Grip Strength in Adults and Children with Cystinosis

Introduction: Chronic kidney disease (CKD) is associated with impaired muscle strength. Patients with cystinosis have an increased risk for impaired muscle strength because of early development of CKD and cystinosis-induced myopathy. This study assesses muscle strength in patients with cystinosis and investigates risk factors of decreased muscle strength.

Methods: Adult and pediatric patients were recruited from Cystinosis Research Network conferences and a large pediatric nephrology clinic between 2017 and 2019. Patients and caregivers completed questionnaires on demographic characteristics, disease course, daily physical activity, and neuromuscular symptoms. Grip strength was assessed using a dynameter and calculated z-scores for age and sex were assessed for associations with patient characteristics.

Results: We included 76 patients with a mean grip strength z-score of -2.1 (SD, 1.1), which was lower than seen in patients with CKD without cystinosis. Male sex and delayed cysteamine initiation were independently associated with impaired grip strength. Among adults, a low level of physical activity was associated with lower grip strength z score, but no association was found in children. A third of the patients reported neuromuscular symptoms, with swallowing issues associated with lower grip strength. There was no significant correlation between eGFR and grip strength z-score.

Conclusion: Patients with cystinosis have impaired muscle strength compared with healthy control subjects and patients with CKD. This impairment is greater in male patients and in patients with late initiation of cysteamine therapy and is associated with lower physical activity. Further studies investigating the effect of different types of physical activities, optimizing cysteamine therapy, and other interventions are needed.