You can perform an offline scan with Windows Defender in Windows 10 build 14271

[Windows Central]

An offline version of Windows Defender has been spotted in the Windows 10 Insider Preview. If you're rocking build 14271, it's possible to reboot the installation into a more secure mode to begin scanning the PC for threats to be removed without requiring the program to be on external storage.

Full story from the WindowsCentral blog...