Upper and lower limb muscle strength in idiopathic interstitial pneumonias (IIP)

Background: While quadriceps muscle weakness is recognised in IIP, the aetiology remains unknown. If disuse atrophy secondary to reduced physical activity (PA) is the principal aetiological factor, weakness would be most marked in the locomotor muscles, whereas if the principal aetiology is systemic loss of muscle, function would be more globally distributed. Methods: In 84 patients with IIP (IPF n=64; NSIP n=14; DIP n=2; COP n=2; LIP n=1; PPFE n=1), handgrip strength (HG), quadriceps maximal voluntary contraction (QMVC), exercise capacity by incremental shuttle walk test (ISW) and self-reported PA were measured. HG and QMVC were normalized to %predicted using population values and weakness was defined as Results: Baseline characteristics: 64% male; mean(SD)/median(25th,75th centiles) age 74(66,79) years; FVC 66(24) %predicted. Overall HG was preserved (86(18)%) whilst QMVC was reduced (61(20)%) (Fig 1). 79% and 35% of patients had quadriceps and HG weakness respectively. Daily time in moderate intensity PA was reduced in patients with quadriceps weakness compared with preserved quadriceps strength (112(34,266) vs (220(111,338), p=0.05). QMVC% correlated with ISW (r=0.50; p Conclusion: We observed differential weakness of lower limb muscles in IIP, explained in part by reduced physical activity and disuse atrophy. Quadriceps weakness may contribute to exercise intolerance. Fig 1