Intracellular elemental composition of single muscle fibres in muscular dystrophy and dystrophia myotonica

Seven patients with myotonic muscle dystrophy (MD), 6 with muscle dystrophy without myotonia (limb-girdle and facio-scapulo-humeral dystrophy) and 6 healthy volunteers were subjected to biopsy from the anterior tibial muscle (TA). Light microscopic examination of cryostat sections revealed pathological changes of different kind and degree--the occurrence of ring fibres and multiple central nuclei was the most consistent in advanced MD. X-ray microanalysis (XRMA) of single muscle fibres demonstrated the intracellular content of such elements as Na, Cl, K, Mg, S and P. The most conspicuous finding was the increase in Na and Cl and decrease in K demonstrated in MD. The highest levels of Na and Cl were found in ring fibres. Decrease in K was as high in structurally normal fibres of MD biopsies as in ring fibres and was also found in the muscle dystrophies without myotonia, but to a lesser degree than in MD. Thus, the decrease in K was not correlated to increase in Na and Cl. These changes in muscle fibre elemental content are discussed in relation to plasma membrane changes of erythrocytes in MD and especially the indications of disturbed anion channels.