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This electron micrograph of two adjacent skeletal muscle cells demonstrates simultaneous exocytosis.  Exocytosis in this case shows extravasation of lysosomes from inside the muscle fiber's cytoplasm by fusion with the plasma membrane (aka sarcolemma) and being expelled into the extracellular space beneath the basement membrane (aka basal lamina).  Exocytosis is one mechanism for remodeling of the sarcolemmal membrane that takes place under physiological and pathophysiological conditions, including trafficking of transmembrane machinery, muscle fiber regeneration following injury, and denervation.  Much has been written on this topic, but the details at the molecular level are still being elucidated.  (Electron micrograph original magnification:...

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These images show skeletal muscle from the thigh of an African-American patient with muscle weakness and elevated CPK levels.  Occasional well-formed non-caseating granulomota with mild surrounding chronic lymphoid inflammation are present. These morphologic findings are consistent with the presence of granulomatous myositis, and compatible with sarcoidosis: clinical correlation is required. (hematoxylin and eosin stained frozen section 100x and 200x magnification).    

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