What could be a cure for some medical conditions that causes bad breath?
Which one? Is this a hypothetical question or related to your own bad breath issue? If it's a hypothetical one, space is limited here and you can research it by doing a google search. If you yourself have bad breath, first rule out any dental causes by seeing a dentist. If your dentist feels the cause may be medical in origin, he\she will refer you to a physician to check you out medically.
Depends.. .. On which medical condition is causing the bad breath.
Gum surgery can treat periodontitis.
Antibiotics can treat sinus infections.
All the best..