Recent applications of X-ray microanalysis in muscle pathology

X-ray microanalysis of single muscle fibres visualized in the scanning- and scanning-transmission mode of electron microscopy has been applied to human muscle biopsies to quantify changes of intracellular elements in different muscle disorders. To detect elements representing diffusible ions, cryofixation and cryosectioning was performed and analyses were conducted on freeze-dried cryosections 6 micron thick. Changes in the concentration of elements were found to differentiate certain muscular disorders. A large increase in sodium (Na) and chlorine (Cl), and a decrease in potassium (K) was typical of myotubular myopathy, while a moderate increase in Na and Cl was found in central core disease and nemaline myopathy. The normal elemental spectrum was found in multicore myopathy and facio- scapulo -humeral muscle dystrophy. In dystrophia myotonica there was constantly a decrease in K whereas in myotonia congenita an increase in K was a common finding. In myotonic dystrophy an increase in Na and Cl seemed to be related to the increase in the ring fibre formation. Experimental tenotomy of the soleus muscle of the rat is characterized by plasma membrane changes and the formation of core fibres. A marked increase in Na and Cl and a decrease in K was found to be a prominent elemental change in such core fibres. We conclude that changes in the concentration of certain intracellular elements demonstrable by X-ray microanalysis on cryosectioned freeze-dried muscle biopsies seem to be an indication of muscle fibre membrane disturbances.