MATLAB is designed to work efficiently with vectors and arrays. Your task would be trivially easy with a vector/matrix.
"I want to find the maximum of all the variables ..."
Those data are very poorly designed for this otherwise very simple task.
"and display the variable name not its value, how is this done ?"
This implies that whoever created that data made the mistake of putting some meta-data into the variable names. Putting meta-data (e.g. patient names, dates/times, pseudo-indices) into variable names makes accessing that data (and meta-data) slow, complex, and inefficient:
You have not told us the most important information: how did you get all of those variables into the MATLAB workspace?
