Thanks for using Healthcaremagic,
Your wife is having cough
for last 5-6 months and hence some cause must be there and even if sputum is negative lungs TB is possible and I am sure there must be some abnormality in x ray
to suggest tubercular possibility.
There are other evidence clinical as well as investigations which need to be correlated.
If there is no other cause, please continue anti tubercular treatment as per advice of Physician which can be reviewed after some time to see there is improvement or not. Possibility of TB is more in endemic areas it is not clear you are staying in which part of world.
If there is any doubt then you can always take second opinion CT scan
of chest and Molecular diagnosis of TB by PCR test may confirm the diagnosis.This will also help to rule out any chance of malignancy.
It is always better to take anti TB medicines empty stomach to have better result.
Dr.Akhilesh Dubey M.D.