Neurology 2021 01 16;96(4):e587-e599. Epub 2020 Oct 16.
From the Dubowitz Neuromuscular Centre (F.T., M.S., M.L.M., F.M.) and Population, Policy and Practice Programme (D.R.), UCL GOS Institute of Child Health, London, UK; DINOGMI, University of Genoa (F.T.), IRCCS Istituto G. Gaslini, Italy; NIHR Great Ormond Street Hospital Biomedical Research Centre (D.R., F.M.), Great Ormond Street Institute of Child Health, University College London, and Great Ormond Street Hospital Trust, UK; Paediatric Neurology (G.C., M.P., E.M.), Catholic University; Centro Clinico Nemo (G.C., M.P., E.M.), Fondazione Policlinico Universitario Agostino Gemelli IRCSS, Rome, Italy; John Walton Muscular Dystrophy Research Centre (R.M.L., C.M.-B.), Newcastle University and Newcastle Hospitals NHS Foundation Trust, Newcastle Upon Tyne, UK; Departments of Neurology and Pediatrics (J.M., D.C.D.V.) and Departments of Rehabilitation and Regenerative Medicine (J.M.), Columbia University Irving Medical Center, New York, NY; Paediatric Neurology and Centro Clinico Nemo (V.S., E.A.), Milan; Unit of Neuromuscular and Neurodegenerative Disorders (A.D., E.B.), Post-Graduate Bambino Gesù Children's Research Hospital, IRCCS, Rome; Department of Clinical and Experimental Medicine (S.M.), University of Messina Paediatric Neurology and Nemo Sud Clinical Centre; Center of Translational and Experimental Myology (C.B.), IRCCS Istituto Giannina Gaslini, Genova, Italy; University Hospitals Birmingham NHSFT (D.P.); Leeds Children Hospital (A.-M.C.); Evelina Children's Hospital (V.G.), London; The Robert Jones and Agnes Hunt Orthopaedic Hospital (T.W.), Oswestry; Sheffield Children's Hospital (M.O.), UK; Department of Neurology (B.T.D.), Boston Children's Hospital and Harvard Medical School, MA; Stanford University (J.D.), Medical Centre, Palo Alto, CA; Divisions of Pediatric Neurology (E.A.K.), Pulmonology (O.H.M.) and Physical Therapy (A.M.G.), The Children's Hospital of Philadelphia, and the Perelman School of Medicine at the University of Pennsylvania, Philadelphia; and Divisions of Neurology (R.S.F.) and Pulmonary Medicine (A.A.N.N.), Department of Pediatrics, Nemours Children's Hospital, Orlando, FL.
Objective: To describe the respiratory trajectories and their correlation with motor function in an international pediatric cohort of patients with type 2 and nonambulant type 3 spinal muscular atrophy (SMA).
Methods: This was an 8-year retrospective observational study of patients in the International SMA Consortium (iSMAc) natural history study. We retrieved anthropometrics, forced vital capacity (FVC) absolute, FVC percent predicted (FVC%P), and noninvasive ventilation (NIV) requirement. Hammersmith Functional Motor Scale (HFMS) and revised Performance of Upper Limb (RULM) scores were correlated with respiratory function. We excluded patients in interventional clinical trials and on nusinersen commercial therapy.
Results: There were 437 patients with SMA: 348 with type 2 and 89 with nonambulant type 3. Mean age at first visit was 6.9 (±4.4) and 11.1 (±4) years. In SMA type 2, FVC%P declined by 4.2%/y from 5 to 13 years, followed by a slower decline (1.0%/y). In type 3, FVC%P declined by 6.3%/y between 8 and 13 years, followed by a slower decline (0.9%/y). Thirty-nine percent with SMA type 2% and 9% with type 3 required NIV at a median age 5.0 (1.8-16.6) and 15.1 (13.8-16.3) years. Eighty-four percent with SMA type 2% and 80% with type 3 had scoliosis; 54% and 46% required surgery, which did not significantly affect respiratory decline. FVC%P positively correlated with HFMS and RULM scores in both subtypes.
Conclusions: In SMA type 2 and nonambulant type 3, lung function declines differently, with a common leveling after age 13 years. Lung and motor function correlated in both subtypes. Our data further define the milder SMA phenotypes and provide information to benchmark the long-term efficacy of new treatments for SMA.