Please see the following message I got when I tried these instructions.
Microsoft Windows [Version 6.3.9600]
(c) 2013 Microsoft Corporation. All rights reserved.
C:\WINDOWS\system32>DISM.exe/Online/Cleanup-image/Scanhealth
Deployment Image Servicing and Management tool
Version: 6.3.9600.16384
Error: 87
The online/cleanup-image/scanhealth option is unknown.
For more information, refer to the help by running DISM.exe /?.
You need spaces between the parameters you pass to DISM.exe:
DISM.exe /Online /Cleanup-image /Scanhealth
Try again with spaces. You should be able to copy/paste the commands directly from this thread.