Yes, I know someone who smoked cannabis only, was later diagnosed with emphysema, & ended up with severely damaged lungs. There was nothing that could be done for her, & she passed away at a very young age.
I do not know anyone who has emphysema, but cannabis is more dangerous than tobacco. See the following article:
SMOKING three cannabis joints will cause you to inhale the same amount of toxic chemicals as a whole packet of cigarettes, according to research published in France today.
Cannabis smoke contains seven times more tar and carbon monoxide, the French National Consumers' Institute concluded in research published in the April edition of its monthly magazine.
The institute tested regular Marlboro cigarettes alongside 280 specially rolled joints of cannabis leaves and resin in an artificial smoking machine.
Emphysema comes from smoking a long time, and since all the cannabis smokers I know are under 30 or stopped after college, they wouldn't have emphysema. I only know people that have mental problems from smoking cannabis.