Questions about EMG results

I refer to my previous question (http://www.medhelp.org/posts/Neurology/Severe-muscle-weakness-cause-unknown/show/1758520#post_8107875)  and have some more details about the outcome of the EMG made. There were no results 4 the legs but 4 the left arm results were as follows:

N. Ulnaris Definite block and significantly delayed motor conduction upper arm. Inching: localization 11,5 CM proximal of mid-sulcus. Delayed motor conduction ellbow. Significantly delayed sensible conduction and probable sensible block upper arm. N. Medianus significantly extended DML, slightly delayed sensible conduction hand. Focal demyelinating injury of motor and sensor nerve fibers N. Ulnaris upper arm. Also possible CTS bdz.

No lesion was found on the MRI of the upper arm.

Questions: can this explain pareses of all fingers except the thumb (fingers are in flex/claw hand). How is it possible nothing was found on the MRI? What therapy would you advice?

Thank you!