Diaphragm thickness and inspiratory strength in patients with Duchenne muscular dystrophy

Background - There is little information on the morphometric characteristics of the diaphragm in patients with Duchenne muscular dystrophy. Methods - The thickness of the diaphragm was measured at the zone of apposition using B mode ultrasonography in 10 boys with Duchenne muscular dystrophy of mean (SD) age 10.3 (1.3) years and 12 normal controls of mean (SD) age 11.3 (2.0) years during relaxation (DiTrelax) and during maximum effort inspiratory manoeuvres (DiTPImax) at functional residual capacity. Results - DiTrelax was greater in the patients with Duchenne muscular dystrophy (1.74 (0.21) mm) than in controls (1.48 (0.20) mm), mean difference (95% CI) 0.26 (0.08 to 0.44), despite considerable impairment of maximum effort inspiratory mouth pressure (PImax) (patients with Duchenne muscular dystrophy -37 (8) cm H2O, controls -80 (33) cm H2O), mean difference (95% CI) 43 (65 to 20). During a PImax manoeuvre, compared with measurements taken during relaxation, the diaphragm thickened 1.6 times in patients with Duchenne muscular dystrophy and 2.3 times in controls (DiTPImax 2.62 (0.7) mm and 3.5 (0.85) mm, respectively), mean difference (95%, CI) -0.88 (-1.58 to -0.18). Conclusions - Resting diaphragm thickness is increased in young patients with Duchenne muscular dystrophy with impaired respiratory muscle force. This finding could be analogous to the pseudohypertrophy that is observed in some limb muscle groups.