Linear hair growth rates in preschool children.

BACKGROUND: Human scalp hair is a validated bio-substrate for monitoring various exposures in childhood including contextual stressors, environmental toxins, prescription or non-prescription drugs. Linear hair growth rates (HGR) are required to accurately interpret hair biomarker concentrations. METHODS: We measured HGR in a prospective cohort of preschool children (N = 266) aged 9-72 months and assessed demographic factors, anthropometrics, and hair protein content (HPC). We examined HGR differences by age, sex, race, height, hair pigment, and season, and used univariable and multivariable linear regression models to identify HGR-related factors. RESULTS: Infants below 1 year (288 ± 61 µm/day) had slower HGR than children aged 2-5 years (p = 0.0073). Dark-haired children (352 ± 52 µm/day) had higher HGR than light-haired children (325 ± 50 µm/day; p = 0.0019). Asian subjects had the highest HGR overall (p = 0.016). Younger children had higher HPC (p = 0.0014) and their HPC-adjusted HGRs were slower than older children (p = 0.0073). Age, height, hair pigmentation, and HPC were related to HGR in multivariable regression models. CONCLUSIONS: We identified age, height, hair pigment, and hair protein concentration as significant determinants of linear HGRs. These findings help explain the known hair biomarker differences between children and adults and aid accurate interpretation of hair biomarker results in preschool children. IMPACT: Discovery of hair biomarkers in the past few decades has transformed scientific disciplines like toxicology, pharmacology, epidemiology, forensics, healthcare, and developmental psychology. Identifying determinants of hair growth in children is essential for accurate interpretation of hair biomarker results in pediatric clinical studies. Childhood hair growth rates define the time-periods of biomarker incorporation into growing hair, essential for interpreting the biomarkers associated with environmental exposures and the mind-brain-body connectome. Our study describes age-, sex-, and height-based distributions of linear hair growth rates and provides determinants of linear hair growth rates in a large population of children. Age, height, hair pigmentation, and hair protein content are determinants of hair growth rates and should be accounted for in child hair biomarkers studies. Our findings on hair protein content and linear hair growth rates may provide physiological explanations for differences in hair growth rates and biomarkers in preschool children as compared to adults.

Facial Nerve Reconstruction With Concurrent Masseteric Nerve Transfer and Cable Grafting.

IMPORTANCE: Reconstruction of the facial nerve after radical parotidectomy is commonly performed with cable grafting, which is associated with slow recovery of nerve function and synkinesis. OBJECTIVE: To describe facial nerve reconstruction after radical parotidectomy using concurrent masseteric nerve transfer and cable grafting. DESIGN, SETTING, AND PARTICIPANTS: This retrospective medical record review at a tertiary referral hospital included 9 patients who underwent concurrent masseteric nerve transfer and cable grafting for facial nerve reconstruction performed by a single surgeon from January 1, 2014, to October 31, 2015. Final follow-up was completed on March 14, 2016. MAIN OUTCOMES AND MEASURES: Improvement in resting facial symmetry and oral commissure excursion and synkinesis. RESULTS: Nine patients (6 women; mean age, 62.6 years; age range, 51-73 years) underwent immediate facial nerve reconstruction after radical parotidectomy using concurrent cable grafting and masseteric nerve transposition. All patients had return of oral commissure motion within 2 to 7 months after surgery with good excursion and minimal synkinesis. CONCLUSIONS AND RELEVANCE: Masseteric nerve transposition can be combined with cable grafting to improve outcomes in facial rehabilitation after radical parotidectomy. LEVEL OF EVIDENCE: 4.