  CONCLUSIONS
  25-OHD deficiency was prevalent in uraemic patients in the present study. Muscle function as determined using sEMG and the Chair Stand Test was not associated with 25-OHD. The results may be biased by the limited variation in 25-OHD and masked by effects of several other variables in this very sick population.
authors.affiliation: Department of Nephrology, Copenhagen University Hospital in Herlev, Herlev, Denmark. heaf @ dadlnet.dk
authors.forename: J G
authors.initials: JG
authors.lastname: Heaf
authors.forename: S
authors.initials: S
authors.lastname: Molsted
authors.forename: A P
authors.initials: AP
authors.lastname: Harrison
authors.forename: P
authors.initials: P
authors.lastname: Eiken
authors.forename: L
authors.initials: L
authors.lastname: Prescott
authors.forename: I
authors.initials: I
authors.lastname: Eidemak
mesh_terms: D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010808:Physical Examination; D013223:Statistics as Topic; D014511:Uremia / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology*; D014808:Vitamin D Deficiency / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology*