[Correlation of muscular impairment rating scale with myopathological changes in myotonic dystrophy type 1]

To explore the relationship between muscular impairment rating scale (MIRS) and myopathological changes of myotonic dystrophy type 1 (DM1).

A total of 46 patients at our hospital from May 2003 to June 2011 were diagnosed as DM1. There were 30 males and 16 females. The age of onset ranged from 10 to 57 years old. The major symptoms included distal extremity weakness and myotonia. They were assessed with MIRS and muscle biopsies. The relationship was examined between MIRS and the variation of fiber size, central nuclear, ragged red fibers, proliferation of connective tissue, sarcoplasmic mass. Statistic analysis of pathological changes was made between the groups of MIRS ≥ 4 and ≤ 3.

The scores of MIRS were 2 (n = 8), 3 (n = 14), 4 (n = 23) and 5 (n = 1). MIRS had significant correlations with variations of fiber size (P = 0.039, r = 0.305), degree of nuclear translocation (P = 0.002, r = 0.451) and ragged red fibers (P = 0.013, r = 0.364). But there was no significant correlation with the proliferation of connective tissue and sarcoplasmic mass. There were significant differences in nuclear translocation and ragged red fibers. But no significant difference existed in variations of fiber size between the groups of MIRS ≥ 4 and ≤ 3.

The rating scale of MIRS has a certain myopathological basis, especially with regards to the changes in nuclear translocation and ragged red fibers.