Abstract
ObjectiveTo study scapular winging or other forms of scapular dyskinesis (condition of alteration of the normal position and motion of the scapula) in myotonic dystrophy type 1 (DM1), which is generally considered to be a distal myopathy, we performed an observational cohort study.MethodsWe performed a prospective cohort study on the clinical features and progression over time of 33 patients with DM1 and pronounced, mostly asymmetric scapular winging or other forms of scapular dyskinesis. We also explored if scapular dyskinesis in DM1 has the same genetic background as in facioscapulohumeral muscular dystrophy type 1 (FSHD1).ResultsThe cohort included patients with congenital (n = 3), infantile (n = 6) and adult-onset DM1 (n = 24). Scapular girdle examination showed moderate shoulder girdle weakness (mean MRC 3) and atrophy of trapezius, infraspinatus, and rhomboid major, seemingly similar as in FSHD1. Shoulder abduction and forward flexion were limited (50–70°). In five patients, scapular dyskinesis was the initial disease symptom; in the others it appeared 1–24 years after disease onset. Follow-up data were available in 29 patients (mean 8 years) and showed mild to severe increase of scapular dyskinesis over time. In only three patients, DM1 coexisted with a FSHD mutation. In all other patients, FSHD was genetically excluded. DM2 was genetically excluded in nine patients. The clinical features of the patients with both DM1 and FSHD1 mutations were similar to those with DM1 only.ConclusionScapular dyskinesis can be considered to be part of DM1 in a small proportion of patients. In spite of the clinical overlap, FSHD can explain scapular dyskinesis only in a small minority. This study is expected to improve the recognition of shoulder girdle involvement in DM1, which will contribute to the management of these patients.
Highlights
Muscle weakness in myotonic dystrophy type 1 (DM1) typically occurs in distal upper and lower limbs, neck and face muscles
Patients meeting the following inclusion criteria were included: (1) DM1 confirmed by genetic testing; (2) more pronounced scapular girdle weakness (modified Medical Research Council (MRC) ≤ 3 and inability to perform the whole range of motion against gravity) than distal muscle weakness in upper and lower limbs (MRC > 3 and ability to perform the whole range of motion against gravity); (3) moderate-to-severe scapular dyskinesis described by two neurologists specialized in neuromuscular diseases (BE and NV) and confirmed by a physical therapist specialized in scapular dyskinesis on photographs and videos (JIJ); (4)
Scapular dyskinesis was defined as an alteration in the normal position or motion of the scapula during coupled scapulohumeral movements, and was classified as prominence of the inferomedial border of the scapula; prominence of the entire medial border, or prominence of the superomedial border (Supplemental Fig. 2) [8]
Summary
Muscle weakness in myotonic dystrophy type 1 (DM1) typically occurs in distal upper and lower limbs, neck and face muscles. It points to a scapular dyskinetic motor profile and not to a movement disorder caused by a central nervous system disease This dyskinesis results in an abnormal scapulohumeral rhythm in all three planes (Supplemental Fig. 1 and 2). DM1 was suspected because of the positive family history in spite of the atypical presentation with scapular winging [7]. These reports call for further research into the prevalence, features and pathophysiology of scapular dyskinesis in DM1. We performed a prospective cohort study of 33 patients with DM1 and pronounced, mostly asymmetric, abnormal scapular position and motion with more pronounced proximal than distal weakness. This study is expected to improve the recognition and understanding of shoulder girdle involvement in DM1, which eventually will contribute to better management of these patients
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