Muscle strength is reduced in children with pulmonary arterial hypertension

Muscle strength is decreased in adults with pulmonary arterial hypertension (PAH). We aim to investigate muscle strength in children with PAH in relation to a cohort of healthy children, and investigate correlations with disease severity markers. This prospective study included children with PAH aged 4-18 years, who visited the Dutch National Referral Center for Pulmonary Hypertension in Childhood between October 2015 and March 2016. Muscle strength was assessed using handgrip strength and maximum voluntary isometric contractility (MVIC) of four peripheral muscles. Dynamic muscle function was evaluated with the Bruininks-Oseretsky test of motor proficiency (BOT-2). These measurements were compared with those in two cohorts of healthy children and correlated with 6-minute walk distance (6MWD), World Health Organization functional class (WHO-FC), N-terminal pro-brain natriuretic peptide (NT-proBNP), and time since diagnosis. Eighteen children with PAH aged 14.0 [interquartile range: 9.9-16.0] years showed reduced muscle strength. Handgrip strength z-score -2.4 ± 1.2, p < 0.001, total MVIC z-score -2.9 ± 1.2, p < 0.001, and BOT-2 z-score -1.0 ± 0.9, p < 0.001. 6MWD (67 ± 11% predicted) correlated with most muscle measurements (r = 0.49-0.71, p = 0.001). Dynamic muscle function (BOT-2) differed between WHO-FC, whereas handgrip strength and MVIC did not. NT-proBNP and time since diagnosis did not show significant correlations with muscle strength measurements. Muscle strength was significantly reduced in children with PAH and correlated with 6MWD, but not with disease severity markers WHO-FC and NT-pro-BNP. The nature of this reduced muscle strength is yet unclear, but its occurrence in children with seemingly mild or well-controlled PAH supports the concept of PAH being a systemic syndrome involving peripheral skeletal muscles.