Can chronic sinusitis cause mild leukopenia?

Usually not. Leukopenia could cause by medications, chemotherapy, radiation therapy, lupus, lymphoma, some cancers or autoimmune disease (hiv or aids), sepsis and other reasons.

Yes. In chronic sinusitis, your body is constantly using up wbcs (white blood cells) and if you end up having a few bad sinus infections, you can deplete your WBC reserves. You may end up with a transient leukopenia but usually it is not permanent. It will usually normalize once the chronic condition improves.

Chronic infections. Maybe. Chronic infections can. Chronic sinusitis is a chronic infection.