What Happened with Muscle Force, Dynamic Stability And Falls? A 10-Year Longitudinal Follow-Up in Adults with Myotonic Dystrophy Type 1

BACKGROUND: Individuals with myotonic dystrophy type 1 (DM1) are known to stumble and fall, but knowledge is scarce regarding dynamic stability in this disorder. OBJECTIVE: To describe disease progress regarding muscle force, dynamic stability and patient reported unintentional falls during a ten-year period, in individuals with DM1. METHODS: Quantification of isometric muscle force in four leg muscle groups and assessment of Timed 10-meter-walk in maximum speed (T10max), Timed Up&Go (TUG) and Step test (STEP) were performed at three occasions in a DM1 cohort, together with self-reported falls. RESULTS: Thirty-four people (m/f:11/23, age: 50.2 + /–9.4) participated. The muscle force loss after ten years was large in the distal ankle muscles. A steeper force decrease was seen in most muscles between year five and ten compared to the former five-year period. Males reported more falls than females, 91% vs 35% had fallen last year. A positive correlation, ρ= 0.633, p < 0.001, was shown between walking time (T10max) and number of falls. Frequent fallers were only seen among those with slower walk (T10max > 10seconds), and fewer steps in the STEP test (STEP≤5 steps). CONCLUSIONS: A diminishing leg muscle strength and worse dynamic stability were seen in the group, with a steeper decrease in the latter five years. Weak ankle dorsiflexors, a slower walk and difficulties to lift the forefoot were related to frequent falls.