Purpose: To determine the association between severity of cerebral palsy with serum creatinine (sCr) and sCr-based equations to estimate glomerular filtration rate (eGFR), a marker of renal function.
Methods: A clinic-based sample of 30-64 year-olds with cerebral palsy was examined and stratified by motor impairment: gross motor function classification system (GMFCS) I/II (n = 79), GMFCS III (n = 78), and GMFCS IV/V (n = 137). sCr, which is influenced by muscle mass, was obtained and sCr-based eGFR was calculated using the Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations.
Results: sCr was lower with increasing GMFCS. The opposite pattern was observed for eGFR: GMFCS IV/V had significantly higher eGFR derived from MDRD compared to other GMFCS groups; GMFCS III had significantly higher eGFR compared to GMFCS I/II. The pattern was similar for CKD-EPI derived eGFR.
Conclusions: According to widely used clinical assessment methods for renal function, higher severity of cerebral palsy among adults is associated with better renal function, which is incongruent with their other biological systems. This paradoxical relationship is likely driven by lower muscle rather than true renal function, and thus, sCr-based eGFR may overestimate renal function, especially for GMFCS IV/V. Further prospective studies are needed.Implications for rehabilitationCommon methods of clinical assessment may over-estimate renal function for adults with cerebral palsy (CP), potentially giving a false positive for normal renal health due to their reliance on muscle mass.This study of a clinic-based sample of middle-aged adults with CP highlights the paradoxical relationship between severity of CP and renal function, which is likely driven by methodological limitations in the presence of low muscle mass rather than actual better renal function.It is recommended that clinicians have a high suspicion of abnormal renal function and the need for a nephrology consultation, especially with changes in creatinine levels, even within the normal range.Rehabilitation for adults with CP must have a strong focus on muscle and kidney health, especially for patients with more severe forms of CP.
Keywords: Cerebral Palsy; Glomerular Filtration Rate; Muscles.