PGDIM and PGDISEM are both courses that one can apply for with a CAT score at NITIE. Here are some differences listed according to some of my friends studying there.

• PGDISEM is a specialized course majoring in industrial safety, sustainability, and the environment. 
• Whereas PGDIM is a general management course with a focus on operations.
• PGDIM is a general management course similar to IIMs. 
• PGDISEM on the other hand caters to a niche segment of students who are highly interested in industrial safety and sustainability of corporate companies.
• Both the courses have a few common subjects and subjects which cater to their specific industries in-depth as well.
• The faculty teaching any of the courses in NITIE are highly experienced.
• From PGDIM, you will majorly get into Operations, IT, Consulting roles, whereas PGDISEM will get you into EHS, Safety, Sustainability, or Environment profiles.
• The placements for both the courses are in different fields. Other than that, the course structure for both courses is similar.

Selecting the right course depending on your interest and preferences is most important. So choose wisely as this will shape your career ahead.