Towards clinical outcome measures in myotonic dystrophy type 2: a systematic review

Purpose of review Myotonic dystrophies are the most frequent muscular dystrophies in adulthood; however, myotonic dystrophy type 2 (DM2) is by far less prevalent than myotonic dystrophy type 1 (DM1). Consequently, studies on large cohorts are lacking and disease-specific outcome measures have not been developed (see video abstract, Supplemental Digital Content 1, https://ift.tt/2PQ1JHu). The aim of this review is to systematically evaluate the outcome measures applied in patients with DM2 and to identify tests adopted from other neuromuscular disorders potentially suitable for DM2. A systematic review of functional tests and patient reported outcomes (PROs) previously used in DM2 has been performed. In addition, we reviewed functional tests and PROs previously used in neuromuscular diseases (NMDs). Based on this approach, we propose a battery of tests to be validated in DM2. Recent findings: No outcome measures or PROs have been validated in DM2. The most used PROs in DM2 were INQoL, SF-36, MPQ, and BPI. It is not clear whether it is better to use MMT or QMT to assess muscle strength. The algometer seems to be a useful tool to assess myalgia. No currently adopted tests or PROs seem effective to assess the mild myotonia of DM2. Several outcome measures used in other NMDs (e.g. 6MWT, QMFT, GSGC) might be suitable for DM2; however, their disease-specific validity needs to be explored. Summary Although DM2 has a milder and more heterogeneous phenotype than DM1, there is an urgent need to develop validated outcome measures in DM2. The current lack of validated DM2 tests will delay the start of therapeutic trials.

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