Longitudinal assessment of low bone mineral density and its association with severe pain in children with cerebral palsy

Longitudinal assessment of low bone mineral density and its association with severe pain in children with cerebral palsy
1 Department of Pediatrics, University of Virgina, Charlottesville, VA;
2 Department of Public Health Services, University of Virgina, VA, USA

Background/Objectives: Determine the relationships between pain, nutritional health, and medication use, on bone mineral density (BMD) over time in children with cerebral palsy (CP).
Design: Prospective, longitudinal cohort.
Participants and Setting: Thirty-six children, 5-18 years with CP (Gross Motor Function Classification System {GMFCS} levels I-V) with at least two visits 10 or more months apart.
Materials/Methods: Anthropometric measurements included triceps skin-fold to assess nutrition status. BMD measurements of the distal lateral femur (DF) were obtained in regions 1, 2 and 3 (R1, R2, R3) using published techniques; the mean BMD z-score among these three regions was examined. Caregivers/children completed Child Health Questionnaire (CHQ) to assess pain. Pain was classified by using the CHQ body pain z-scores normalized on age and gender: those with z-scores < -1.645 was considered to be in “more pain” while those with z-scores ≥ -1.645 were considered to be in “less pain”. Mixed models were utilized to estimate associations between BMD z-score: both for overall (baseline) differences as well as changes in BMD z-score over an average 12-month span. We examined: gender, age, GMFCS (grouped into two groups: “less severe” (GMFCS=1 or 2) and “more severe” (GMFCS=3, 4, 5), baseline triceps z-score (indicator of nutritional status), seizure medication usage at baseline, vitamin usage (Multivitamin, Calcium, Vitamin D) at baseline, and baseline pain.
Results: Of 36 children (mean age =10.9 years), 31% had GMFCS level I or II and 69% had GMFCS levels III, IV, or V, and 61% were male. Mean (±SD) DF and triceps z-score were -2.1+1.6 and 0.0 ±1.4, respectively. 39% were on a seizure medication at baseline and 31% were taking a vitamin at baseline. The mean time between two visits was 14.7 months. In assessing pain by the CHQ, 28% reported moderate to severe pain with a z-score <-1.65 whereas only 5% of the general population is expected to have z-scores < -1.65. Age, triceps z-score, seizure medication and vitamin usage were significantly associated with baseline BMD z-score. Children taking seizure medication had an average decrease of 1.1 in the BMD z-score (P<0.05); those taking vitamins at baseline had an average increase of 0.8 in the BMD z-score at baseline (P<0.05). Gender, GMFCS severity, and baseline body pain were not significantly associated with BMD z-score at baseline. The only factor that was significantly associated with change in BMD z-score over time was baseline body pain (P<0.05). Those exhibiting “more pain” at baseline lost an average of -0.3 standard deviations more than those with “less pain” at 1 year.
Conclusions/Significance: Children with CP are at risk for osteoporosis. The use of seizure medications, low nutritional status, and increasing age was associated with lower BMD. More severe pain was associated with lower BMD over time. Interventions should be aimed at improving nutrition and bone health which may in turn improve pain. Further research on pain as a primary outcome measure is needed.

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