When one wishes to edit a file in Photoshop from Lightroom the usual method is to setup Photoshop as an external editor in Lightroom and then choose the option to edit a copy with Lightroom adjustments from Photoshop. This enables the Lightroom adjustments to be passed on to Photoshop. One then saves the edited file from Photoshop and returns to Lightroom and the edited file is saved as a TIFF (if TIFF was chosen in the external editor setup) as <filename>-Edit.TIFF.
If one wishes to re-edit the image in Photoshop again, Scott Kelby (in his Lightroom 5 book) suggests that one can again use Photoshop as an external editor and this time choose Edit Original.
If one wishes to perform multiple sessions in Photoshop, another option is open the file directly in Photoshop (Lightroom may not even be running), perform the edit, and save from Photoshop. Which method is preferred? Either seems to work.
Thanks for your help,